Initial Drupal 11 with DDEV setup

web/core/modules/block/block.api.php

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+<?php
+
+/**
+ * @file
+ * Hooks provided by the Block module.
+ */
+
+use Drupal\Core\Block\BlockPluginInterface;
+use Drupal\block\Entity\Block;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\Access\AccessResult;
+
+/**
+ * @defgroup block_api Block API
+ * @{
+ * Information about the classes and interfaces that make up the Block API.
+ *
+ * @section sec_overview Overview
+ * Blocks are a combination of a configuration entity and a plugin. The
+ * configuration entity stores placement information (theme, region, weight) and
+ * any other configuration that is specific to the block. The block plugin does
+ * the work of rendering the block's content for display.
+ *
+ * @section sec_requirements Basic requirements
+ * To define a block in a module you need to:
+ * - Define a Block plugin by creating a new class that implements the
+ *   \Drupal\Core\Block\BlockPluginInterface, in namespace Plugin\Block under
+ *   your module namespace. For more information about creating plugins, see the
+ *   @link plugin_api Plugin API topic. @endlink
+ * - Usually you will want to extend the \Drupal\Core\Block\BlockBase class,
+ *   which provides a common configuration form and utility methods for getting
+ *   and setting configuration in the block configuration entity.
+ * - Block plugins use the annotations defined by
+ *   \Drupal\Core\Block\Annotation\Block. See the
+ *   @link annotation Annotations topic @endlink for more information about
+ *   annotations.
+ *
+ * This is an example of a basic block plugin class:
+ * @code
+ * namespace Drupal\my_module\Plugin\Block;
+ *
+ * use Drupal\Core\Block\BlockBase;
+ * #[Block(
+ *   id: "my_block",
+ *   admin_label: new TranslatableMarkup("My Block"),
+ * )]
+ * class MyBlock extends BlockBase {
+ *   public function build() {
+ *     return [
+ *       '#type' => '#markup',
+ *       '#markup' => 'Example block',
+ *     ];
+ *   }
+ * }
+ * @endcode
+ *
+ * More examples are available at the links below.
+ *
+ * @section sec_extending Extending blocks with conditions and hooks
+ * The Block API also makes use of Condition plugins, for conditional block
+ * placement. Condition plugins have interface
+ * \Drupal\Core\Condition\ConditionInterface, base class
+ * \Drupal\Core\Condition\ConditionPluginBase, and go in plugin namespace
+ * Plugin\Condition. Again, see the Plugin API and Annotations topics for
+ * details of how to create a plugin class and annotate it.
+ *
+ * There are also several block-related hooks, which allow you to affect
+ * the content and access permissions for blocks:
+ * - hook_block_view_alter()
+ * - hook_block_view_BASE_BLOCK_ID_alter()
+ * - hook_block_access()
+ *
+ * @section sec_further_information Further information
+ * - \Drupal\system\Plugin\Block\SystemPoweredByBlock provides a simple example
+ *   of defining a block.
+ * - \Drupal\user\Plugin\Condition\UserRole is a straightforward example of a
+ *   block placement condition plugin.
+ * - \Drupal\system\Plugin\Block\SystemMenuBlock is an example of a block with
+ *   a custom configuration form.
+ * - For a more in-depth discussion of the Block API, see
+ *   https://www.drupal.org/docs/drupal-apis/block-api/block-api-overview.
+ * - The Examples for Developers project also provides a Block example in
+ *   https://www.drupal.org/project/examples.
+ * @}
+ */
+
+/**
+ * @addtogroup hooks
+ * @{
+ */
+
+/**
+ * Alter the result of \Drupal\Core\Block\BlockBase::build().
+ *
+ * This hook is called after the content has been assembled in a structured
+ * array and may be used for doing processing which requires that the complete
+ * block content structure has been built.
+ *
+ * If the module wishes to act on the rendered HTML of the block rather than
+ * the structured content array, it may use this hook to add a #post_render
+ * callback. Alternatively, it could also implement hook_preprocess_HOOK() for
+ * block.html.twig. See \Drupal\Core\Render\RendererInterface::render()
+ * documentation or the @link themeable Default theme implementations topic
+ * @endlink for details.
+ *
+ * In addition to hook_block_view_alter(), which is called for all blocks, there
+ * is hook_block_view_BASE_BLOCK_ID_alter(), which can be used to target a
+ * specific block or set of similar blocks.
+ *
+ * @param array &$build
+ *   A renderable array of data, as returned from the build() implementation of
+ *   the plugin that defined the block:
+ *   - #title: The default localized title of the block.
+ * @param \Drupal\Core\Block\BlockPluginInterface $block
+ *   The block plugin instance.
+ *
+ * @see hook_block_view_BASE_BLOCK_ID_alter()
+ * @see entity_crud
+ *
+ * @ingroup block_api
+ */
+function hook_block_view_alter(array &$build, BlockPluginInterface $block) {
+  // Remove the contextual links on all blocks that provide them.
+  if (isset($build['#contextual_links'])) {
+    unset($build['#contextual_links']);
+  }
+}
+
+/**
+ * Provide a block plugin specific block_view alteration.
+ *
+ * In this hook name, BASE_BLOCK_ID refers to the block implementation's plugin
+ * id, regardless of whether the plugin supports derivatives. For example, for
+ * the \Drupal\system\Plugin\Block\SystemPoweredByBlock block, this would be
+ * 'system_powered_by_block' as per that class's annotation. And for the
+ * \Drupal\system\Plugin\Block\SystemMenuBlock block, it would be
+ * 'system_menu_block' as per that class's annotation, regardless of which menu
+ * the derived block is for.
+ *
+ * @param array $build
+ *   A renderable array of data, as returned from the build() implementation of
+ *   the plugin that defined the block:
+ *   - #title: The default localized title of the block.
+ * @param \Drupal\Core\Block\BlockPluginInterface $block
+ *   The block plugin instance.
+ *
+ * @see hook_block_view_alter()
+ * @see entity_crud
+ *
+ * @ingroup block_api
+ */
+function hook_block_view_BASE_BLOCK_ID_alter(array &$build, BlockPluginInterface $block) {
+  // Change the title of the specific block.
+  $build['#title'] = t('New title of the block');
+}
+
+/**
+ * Alter the result of \Drupal\Core\Block\BlockBase::build().
+ *
+ * Unlike hook_block_view_alter(), this hook is called very early, before the
+ * block is being assembled. Therefore, it is early enough to alter the
+ * cacheability metadata (change #cache), or to explicitly placeholder the block
+ * (set #create_placeholder).
+ *
+ * In addition to hook_block_build_alter(), which is called for all blocks,
+ * there is hook_block_build_BASE_BLOCK_ID_alter(), which can be used to target
+ * a specific block or set of similar blocks.
+ *
+ * @param array &$build
+ *   A renderable array of data, only containing #cache.
+ * @param \Drupal\Core\Block\BlockPluginInterface $block
+ *   The block plugin instance.
+ *
+ * @see hook_block_build_BASE_BLOCK_ID_alter()
+ * @see entity_crud
+ *
+ * @ingroup block_api
+ */
+function hook_block_build_alter(array &$build, BlockPluginInterface $block) {
+  // Add the 'user' cache context to some blocks.
+  if ($block->label() === 'some condition') {
+    $build['#cache']['contexts'][] = 'user';
+  }
+}
+
+/**
+ * Provide a block plugin specific block_build alteration.
+ *
+ * In this hook name, BASE_BLOCK_ID refers to the block implementation's plugin
+ * id, regardless of whether the plugin supports derivatives. For example, for
+ * the \Drupal\system\Plugin\Block\SystemPoweredByBlock block, this would be
+ * 'system_powered_by_block' as per that class's annotation. And for the
+ * \Drupal\system\Plugin\Block\SystemMenuBlock block, it would be
+ * 'system_menu_block' as per that class's annotation, regardless of which menu
+ * the derived block is for.
+ *
+ * @param array $build
+ *   A renderable array of data, only containing #cache.
+ * @param \Drupal\Core\Block\BlockPluginInterface $block
+ *   The block plugin instance.
+ *
+ * @see hook_block_build_alter()
+ * @see entity_crud
+ *
+ * @ingroup block_api
+ */
+function hook_block_build_BASE_BLOCK_ID_alter(array &$build, BlockPluginInterface $block) {
+  // Explicitly enable placeholdering of the specific block.
+  $build['#create_placeholder'] = TRUE;
+}
+
+/**
+ * Control access to a block instance.
+ *
+ * Modules may implement this hook if they want to have a say in whether or not
+ * a given user has access to perform a given operation on a block instance.
+ *
+ * @param \Drupal\block\Entity\Block $block
+ *   The block instance.
+ * @param string $operation
+ *   The operation to be performed; for instance, 'view', 'create', 'delete', or
+ *   'update'.
+ * @param \Drupal\Core\Session\AccountInterface $account
+ *   The user object to perform the access check operation on.
+ *
+ * @return \Drupal\Core\Access\AccessResultInterface
+ *   The access result. If all implementations of this hook return
+ *   AccessResultInterface objects whose value is !isAllowed() and
+ *   !isForbidden(), then default access rules from
+ *   \Drupal\block\BlockAccessControlHandler::checkAccess() are used.
+ *
+ * @see \Drupal\Core\Entity\EntityAccessControlHandler::access()
+ * @see \Drupal\block\BlockAccessControlHandler::checkAccess()
+ * @ingroup block_api
+ */
+function hook_block_access(Block $block, $operation, AccountInterface $account) {
+  // Example code that would prevent displaying the 'Powered by Drupal' block in
+  // a region different than the footer.
+  if ($operation == 'view' && $block->getPluginId() == 'system_powered_by_block') {
+    return AccessResult::forbiddenIf($block->getRegion() != 'footer')->addCacheableDependency($block);
+  }
+
+  // No opinion.
+  return AccessResult::neutral();
+}
+
+/**
+ * Allow modules to alter the block plugin definitions.
+ *
+ * @param array[] $definitions
+ *   The array of block definitions, keyed by plugin ID.
+ *
+ * @ingroup block_api
+ */
+function hook_block_alter(&$definitions) {
+  foreach ($definitions as $id => $definition) {
+    if (str_starts_with($id, 'system_menu_block:')) {
+      // Replace $definition properties: id, deriver, class, provider to ones
+      // provided by this custom module.
+    }
+  }
+}
+
+/**
+ * @} End of "addtogroup hooks".
+ */

web/core/modules/block/block.info.yml

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+name: Block
+type: module
+description: 'Allows users to configure blocks (containing content, forms, etc.) and to place them in the regions of a theme.'
+package: Core
+version: VERSION
+configure: block.admin_display

web/core/modules/block/block.install

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+<?php
+
+/**
+ * @file
+ * Contains install and update functions for Block.
+ */
+
+use Drupal\Core\Cache\Cache;
+
+/**
+ * Implements hook_install().
+ */
+function block_install(): void {
+  // Because the Block module upon installation unconditionally overrides all
+  // HTML output by selecting a different page display variant, we must
+  // invalidate all cached HTML output.
+  Cache::invalidateTags(['rendered']);
+}
+
+/**
+ * Implements hook_update_last_removed().
+ */
+function block_update_last_removed(): int {
+  return 8003;
+}

web/core/modules/block/block.libraries.yml

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+drupal.block:
+  version: VERSION
+  js:
+    js/block.js: {}
+  dependencies:
+    - core/jquery
+    - core/drupal
+    - core/once
+
+drupal.block.admin:
+  version: VERSION
+  js:
+    js/block.admin.js: {}
+  css:
+    theme:
+      css/block.admin.css: {}
+  dependencies:
+    - core/jquery
+    - core/drupal
+    - core/drupal.announce
+    - core/drupal.debounce
+    - core/drupal.dialog.ajax
+    - core/drupal.tabledrag
+    - core/drupal.vertical-tabs
+    - core/once

web/core/modules/block/block.links.contextual.yml

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+block_configure:
+  title: 'Configure block'
+  route_name: 'entity.block.edit_form'
+  group: 'block'
+
+block_remove:
+  title: 'Remove block'
+  route_name: 'entity.block.delete_form'
+  group: 'block'

web/core/modules/block/block.links.menu.yml

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+block.admin_display:
+  title: 'Block layout'
+  parent: system.admin_structure
+  description: 'Configure what block content appears in your site''s sidebars and other regions.'
+  route_name: block.admin_display

web/core/modules/block/block.links.task.yml

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+entity.block.edit_form:
+  title: 'Configure block'
+  route_name: entity.block.edit_form
+  base_route: entity.block.edit_form
+
+# Per theme block layout pages.
+block.admin_display:
+  title: 'Block layout'
+  route_name: block.admin_display
+  base_route: block.admin_display
+block.admin_display_theme:
+  title: 'Block layout'
+  route_name: block.admin_display_theme
+  parent_id: block.admin_display
+  deriver: 'Drupal\block\Plugin\Derivative\ThemeLocalTask'

web/core/modules/block/block.module

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+<?php
+
+/**
+ * @file
+ */
+
+use Drupal\block\Hook\BlockHooks;
+use Drupal\Core\Installer\InstallerKernel;
+
+/**
+ * Initializes blocks for installed themes.
+ *
+ * @param string[] $theme_list
+ *   An array of theme names.
+ *
+ * @see block_modules_installed()
+ */
+function block_themes_installed($theme_list): void {
+  // Do not create blocks during config sync.
+  if (\Drupal::service('config.installer')->isSyncing()) {
+    return;
+  }
+  // Disable this functionality prior to install profile installation because
+  // block configuration is often optional or provided by the install profile
+  // itself. block_theme_initialize() will be called when the install profile is
+  // installed.
+  if (InstallerKernel::installationAttempted() && \Drupal::config('core.extension')->get('module.' . \Drupal::installProfile()) === NULL) {
+    return;
+  }
+
+  foreach ($theme_list as $theme) {
+    // Don't initialize themes that are not displayed in the UI.
+    if (\Drupal::service('theme_handler')->hasUi($theme)) {
+      block_theme_initialize($theme);
+    }
+  }
+}
+
+/**
+ * Assigns an initial, default set of blocks for a theme.
+ *
+ * This function is called the first time a new theme is installed. The new
+ * theme gets a copy of the default theme's blocks, with the difference that if
+ * a particular region isn't available in the new theme, the block is assigned
+ * to the new theme's default region.
+ *
+ * @param string $theme
+ *   The name of a theme.
+ */
+function block_theme_initialize($theme): void {
+  // Initialize theme's blocks if none already registered.
+  $has_blocks = \Drupal::entityTypeManager()->getStorage('block')->loadByProperties(['theme' => $theme]);
+  if (!$has_blocks) {
+    $default_theme = \Drupal::config('system.theme')->get('default');
+    // Apply only to new theme's visible regions.
+    $regions = system_region_list($theme, REGIONS_VISIBLE);
+    $default_theme_blocks = \Drupal::entityTypeManager()->getStorage('block')->loadByProperties(['theme' => $default_theme]);
+    foreach ($default_theme_blocks as $default_theme_block_id => $default_theme_block) {
+      if (str_starts_with($default_theme_block_id, $default_theme . '_')) {
+        $id = str_replace($default_theme . '_', '', $default_theme_block_id);
+      }
+      else {
+        $id = $default_theme_block_id;
+      }
+      $id = \Drupal::service('block.repository')->getUniqueMachineName($id, $theme);
+      $block = $default_theme_block->createDuplicateBlock($id, $theme);
+      // If the region isn't supported by the theme, assign the block to the
+      // theme's default region.
+      if (!isset($regions[$block->getRegion()])) {
+        $block->setRegion(system_default_region($theme));
+      }
+      $block->save();
+    }
+  }
+}
+
+/**
+ * Implements hook_theme_suggestions_HOOK().
+ */
+function block_theme_suggestions_block(array $variables): array {
+  $suggestions = [];
+
+  $suggestions[] = 'block__' . $variables['elements']['#configuration']['provider'];
+  // Hyphens (-) and underscores (_) play a special role in theme suggestions.
+  // Theme suggestions should only contain underscores, because within
+  // drupal_find_theme_templates(), underscores are converted to hyphens to
+  // match template file names, and then converted back to underscores to match
+  // pre-processing and other function names. So if your theme suggestion
+  // contains a hyphen, it will end up as an underscore after this conversion,
+  // and your function names won't be recognized. So, we need to convert
+  // hyphens to underscores in block deltas for the theme suggestions.
+
+  // We can safely explode on : because we know the Block plugin type manager
+  // enforces that delimiter for all derivatives.
+  $parts = explode(':', $variables['elements']['#plugin_id']);
+  $suggestion = 'block';
+  while ($part = array_shift($parts)) {
+    $suggestions[] = $suggestion .= '__' . strtr($part, '-', '_');
+  }
+
+  if (!empty($variables['elements']['#id'])) {
+    $suggestions[] = 'block__' . $variables['elements']['#id'];
+  }
+
+  return $suggestions;
+}
+
+/**
+ * Prepares variables for block templates.
+ *
+ * Default template: block.html.twig.
+ *
+ * Prepares the values passed to the theme_block function to be passed
+ * into a pluggable template engine. Uses block properties to generate a
+ * series of template file suggestions. If none are found, the default
+ * block.html.twig is used.
+ *
+ * Most themes use their own copy of block.html.twig. The default is located
+ * inside "core/modules/block/templates/block.html.twig". Look in there for the
+ * full list of available variables.
+ *
+ * @param array $variables
+ *   An associative array containing:
+ *   - elements: An associative array containing the properties of the element.
+ *     Properties used: #block, #configuration, #children, #plugin_id.
+ *
+ * @deprecated in drupal:11.2.0 and is removed from drupal:12.0.0. Initial
+ *  template_preprocess functions are registered directly in hook_theme().
+ *
+ * @see https://www.drupal.org/node/3504125
+ */
+function template_preprocess_block(&$variables): void {
+  @trigger_error(__FUNCTION__ . '() is deprecated in drupal:11.2.0 and is removed from drupal:12.0.0. Initial template_preprocess functions are registered directly in hook_theme(). See https://www.drupal.org/node/3504125', E_USER_DEPRECATED);
+  \Drupal::service(BlockHooks::class)->preprocessBlock($variables);
+}

web/core/modules/block/block.permissions.yml

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+administer blocks:
+  title: 'Administer blocks'

web/core/modules/block/block.post_update.php

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+<?php
+
+/**
+ * @file
+ * Post update functions for Block.
+ */
+
+use Drupal\block\BlockInterface;
+use Drupal\Core\Config\Entity\ConfigEntityUpdater;
+
+/**
+ * Implements hook_removed_post_updates().
+ */
+function block_removed_post_updates(): array {
+  return [
+    'block_post_update_disable_blocks_with_missing_contexts' => '9.0.0',
+    'block_post_update_disabled_region_update' => '9.0.0',
+    'block_post_update_fix_negate_in_conditions' => '9.0.0',
+    'block_post_update_replace_node_type_condition' => '10.0.0',
+  ];
+}
+
+/**
+ * Ensures that all block weights are integers.
+ */
+function block_post_update_make_weight_integer(array &$sandbox = []): void {
+  \Drupal::classResolver(ConfigEntityUpdater::class)
+    ->update($sandbox, 'block', function (BlockInterface $block): bool {
+      $weight = $block->getWeight();
+      if (!is_int($weight)) {
+        $block->setWeight($weight);
+        return TRUE;
+      }
+      return FALSE;
+    });
+}
+
+/**
+ * Updates the `depth` setting to NULL if it is 0 in any menu blocks.
+ */
+function block_post_update_set_menu_block_depth_to_null_if_zero(array &$sandbox = []): void {
+  \Drupal::classResolver(ConfigEntityUpdater::class)
+    ->update($sandbox, 'block', function (BlockInterface $block): bool {
+      if ($block->getPlugin()->getBaseId() === 'system_menu_block') {
+        $settings = $block->get('settings');
+        // Use `empty()` to account for either integer 0, or '0'.
+        if (empty($settings['depth'])) {
+          $settings['depth'] = NULL;
+        }
+        $block->set('settings', $settings);
+        return TRUE;
+      }
+      return FALSE;
+    });
+}

web/core/modules/block/block.routing.yml

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+block.admin_demo:
+  path: '/admin/structure/block/demo/{theme}'
+  defaults:
+    _controller: '\Drupal\block\Controller\BlockController::demo'
+    _title_callback: 'theme_handler:getName'
+  requirements:
+    _access_theme: 'TRUE'
+    _permission: 'administer blocks'
+  options:
+    _admin_route: FALSE
+
+entity.block.delete_form:
+  path: '/admin/structure/block/manage/{block}/delete'
+  defaults:
+    _entity_form: 'block.delete'
+    _title: 'Remove block'
+  requirements:
+    _permission: 'administer blocks'
+
+entity.block.edit_form:
+  path: '/admin/structure/block/manage/{block}'
+  defaults:
+    _entity_form: 'block.default'
+    _title: 'Configure block'
+  requirements:
+    _entity_access: 'block.update'
+
+entity.block.enable:
+  path: '/admin/structure/block/manage/{block}/enable'
+  defaults:
+    _controller: '\Drupal\block\Controller\BlockController::performOperation'
+    op: enable
+  requirements:
+    _entity_access: 'block.enable'
+    _csrf_token: 'TRUE'
+
+entity.block.disable:
+  path: '/admin/structure/block/manage/{block}/disable'
+  defaults:
+    _controller: '\Drupal\block\Controller\BlockController::performOperation'
+    op: disable
+  requirements:
+    _entity_access: 'block.disable'
+    _csrf_token: 'TRUE'
+
+block.admin_display:
+  path: '/admin/structure/block'
+  defaults:
+    _controller: '\Drupal\block\Controller\BlockListController::listing'
+    _title: 'Block layout'
+  requirements:
+    _permission: 'administer blocks'
+
+block.admin_display_theme:
+  path: '/admin/structure/block/list/{theme}'
+  defaults:
+    _controller: '\Drupal\block\Controller\BlockListController::listing'
+    _title: 'Block layout'
+  requirements:
+    _access_theme: 'TRUE'
+    _permission: 'administer blocks'
+
+block.admin_library:
+  path: '/admin/structure/block/library/{theme}'
+  defaults:
+    _controller: '\Drupal\block\Controller\BlockLibraryController::listBlocks'
+    _title: 'Place block'
+  requirements:
+    _access_theme: 'TRUE'
+    _permission: 'administer blocks'
+
+block.admin_add:
+  path: '/admin/structure/block/add/{plugin_id}/{theme}'
+  defaults:
+    _controller: '\Drupal\block\Controller\BlockAddController::blockAddConfigureForm'
+    theme: null
+    _title: 'Configure block'
+  requirements:
+    _permission: 'administer blocks'
+
+block.category_autocomplete:
+  path: '/block-category/autocomplete'
+  defaults:
+    _controller: '\Drupal\block\Controller\CategoryAutocompleteController::autocomplete'
+  requirements:
+    _permission: 'administer blocks'

web/core/modules/block/block.services.yml

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+services:
+  _defaults:
+    autoconfigure: true
+  theme.negotiator.block.admin_demo:
+    class: Drupal\block\Theme\AdminDemoNegotiator
+    tags:
+      - { name: theme_negotiator, priority: 1000 }
+  block.page_display_variant_subscriber:
+    class: Drupal\block\EventSubscriber\BlockPageDisplayVariantSubscriber
+  block.repository:
+    class: Drupal\block\BlockRepository
+    arguments: ['@entity_type.manager', '@theme.manager', '@context.handler']
+  Drupal\block\BlockRepositoryInterface: '@block.repository'

web/core/modules/block/config/schema/block.schema.yml

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+# Schema for the configuration files of the Block module.
+
+block.block.*:
+  type: config_entity
+  label: 'Block'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    id:
+      type: machine_name
+      label: 'ID'
+      # Blocks have atypical machine names: they allow periods for historical reasons.
+      # @see https://www.drupal.org/project/drupal/issues/2685917
+      # @see https://www.drupal.org/project/drupal/issues/2043527
+      constraints:
+        Regex:
+          pattern: '/^[a-z0-9_.]+$/'
+          message: "The %value machine name is not valid."
+    theme:
+      type: string
+      label: 'Theme'
+      constraints:
+        NotBlank: []
+        ExtensionName: []
+        ExtensionExists: theme
+    region:
+      type: string
+      label: 'Region'
+      constraints:
+        NotBlank: []
+        Callback: ['\Drupal\block\Entity\Block', validateRegion]
+    weight:
+      type: weight
+      label: 'Weight'
+    provider:
+      # @todo Deprecate this from config schema and remove it from the `config_export` definition in https://www.drupal.org/project/drupal/issues/3426278
+      nullable: true
+      type: string
+      label: 'Provider'
+    plugin:
+      type: string
+      label: 'Plugin'
+      constraints:
+        PluginExists:
+          manager: plugin.manager.block
+          interface: Drupal\Core\Block\BlockPluginInterface
+          # Block plugin IDs may not be valid in blocks that are backed by
+          # block_content entities that don't exist yet. Therefore, it's okay
+          # to consider the fallback plugin ID as valid.
+          allowFallback: true
+    settings:
+      type: block.settings.[%parent.plugin]
+    visibility:
+      type: sequence
+      label: 'Visibility Conditions'
+      sequence:
+        type: condition.plugin.[id]
+        label: 'Visibility Condition'

web/core/modules/block/css/block.admin.css

@@ -0,0 +1,47 @@
+/* Block listing page */
+.region-title__action {
+  display: inline-block;
+  margin-left: 1em; /* LTR */
+}
+[dir="rtl"] .region-title__action {
+  margin-right: 1em;
+  margin-left: 0;
+}
+
+/* Block demo mode */
+.block-region {
+  margin-top: 4px;
+  margin-bottom: 4px;
+  padding: 3px;
+  color: #000;
+  background-color: #ff6;
+}
+a.block-demo-backlink,
+a.block-demo-backlink:link,
+a.block-demo-backlink:visited {
+  position: fixed;
+  z-index: 499;
+  left: 20px; /* LTR */
+  padding: 5px 10px;
+  color: #000;
+  border-radius: 0 0 10px 10px;
+  background-color: #b4d7f0;
+  font-family: "Lucida Grande", Verdana, sans-serif;
+  font-size: small;
+  line-height: 20px;
+}
+a.block-demo-backlink:hover {
+  text-decoration: underline;
+}
+
+/* Configure block form - Block description */
+.block-form .form-item-settings-admin-label label {
+  display: inline;
+}
+.block-form .form-item-settings-admin-label label::after {
+  content: ":";
+}
+.block-disabled:not(:hover) {
+  opacity: 0.675;
+  background: #fcfcfa;
+}

web/core/modules/block/help_topics/block.configure.html.twig

@@ -0,0 +1,27 @@
+---
+label: 'Configuring a previously-placed block'
+related:
+  - block.overview
+  - core.ui_accessibility
+---
+{% set layout_link_text %}{% trans %}Block layout{% endtrans %}{% endset %}
+{% set layout_link = render_var(help_route_link(layout_link_text, 'block.admin_display')) %}
+<h2>{% trans %}Goal{% endtrans %}</h2>
+<p>{% trans %}Configure the settings of a block that was previously placed in a region of a theme.{% endtrans %}</p>
+<h2>{% trans %}Steps{% endtrans %}</h2>
+<ol>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Structure</em> &gt; <em>{{ layout_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}Click the name of the theme that contains the block.{% endtrans %}</li>
+  <li>{% trans %}Optionally, click <em>Demonstrate block regions</em> to see the regions of the theme.{% endtrans %}</li>
+  <li>{% trans %}If you only want to change the region where a block is located, or the ordering of blocks within a region, drag blocks to their desired positions and click <em>Save blocks</em>.{% endtrans %}</li>
+<li>{% trans %}If you want to change additional settings, find the region where the block you want to update is currently located, and click <em>Configure</em> in the line of the block description.{% endtrans %}</li>
+  <li>{% trans %}Edit the block's settings. The available settings vary depending on the module that provides the block, but for all blocks you can change:{% endtrans %}
+    <ul>
+      <li>{% trans %}<em>Block title</em>: The heading for the block on your site -- for some blocks, you will need to check the <em>Override title</em> checkbox in order to enter a title{% endtrans %}</li>
+      <li>{% trans %}<em>Display title</em>: Check the box if you want the title displayed{% endtrans %}</li>
+      <li>{% trans %}<em>Visibility</em>: Add conditions for when the block should be displayed{% endtrans %}</li>
+      <li>{% trans %}<em>Region</em>: Change the theme region the block is displayed in{% endtrans %}</li>
+    </ul>
+  </li>
+  <li>{% trans %}Click <em>Save block</em>.{% endtrans %}</li>
+</ol>

web/core/modules/block/help_topics/block.overview.html.twig

@@ -0,0 +1,20 @@
+---
+label: 'Managing blocks'
+top_level: true
+related:
+  - core.content_structure
+---
+<h2>{% trans %}What are blocks?{% endtrans %}</h2>
+<p>{% trans %}Blocks are boxes of content rendered into an area, or region, of a web page of your site. Blocks are placed and configured specifically for each theme.{% endtrans %}</p>
+<h2>{% trans %}What are content blocks?{% endtrans %}</h2>
+<p>{% trans %}Content blocks are blocks whose content you can edit. You can define one or more <em>block types</em>, and attach fields to each block type. Content blocks can be placed just like blocks provided by other modules.{% endtrans %}</p>
+<h2>{% trans %}What is the block description?{% endtrans %}</h2>
+<p>{% trans %}The block description is an identification name for a block, which is shown in the administrative interface. It is not displayed on the site.{% endtrans %}</p>
+<h2>{% trans %}What is the block title?{% endtrans %}</h2>
+<p>{% trans %}The block title is the heading that is optionally shown to site visitors when the block is placed in a region.{% endtrans %}</p>
+<h2>{% trans %}Overview for managing blocks{% endtrans %}</h2>
+<p>{% trans %}The <em>Block</em> module allows you to place blocks in regions of your installed themes, and configure block settings. The <em>Block Content</em> module allows you to manage block types and content blocks. See the related topics listed below for specific tasks.{% endtrans %}</p>
+<h2>{% trans %}Additional resources{% endtrans %}</h2>
+<ul>
+  <li>{% trans %}<a href="https://www.drupal.org/docs/user_guide/en/blocks-chapter.html">Blocks (Drupal User Guide)</a>{% endtrans %}</li>
+</ul>

web/core/modules/block/help_topics/block.place.html.twig

@@ -0,0 +1,22 @@
+---
+label: 'Placing a block'
+related:
+  - block.overview
+  - block.configure
+---
+{% set layout_link_text %}
+{% trans %}Block layout{% endtrans %}
+{% endset %}
+{% set layout_link = render_var(help_route_link(layout_link_text, 'block.admin_display')) %}
+{% set configure_topic = render_var(help_topic_link('block.configure')) %}
+<h2>{% trans %}Goal{% endtrans %}</h2>
+<p>{% trans %}Place a block into a theme's region. {% endtrans %}</p>
+<h2>{% trans %}Steps{% endtrans %}</h2>
+<ol>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Structure</em> &gt; {{ layout_link }}.{% endtrans %}</li>
+  <li>{% trans %}Click the name of the theme that you want to place the block in.{% endtrans %}</li>
+  <li>{% trans %}Optionally, click <em>Demonstrate block regions</em> to see the regions of the theme.{% endtrans %}</li>
+  <li>{% trans %}Find the region where you want the block, and click <em>Place block</em> in that region. A modal dialog will pop up.{% endtrans %}</li>
+  <li>{% trans %}Find the block you want to place and click <em>Place block</em>. A <em>Configure block</em> modal dialog will pop up.{% endtrans %}</li>
+  <li>{% trans %}Configure the block and click <em>Save block</em>; see {{ configure_topic }} for configuration details.{% endtrans %}</li>
+</ol>

web/core/modules/block/js/block.admin.js

@@ -0,0 +1,105 @@
+/**
+ * @file
+ * Block admin behaviors.
+ */
+
+(function ($, Drupal, debounce, once) {
+  /**
+   * Filters the block list by a text input search string.
+   *
+   * The text input will have the selector `input.block-filter-text`.
+   *
+   * The target element to do searching in will be in the selector
+   * `input.block-filter-text[data-element]`
+   *
+   * The text source where the text should be found will have the selector
+   * `.block-filter-text-source`
+   *
+   * @type {Drupal~behavior}
+   *
+   * @prop {Drupal~behaviorAttach} attach
+   *   Attaches the behavior for the block filtering.
+   */
+  Drupal.behaviors.blockFilterByText = {
+    attach(context, settings) {
+      const $input = $(once('block-filter-text', 'input.block-filter-text'));
+      const $table = $($input.attr('data-element'));
+      let $filterRows;
+
+      /**
+       * Filters the block list.
+       *
+       * @param {jQuery.Event} e
+       *   The jQuery event for the keyup event that triggered the filter.
+       */
+      function filterBlockList(e) {
+        const query = e.target.value.toLowerCase();
+
+        /**
+         * Shows or hides the block entry based on the query.
+         *
+         * @param {number} index
+         *   The index in the loop, as provided by `jQuery.each`
+         * @param {HTMLElement} label
+         *   The label of the block.
+         */
+        function toggleBlockEntry(index, label) {
+          const $row = $(label).parent().parent();
+          const textMatch = label.textContent.toLowerCase().includes(query);
+          $row.toggle(textMatch);
+        }
+
+        // Filter if the length of the query is at least 2 characters.
+        if (query.length >= 2) {
+          $filterRows.each(toggleBlockEntry);
+          Drupal.announce(
+            Drupal.formatPlural(
+              $table.find('tr:visible').length - 1,
+              '1 block is available in the modified list.',
+              '@count blocks are available in the modified list.',
+            ),
+          );
+        } else {
+          $filterRows.each(function (index) {
+            $(this).parent().parent().show();
+          });
+        }
+      }
+
+      if ($table.length) {
+        $filterRows = $table.find('div.block-filter-text-source');
+        $input.on('keyup', debounce(filterBlockList, 200));
+      }
+    },
+  };
+
+  /**
+   * Highlights the block that was just placed into the block listing.
+   *
+   * @type {Drupal~behavior}
+   *
+   * @prop {Drupal~behaviorAttach} attach
+   *   Attaches the behavior for the block placement highlighting.
+   */
+  Drupal.behaviors.blockHighlightPlacement = {
+    attach(context, settings) {
+      // Ensure that the block we are attempting to scroll to actually exists.
+      if (settings.blockPlacement && $('.js-block-placed').length) {
+        once(
+          'block-highlight',
+          '[data-drupal-selector="edit-blocks"]',
+          context,
+        ).forEach((container) => {
+          const $container = $(container);
+          window.scrollTo({
+            top:
+              $('.js-block-placed').offset().top -
+              $container.offset().top +
+              $container.scrollTop(),
+            behavior: 'smooth',
+          });
+        });
+      }
+    },
+  };
+})(jQuery, Drupal, Drupal.debounce, once);

web/core/modules/block/js/block.js

@@ -0,0 +1,258 @@
+/**
+ * @file
+ * Block behaviors.
+ */
+
+(function ($, window, Drupal, once) {
+  /**
+   * Provide the summary information for the block settings vertical tabs.
+   *
+   * @type {Drupal~behavior}
+   *
+   * @prop {Drupal~behaviorAttach} attach
+   *   Attaches the behavior for the block settings summaries.
+   */
+  Drupal.behaviors.blockSettingsSummary = {
+    attach() {
+      // The drupalSetSummary method required for this behavior is not available
+      // on the Blocks administration page, so we need to make sure this
+      // behavior is processed only if drupalSetSummary is defined.
+      if (typeof $.fn.drupalSetSummary === 'undefined') {
+        return;
+      }
+
+      /**
+       * Create a summary for checkboxes in the provided context.
+       *
+       * @param {Document|HTMLElement} context
+       *   A context where one would find checkboxes to summarize.
+       *
+       * @return {string}
+       *   A string with the summary.
+       */
+      function checkboxesSummary(context) {
+        const values = [];
+        const $checkboxes = $(context).find(
+          'input[type="checkbox"]:checked + label',
+        );
+        const il = $checkboxes.length;
+        for (let i = 0; i < il; i++) {
+          values.push($($checkboxes[i]).html());
+        }
+        if (!values.length) {
+          values.push(Drupal.t('Not restricted'));
+        }
+        return values.join(', ');
+      }
+
+      $(
+        '[data-drupal-selector="edit-visibility-node-type"], [data-drupal-selector="edit-visibility-entity-bundlenode"], [data-drupal-selector="edit-visibility-language"], [data-drupal-selector="edit-visibility-user-role"], [data-drupal-selector="edit-visibility-response-status"]',
+      ).drupalSetSummary(checkboxesSummary);
+
+      $(
+        '[data-drupal-selector="edit-visibility-request-path"]',
+      ).drupalSetSummary((context) => {
+        const $pages = $(context).find(
+          'textarea[name="visibility[request_path][pages]"]',
+        );
+        if (!$pages.length || !$pages[0].value) {
+          return Drupal.t('Not restricted');
+        }
+
+        return Drupal.t('Restricted to certain pages');
+      });
+    },
+  };
+
+  /**
+   * Move a block in the blocks table between regions via select list.
+   *
+   * This behavior is dependent on the tableDrag behavior, since it uses the
+   * objects initialized in that behavior to update the row.
+   *
+   * @type {Drupal~behavior}
+   *
+   * @prop {Drupal~behaviorAttach} attach
+   *   Attaches the tableDrag behavior for blocks in block administration.
+   */
+  Drupal.behaviors.blockDrag = {
+    attach(context, settings) {
+      // tableDrag is required and we should be on the blocks admin page.
+      if (typeof Drupal?.tableDrag?.blocks === 'undefined') {
+        return;
+      }
+
+      /**
+       * Function to check empty regions and toggle classes based on this.
+       *
+       * @param {jQuery} table
+       *   The jQuery object representing the table to inspect.
+       * @param {Drupal.tableDrag.row} rowObject
+       *   Drupal table drag row dropped.
+       */
+      function checkEmptyRegions(table, rowObject) {
+        table.find('tr.region-message').each(function () {
+          const $this = $(this);
+          // If the dragged row is in this region, but above the message row,
+          // swap it down one space.
+          if ($this.prev('tr').get(0) === rowObject.element) {
+            // Prevent a recursion problem when using the keyboard to move rows
+            // up.
+            if (
+              rowObject.method !== 'keyboard' ||
+              rowObject.direction === 'down'
+            ) {
+              rowObject.swap('after', this);
+            }
+          }
+          // This region has become empty.
+          if (
+            $this.next('tr').length === 0 ||
+            !$this.next('tr')[0].matches('.draggable')
+          ) {
+            $this.removeClass('region-populated').addClass('region-empty');
+          }
+          // This region has become populated.
+          else if (this.matches('.region-empty')) {
+            $this.removeClass('region-empty').addClass('region-populated');
+          }
+        });
+      }
+
+      /**
+       * Function to update the last placed row with the correct classes.
+       *
+       * @param {jQuery} table
+       *   The jQuery object representing the table to inspect.
+       * @param {Drupal.tableDrag.row} rowObject
+       *   Drupal table drag row dropped.
+       */
+      function updateLastPlaced(table, rowObject) {
+        // Remove the color-success class from new block if applicable.
+        table.find('.color-success').removeClass('color-success');
+        const $rowObject = $(rowObject);
+        if (!rowObject.element.matches('.drag-previous')) {
+          table.find('.drag-previous').removeClass('drag-previous');
+          $rowObject.addClass('drag-previous');
+        }
+      }
+
+      /**
+       * Update block weights in the given region.
+       *
+       * @param {jQuery} table
+       *   Table with draggable items.
+       * @param {string} region
+       *   Machine name of region containing blocks to update.
+       */
+      function updateBlockWeights(table, region) {
+        // Calculate minimum weight.
+        let weight = -Math.round(table.find('.draggable').length / 2);
+        // Update the block weights.
+        table
+          .find(`.region-${region}-message`)
+          .nextUntil('.region-title')
+          .find('select.block-weight')
+          .each(function () {
+            // Increment the weight before assigning it to prevent using the
+            // absolute minimum available weight. This way we always have an
+            // unused upper and lower bound, which makes manually setting the
+            // weights easier for users who prefer to do it that way.
+            this.value = ++weight;
+          });
+      }
+
+      const table = $('#blocks');
+      // Get the blocks tableDrag object.
+      const tableDrag = Drupal.tableDrag.blocks;
+      // Add a handler for when a row is swapped, update empty regions.
+      tableDrag.row.prototype.onSwap = function (swappedRow) {
+        checkEmptyRegions(table, this);
+        updateLastPlaced(table, this);
+      };
+
+      // Add a handler so when a row is dropped, update fields dropped into
+      // new regions.
+      tableDrag.onDrop = function () {
+        const dragObject = this;
+        const $rowElement = $(dragObject.rowObject.element);
+        // Use "region-message" row instead of "region" row because
+        // "region-{region_name}-message" is less prone to regexp match errors.
+        const regionRow = $rowElement.prevAll('tr.region-message').get(0);
+        const regionName = regionRow.className.replace(
+          /([^ ]+[ ]+)*region-([^ ]+)-message([ ]+[^ ]+)*/,
+          '$2',
+        );
+        const regionField = $rowElement.find('select.block-region-select');
+        // Check whether the newly picked region is available for this block.
+        if (regionField.find(`option[value=${regionName}]`).length === 0) {
+          // If not, alert the user and keep the block in its old region
+          // setting.
+          window.alert(Drupal.t('The block cannot be placed in this region.'));
+          // Simulate that there was a selected element change, so the row is
+          // put back to from where the user tried to drag it.
+          regionField.trigger('change');
+        }
+
+        // Update region and weight fields if the region has been changed.
+        if (!regionField[0].matches(`.block-region-${regionName}`)) {
+          const weightField = $rowElement.find('select.block-weight');
+          const oldRegionName = weightField[0].className.replace(
+            /([^ ]+[ ]+)*block-weight-([^ ]+)([ ]+[^ ]+)*/,
+            '$2',
+          );
+          regionField
+            .removeClass(`block-region-${oldRegionName}`)
+            .addClass(`block-region-${regionName}`);
+          weightField
+            .removeClass(`block-weight-${oldRegionName}`)
+            .addClass(`block-weight-${regionName}`);
+          regionField[0].value = regionName;
+        }
+
+        updateBlockWeights(table, regionName);
+      };
+
+      // Add the behavior to each region select list.
+      $(once('block-region-select', 'select.block-region-select', context)).on(
+        'change',
+        function (event) {
+          // Make our new row and select field.
+          const row = $(this).closest('tr');
+          const select = $(this);
+          // Find the correct region and insert the row as the last in the
+          // region.
+          tableDrag.rowObject = new tableDrag.row(row[0]);
+          const regionMessage = table.find(
+            `.region-${select[0].value}-message`,
+          );
+          const regionItems = regionMessage.nextUntil(
+            '.region-message, .region-title',
+          );
+          if (regionItems.length) {
+            regionItems.last().after(row);
+          }
+          // We found that regionMessage is the last row.
+          else {
+            regionMessage.after(row);
+          }
+          updateBlockWeights(table, select[0].value);
+          // Modify empty regions with added or removed fields.
+          checkEmptyRegions(table, tableDrag.rowObject);
+          // Update last placed block indication.
+          updateLastPlaced(table, tableDrag.rowObject);
+          // Show unsaved changes warning.
+          if (!tableDrag.changed) {
+            $(Drupal.theme('tableDragChangedWarning'))
+              .insertBefore(tableDrag.table)
+              .hide()
+              .fadeIn('slow');
+            tableDrag.changed = true;
+          }
+          // Remove focus from selectbox.
+          select.trigger('blur');
+        },
+      );
+    },
+  };
+})(jQuery, window, Drupal, once);

web/core/modules/block/migrations/d6_block.yml

@@ -0,0 +1,130 @@
+id: d6_block
+label: Blocks
+# This configuration migration depends on the d6_custom_block content migration.
+migration_tags:
+  - Drupal 6
+  - Configuration
+source:
+  plugin: block
+process:
+  # Block status is not a thing in Drupal 8, so this is how we skip over
+  # disabled blocks.
+  status:
+    plugin: skip_on_empty
+    method: row
+    source: status
+  id:
+    # We need something unique, so book, book_1 etc will do.
+    plugin: make_unique_entity_field
+
+    entity_type: block
+    field: id
+    postfix: _
+    length: 29
+    source: module
+  _block_module_plugin_id:
+    -
+      plugin: static_map
+      source:
+        - module
+      map:
+        block: block
+      default_value: ''
+    -
+      plugin: skip_on_empty
+      method: process
+    -
+      plugin: migration_lookup
+      migration:
+        - d6_custom_block
+      source:
+        - delta
+  plugin:
+    -
+      plugin: static_map
+      bypass: true
+      source:
+        - module
+        - delta
+      map:
+        book:
+          0: book_navigation
+        comment:
+          0: views_block:comments_recent-block_1
+        forum:
+          0: forum_active_block
+          1: forum_new_block
+        locale:
+          0: language_block
+        search:
+          0: search_form_block
+        statistics:
+          0: statistics_popular_block
+        system:
+          0: system_powered_by_block
+        user:
+          0: user_login_block
+          1: system_menu_block:tools
+          2: views_block:who_s_new-block_1
+          3: views_block:who_s_online-who_s_online_block
+    -
+      plugin: block_plugin_id
+    -
+      plugin: skip_on_empty
+      method: row
+  theme:
+    plugin: block_theme
+    source:
+      - theme
+      - default_theme
+      - admin_theme
+  region:
+    plugin: block_region
+    source:
+      - theme
+      - '@theme'
+      - region
+    map:
+      garland:
+        olivero:
+          # Garland 6.x --> Olivero
+          header: header
+          footer: footer_top
+          left: sidebar
+          right: sidebar
+    # If mapping fails, put the block in the content region.
+    default_value: content
+  weight:
+    -
+      plugin: get
+      source: weight
+    -
+      # Block weights must be integers.
+      plugin: callback
+      callable: intval
+  settings:
+    plugin: block_settings
+    source:
+      - '@plugin'
+      - delta
+      - settings
+      - title
+  _role_ids:
+    plugin: roles_lookup
+    migration: d6_user_role
+  visibility:
+    plugin: block_visibility
+    source:
+      - visibility
+      - pages
+      - roles
+    # If the block uses PHP visibility, don't migrate it unless the PHP module
+    # is enabled.
+    skip_php: true
+destination:
+  plugin: entity:block
+migration_dependencies:
+  required:
+    - d6_menu
+    - d6_custom_block
+    - d6_user_role

web/core/modules/block/migrations/d7_block.yml

@@ -0,0 +1,150 @@
+# cspell:ignore firstcolumn secondcolumn thirdcolumn fourthcolumn
+id: d7_block
+label: Blocks
+# This configuration migration depends on the d7_custom_block content migration.
+migration_tags:
+  - Drupal 7
+  - Configuration
+source:
+  plugin: block
+process:
+  # Block status is not a thing in Drupal 8, so this is how we skip over
+  # disabled blocks.
+  status:
+    plugin: skip_on_empty
+    method: row
+    source: status
+  id:
+    -
+      plugin: concat
+      source:
+        - theme
+        - module
+        - delta
+      delimiter: _
+    -
+      plugin: machine_name
+      field: id
+  _block_module_plugin_id:
+    -
+      plugin: static_map
+      source:
+        - module
+      map:
+        block: block
+      default_value: ''
+    -
+      plugin: skip_on_empty
+      method: process
+    -
+      plugin: migration_lookup
+      migration:
+        - d7_custom_block
+      source:
+        - delta
+  plugin:
+    -
+      plugin: static_map
+      bypass: true
+      source:
+        - module
+        - delta
+      map:
+        book:
+          navigation: book_navigation
+        comment:
+          recent: views_block:comments_recent-block_1
+        forum:
+          active: forum_active_block
+          new: forum_new_block
+        # locale:
+        #  0: language_block
+        search:
+          form: search_form_block
+        statistics:
+          popular: statistics_popular_block
+        system:
+          main: system_main_block
+          'powered-by': system_powered_by_block
+        user:
+          login: user_login_block
+          # 1: system_menu_block:tools
+          new: views_block:who_s_new-block_1
+          online: views_block:who_s_online-who_s_online_block
+    -
+      plugin: block_plugin_id
+    -
+      plugin: skip_on_empty
+      method: row
+  theme:
+    plugin: block_theme
+    source:
+      - theme
+      - default_theme
+      - admin_theme
+  region:
+    plugin: block_region
+    source:
+      - theme
+      - '@theme'
+      - region
+    map:
+      bartik:
+        # Bartik 7.x --> Olivero 9.4.x
+        olivero:
+          featured: highlighted
+          triptych_first: content_below
+          triptych_middle: content_below
+          triptych_last: content_below
+          footer_firstcolumn: footer_top
+          footer_secondcolumn: footer_top
+          footer_thirdcolumn: footer_top
+          footer_fourthcolumn: footer_top
+          footer: footer_bottom
+      seven:
+        # Seven 7.x --> Claro 9.4.x
+        claro:
+          header: 'header'
+          pre_content: 'pre_content'
+          breadcrumb: 'breadcrumb'
+          highlighted: 'highlighted'
+          help: 'help'
+          content: 'content'
+          page_top: 'page_top'
+          page_bottom: 'page_bottom'
+          sidebar_first: 'sidebar_first'
+    # If mapping fails, put the block in the content region.
+    default_value: content
+  weight:
+    -
+      plugin: get
+      source: weight
+    -
+      # Block weights must be integers.
+      plugin: callback
+      callable: intval
+  settings:
+    plugin: block_settings
+    source:
+      - '@plugin'
+      - delta
+      - settings
+      - title
+  _role_ids:
+    plugin: roles_lookup
+    migration: d7_user_role
+  visibility:
+    plugin: block_visibility
+    source:
+      - visibility
+      - pages
+      - roles
+    # If the block uses PHP visibility, don't migrate it unless the PHP module
+    # is enabled.
+    skip_php: true
+destination:
+  plugin: entity:block
+migration_dependencies:
+  optional:
+    - d7_custom_block
+    - d7_user_role

web/core/modules/block/migrations/state/block.migrate_drupal.yml

@@ -0,0 +1,5 @@
+finished:
+  6:
+    block: block
+  7:
+    block: block

web/core/modules/block/src/BlockAccessControlHandler.php

@@ -0,0 +1,170 @@
+<?php
+
+namespace Drupal\block;
+
+use Drupal\Component\Plugin\Exception\ContextException;
+use Drupal\Component\Plugin\Exception\MissingValueContextException;
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Cache\CacheableDependencyInterface;
+use Drupal\Core\Condition\ConditionAccessResolverTrait;
+use Drupal\Core\Entity\EntityAccessControlHandler;
+use Drupal\Core\Entity\EntityHandlerInterface;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Plugin\Context\ContextHandlerInterface;
+use Drupal\Core\Plugin\Context\ContextRepositoryInterface;
+use Drupal\Core\Plugin\ContextAwarePluginInterface;
+use Drupal\Core\Session\AccountInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Defines the access control handler for the content block entity type.
+ *
+ * @see \Drupal\block\Entity\Block
+ */
+class BlockAccessControlHandler extends EntityAccessControlHandler implements EntityHandlerInterface {
+
+  use ConditionAccessResolverTrait;
+
+  /**
+   * The plugin context handler.
+   *
+   * @var \Drupal\Core\Plugin\Context\ContextHandlerInterface
+   */
+  protected $contextHandler;
+
+  /**
+   * The context manager service.
+   *
+   * @var \Drupal\Core\Plugin\Context\ContextRepositoryInterface
+   */
+  protected $contextRepository;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
+    return new static(
+      $entity_type,
+      $container->get('context.handler'),
+      $container->get('context.repository')
+    );
+  }
+
+  /**
+   * Constructs the block access control handler instance.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type definition.
+   * @param \Drupal\Core\Plugin\Context\ContextHandlerInterface $context_handler
+   *   The ContextHandler for applying contexts to conditions properly.
+   * @param \Drupal\Core\Plugin\Context\ContextRepositoryInterface $context_repository
+   *   The lazy context repository service.
+   */
+  public function __construct(EntityTypeInterface $entity_type, ContextHandlerInterface $context_handler, ContextRepositoryInterface $context_repository) {
+    parent::__construct($entity_type);
+    $this->contextHandler = $context_handler;
+    $this->contextRepository = $context_repository;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function checkAccess(EntityInterface $entity, $operation, AccountInterface $account) {
+    /** @var \Drupal\block\BlockInterface $entity */
+    if ($operation != 'view') {
+      return parent::checkAccess($entity, $operation, $account);
+    }
+
+    // Don't grant access to disabled blocks.
+    if (!$entity->status()) {
+      return AccessResult::forbidden()->addCacheableDependency($entity);
+    }
+    else {
+      $conditions = [];
+      $missing_context = FALSE;
+      $missing_value = FALSE;
+      foreach ($entity->getVisibilityConditions() as $condition_id => $condition) {
+        if ($condition instanceof ContextAwarePluginInterface) {
+          try {
+            $contexts = $this->contextRepository->getRuntimeContexts(array_values($condition->getContextMapping()));
+            $this->contextHandler->applyContextMapping($condition, $contexts);
+          }
+          catch (MissingValueContextException) {
+            $missing_value = TRUE;
+          }
+          catch (ContextException) {
+            $missing_context = TRUE;
+          }
+        }
+        $conditions[$condition_id] = $condition;
+      }
+
+      if ($missing_context) {
+        // If any context is missing then we might be missing cacheable
+        // metadata, and don't know based on what conditions the block is
+        // accessible or not. Make sure the result cannot be cached.
+        $access = AccessResult::forbidden()->setCacheMaxAge(0);
+      }
+      elseif ($missing_value) {
+        // The contexts exist but have no value. Deny access without
+        // disabling caching. For example the node type condition will have a
+        // missing context on any non-node route like the frontpage.
+        $access = AccessResult::forbidden();
+      }
+      elseif ($this->resolveConditions($conditions, 'and') !== FALSE) {
+        // Delegate to the plugin.
+        $block_plugin = $entity->getPlugin();
+        try {
+          if ($block_plugin instanceof ContextAwarePluginInterface) {
+            $contexts = $this->contextRepository->getRuntimeContexts(array_values($block_plugin->getContextMapping()));
+            $this->contextHandler->applyContextMapping($block_plugin, $contexts);
+          }
+          $access = $block_plugin->access($account, TRUE);
+        }
+        catch (MissingValueContextException) {
+          // The contexts exist but have no value. Deny access without
+          // disabling caching.
+          $access = AccessResult::forbidden();
+        }
+        catch (ContextException) {
+          // If any context is missing then we might be missing cacheable
+          // metadata, and don't know based on what conditions the block is
+          // accessible or not. Make sure the result cannot be cached.
+          $access = AccessResult::forbidden()->setCacheMaxAge(0);
+        }
+      }
+      else {
+        $reason = count($conditions) > 1
+          ? "One of the block visibility conditions ('%s') denied access."
+          : "The block visibility condition '%s' denied access.";
+        $access = AccessResult::forbidden(sprintf($reason, implode("', '", array_keys($conditions))));
+      }
+
+      $this->mergeCacheabilityFromConditions($access, $conditions);
+
+      // Ensure that access is evaluated again when the block changes.
+      return $access->addCacheableDependency($entity);
+    }
+  }
+
+  /**
+   * Merges cacheable metadata from conditions onto the access result object.
+   *
+   * @param \Drupal\Core\Access\AccessResult $access
+   *   The access result object.
+   * @param \Drupal\Core\Condition\ConditionInterface[] $conditions
+   *   List of visibility conditions.
+   */
+  protected function mergeCacheabilityFromConditions(AccessResult $access, array $conditions) {
+    foreach ($conditions as $condition) {
+      if ($condition instanceof CacheableDependencyInterface) {
+        $access->addCacheTags($condition->getCacheTags());
+        $access->addCacheContexts($condition->getCacheContexts());
+        $access->setCacheMaxAge(Cache::mergeMaxAges($access->getCacheMaxAge(), $condition->getCacheMaxAge()));
+      }
+    }
+  }
+
+}

web/core/modules/block/src/BlockForm.php

@@ -0,0 +1,414 @@
+<?php
+
+namespace Drupal\block;
+
+use Drupal\Component\Utility\Html;
+use Drupal\Core\Plugin\PluginFormFactoryInterface;
+use Drupal\Core\Block\BlockPluginInterface;
+use Drupal\Core\Entity\EntityForm;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Executable\ExecutableManagerInterface;
+use Drupal\Core\Extension\ThemeHandlerInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Form\SubformState;
+use Drupal\Core\Language\LanguageManagerInterface;
+use Drupal\Core\Plugin\ContextAwarePluginInterface;
+use Drupal\Core\Plugin\Context\ContextRepositoryInterface;
+use Drupal\Core\Plugin\PluginWithFormsInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides form for block instance forms.
+ *
+ * @internal
+ */
+class BlockForm extends EntityForm {
+
+  /**
+   * The block entity.
+   *
+   * @var \Drupal\block\BlockInterface
+   */
+  protected $entity;
+
+  /**
+   * The block storage.
+   *
+   * @var \Drupal\Core\Config\Entity\ConfigEntityStorageInterface
+   */
+  protected $storage;
+
+  /**
+   * The condition plugin manager.
+   *
+   * @var \Drupal\Core\Condition\ConditionManager
+   */
+  protected $manager;
+
+  /**
+   * The language manager service.
+   *
+   * @var \Drupal\Core\Language\LanguageManagerInterface
+   */
+  protected $language;
+
+  /**
+   * The theme handler.
+   *
+   * @var \Drupal\Core\Extension\ThemeHandler
+   */
+  protected $themeHandler;
+
+  /**
+   * The context repository service.
+   *
+   * @var \Drupal\Core\Plugin\Context\ContextRepositoryInterface
+   */
+  protected $contextRepository;
+
+  /**
+   * The plugin form manager.
+   *
+   * @var \Drupal\Core\Plugin\PluginFormFactoryInterface
+   */
+  protected $pluginFormFactory;
+
+  /**
+   * Constructs a BlockForm object.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   * @param \Drupal\Core\Executable\ExecutableManagerInterface $manager
+   *   The ConditionManager for building the visibility UI.
+   * @param \Drupal\Core\Plugin\Context\ContextRepositoryInterface $context_repository
+   *   The lazy context repository service.
+   * @param \Drupal\Core\Language\LanguageManagerInterface $language
+   *   The language manager.
+   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
+   *   The theme handler.
+   * @param \Drupal\Core\Plugin\PluginFormFactoryInterface $plugin_form_manager
+   *   The plugin form manager.
+   * @param \Drupal\block\BlockRepositoryInterface $blockRepository
+   *   The block repository service.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, ExecutableManagerInterface $manager, ContextRepositoryInterface $context_repository, LanguageManagerInterface $language, ThemeHandlerInterface $theme_handler, PluginFormFactoryInterface $plugin_form_manager, protected BlockRepositoryInterface $blockRepository) {
+    $this->storage = $entity_type_manager->getStorage('block');
+    $this->manager = $manager;
+    $this->contextRepository = $context_repository;
+    $this->language = $language;
+    $this->themeHandler = $theme_handler;
+    $this->pluginFormFactory = $plugin_form_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity_type.manager'),
+      $container->get('plugin.manager.condition'),
+      $container->get('context.repository'),
+      $container->get('language_manager'),
+      $container->get('theme_handler'),
+      $container->get('plugin_form.factory'),
+      $container->get('block.repository')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function form(array $form, FormStateInterface $form_state) {
+    $entity = $this->entity;
+
+    // Store the gathered contexts in the form state for other objects to use
+    // during form building.
+    $form_state->setTemporaryValue('gathered_contexts', $this->contextRepository->getAvailableContexts());
+
+    $form['#tree'] = TRUE;
+    $form['settings'] = [];
+    $subform_state = SubformState::createForSubform($form['settings'], $form, $form_state);
+    $form['settings'] = $this->getPluginForm($entity->getPlugin())->buildConfigurationForm($form['settings'], $subform_state);
+    $form['visibility'] = $this->buildVisibilityInterface([], $form_state);
+
+    // If creating a new block, calculate a safe default machine name.
+    $form['id'] = [
+      '#type' => 'machine_name',
+      '#maxlength' => 64,
+      '#description' => $this->t('A unique name for this block instance. Must be alpha-numeric and underscore separated.'),
+      '#default_value' => !$entity->isNew() ? $entity->id() : $this->getUniqueMachineName($entity),
+      '#machine_name' => [
+        'exists' => '\Drupal\block\Entity\Block::load',
+        'replace_pattern' => '[^a-z0-9_.]+',
+        'source' => ['settings', 'label'],
+      ],
+      '#required' => TRUE,
+      '#disabled' => !$entity->isNew(),
+    ];
+
+    // Theme settings.
+    if ($theme = $entity->getTheme()) {
+      $form['theme'] = [
+        '#type' => 'value',
+        '#value' => $theme,
+      ];
+    }
+    else {
+      $theme = $this->config('system.theme')->get('default');
+      $theme_options = [];
+      foreach ($this->themeHandler->listInfo() as $theme_name => $theme_info) {
+        if (!empty($theme_info->status)) {
+          $theme_options[$theme_name] = $theme_info->info['name'];
+        }
+      }
+      $form['theme'] = [
+        '#type' => 'select',
+        '#options' => $theme_options,
+        '#title' => $this->t('Theme'),
+        '#default_value' => $theme,
+        '#ajax' => [
+          'callback' => '::themeSwitch',
+          'wrapper' => 'edit-block-region-wrapper',
+        ],
+      ];
+    }
+
+    // Hidden weight setting.
+    $weight = $entity->isNew() ? $this->getRequest()->query->getInt('weight') : $entity->getWeight();
+    $form['weight'] = [
+      '#type' => 'hidden',
+      '#default_value' => $weight,
+    ];
+
+    // Region settings.
+    $entity_region = $entity->getRegion();
+    $region = $entity->isNew() ? $this->getRequest()->query->get('region', $entity_region) : $entity_region;
+    $form['region'] = [
+      '#type' => 'select',
+      '#title' => $this->t('Region'),
+      '#description' => $this->t('Select the region where this block should be displayed.'),
+      '#default_value' => $region,
+      '#required' => TRUE,
+      '#options' => system_region_list($form_state->getValue('theme', $theme), REGIONS_VISIBLE),
+      '#prefix' => '<div id="edit-block-region-wrapper">',
+      '#suffix' => '</div>',
+    ];
+    $form['#attached']['library'][] = 'block/drupal.block.admin';
+    return $form;
+  }
+
+  /**
+   * Handles switching the available regions based on the selected theme.
+   */
+  public function themeSwitch($form, FormStateInterface $form_state) {
+    return $form['region'];
+  }
+
+  /**
+   * Helper function for building the visibility UI form.
+   *
+   * @param array $form
+   *   An associative array containing the structure of the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   *
+   * @return array
+   *   The form array with the visibility UI added in.
+   */
+  protected function buildVisibilityInterface(array $form, FormStateInterface $form_state) {
+    $form['visibility_tabs'] = [
+      '#type' => 'vertical_tabs',
+      '#title' => $this->t('Visibility'),
+      '#parents' => ['visibility_tabs'],
+      '#attached' => [
+        'library' => [
+          'block/drupal.block',
+        ],
+      ],
+    ];
+    // @todo Allow list of conditions to be configured in
+    //   https://www.drupal.org/node/2284687.
+    $visibility = $this->entity->getVisibility();
+    $definitions = $this->manager->getFilteredDefinitions('block_ui', $form_state->getTemporaryValue('gathered_contexts'), ['block' => $this->entity]);
+    foreach ($definitions as $condition_id => $definition) {
+      // Don't display the current theme condition.
+      if ($condition_id == 'current_theme') {
+        continue;
+      }
+      // Don't display the language condition until we have multiple languages.
+      if ($condition_id == 'language' && !$this->language->isMultilingual()) {
+        continue;
+      }
+
+      /** @var \Drupal\Core\Condition\ConditionInterface $condition */
+      $condition = $this->manager->createInstance($condition_id, $visibility[$condition_id] ?? []);
+      $form_state->set(['conditions', $condition_id], $condition);
+      $condition_form = $condition->buildConfigurationForm([], $form_state);
+      $condition_form['#type'] = 'details';
+      $condition_form['#title'] = $condition->getPluginDefinition()['label'];
+      $condition_form['#group'] = 'visibility_tabs';
+      $form[$condition_id] = $condition_form;
+    }
+
+    // Disable negation for specific conditions.
+    $disable_negation = [
+      'entity_bundle:node',
+      'language',
+      'response_status',
+      'user_role',
+    ];
+    foreach ($disable_negation as $condition) {
+      if (isset($form[$condition])) {
+        $form[$condition]['negate']['#type'] = 'value';
+        $form[$condition]['negate']['#value'] = $form[$condition]['negate']['#default_value'];
+      }
+    }
+
+    if (isset($form['user_role'])) {
+      $form['user_role']['#title'] = $this->t('Roles');
+      unset($form['user_role']['roles']['#description']);
+    }
+    if (isset($form['request_path'])) {
+      $form['request_path']['#title'] = $this->t('Pages');
+      $form['request_path']['negate']['#type'] = 'radios';
+      $form['request_path']['negate']['#default_value'] = (int) $form['request_path']['negate']['#default_value'];
+      $form['request_path']['negate']['#title_display'] = 'invisible';
+      $form['request_path']['negate']['#options'] = [
+        $this->t('Show for the listed pages'),
+        $this->t('Hide for the listed pages'),
+      ];
+    }
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function actions(array $form, FormStateInterface $form_state) {
+    $actions = parent::actions($form, $form_state);
+    $actions['submit']['#value'] = $this->t('Save block');
+    $actions['delete']['#title'] = $this->t('Remove block');
+    return $actions;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    parent::validateForm($form, $form_state);
+
+    $form_state->setValue('weight', (int) $form_state->getValue('weight'));
+    // The Block Entity form puts all block plugin form elements in the
+    // settings form element, so just pass that to the block for validation.
+    $this->getPluginForm($this->entity->getPlugin())->validateConfigurationForm($form['settings'], SubformState::createForSubform($form['settings'], $form, $form_state));
+    $this->validateVisibility($form, $form_state);
+  }
+
+  /**
+   * Helper function to independently validate the visibility UI.
+   *
+   * @param array $form
+   *   A nested array form elements comprising the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   */
+  protected function validateVisibility(array $form, FormStateInterface $form_state) {
+    // Validate visibility condition settings.
+    foreach ($form_state->getValue('visibility') as $condition_id => $values) {
+      // Allow the condition to validate the form.
+      $condition = $form_state->get(['conditions', $condition_id]);
+      $condition->validateConfigurationForm($form['visibility'][$condition_id], SubformState::createForSubform($form['visibility'][$condition_id], $form, $form_state));
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    parent::submitForm($form, $form_state);
+
+    $entity = $this->entity;
+    // The Block Entity form puts all block plugin form elements in the
+    // settings form element, so just pass that to the block for submission.
+    $sub_form_state = SubformState::createForSubform($form['settings'], $form, $form_state);
+    // Call the plugin submit handler.
+    $block = $entity->getPlugin();
+    $this->getPluginForm($block)->submitConfigurationForm($form, $sub_form_state);
+    // If this block is context-aware, set the context mapping.
+    if ($block instanceof ContextAwarePluginInterface && $block->getContextDefinitions()) {
+      $context_mapping = $sub_form_state->getValue('context_mapping', []);
+      $block->setContextMapping($context_mapping);
+    }
+
+    $this->submitVisibility($form, $form_state);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function save(array $form, FormStateInterface $form_state) {
+    $value = parent::save($form, $form_state);
+
+    $this->messenger()->addStatus($this->t('The block configuration has been saved.'));
+    $form_state->setRedirect(
+      'block.admin_display_theme',
+      [
+        'theme' => $form_state->getValue('theme'),
+      ],
+      ['query' => ['block-placement' => Html::getClass($this->entity->id())]]
+    );
+
+    return $value;
+  }
+
+  /**
+   * Helper function to independently submit the visibility UI.
+   *
+   * @param array $form
+   *   A nested array form elements comprising the form.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   */
+  protected function submitVisibility(array $form, FormStateInterface $form_state) {
+    foreach ($form_state->getValue('visibility') as $condition_id => $values) {
+      // Allow the condition to submit the form.
+      $condition = $form_state->get(['conditions', $condition_id]);
+      $condition->submitConfigurationForm($form['visibility'][$condition_id], SubformState::createForSubform($form['visibility'][$condition_id], $form, $form_state));
+
+      $condition_configuration = $condition->getConfiguration();
+      // Update the visibility conditions on the block.
+      $this->entity->getVisibilityConditions()->addInstanceId($condition_id, $condition_configuration);
+    }
+  }
+
+  /**
+   * Generates a unique machine name for a block based on a suggested string.
+   *
+   * @param \Drupal\block\BlockInterface $block
+   *   The block entity.
+   *
+   * @return string
+   *   Returns the unique name.
+   */
+  public function getUniqueMachineName(BlockInterface $block) {
+    $suggestion = $block->getPlugin()->getMachineNameSuggestion();
+    return $this->blockRepository->getUniqueMachineName($suggestion, $block->getTheme());
+  }
+
+  /**
+   * Retrieves the plugin form for a given block and operation.
+   *
+   * @param \Drupal\Core\Block\BlockPluginInterface $block
+   *   The block plugin.
+   *
+   * @return \Drupal\Core\Plugin\PluginFormInterface
+   *   The plugin form for the block.
+   */
+  protected function getPluginForm(BlockPluginInterface $block) {
+    if ($block instanceof PluginWithFormsInterface) {
+      return $this->pluginFormFactory->createInstance($block, 'configure');
+    }
+    return $block;
+  }
+
+}

web/core/modules/block/src/BlockInterface.php

@@ -0,0 +1,125 @@
+<?php
+
+namespace Drupal\block;
+
+use Drupal\Core\Config\Entity\ConfigEntityInterface;
+
+/**
+ * Provides an interface defining a block entity.
+ */
+interface BlockInterface extends ConfigEntityInterface {
+
+  /**
+   * Returns the plugin instance.
+   *
+   * @return \Drupal\Core\Block\BlockPluginInterface
+   *   The plugin instance for this block.
+   */
+  public function getPlugin();
+
+  /**
+   * Returns the plugin ID.
+   *
+   * @return string
+   *   The plugin ID for this block.
+   */
+  public function getPluginId();
+
+  /**
+   * Returns the region this block is placed in.
+   *
+   * @return string
+   *   The region this block is placed in.
+   */
+  public function getRegion();
+
+  /**
+   * Returns the theme ID.
+   *
+   * @return string
+   *   The theme ID for this block instance.
+   */
+  public function getTheme();
+
+  /**
+   * Returns an array of visibility condition configurations.
+   *
+   * @return array
+   *   An array of visibility condition configuration keyed by the condition ID.
+   */
+  public function getVisibility();
+
+  /**
+   * Gets conditions for this block.
+   *
+   * @return \Drupal\Core\Condition\ConditionInterface[]|\Drupal\Core\Condition\ConditionPluginCollection
+   *   An array or collection of configured condition plugins.
+   */
+  public function getVisibilityConditions();
+
+  /**
+   * Gets a visibility condition plugin instance.
+   *
+   * @param string $instance_id
+   *   The condition plugin instance ID.
+   *
+   * @return \Drupal\Core\Condition\ConditionInterface
+   *   A condition plugin.
+   */
+  public function getVisibilityCondition($instance_id);
+
+  /**
+   * Sets the visibility condition configuration.
+   *
+   * @param string $instance_id
+   *   The condition instance ID.
+   * @param array $configuration
+   *   The condition configuration.
+   *
+   * @return $this
+   */
+  public function setVisibilityConfig($instance_id, array $configuration);
+
+  /**
+   * Returns the weight of this block (used for sorting).
+   *
+   * @return int
+   *   The block weight.
+   */
+  public function getWeight();
+
+  /**
+   * Sets the region this block is placed in.
+   *
+   * @param string $region
+   *   The region to place this block in.
+   *
+   * @return $this
+   */
+  public function setRegion($region);
+
+  /**
+   * Sets the block weight.
+   *
+   * @param int $weight
+   *   The desired weight.
+   *
+   * @return $this
+   */
+  public function setWeight($weight);
+
+  /**
+   * Creates a duplicate of the block entity.
+   *
+   * @param string $new_id
+   *   (optional) The new ID on the duplicate block.
+   * @param string $new_theme
+   *   (optional) The theme on the duplicate block.
+   *
+   * @return static
+   *   A clone of $this with all identifiers unset, so saving it inserts a new
+   *   entity into the storage system.
+   */
+  public function createDuplicateBlock($new_id = NULL, $new_theme = NULL);
+
+}

web/core/modules/block/src/BlockListBuilder.php

@@ -0,0 +1,405 @@
+<?php
+
+namespace Drupal\block;
+
+use Drupal\Component\Utility\Html;
+use Drupal\Component\Serialization\Json;
+use Drupal\Core\Config\Entity\ConfigEntityListBuilder;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Form\FormBuilderInterface;
+use Drupal\Core\Form\FormInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Messenger\MessengerInterface;
+use Drupal\Core\Theme\ThemeManagerInterface;
+use Drupal\Core\Url;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Defines a class to build a listing of block entities.
+ *
+ * @see \Drupal\block\Entity\Block
+ */
+class BlockListBuilder extends ConfigEntityListBuilder implements FormInterface {
+
+  /**
+   * The theme containing the blocks.
+   *
+   * @var string
+   */
+  protected $theme;
+
+  /**
+   * The current request.
+   *
+   * @var \Symfony\Component\HttpFoundation\Request
+   */
+  protected $request;
+
+  /**
+   * The theme manager.
+   *
+   * @var \Drupal\Core\Theme\ThemeManagerInterface
+   */
+  protected $themeManager;
+
+  /**
+   * The form builder.
+   *
+   * @var \Drupal\Core\Form\FormBuilderInterface
+   */
+  protected $formBuilder;
+
+  /**
+   * The messenger.
+   *
+   * @var \Drupal\Core\Messenger\MessengerInterface
+   */
+  protected $messenger;
+
+  /**
+   * Constructs a new BlockListBuilder object.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
+   *   The entity type definition.
+   * @param \Drupal\Core\Entity\EntityStorageInterface $storage
+   *   The entity storage class.
+   * @param \Drupal\Core\Theme\ThemeManagerInterface $theme_manager
+   *   The theme manager.
+   * @param \Drupal\Core\Form\FormBuilderInterface $form_builder
+   *   The form builder.
+   * @param \Drupal\Core\Messenger\MessengerInterface $messenger
+   *   The messenger service.
+   */
+  public function __construct(EntityTypeInterface $entity_type, EntityStorageInterface $storage, ThemeManagerInterface $theme_manager, FormBuilderInterface $form_builder, MessengerInterface $messenger) {
+    parent::__construct($entity_type, $storage);
+
+    $this->themeManager = $theme_manager;
+    $this->formBuilder = $form_builder;
+    $this->messenger = $messenger;
+    $this->limit = FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
+    return new static(
+      $entity_type,
+      $container->get('entity_type.manager')->getStorage($entity_type->id()),
+      $container->get('theme.manager'),
+      $container->get('form_builder'),
+      $container->get('messenger')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   *
+   * @param string|null $theme
+   *   (optional) The theme to display the blocks for. If NULL, the current
+   *   theme will be used.
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request.
+   *
+   * @return array
+   *   The block list as a renderable array.
+   */
+  public function render($theme = NULL, ?Request $request = NULL) {
+    $this->request = $request;
+    $this->theme = $theme;
+
+    return $this->formBuilder->getForm($this);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'block_admin_display_form';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form['#attached']['library'][] = 'core/drupal.tableheader';
+    $form['#attached']['library'][] = 'block/drupal.block';
+    $form['#attached']['library'][] = 'block/drupal.block.admin';
+    $form['#attributes']['class'][] = 'clearfix';
+
+    // Build the form tree.
+    $form['blocks'] = $this->buildBlocksForm();
+
+    $form['actions'] = [
+      '#tree' => FALSE,
+      '#type' => 'actions',
+    ];
+    $form['actions']['submit'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Save blocks'),
+      '#button_type' => 'primary',
+    ];
+
+    return $form;
+  }
+
+  /**
+   * Builds the main "Blocks" portion of the form.
+   *
+   * @return array
+   *   An array representing the blocks form structure.
+   */
+  protected function buildBlocksForm() {
+    // Build blocks first for each region.
+    $blocks = [];
+    $entities = $this->load();
+    /** @var \Drupal\block\BlockInterface[] $entities */
+    foreach ($entities as $entity_id => $entity) {
+      $definition = $entity->getPlugin()->getPluginDefinition();
+      $blocks[$entity->getRegion()][$entity_id] = [
+        'label' => $entity->label(),
+        'entity_id' => $entity_id,
+        'weight' => $entity->getWeight(),
+        'entity' => $entity,
+        'category' => $definition['category'],
+        'status' => $entity->status(),
+      ];
+    }
+
+    $form = [
+      '#type' => 'table',
+      '#header' => [
+        $this->t('Block'),
+        $this->t('Category'),
+        $this->t('Region'),
+        $this->t('Weight'),
+        $this->t('Operations'),
+      ],
+      '#attributes' => [
+        'id' => 'blocks',
+      ],
+    ];
+
+    // Weights range from -delta to +delta, so delta should be at least half
+    // of the amount of blocks present. This makes sure all blocks in the same
+    // region get a unique weight.
+    $weight_delta = round(count($entities) / 2);
+
+    $placement = FALSE;
+    if ($this->request->query->has('block-placement')) {
+      $placement = $this->request->query->get('block-placement');
+      $form['#attached']['drupalSettings']['blockPlacement'] = $placement;
+      // Remove the block placement from the current request so that it is not
+      // passed on to any redirect destinations.
+      $this->request->query->remove('block-placement');
+    }
+
+    // Loop over each region and build blocks.
+    $regions = $this->systemRegionList($this->getThemeName(), REGIONS_VISIBLE);
+    foreach ($regions as $region => $title) {
+      $form['#tabledrag'][] = [
+        'action' => 'match',
+        'relationship' => 'sibling',
+        'group' => 'block-region-select',
+        'subgroup' => 'block-region-' . $region,
+        'hidden' => FALSE,
+      ];
+      $form['#tabledrag'][] = [
+        'action' => 'order',
+        'relationship' => 'sibling',
+        'group' => 'block-weight',
+        'subgroup' => 'block-weight-' . $region,
+      ];
+
+      $form['region-' . $region] = [
+        '#attributes' => [
+          'class' => ['region-title', 'region-title-' . $region],
+          'no_striping' => TRUE,
+        ],
+      ];
+      $form['region-' . $region]['title'] = [
+        '#theme_wrappers' => [
+          'container' => [
+            '#attributes' => ['class' => 'region-title__action'],
+          ],
+        ],
+        '#prefix' => $title,
+        '#type' => 'link',
+        '#title' => $this->t('Place block <span class="visually-hidden">in the %region region</span>', ['%region' => $title]),
+        '#url' => Url::fromRoute('block.admin_library', ['theme' => $this->getThemeName()], ['query' => ['region' => $region]]),
+        '#wrapper_attributes' => [
+          'colspan' => 5,
+        ],
+        '#attributes' => [
+          'class' => ['use-ajax', 'button', 'button--small'],
+          'data-dialog-type' => 'modal',
+          'data-dialog-options' => Json::encode([
+            'width' => 880,
+          ]),
+        ],
+      ];
+
+      $form['region-' . $region . '-message'] = [
+        '#attributes' => [
+          'class' => [
+            'region-message',
+            'region-' . $region . '-message',
+            empty($blocks[$region]) ? 'region-empty' : 'region-populated',
+          ],
+        ],
+      ];
+      $form['region-' . $region . '-message']['message'] = [
+        '#markup' => '<em>' . $this->t('No blocks in this region') . '</em>',
+        '#wrapper_attributes' => [
+          'colspan' => 5,
+        ],
+      ];
+
+      if (isset($blocks[$region])) {
+        foreach ($blocks[$region] as $info) {
+          $entity_id = $info['entity_id'];
+
+          $form[$entity_id] = [
+            '#attributes' => [
+              'class' => ['draggable'],
+            ],
+          ];
+          $form[$entity_id]['#attributes']['class'][] = $info['status'] ? 'block-enabled' : 'block-disabled';
+          if ($placement && $placement == Html::getClass($entity_id)) {
+            $form[$entity_id]['#attributes']['class'][] = 'color-success';
+            $form[$entity_id]['#attributes']['class'][] = 'js-block-placed';
+          }
+          $form[$entity_id]['info'] = [
+            '#wrapper_attributes' => [
+              'class' => ['block'],
+            ],
+          ];
+          // Ensure that the label is always rendered as plain text. Render
+          // array #plain_text key is essentially treated same as @ placeholder
+          // in translatable markup.
+          if ($info['status']) {
+            $form[$entity_id]['info']['#plain_text'] = $info['label'];
+          }
+          else {
+            $form[$entity_id]['info']['#markup'] = $this->t('@label (disabled)', ['@label' => $info['label']]);
+          }
+
+          $form[$entity_id]['type'] = [
+            '#markup' => $info['category'],
+          ];
+          $form[$entity_id]['region-theme']['region'] = [
+            '#type' => 'select',
+            '#default_value' => $region,
+            '#required' => TRUE,
+            '#title' => $this->t('Region for @block block', ['@block' => $info['label']]),
+            '#title_display' => 'invisible',
+            '#options' => $regions,
+            '#attributes' => [
+              'class' => ['block-region-select', 'block-region-' . $region],
+            ],
+            '#parents' => ['blocks', $entity_id, 'region'],
+          ];
+          $form[$entity_id]['region-theme']['theme'] = [
+            '#type' => 'hidden',
+            '#value' => $this->getThemeName(),
+            '#parents' => ['blocks', $entity_id, 'theme'],
+          ];
+          $form[$entity_id]['weight'] = [
+            '#type' => 'weight',
+            '#default_value' => $info['weight'],
+            '#delta' => $weight_delta,
+            '#title' => $this->t('Weight for @block block', ['@block' => $info['label']]),
+            '#title_display' => 'invisible',
+            '#attributes' => [
+              'class' => ['block-weight', 'block-weight-' . $region],
+            ],
+          ];
+          $form[$entity_id]['operations'] = $this->buildOperations($info['entity']);
+        }
+      }
+    }
+
+    // Do not allow disabling the main system content block when it is present.
+    if (isset($form['system_main']['region'])) {
+      $form['system_main']['region']['#required'] = TRUE;
+    }
+    return $form;
+  }
+
+  /**
+   * Gets the name of the theme used for this block listing.
+   *
+   * @return string
+   *   The name of the theme.
+   */
+  protected function getThemeName() {
+    // If no theme was specified, use the current theme.
+    if (!$this->theme) {
+      $this->theme = $this->themeManager->getActiveTheme()->getName();
+    }
+    return $this->theme;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEntityIds() {
+    return $this->getStorage()->getQuery()
+      ->condition('theme', $this->getThemeName())
+      ->sort($this->entityType->getKey('id'))
+      ->execute();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDefaultOperations(EntityInterface $entity) {
+    $operations = parent::getDefaultOperations($entity);
+
+    if (isset($operations['edit'])) {
+      $operations['edit']['title'] = $this->t('Configure');
+    }
+
+    if (isset($operations['delete'])) {
+      $operations['delete']['title'] = $this->t('Remove');
+    }
+    return $operations;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    if (empty($form_state->getValue('blocks'))) {
+      $form_state->setErrorByName('blocks', $this->t('No blocks settings to update.'));
+    }
+
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $blocks = $form_state->getValue('blocks');
+    $entities = $this->storage->loadMultiple(array_keys($blocks));
+    /** @var \Drupal\block\BlockInterface[] $entities */
+    foreach ($entities as $entity_id => $entity) {
+      $entity_values = $form_state->getValue(['blocks', $entity_id]);
+      $entity->setWeight($entity_values['weight']);
+      $entity->setRegion($entity_values['region']);
+      $entity->save();
+    }
+    $this->messenger->addStatus($this->t('The block settings have been updated.'));
+  }
+
+  /**
+   * Wraps system_region_list().
+   */
+  protected function systemRegionList($theme, $show = REGIONS_ALL) {
+    return system_region_list($theme, $show);
+  }
+
+}

web/core/modules/block/src/BlockPluginCollection.php

@@ -0,0 +1,71 @@
+<?php
+
+namespace Drupal\block;
+
+use Drupal\Component\Plugin\Exception\PluginException;
+use Drupal\Component\Plugin\PluginManagerInterface;
+use Drupal\Core\Plugin\DefaultSingleLazyPluginCollection;
+
+/**
+ * Provides a collection of block plugins.
+ */
+class BlockPluginCollection extends DefaultSingleLazyPluginCollection {
+
+  /**
+   * The block ID this plugin collection belongs to.
+   *
+   * @var string
+   */
+  protected $blockId;
+
+  /**
+   * Constructs a new BlockPluginCollection.
+   *
+   * @param \Drupal\Component\Plugin\PluginManagerInterface $manager
+   *   The manager to be used for instantiating plugins.
+   * @param string $instance_id
+   *   The ID of the plugin instance.
+   * @param array $configuration
+   *   An array of configuration.
+   * @param string $block_id
+   *   The unique ID of the block entity using this plugin.
+   */
+  public function __construct(PluginManagerInterface $manager, $instance_id, array $configuration, $block_id) {
+    parent::__construct($manager, $instance_id, $configuration);
+
+    $this->blockId = $block_id;
+  }
+
+  /**
+   * {@inheritdoc}
+   *
+   * @return \Drupal\Core\Block\BlockPluginInterface
+   *   The block plugin instance.
+   */
+  public function &get($instance_id) {
+    return parent::get($instance_id);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function initializePlugin($instance_id) {
+    if (!$instance_id) {
+      throw new PluginException("The block '{$this->blockId}' did not specify a plugin.");
+    }
+
+    try {
+      parent::initializePlugin($instance_id);
+    }
+    catch (PluginException $e) {
+      $module = $this->configuration['provider'];
+      // Ignore blocks belonging to uninstalled modules, but re-throw valid
+      // exceptions when the module is installed and the plugin is
+      // misconfigured.
+      if (!$module || \Drupal::moduleHandler()->moduleExists($module)) {
+        throw $e;
+      }
+    }
+  }
+
+}

web/core/modules/block/src/BlockRepository.php

@@ -0,0 +1,114 @@
+<?php
+
+namespace Drupal\block;
+
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Plugin\Context\ContextHandlerInterface;
+use Drupal\Core\Theme\ThemeManagerInterface;
+
+/**
+ * Provides a repository for Block config entities.
+ */
+class BlockRepository implements BlockRepositoryInterface {
+
+  /**
+   * The block storage.
+   *
+   * @var \Drupal\Core\Entity\EntityStorageInterface
+   */
+  protected $blockStorage;
+
+  /**
+   * The theme manager.
+   *
+   * @var \Drupal\Core\Theme\ThemeManagerInterface
+   */
+  protected $themeManager;
+
+  /**
+   * The context handler.
+   *
+   * @var \Drupal\Core\Plugin\Context\ContextHandlerInterface
+   */
+  protected $contextHandler;
+
+  /**
+   * Constructs a new BlockRepository.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager service.
+   * @param \Drupal\Core\Theme\ThemeManagerInterface $theme_manager
+   *   The theme manager.
+   * @param \Drupal\Core\Plugin\Context\ContextHandlerInterface $context_handler
+   *   The plugin context handler.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, ThemeManagerInterface $theme_manager, ContextHandlerInterface $context_handler) {
+    $this->blockStorage = $entity_type_manager->getStorage('block');
+    $this->themeManager = $theme_manager;
+    $this->contextHandler = $context_handler;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getVisibleBlocksPerRegion(array &$cacheable_metadata = []) {
+    $active_theme = $this->themeManager->getActiveTheme();
+    // Build an array of the region names in the right order.
+    $empty = array_fill_keys($active_theme->getRegions(), []);
+
+    $full = [];
+    foreach ($this->blockStorage->loadByProperties(['theme' => $active_theme->getName()]) as $block_id => $block) {
+      /** @var \Drupal\block\BlockInterface $block */
+      $access = $block->access('view', NULL, TRUE);
+      $region = $block->getRegion();
+      if (!isset($cacheable_metadata[$region])) {
+        $cacheable_metadata[$region] = CacheableMetadata::createFromObject($access);
+      }
+      else {
+        $cacheable_metadata[$region] = $cacheable_metadata[$region]->merge(CacheableMetadata::createFromObject($access));
+      }
+
+      // Set the contexts on the block before checking access.
+      if ($access->isAllowed()) {
+        $full[$region][$block_id] = $block;
+      }
+    }
+
+    // Merge it with the actual values to maintain the region ordering.
+    $assignments = array_intersect_key(array_merge($empty, $full), $empty);
+    foreach ($assignments as &$assignment) {
+      uasort($assignment, 'Drupal\block\Entity\Block::sort');
+    }
+    return $assignments;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getUniqueMachineName(string $suggestion, ?string $theme = NULL): string {
+    if ($theme) {
+      $suggestion = $theme . '_' . $suggestion;
+    }
+    // Get all the block machine names that begin with the suggested string.
+    $query = $this->blockStorage->getQuery();
+    $query->accessCheck(FALSE);
+    $query->condition('id', $suggestion, 'CONTAINS');
+    $block_ids = $query->execute();
+
+    $block_ids = array_map(function ($block_id) {
+      $parts = explode('.', $block_id);
+      return end($parts);
+    }, $block_ids);
+
+    // Iterate through potential IDs until we get a new one. E.g.
+    // For example, 'plugin', 'plugin_2', 'plugin_3', etc.
+    $count = 1;
+    $machine_default = $suggestion;
+    while (in_array($machine_default, $block_ids)) {
+      $machine_default = $suggestion . '_' . ++$count;
+    }
+    return $machine_default;
+  }
+
+}

web/core/modules/block/src/BlockRepositoryInterface.php

@@ -0,0 +1,50 @@
+<?php
+
+namespace Drupal\block;
+
+/**
+ * Provides an interface for the block repository.
+ */
+interface BlockRepositoryInterface {
+
+  /**
+   * Return only visible regions.
+   *
+   * @see system_region_list()
+   */
+  const REGIONS_VISIBLE = 'visible';
+
+  /**
+   * Return all regions.
+   *
+   * @see system_region_list()
+   */
+  const REGIONS_ALL = 'all';
+
+  /**
+   * Returns an array of regions and their block entities.
+   *
+   * @param \Drupal\Core\Cache\CacheableMetadata[] $cacheable_metadata
+   *   (optional) List of CacheableMetadata objects, keyed by region. This is
+   *   by reference and is used to pass this information back to the caller.
+   *
+   * @return array
+   *   The array is first keyed by region machine name, with the values
+   *   containing an array keyed by block ID, with block entities as the values.
+   */
+  public function getVisibleBlocksPerRegion(array &$cacheable_metadata = []);
+
+  /**
+   * Based on a suggested string generates a unique machine name for a block.
+   *
+   * @param string $suggestion
+   *   The suggested block ID.
+   * @param string $theme
+   *   The machine name of the theme.
+   *
+   * @return string
+   *   Returns the unique name.
+   */
+  public function getUniqueMachineName(string $suggestion, string $theme): string;
+
+}

web/core/modules/block/src/BlockViewBuilder.php

@@ -0,0 +1,234 @@
+<?php
+
+namespace Drupal\block;
+
+use Drupal\Core\Block\MainContentBlockPluginInterface;
+use Drupal\Core\Block\TitleBlockPluginInterface;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Entity\EntityViewBuilder;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Plugin\ContextAwarePluginInterface;
+use Drupal\Core\Render\Element;
+use Drupal\block\Entity\Block;
+use Drupal\Core\Security\TrustedCallbackInterface;
+
+/**
+ * Provides a Block view builder.
+ */
+class BlockViewBuilder extends EntityViewBuilder implements TrustedCallbackInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildComponents(array &$build, array $entities, array $displays, $view_mode) {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function view(EntityInterface $entity, $view_mode = 'full', $langcode = NULL) {
+    $build = $this->viewMultiple([$entity], $view_mode, $langcode);
+    return reset($build);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function viewMultiple(array $entities = [], $view_mode = 'full', $langcode = NULL) {
+    /** @var \Drupal\block\BlockInterface[] $entities */
+    $build = [];
+    foreach ($entities as $entity) {
+      $entity_id = $entity->id();
+      $plugin = $entity->getPlugin();
+
+      $cache_tags = Cache::mergeTags($this->getCacheTags(), $entity->getCacheTags());
+      $cache_tags = Cache::mergeTags($cache_tags, $plugin->getCacheTags());
+
+      // Create the render array for the block as a whole.
+      // @see template_preprocess_block().
+      $build[$entity_id] = [
+        '#cache' => [
+          'keys' => ['entity_view', 'block', $entity->id()],
+          'contexts' => Cache::mergeContexts(
+            $entity->getCacheContexts(),
+            $plugin->getCacheContexts()
+          ),
+          'tags' => $cache_tags,
+          'max-age' => $plugin->getCacheMaxAge(),
+        ],
+        '#weight' => $entity->getWeight(),
+      ];
+
+      // Allow altering of cacheability metadata or setting #create_placeholder.
+      $this->moduleHandler->alter(['block_build', "block_build_" . $plugin->getBaseId()], $build[$entity_id], $plugin);
+
+      if ($plugin instanceof MainContentBlockPluginInterface || $plugin instanceof TitleBlockPluginInterface) {
+        // Immediately build a #pre_render-able block, since this block cannot
+        // be built lazily.
+        $cacheableMetadata = CacheableMetadata::createFromRenderArray($build[$entity_id]);
+        $preRenderableBlock = static::buildPreRenderableBlock($entity, $this->moduleHandler());
+        $cacheableMetadata->addCacheableDependency(CacheableMetadata::createFromRenderArray($preRenderableBlock));
+        $build[$entity_id] += $preRenderableBlock;
+        $cacheableMetadata->applyTo($build[$entity_id]);
+      }
+      else {
+        // Assign a #lazy_builder callback, which will generate a #pre_render-
+        // able block lazily (when necessary).
+        $build[$entity_id] += [
+          '#lazy_builder' => [static::class . '::lazyBuilder', [$entity_id, $view_mode, $langcode]],
+        ];
+        // Only add create_placeholder if it's explicitly set to TRUE, so it can
+        // be set to TRUE by automatic placeholdering conditions if it's absent.
+        if ($plugin->createPlaceholder()) {
+          $build[$entity_id] += [
+            '#create_placeholder' => TRUE,
+          ];
+        }
+      }
+    }
+
+    return $build;
+  }
+
+  /**
+   * Builds a #pre_render-able block render array.
+   *
+   * @param \Drupal\block\BlockInterface $entity
+   *   A block config entity.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   *   The module handler service.
+   *
+   * @return array
+   *   A render array with a #pre_render callback to render the block.
+   */
+  protected static function buildPreRenderableBlock(BlockInterface $entity, ModuleHandlerInterface $module_handler) {
+    $plugin = $entity->getPlugin();
+    $plugin_id = $plugin->getPluginId();
+    $base_id = $plugin->getBaseId();
+    $derivative_id = $plugin->getDerivativeId();
+    $configuration = $plugin->getConfiguration();
+
+    // Inject runtime contexts.
+    if ($plugin instanceof ContextAwarePluginInterface) {
+      $contexts = \Drupal::service('context.repository')->getRuntimeContexts($plugin->getContextMapping());
+      \Drupal::service('context.handler')->applyContextMapping($plugin, $contexts);
+    }
+
+    // Create the render array for the block as a whole.
+    // @see template_preprocess_block().
+    $build = [
+      '#theme' => 'block',
+      '#attributes' => [],
+      // All blocks get a "Configure block" contextual link.
+      '#contextual_links' => [
+        'block' => [
+          'route_parameters' => ['block' => $entity->id()],
+        ],
+      ],
+      '#weight' => $entity->getWeight(),
+      '#configuration' => $configuration,
+      '#plugin_id' => $plugin_id,
+      '#base_plugin_id' => $base_id,
+      '#derivative_plugin_id' => $derivative_id,
+      '#id' => $entity->id(),
+      '#pre_render' => [
+        static::class . '::preRender',
+      ],
+      // Add the entity so that it can be used in the #pre_render method.
+      '#block' => $entity,
+    ];
+
+    // If an alter hook wants to modify the block contents, it can append
+    // another #pre_render hook.
+    $module_handler->alter(['block_view', "block_view_$base_id"], $build, $plugin);
+
+    return $build;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function trustedCallbacks() {
+    return ['preRender', 'lazyBuilder'];
+  }
+
+  /**
+   * Render API callback: Builds a block that can be pre-rendered.
+   *
+   * This function is assigned as a #lazy_builder callback.
+   *
+   * @param string $entity_id
+   *   A block config entity ID.
+   * @param string $view_mode
+   *   The view mode the block is being viewed in.
+   *
+   * @return array
+   *   A render array with a #pre_render callback to render the block.
+   */
+  public static function lazyBuilder($entity_id, $view_mode) {
+    return static::buildPreRenderableBlock(Block::load($entity_id), \Drupal::service('module_handler'));
+  }
+
+  /**
+   * Render API callback: Builds a block.
+   *
+   * This function is assigned as a #pre_render callback.
+   *
+   * Renders the content using the provided block plugin, and then:
+   * - if there is no content, aborts rendering, and makes sure the block won't
+   *   be rendered.
+   * - if there is content, moves the contextual links from the block content to
+   *   the block itself.
+   */
+  public static function preRender($build) {
+    $content = $build['#block']->getPlugin()->build();
+    // Remove the block entity from the render array, to ensure that blocks
+    // can be rendered without the block config entity.
+    unset($build['#block']);
+    if ($content !== NULL && !Element::isEmpty($content)) {
+      // Place the $content returned by the block plugin into a 'content' child
+      // element, as a way to allow the plugin to have complete control of its
+      // properties and rendering (for instance, its own #theme) without
+      // conflicting with the properties used above, or alternate ones used by
+      // alternate block rendering approaches in contrib (for instance, Panels).
+      // However, the use of a child element is an implementation detail of this
+      // particular block rendering approach. Semantically, the content returned
+      // by the plugin "is the" block, and in particular, #attributes and
+      // #contextual_links is information about the *entire* block. Therefore,
+      // we must move these properties from $content and merge them into the
+      // top-level element.
+      foreach (['#attributes', '#contextual_links'] as $property) {
+        if (isset($content[$property])) {
+          $build[$property] += $content[$property];
+          unset($content[$property]);
+        }
+      }
+      $build['content'] = $content;
+    }
+    // Either the block's content is completely empty, or it consists only of
+    // cacheability metadata.
+    else {
+      // Abort rendering: render as the empty string and ensure this block is
+      // render cached, so we can avoid the work of having to repeatedly
+      // determine whether the block is empty. For instance, modifying or adding
+      // entities could cause the block to no longer be empty.
+      $build = [
+        '#markup' => '',
+        '#cache' => $build['#cache'],
+      ];
+      // If $content is not empty, then it contains cacheability metadata, and
+      // we must merge it with the existing cacheability metadata. This allows
+      // blocks to be empty, yet still bubble cacheability metadata, to indicate
+      // why they are empty.
+      if (!empty($content)) {
+        CacheableMetadata::createFromRenderArray($build)
+          ->merge(CacheableMetadata::createFromRenderArray($content))
+          ->applyTo($build);
+      }
+    }
+    return $build;
+  }
+
+}

web/core/modules/block/src/Controller/BlockAddController.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace Drupal\block\Controller;
+
+use Drupal\Core\Controller\ControllerBase;
+
+/**
+ * Controller for building the block instance add form.
+ */
+class BlockAddController extends ControllerBase {
+
+  /**
+   * Build the block instance add form.
+   *
+   * @param string $plugin_id
+   *   The plugin ID for the block instance.
+   * @param string $theme
+   *   The name of the theme for the block instance.
+   *
+   * @return array
+   *   The block instance edit form.
+   */
+  public function blockAddConfigureForm($plugin_id, $theme) {
+    // Create a block entity.
+    $entity = $this->entityTypeManager()->getStorage('block')->create(['plugin' => $plugin_id, 'theme' => $theme]);
+
+    return $this->entityFormBuilder()->getForm($entity);
+  }
+
+}

web/core/modules/block/src/Controller/BlockController.php

@@ -0,0 +1,108 @@
+<?php
+
+namespace Drupal\block\Controller;
+
+use Drupal\Component\Utility\Html;
+use Drupal\block\BlockInterface;
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\Extension\ThemeHandlerInterface;
+use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
+
+/**
+ * Controller routines for admin block routes.
+ */
+class BlockController extends ControllerBase {
+
+  /**
+   * The theme handler.
+   *
+   * @var \Drupal\Core\Extension\ThemeHandlerInterface
+   */
+  protected $themeHandler;
+
+  /**
+   * Constructs a new BlockController instance.
+   *
+   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
+   *   The theme handler.
+   */
+  public function __construct(ThemeHandlerInterface $theme_handler) {
+    $this->themeHandler = $theme_handler;
+  }
+
+  /**
+   * Calls a method on a block and reloads the listing page.
+   *
+   * @param \Drupal\block\BlockInterface $block
+   *   The block being acted upon.
+   * @param string $op
+   *   The operation to perform, e.g., 'enable' or 'disable'.
+   *
+   * @return \Symfony\Component\HttpFoundation\RedirectResponse
+   *   A redirect back to the listing page.
+   */
+  public function performOperation(BlockInterface $block, $op) {
+    $block->$op()->save();
+    $this->messenger()->addStatus($this->t('The block settings have been updated.'));
+    return $this->redirect('block.admin_display');
+  }
+
+  /**
+   * Returns a block theme demo page.
+   *
+   * @param string $theme
+   *   The name of the theme.
+   *
+   * @return array
+   *   A #type 'page' render array containing the block region demo.
+   */
+  public function demo($theme) {
+    if (!$this->themeHandler->hasUi($theme)) {
+      throw new NotFoundHttpException();
+    }
+
+    $page = [
+      '#title' => Html::escape($this->themeHandler->getName($theme)),
+      '#type' => 'page',
+      '#attached' => [
+        'drupalSettings' => [
+          // The block demonstration page is not marked as an administrative
+          // page by \Drupal::service('router.admin_context')->isAdminRoute()
+          // function in order to use the frontend theme. Since JavaScript
+          // relies on a proper separation of admin pages, it needs to know this
+          // is an actual administrative page.
+          'path' => ['currentPathIsAdmin' => TRUE],
+        ],
+        'library' => [
+          'block/drupal.block.admin',
+        ],
+      ],
+    ];
+
+    // Show descriptions in each visible page region, nothing else.
+    $visible_regions = $this->getVisibleRegionNames($theme);
+    foreach (array_keys($visible_regions) as $region) {
+      $page[$region]['block_description'] = [
+        '#type' => 'inline_template',
+        '#template' => '<div class="block-region demo-block">{{ region_name }}</div>',
+        '#context' => ['region_name' => $visible_regions[$region]],
+      ];
+    }
+
+    return $page;
+  }
+
+  /**
+   * Returns the human-readable list of regions keyed by machine name.
+   *
+   * @param string $theme
+   *   The name of the theme.
+   *
+   * @return array
+   *   An array of human-readable region names keyed by machine name.
+   */
+  protected function getVisibleRegionNames($theme) {
+    return system_region_list($theme, REGIONS_VISIBLE);
+  }
+
+}

web/core/modules/block/src/Controller/BlockLibraryController.php

@@ -0,0 +1,186 @@
+<?php
+
+namespace Drupal\block\Controller;
+
+use Drupal\Component\Serialization\Json;
+use Drupal\Core\Block\BlockManagerInterface;
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
+use Drupal\Core\Menu\LocalActionManagerInterface;
+use Drupal\Core\Plugin\Context\ContextRepositoryInterface;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Url;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Provides a list of block plugins to be added to the layout.
+ */
+class BlockLibraryController extends ControllerBase {
+
+  /**
+   * The block manager.
+   *
+   * @var \Drupal\Core\Block\BlockManagerInterface
+   */
+  protected $blockManager;
+
+  /**
+   * The context repository.
+   *
+   * @var \Drupal\Core\Plugin\Context\LazyContextRepository
+   */
+  protected $contextRepository;
+
+  /**
+   * The route match.
+   *
+   * @var \Drupal\Core\Routing\RouteMatchInterface
+   */
+  protected $routeMatch;
+
+  /**
+   * The local action manager.
+   *
+   * @var \Drupal\Core\Menu\LocalActionManagerInterface
+   */
+  protected $localActionManager;
+
+  /**
+   * Constructs a BlockLibraryController object.
+   *
+   * @param \Drupal\Core\Block\BlockManagerInterface $block_manager
+   *   The block manager.
+   * @param \Drupal\Core\Plugin\Context\ContextRepositoryInterface $context_repository
+   *   The context repository.
+   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
+   *   The current route match.
+   * @param \Drupal\Core\Menu\LocalActionManagerInterface $local_action_manager
+   *   The local action manager.
+   */
+  public function __construct(BlockManagerInterface $block_manager, ContextRepositoryInterface $context_repository, RouteMatchInterface $route_match, LocalActionManagerInterface $local_action_manager) {
+    $this->blockManager = $block_manager;
+    $this->routeMatch = $route_match;
+    $this->localActionManager = $local_action_manager;
+    $this->contextRepository = $context_repository;
+  }
+
+  /**
+   * Shows a list of blocks that can be added to a theme's layout.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request.
+   * @param string $theme
+   *   Theme key of the block list.
+   *
+   * @return array
+   *   A render array as expected by the renderer.
+   */
+  public function listBlocks(Request $request, $theme) {
+    // Since modals do not render any other part of the page, we need to render
+    // them manually as part of this listing.
+    if ($request->query->get(MainContentViewSubscriber::WRAPPER_FORMAT) === 'drupal_modal') {
+      $build['local_actions'] = $this->buildLocalActions();
+    }
+
+    $headers = [
+      ['data' => $this->t('Block')],
+      ['data' => $this->t('Category')],
+      ['data' => $this->t('Operations')],
+    ];
+
+    $region = $request->query->get('region');
+    $weight = $request->query->get('weight');
+
+    // Only add blocks which work without any available context.
+    $definitions = $this->blockManager->getFilteredDefinitions('block_ui', $this->contextRepository->getAvailableContexts(), [
+      'theme' => $theme,
+      'region' => $region,
+    ]);
+    // Order by category, and then by admin label.
+    $definitions = $this->blockManager->getSortedDefinitions($definitions);
+    // Filter out definitions that are not intended to be placed by the UI.
+    $definitions = array_filter($definitions, function (array $definition) {
+      return empty($definition['_block_ui_hidden']);
+    });
+
+    $rows = [];
+    foreach ($definitions as $plugin_id => $plugin_definition) {
+      $row = [];
+      $row['title']['data'] = [
+        '#type' => 'inline_template',
+        '#template' => '<div class="block-filter-text-source">{{ label }}</div>',
+        '#context' => [
+          'label' => $plugin_definition['admin_label'],
+        ],
+      ];
+      $row['category']['data'] = $plugin_definition['category'];
+      $links['add'] = [
+        'title' => $this->t('Place block'),
+        'url' => Url::fromRoute('block.admin_add', ['plugin_id' => $plugin_id, 'theme' => $theme]),
+        'attributes' => [
+          'class' => ['use-ajax'],
+          'data-dialog-type' => 'modal',
+          'data-dialog-options' => Json::encode([
+            'width' => 970,
+          ]),
+        ],
+      ];
+      if ($region) {
+        $links['add']['query']['region'] = $region;
+      }
+      if (isset($weight)) {
+        $links['add']['query']['weight'] = $weight;
+      }
+      $row['operations']['data'] = [
+        '#type' => 'operations',
+        '#links' => $links,
+      ];
+      $rows[] = $row;
+    }
+
+    $build['#attached']['library'][] = 'block/drupal.block.admin';
+
+    $build['filter'] = [
+      '#type' => 'search',
+      '#title' => $this->t('Filter'),
+      '#title_display' => 'invisible',
+      '#size' => 30,
+      '#placeholder' => $this->t('Filter by block name'),
+      '#attributes' => [
+        'class' => ['block-filter-text'],
+        'data-element' => '.block-add-table',
+        'title' => $this->t('Enter a part of the block name to filter by.'),
+      ],
+    ];
+
+    $build['blocks'] = [
+      '#type' => 'table',
+      '#header' => $headers,
+      '#rows' => $rows,
+      '#empty' => $this->t('No blocks available.'),
+      '#attributes' => [
+        'class' => ['block-add-table'],
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Builds the local actions for this listing.
+   *
+   * @return array
+   *   An array of local actions for this listing.
+   */
+  protected function buildLocalActions() {
+    $build = $this->localActionManager->getActionsForRoute($this->routeMatch->getRouteName());
+    // Without this workaround, the action links will be rendered as <li> with
+    // no wrapping <ul> element.
+    if (!empty($build)) {
+      $build['#prefix'] = '<ul class="action-links">';
+      $build['#suffix'] = '</ul>';
+    }
+    return $build;
+  }
+
+}

web/core/modules/block/src/Controller/BlockListController.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace Drupal\block\Controller;
+
+use Drupal\Core\Entity\Controller\EntityListController;
+use Drupal\Core\Extension\ThemeHandlerInterface;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
+
+/**
+ * Defines a controller to list blocks.
+ */
+class BlockListController extends EntityListController {
+
+  /**
+   * The theme handler.
+   *
+   * @var \Drupal\Core\Extension\ThemeHandlerInterface
+   */
+  protected $themeHandler;
+
+  /**
+   * Constructs the BlockListController.
+   *
+   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
+   *   The theme handler.
+   */
+  public function __construct(ThemeHandlerInterface $theme_handler) {
+    $this->themeHandler = $theme_handler;
+  }
+
+  /**
+   * Shows the block administration page.
+   *
+   * @param string|null $theme
+   *   Theme key of block list.
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request.
+   *
+   * @return array
+   *   A render array as expected by
+   *   \Drupal\Core\Render\RendererInterface::render().
+   */
+  public function listing($theme = NULL, ?Request $request = NULL) {
+    $theme = $theme ?: $this->config('system.theme')->get('default');
+    if (!$this->themeHandler->hasUi($theme)) {
+      throw new NotFoundHttpException();
+    }
+
+    return $this->entityTypeManager()->getListBuilder('block')->render($theme, $request);
+  }
+
+}

web/core/modules/block/src/Controller/CategoryAutocompleteController.php

@@ -0,0 +1,63 @@
+<?php
+
+namespace Drupal\block\Controller;
+
+use Drupal\Component\Utility\Html;
+use Drupal\Core\Block\BlockManagerInterface;
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpFoundation\JsonResponse;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Returns autocomplete responses for block categories.
+ */
+class CategoryAutocompleteController implements ContainerInjectionInterface {
+
+  /**
+   * The block manager.
+   *
+   * @var \Drupal\Core\Block\BlockManagerInterface
+   */
+  protected $blockManager;
+
+  /**
+   * Constructs a new CategoryAutocompleteController.
+   *
+   * @param \Drupal\Core\Block\BlockManagerInterface $block_manager
+   *   The block manager.
+   */
+  public function __construct(BlockManagerInterface $block_manager) {
+    $this->blockManager = $block_manager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('plugin.manager.block')
+    );
+  }
+
+  /**
+   * Retrieves suggestions for block category autocompletion.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request.
+   *
+   * @return \Symfony\Component\HttpFoundation\JsonResponse
+   *   A JSON response containing autocomplete suggestions.
+   */
+  public function autocomplete(Request $request) {
+    $typed_category = $request->query->get('q');
+    $matches = [];
+    foreach ($this->blockManager->getCategories() as $category) {
+      if (stripos($category, $typed_category) === 0) {
+        $matches[] = ['value' => $category, 'label' => Html::escape($category)];
+      }
+    }
+    return new JsonResponse($matches);
+  }
+
+}

web/core/modules/block/src/Entity/Block.php

@@ -0,0 +1,391 @@
+<?php
+
+namespace Drupal\block\Entity;
+
+use Drupal\block\BlockAccessControlHandler;
+use Drupal\block\BlockForm;
+use Drupal\block\BlockListBuilder;
+use Drupal\block\BlockViewBuilder;
+use Drupal\block\Form\BlockDeleteForm;
+use Drupal\Core\Entity\Attribute\ConfigEntityType;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Condition\ConditionPluginCollection;
+use Drupal\Core\Config\Action\Attribute\ActionMethod;
+use Drupal\Core\Config\Entity\ConfigEntityBase;
+use Drupal\block\BlockPluginCollection;
+use Drupal\block\BlockInterface;
+use Drupal\Core\Config\Entity\ConfigEntityInterface;
+use Drupal\Core\Entity\EntityWithPluginCollectionInterface;
+use Drupal\Core\Entity\EntityStorageInterface;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Defines a Block configuration entity class.
+ */
+#[ConfigEntityType(
+  id: 'block',
+  label: new TranslatableMarkup('Block'),
+  label_collection: new TranslatableMarkup('Blocks'),
+  label_singular: new TranslatableMarkup('block'),
+  label_plural: new TranslatableMarkup('blocks'),
+  entity_keys: [
+    'id' => 'id',
+    'status' => 'status',
+  ],
+  handlers: [
+    'access' => BlockAccessControlHandler::class,
+    'view_builder' => BlockViewBuilder::class,
+    'list_builder' => BlockListBuilder::class,
+    'form' => [
+      'default' => BlockForm::class,
+      'delete' => BlockDeleteForm::class,
+    ],
+  ],
+  links: [
+    'delete-form' => '/admin/structure/block/manage/{block}/delete',
+    'edit-form' => '/admin/structure/block/manage/{block}',
+    'enable' => '/admin/structure/block/manage/{block}/enable',
+    'disable' => '/admin/structure/block/manage/{block}/disable',
+  ],
+  admin_permission: 'administer blocks',
+  label_count: [
+    'singular' => '@count block',
+    'plural' => '@count blocks',
+  ],
+  lookup_keys: [
+    'theme',
+  ],
+  config_export: [
+    'id',
+    'theme',
+    'region',
+    'weight',
+    'provider',
+    'plugin',
+    'settings',
+    'visibility',
+  ],
+)]
+class Block extends ConfigEntityBase implements BlockInterface, EntityWithPluginCollectionInterface {
+
+  /**
+   * The ID of the block.
+   *
+   * @var string
+   */
+  protected $id;
+
+  /**
+   * The plugin instance settings.
+   *
+   * @var array
+   */
+  protected $settings = [];
+
+  /**
+   * The region this block is placed in.
+   *
+   * @var string
+   */
+  protected $region;
+
+  /**
+   * The block weight.
+   *
+   * @var int
+   */
+  protected $weight = 0;
+
+  /**
+   * The plugin instance ID.
+   *
+   * @var string
+   */
+  protected $plugin;
+
+  /**
+   * The visibility settings for this block.
+   *
+   * @var array
+   */
+  protected $visibility = [];
+
+  /**
+   * The plugin collection that holds the block plugin for this entity.
+   *
+   * @var \Drupal\block\BlockPluginCollection
+   */
+  protected $pluginCollection;
+
+  /**
+   * The available contexts for this block and its visibility conditions.
+   *
+   * @var array
+   */
+  protected $contexts = [];
+
+  /**
+   * The visibility collection.
+   *
+   * @var \Drupal\Core\Condition\ConditionPluginCollection
+   */
+  protected $visibilityCollection;
+
+  /**
+   * The condition plugin manager.
+   *
+   * @var \Drupal\Core\Executable\ExecutableManagerInterface
+   */
+  protected $conditionPluginManager;
+
+  /**
+   * The theme that includes the block plugin for this entity.
+   *
+   * @var string
+   */
+  protected $theme;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getPlugin() {
+    return $this->getPluginCollection()->get($this->plugin);
+  }
+
+  /**
+   * Encapsulates the creation of the block's LazyPluginCollection.
+   *
+   * @return \Drupal\Component\Plugin\LazyPluginCollection
+   *   The block's plugin collection.
+   */
+  protected function getPluginCollection() {
+    if (!$this->pluginCollection) {
+      $this->pluginCollection = new BlockPluginCollection(\Drupal::service('plugin.manager.block'), $this->plugin, $this->get('settings'), $this->id());
+    }
+    return $this->pluginCollection;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getPluginCollections() {
+    return [
+      'settings' => $this->getPluginCollection(),
+      'visibility' => $this->getVisibilityConditions(),
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getPluginId() {
+    return $this->plugin;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getRegion() {
+    return $this->region;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTheme() {
+    return $this->theme;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getWeight() {
+    return $this->weight;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function label() {
+    $settings = $this->get('settings');
+    if ($settings['label']) {
+      return $settings['label'];
+    }
+    else {
+      $definition = $this->getPlugin()->getPluginDefinition();
+      return $definition['admin_label'];
+    }
+  }
+
+  /**
+   * Sorts active blocks by weight; sorts inactive blocks by name.
+   */
+  public static function sort(ConfigEntityInterface $a, ConfigEntityInterface $b) {
+    // Separate enabled from disabled.
+    $status = (int) $b->status() - (int) $a->status();
+    if ($status !== 0) {
+      return $status;
+    }
+
+    // Sort by weight.
+    $weight = $a->getWeight() - $b->getWeight();
+    if ($weight) {
+      return $weight;
+    }
+
+    // Sort by label.
+    return strcmp($a->label(), $b->label());
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function calculateDependencies() {
+    parent::calculateDependencies();
+    $this->addDependency('theme', $this->theme);
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function postSave(EntityStorageInterface $storage, $update = TRUE) {
+    parent::postSave($storage, $update);
+
+    // EntityBase::postSave() calls EntityBase::invalidateTagsOnSave(), which
+    // only handles the regular cases. The Block entity has one special case: a
+    // newly created block may *also* appear on any page in the current theme,
+    // so we must invalidate the associated block's cache tag (which includes
+    // the theme cache tag).
+    if (!$update) {
+      Cache::invalidateTags($this->getCacheTagsToInvalidate());
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getVisibility() {
+    return $this->getVisibilityConditions()->getConfiguration();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setVisibilityConfig($instance_id, array $configuration) {
+    $conditions = $this->getVisibilityConditions();
+    if (!$conditions->has($instance_id)) {
+      $configuration['id'] = $instance_id;
+      $conditions->addInstanceId($instance_id, $configuration);
+    }
+    else {
+      $conditions->setInstanceConfiguration($instance_id, $configuration);
+    }
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getVisibilityConditions() {
+    if (!isset($this->visibilityCollection)) {
+      $this->visibilityCollection = new ConditionPluginCollection($this->conditionPluginManager(), $this->get('visibility'));
+    }
+    return $this->visibilityCollection;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getVisibilityCondition($instance_id) {
+    return $this->getVisibilityConditions()->get($instance_id);
+  }
+
+  /**
+   * Gets the condition plugin manager.
+   *
+   * @return \Drupal\Core\Executable\ExecutableManagerInterface
+   *   The condition plugin manager.
+   */
+  protected function conditionPluginManager() {
+    if (!isset($this->conditionPluginManager)) {
+      $this->conditionPluginManager = \Drupal::service('plugin.manager.condition');
+    }
+    return $this->conditionPluginManager;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  #[ActionMethod(adminLabel: new TranslatableMarkup('Set block region'), pluralize: FALSE)]
+  public function setRegion($region) {
+    $this->region = $region;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  #[ActionMethod(adminLabel: new TranslatableMarkup('Set block weight'), pluralize: FALSE)]
+  public function setWeight($weight) {
+    $this->weight = (int) $weight;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function createDuplicateBlock($new_id = NULL, $new_theme = NULL) {
+    $duplicate = parent::createDuplicate();
+    if (!empty($new_id)) {
+      $duplicate->id = $new_id;
+    }
+    if (!empty($new_theme)) {
+      $duplicate->theme = $new_theme;
+    }
+    return $duplicate;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function preSave(EntityStorageInterface $storage) {
+    parent::preSave($storage);
+
+    if (!is_int($this->weight)) {
+      @trigger_error('Saving a block with a non-integer weight is deprecated in drupal:11.1.0 and removed in drupal:12.0.0. See https://www.drupal.org/node/3462474', E_USER_DEPRECATED);
+      $this->setWeight((int) $this->weight);
+    }
+
+    // Ensure the region is valid to mirror the behavior of block_rebuild().
+    // This is done primarily for backwards compatibility support of
+    // \Drupal\block\BlockInterface::BLOCK_REGION_NONE.
+    $regions = system_region_list($this->theme);
+    if (!isset($regions[$this->region]) && $this->status()) {
+      $this
+        ->setRegion(system_default_region($this->theme))
+        ->disable();
+    }
+  }
+
+  /**
+   * Validates that a region exists in the active theme.
+   *
+   * @param null|string $region
+   *   The region to validate.
+   * @param \Symfony\Component\Validator\Context\ExecutionContextInterface $context
+   *   The validation context.
+   */
+  public static function validateRegion(?string $region, ExecutionContextInterface $context): void {
+    if ($theme = $context->getRoot()->get('theme')->getValue()) {
+      if (!array_key_exists($region, system_region_list($theme))) {
+        $context->addViolation('This is not a valid region of the %theme theme.', ['%theme' => $theme]);
+      }
+    }
+    else {
+      $context->addViolation('This block does not say which theme it appears in.');
+    }
+  }
+
+}

web/core/modules/block/src/EventSubscriber/BlockPageDisplayVariantSubscriber.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace Drupal\block\EventSubscriber;
+
+use Drupal\Core\Render\PageDisplayVariantSelectionEvent;
+use Drupal\Core\Render\RenderEvents;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+/**
+ * Selects the block page display variant.
+ *
+ * @see \Drupal\block\Plugin\DisplayVariant\BlockPageVariant
+ */
+class BlockPageDisplayVariantSubscriber implements EventSubscriberInterface {
+
+  /**
+   * Selects the block page display variant.
+   *
+   * @param \Drupal\Core\Render\PageDisplayVariantSelectionEvent $event
+   *   The event to process.
+   */
+  public function onSelectPageDisplayVariant(PageDisplayVariantSelectionEvent $event) {
+    $event->setPluginId('block_page');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents(): array {
+    $events[RenderEvents::SELECT_PAGE_DISPLAY_VARIANT][] = ['onSelectPageDisplayVariant'];
+    return $events;
+  }
+
+}

web/core/modules/block/src/Form/BlockDeleteForm.php

@@ -0,0 +1,71 @@
+<?php
+
+namespace Drupal\block\Form;
+
+use Drupal\Core\Entity\EntityDeleteForm;
+use Drupal\Core\Url;
+
+/**
+ * Provides a deletion confirmation form for the block instance deletion form.
+ *
+ * @internal
+ */
+class BlockDeleteForm extends EntityDeleteForm {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCancelUrl() {
+    return new Url('block.admin_display');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getConfirmText() {
+    return $this->t('Remove');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getQuestion() {
+    $entity = $this->getEntity();
+    $regions = $this->systemRegionList($entity->getTheme(), REGIONS_VISIBLE);
+    return $this->t('Are you sure you want to remove the @entity-type %label from the %region region?', [
+      '@entity-type' => $entity->getEntityType()->getSingularLabel(),
+      '%label' => $entity->label(),
+      '%region' => $regions[$entity->getRegion()],
+    ]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDescription() {
+    return $this->t('This will remove the block placement. You will need to <a href=":url">place it again</a> in order to undo this action.', [
+      ':url' => Url::fromRoute('block.admin_display_theme', ['theme' => $this->getEntity()->getTheme()])->toString(),
+    ]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getDeletionMessage() {
+    $entity = $this->getEntity();
+    $regions = $this->systemRegionList($entity->getTheme(), REGIONS_VISIBLE);
+    return $this->t('The @entity-type %label has been removed from the %region region.', [
+      '@entity-type' => $entity->getEntityType()->getSingularLabel(),
+      '%label' => $entity->label(),
+      '%region' => $regions[$entity->getRegion()],
+    ]);
+  }
+
+  /**
+   * Wraps system_region_list().
+   */
+  protected function systemRegionList($theme, $show = REGIONS_ALL) {
+    return system_region_list($theme, $show);
+  }
+
+}

web/core/modules/block/src/Hook/BlockHooks.php

@@ -0,0 +1,269 @@
+<?php
+
+namespace Drupal\block\Hook;
+
+use Drupal\Component\Utility\Html;
+use Drupal\Core\Block\BlockPluginInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\language\ConfigurableLanguageInterface;
+use Drupal\system\Entity\Menu;
+use Drupal\block\Entity\Block;
+use Drupal\Core\Link;
+use Drupal\Core\Url;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Hook\Attribute\Hook;
+
+/**
+ * Hook implementations for block.
+ */
+class BlockHooks {
+
+  use StringTranslationTrait;
+
+  /**
+   * Implements hook_help().
+   */
+  #[Hook('help')]
+  public function help($route_name, RouteMatchInterface $route_match): ?string {
+    switch ($route_name) {
+      case 'help.page.block':
+        $block_content = \Drupal::moduleHandler()->moduleExists('block_content') ? Url::fromRoute('help.page', ['name' => 'block_content'])->toString() : '#';
+        $output = '';
+        $output .= '<h2>' . $this->t('About') . '</h2>';
+        $output .= '<p>' . $this->t('The Block module allows you to place blocks in regions of your installed themes, and configure block settings. For more information, see the <a href=":blocks-documentation">online documentation for the Block module</a>.', [':blocks-documentation' => 'https://www.drupal.org/documentation/modules/block/']) . '</p>';
+        $output .= '<h2>' . $this->t('Uses') . '</h2>';
+        $output .= '<dl>';
+        $output .= '<dt>' . $this->t('Placing and moving blocks') . '</dt>';
+        $output .= '<dd>' . $this->t('You can place a new block in a region by selecting <em>Place block</em> on the <a href=":blocks">Block layout page</a>. Once a block is placed, it can be moved to a different region by drag-and-drop or by using the <em>Region</em> drop-down list, and then clicking <em>Save blocks</em>.', [':blocks' => Url::fromRoute('block.admin_display')->toString()]) . '</dd>';
+        $output .= '<dt>' . $this->t('Toggling between different themes') . '</dt>';
+        $output .= '<dd>' . $this->t('Blocks are placed and configured specifically for each theme. The Block layout page opens with the default theme, but you can toggle to other installed themes.') . '</dd>';
+        $output .= '<dt>' . $this->t('Demonstrating block regions for a theme') . '</dt>';
+        $output .= '<dd>' . $this->t('You can see where the regions are for the current theme by clicking the <em>Demonstrate block regions</em> link on the <a href=":blocks">Block layout page</a>. Regions are specific to each theme.', [':blocks' => Url::fromRoute('block.admin_display')->toString()]) . '</dd>';
+        $output .= '<dt>' . $this->t('Configuring block settings') . '</dt>';
+        $output .= '<dd>' . $this->t('To change the settings of an individual block click on the <em>Configure</em> link on the <a href=":blocks">Block layout page</a>. The available options vary depending on the module that provides the block. For all blocks you can change the block title and toggle whether to display it.', [':blocks' => Url::fromRoute('block.admin_display')->toString()]) . '</dd>';
+        $output .= '<dt>' . $this->t('Controlling visibility') . '</dt>';
+        $output .= '<dd>' . $this->t('You can control the visibility of a block by restricting it to specific pages, content types, and/or roles by setting the appropriate options under <em>Visibility settings</em> of the block configuration.') . '</dd>';
+        $output .= '<dt>' . $this->t('Adding content blocks') . '</dt>';
+        $output .= '<dd>' . $this->t('You can add content blocks, if the <em>Block Content</em> module is installed. For more information, see the <a href=":blockcontent-help">Block Content help page</a>.', [':blockcontent-help' => $block_content]) . '</dd>';
+        $output .= '</dl>';
+        return $output;
+    }
+    if ($route_name == 'block.admin_display' || $route_name == 'block.admin_display_theme') {
+      $demo_theme = $route_match->getParameter('theme') ?: \Drupal::config('system.theme')->get('default');
+      $themes = \Drupal::service('theme_handler')->listInfo();
+      $output = '<p>' . $this->t('Block placement is specific to each theme on your site. Changes will not be saved until you click <em>Save blocks</em> at the bottom of the page.') . '</p>';
+      $output .= '<p>' . Link::fromTextAndUrl($this->t('Demonstrate block regions (@theme)', ['@theme' => $themes[$demo_theme]->info['name']]), Url::fromRoute('block.admin_demo', ['theme' => $demo_theme]))->toString() . '</p>';
+      return $output;
+    }
+    return NULL;
+  }
+
+  /**
+   * Implements hook_theme().
+   */
+  #[Hook('theme')]
+  public function theme() : array {
+    return [
+      'block' => [
+        'render element' => 'elements',
+        'initial preprocess' => static::class . ':preprocessBlock',
+      ],
+    ];
+  }
+
+  /**
+   * Prepares variables for block templates.
+   *
+   * Default template: block.html.twig.
+   *
+   * Prepares the values passed to the theme_block function to be passed
+   * into a pluggable template engine. Uses block properties to generate a
+   * series of template file suggestions. If none are found, the default
+   * block.html.twig is used.
+   *
+   * Most themes use their own copy of block.html.twig. The default is located
+   * inside "core/modules/block/templates/block.html.twig". Look in there for
+   * the full list of available variables.
+   *
+   * @param array $variables
+   *   An associative array containing:
+   *   - elements: An associative array containing the properties of the
+   *     element. Properties used: #block, #configuration, #children,
+   *     and #plugin_id.
+   */
+  public function preprocessBlock(&$variables): void {
+    $variables['configuration'] = $variables['elements']['#configuration'];
+    $variables['plugin_id'] = $variables['elements']['#plugin_id'];
+    $variables['base_plugin_id'] = $variables['elements']['#base_plugin_id'];
+    $variables['derivative_plugin_id'] = $variables['elements']['#derivative_plugin_id'];
+    $variables['in_preview'] = $variables['elements']['#in_preview'] ?? FALSE;
+    $variables['label'] = !empty($variables['configuration']['label_display']) ? $variables['configuration']['label'] : '';
+    $variables['content'] = $variables['elements']['content'];
+    // A block's label is configuration: it is static. Allow dynamic labels to
+    // be set in the render array.
+    if (isset($variables['elements']['content']['#title']) && !empty($variables['configuration']['label_display'])) {
+      $variables['label'] = $variables['elements']['content']['#title'];
+    }
+
+    // Create a valid HTML ID and make sure it is unique.
+    if (!empty($variables['elements']['#id'])) {
+      $variables['attributes']['id'] = Html::getUniqueId('block-' . $variables['elements']['#id']);
+    }
+
+    // Proactively add aria-describedby if possible to improve accessibility.
+    if ($variables['label'] && isset($variables['attributes']['role'])) {
+      $variables['title_attributes']['id'] = Html::getUniqueId($variables['label']);
+      $variables['attributes']['aria-describedby'] = $variables['title_attributes']['id'];
+    }
+  }
+
+  /**
+   * Implements hook_page_top().
+   */
+  #[Hook('page_top')]
+  public function pageTop(array &$page_top): void {
+    if (\Drupal::routeMatch()->getRouteName() === 'block.admin_demo') {
+      $theme = \Drupal::theme()->getActiveTheme()->getName();
+      $page_top['backlink'] = [
+        '#type' => 'link',
+        '#title' => $this->t('Exit block region demonstration'),
+        '#options' => [
+          'attributes' => [
+            'class' => [
+              'block-demo-backlink',
+            ],
+          ],
+        ],
+        '#weight' => -10,
+      ];
+      if (\Drupal::config('system.theme')->get('default') == $theme) {
+        $page_top['backlink']['#url'] = Url::fromRoute('block.admin_display');
+      }
+      else {
+        $page_top['backlink']['#url'] = Url::fromRoute('block.admin_display_theme', ['theme' => $theme]);
+      }
+    }
+  }
+
+  /**
+   * Implements hook_modules_installed().
+   *
+   * @see block_themes_installed()
+   */
+  #[Hook('modules_installed')]
+  public function modulesInstalled($modules, bool $is_syncing): void {
+    // Do not create blocks during config sync.
+    if ($is_syncing) {
+      return;
+    }
+
+    // BlockHooks::themesInstalled() does not call block_theme_initialize()
+    // during site installation because block configuration can be optional or
+    // provided by the profile. Now, when the profile is installed, this
+    // configuration exists, call block_theme_initialize() for all installed
+    // themes.
+    $profile = \Drupal::installProfile();
+    if (in_array($profile, $modules, TRUE)) {
+      foreach (\Drupal::service('theme_handler')->listInfo() as $theme => $data) {
+        block_theme_initialize($theme);
+      }
+    }
+  }
+
+  /**
+   * Implements hook_rebuild().
+   */
+  #[Hook('rebuild')]
+  public function rebuild(): void {
+    foreach (\Drupal::service('theme_handler')->listInfo() as $theme => $data) {
+      if ($data->status) {
+        $regions = system_region_list($theme);
+        /** @var \Drupal\block\BlockInterface[] $blocks */
+        $blocks = \Drupal::entityTypeManager()->getStorage('block')->loadByProperties(['theme' => $theme]);
+        foreach ($blocks as $block_id => $block) {
+          // Disable blocks in invalid regions.
+          if (!isset($regions[$block->getRegion()])) {
+            if ($block->status()) {
+              \Drupal::messenger()->addWarning($this->t('The block %info was assigned to the invalid region %region and has been disabled.', ['%info' => $block_id, '%region' => $block->getRegion()]));
+            }
+            $block->setRegion(system_default_region($theme))->disable()->save();
+          }
+        }
+      }
+    }
+  }
+
+  /**
+   * Implements hook_ENTITY_TYPE_delete() for user_role entities.
+   *
+   * Removes deleted role from blocks that use it.
+   */
+  #[Hook('user_role_delete')]
+  public function userRoleDelete($role): void {
+    foreach (Block::loadMultiple() as $block) {
+      /** @var \Drupal\block\BlockInterface $block */
+      $visibility = $block->getVisibility();
+      if (isset($visibility['user_role']['roles'][$role->id()])) {
+        unset($visibility['user_role']['roles'][$role->id()]);
+        $block->setVisibilityConfig('user_role', $visibility['user_role']);
+        $block->save();
+      }
+    }
+  }
+
+  /**
+   * Implements hook_ENTITY_TYPE_delete() for menu entities.
+   */
+  #[Hook('menu_delete')]
+  public function menuDelete(Menu $menu): void {
+    if (!$menu->isSyncing()) {
+      foreach (Block::loadMultiple() as $block) {
+        if ($block->getPluginId() == 'system_menu_block:' . $menu->id()) {
+          $block->delete();
+        }
+      }
+    }
+  }
+
+  /**
+   * Implements hook_ENTITY_TYPE_delete() for 'configurable_language'.
+   *
+   * Delete the potential block visibility settings of the deleted language.
+   */
+  #[Hook('configurable_language_delete')]
+  public function configurableLanguageDelete(ConfigurableLanguageInterface $language): void {
+    // Remove the block visibility settings for the deleted language.
+    foreach (Block::loadMultiple() as $block) {
+      /** @var \Drupal\block\BlockInterface $block */
+      $visibility = $block->getVisibility();
+      if (isset($visibility['language']['langcodes'][$language->id()])) {
+        unset($visibility['language']['langcodes'][$language->id()]);
+        $block->setVisibilityConfig('language', $visibility['language']);
+        $block->save();
+      }
+    }
+  }
+
+  /**
+   * Implements hook_block_build_BASE_BLOCK_ID_alter().
+   */
+  #[Hook('block_build_local_actions_block_alter')]
+  public function blockBuildLocalActionsBlockAlter(array &$build, BlockPluginInterface $block): void {
+    $build['#lazy_builder_preview'] = [
+      '#type' => 'container',
+      '#attributes' => [
+        'class' => [
+          'invisible',
+        ],
+      ],
+      'actions' => [
+        '#theme' => 'menu_local_action',
+        '#link' => [
+          'title' => $this->t('Add'),
+          'url' => Url::fromUserInput('#'),
+        ],
+      ],
+    ];
+  }
+
+}

web/core/modules/block/src/Plugin/ConfigAction/PlaceBlock.php

@@ -0,0 +1,97 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block\Plugin\ConfigAction;
+
+use Drupal\block\BlockInterface;
+use Drupal\Core\Config\Action\Attribute\ConfigAction;
+use Drupal\Core\Config\Action\ConfigActionException;
+use Drupal\Core\Config\Action\ConfigActionPluginInterface;
+use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\Config\Entity\ConfigEntityStorageInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Places a block in either the admin or default theme.
+ *
+ * @internal
+ *   This API is experimental.
+ */
+#[ConfigAction(
+  id: 'placeBlock',
+  admin_label: new TranslatableMarkup('Place a block'),
+  entity_types: ['block'],
+  deriver: PlaceBlockDeriver::class,
+)]
+final class PlaceBlock implements ConfigActionPluginInterface, ContainerFactoryPluginInterface {
+
+  public function __construct(
+    private readonly ConfigActionPluginInterface $createAction,
+    private readonly string $whichTheme,
+    private readonly ConfigFactoryInterface $configFactory,
+    private readonly ConfigEntityStorageInterface $blockStorage,
+  ) {}
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $container->get('plugin.manager.config_action')->createInstance('entity_create:createIfNotExists'),
+      $plugin_definition['which_theme'],
+      $container->get(ConfigFactoryInterface::class),
+      $container->get(EntityTypeManagerInterface::class)->getStorage('block'),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function apply(string $configName, mixed $value): void {
+    assert(is_array($value));
+
+    $theme = $this->configFactory->get('system.theme')->get($this->whichTheme);
+    $value['theme'] = $theme;
+
+    if (array_key_exists('region', $value) && is_array($value['region'])) {
+      // Since the recipe author might not know ahead of time what theme the
+      // block is in, they should supply a map whose keys are theme names and
+      // values are region names, so we know where to place this block. If the
+      // target theme is not in the map, they should supply the name of a
+      // fallback region. If all that fails, give up with an exception.
+      $value['region'] = $value['region'][$theme] ?? $value['default_region'] ?? throw new ConfigActionException("Cannot determine which region to place this block into, because no default region was provided.");
+    }
+
+    // Allow the recipe author to position the block in the region without
+    // needing to know exact weights.
+    if (array_key_exists('position', $value)) {
+      $blocks = $this->blockStorage->loadByProperties([
+        'theme' => $theme,
+        'region' => $value['region'],
+      ]);
+      if ($blocks) {
+        // Sort the blocks by weight. Don't use
+        // \Drupal\block\Entity\Block::sort() here because it seems to be
+        // intended to sort blocks in the UI, where we really just want to get
+        // the weights right in this situation.
+        uasort($blocks, fn (BlockInterface $a, BlockInterface $b) => $a->getWeight() <=> $b->getWeight());
+
+        $value['weight'] = match ($value['position']) {
+          'first' => reset($blocks)->getWeight() - 1,
+          'last' => end($blocks)->getWeight() + 1,
+        };
+      }
+    }
+    // Remove values that are not valid properties of block entities.
+    unset($value['position'], $value['default_region']);
+    // Ensure a weight is set by default.
+    $value += ['weight' => 0];
+
+    $this->createAction->apply($configName, $value);
+  }
+
+}

web/core/modules/block/src/Plugin/ConfigAction/PlaceBlockDeriver.php

@@ -0,0 +1,32 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block\Plugin\ConfigAction;
+
+use Drupal\Component\Plugin\Derivative\DeriverBase;
+
+/**
+ * Defines a deriver for the `placeBlock` config action.
+ *
+ * This creates two actions: `placeBlockInDefaultTheme`, and
+ * `placeBlockInAdminTheme`. They behave identically except for which theme
+ * they target.
+ */
+final class PlaceBlockDeriver extends DeriverBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDerivativeDefinitions($base_plugin_definition) {
+    $this->derivatives['placeBlockInAdminTheme'] = [
+      'which_theme' => 'admin',
+    ] + $base_plugin_definition;
+    $this->derivatives['placeBlockInDefaultTheme'] = [
+      'which_theme' => 'default',
+    ] + $base_plugin_definition;
+
+    return parent::getDerivativeDefinitions($base_plugin_definition);
+  }
+
+}

web/core/modules/block/src/Plugin/Derivative/ThemeLocalTask.php

@@ -0,0 +1,66 @@
+<?php
+
+namespace Drupal\block\Plugin\Derivative;
+
+use Drupal\Component\Plugin\Derivative\DeriverBase;
+use Drupal\Core\Extension\ThemeHandlerInterface;
+use Drupal\Core\Plugin\Discovery\ContainerDeriverInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides dynamic tabs based on active themes.
+ */
+class ThemeLocalTask extends DeriverBase implements ContainerDeriverInterface {
+
+  /**
+   * The theme handler.
+   *
+   * @var \Drupal\Core\Extension\ThemeHandlerInterface
+   */
+  protected $themeHandler;
+
+  /**
+   * Constructs a new ThemeLocalTask.
+   *
+   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
+   *   The theme handler.
+   */
+  public function __construct(ThemeHandlerInterface $theme_handler) {
+    $this->themeHandler = $theme_handler;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, $base_plugin_id) {
+    return new static(
+      $container->get('theme_handler')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDerivativeDefinitions($base_plugin_definition) {
+    $default_theme = $this->themeHandler->getDefault();
+
+    foreach ($this->themeHandler->listInfo() as $theme_name => $theme) {
+      if ($this->themeHandler->hasUi($theme_name)) {
+        $this->derivatives[$theme_name] = $base_plugin_definition;
+        $this->derivatives[$theme_name]['title'] = $theme->info['name'];
+        $this->derivatives[$theme_name]['route_parameters'] = ['theme' => $theme_name];
+      }
+      // Default task!
+      if ($default_theme == $theme_name) {
+        $this->derivatives[$theme_name]['route_name'] = $base_plugin_definition['parent_id'];
+        // Emulate default logic because without the base plugin id we can't
+        // change the base_route.
+        $this->derivatives[$theme_name]['weight'] = -10;
+
+        unset($this->derivatives[$theme_name]['route_parameters']);
+      }
+    }
+    return $this->derivatives;
+  }
+
+}

web/core/modules/block/src/Plugin/DisplayVariant/BlockPageVariant.php

@@ -0,0 +1,205 @@
+<?php
+
+namespace Drupal\block\Plugin\DisplayVariant;
+
+use Drupal\block\BlockRepositoryInterface;
+use Drupal\Core\Block\MainContentBlockPluginInterface;
+use Drupal\Core\Block\TitleBlockPluginInterface;
+use Drupal\Core\Block\MessagesBlockPluginInterface;
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Display\Attribute\PageDisplayVariant;
+use Drupal\Core\Display\PageVariantInterface;
+use Drupal\Core\Entity\EntityViewBuilderInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\Display\VariantBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a page display variant that decorates the main content with blocks.
+ *
+ * To ensure essential information is displayed, each essential part of a page
+ * has a corresponding block plugin interface, so that BlockPageVariant can
+ * automatically provide a fallback in case no block for each of these
+ * interfaces is placed.
+ *
+ * @see \Drupal\Core\Block\MainContentBlockPluginInterface
+ * @see \Drupal\Core\Block\MessagesBlockPluginInterface
+ */
+#[PageDisplayVariant(
+  id: 'block_page',
+  admin_label: new TranslatableMarkup('Page with blocks')
+)]
+class BlockPageVariant extends VariantBase implements PageVariantInterface, ContainerFactoryPluginInterface {
+
+  /**
+   * The block repository.
+   *
+   * @var \Drupal\block\BlockRepositoryInterface
+   */
+  protected $blockRepository;
+
+  /**
+   * The block view builder.
+   *
+   * @var \Drupal\Core\Entity\EntityViewBuilderInterface
+   */
+  protected $blockViewBuilder;
+
+  /**
+   * The Block entity type list cache tags.
+   *
+   * @var string[]
+   */
+  protected $blockListCacheTags;
+
+  /**
+   * The render array representing the main page content.
+   *
+   * @var array
+   */
+  protected $mainContent = [];
+
+  /**
+   * The page title: a string (plain title) or a render array (formatted title).
+   *
+   * @var string|array
+   */
+  protected $title = '';
+
+  /**
+   * Constructs a new BlockPageVariant.
+   *
+   * @param array $configuration
+   *   A configuration array containing information about the plugin instance.
+   * @param string $plugin_id
+   *   The plugin ID for the plugin instance.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\block\BlockRepositoryInterface $block_repository
+   *   The block repository.
+   * @param \Drupal\Core\Entity\EntityViewBuilderInterface $block_view_builder
+   *   The block view builder.
+   * @param string[] $block_list_cache_tags
+   *   The Block entity type list cache tags.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, BlockRepositoryInterface $block_repository, EntityViewBuilderInterface $block_view_builder, array $block_list_cache_tags) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->blockRepository = $block_repository;
+    $this->blockViewBuilder = $block_view_builder;
+    $this->blockListCacheTags = $block_list_cache_tags;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('block.repository'),
+      $container->get('entity_type.manager')->getViewBuilder('block'),
+      $container->get('entity_type.manager')->getDefinition('block')->getListCacheTags()
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setMainContent(array $main_content) {
+    $this->mainContent = $main_content;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setTitle($title) {
+    $this->title = $title;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    // Track whether blocks showing the main content and messages are displayed.
+    $main_content_block_displayed = FALSE;
+    $messages_block_displayed = FALSE;
+
+    $build = [
+      '#cache' => [
+        'tags' => $this->blockListCacheTags,
+      ],
+    ];
+    // Load all region content assigned via blocks.
+    $cacheable_metadata_list = [];
+    foreach ($this->blockRepository->getVisibleBlocksPerRegion($cacheable_metadata_list) as $region => $blocks) {
+      /** @var \Drupal\block\BlockInterface[] $blocks */
+      foreach ($blocks as $key => $block) {
+        $block_plugin = $block->getPlugin();
+        if ($block_plugin instanceof MainContentBlockPluginInterface) {
+          $block_plugin->setMainContent($this->mainContent);
+          $main_content_block_displayed = TRUE;
+        }
+        elseif ($block_plugin instanceof TitleBlockPluginInterface) {
+          $block_plugin->setTitle($this->title);
+        }
+        elseif ($block_plugin instanceof MessagesBlockPluginInterface) {
+          $messages_block_displayed = TRUE;
+        }
+        $build[$region][$key] = $this->blockViewBuilder->view($block);
+
+        // The main content block cannot be cached: it is a placeholder for the
+        // render array returned by the controller. It should be rendered as-is,
+        // with other placed blocks "decorating" it. Analogous reasoning for the
+        // title block.
+        if ($block_plugin instanceof MainContentBlockPluginInterface || $block_plugin instanceof TitleBlockPluginInterface) {
+          unset($build[$region][$key]['#cache']['keys']);
+        }
+      }
+      if (!empty($build[$region])) {
+        // \Drupal\block\BlockRepositoryInterface::getVisibleBlocksPerRegion()
+        // returns the blocks in sorted order.
+        $build[$region]['#sorted'] = TRUE;
+      }
+    }
+
+    // If no block that shows the main content is displayed, still show the main
+    // content. Otherwise the end user will see all displayed blocks, but not
+    // the main content they came for.
+    if (!$main_content_block_displayed) {
+      $build['content']['system_main'] = $this->mainContent;
+    }
+
+    // If no block displays status messages, still render them.
+    if (!$messages_block_displayed) {
+      $build['content']['messages'] = [
+        '#weight' => -1000,
+        '#type' => 'status_messages',
+        '#include_fallback' => TRUE,
+      ];
+    }
+
+    // If any render arrays are manually placed, render arrays and blocks must
+    // be sorted.
+    if (!$main_content_block_displayed || !$messages_block_displayed) {
+      unset($build['content']['#sorted']);
+    }
+
+    // The access results' cacheability is currently added to the top level of
+    // the render array. This is done to prevent issues with empty regions being
+    // displayed.
+    // This would need to be changed to allow caching of block regions, as each
+    // region must then have the relevant cacheable metadata.
+    $merged_cacheable_metadata = CacheableMetadata::createFromRenderArray($build);
+    foreach ($cacheable_metadata_list as $cacheable_metadata) {
+      $merged_cacheable_metadata = $merged_cacheable_metadata->merge($cacheable_metadata);
+    }
+    $merged_cacheable_metadata->applyTo($build);
+
+    return $build;
+  }
+
+}

web/core/modules/block/src/Plugin/migrate/destination/EntityBlock.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace Drupal\block\Plugin\migrate\destination;
+
+use Drupal\Core\Config\Schema\SchemaIncompleteException;
+use Drupal\migrate\Attribute\MigrateDestination;
+use Drupal\migrate\MigrateException;
+use Drupal\migrate\Plugin\migrate\destination\EntityConfigBase;
+use Drupal\migrate\Row;
+
+/**
+ * Migrate destination for block entity.
+ */
+#[MigrateDestination('entity:block')]
+class EntityBlock extends EntityConfigBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getEntityId(Row $row) {
+    // Try to find the block by its plugin ID and theme.
+    $properties = [
+      'plugin' => $row->getDestinationProperty('plugin'),
+      'theme' => $row->getDestinationProperty('theme'),
+    ];
+    $blocks = array_keys($this->storage->loadByProperties($properties));
+    return reset($blocks);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function import(Row $row, array $old_destination_id_values = []) {
+    try {
+      $entity_ids = parent::import($row, $old_destination_id_values);
+    }
+    catch (SchemaIncompleteException $e) {
+      throw new MigrateException($e->getMessage());
+    }
+    return $entity_ids;
+  }
+
+}

web/core/modules/block/src/Plugin/migrate/process/BlockPluginId.php

@@ -0,0 +1,115 @@
+<?php
+
+namespace Drupal\block\Plugin\migrate\process;
+
+use Drupal\Core\Entity\EntityStorageInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\migrate\Attribute\MigrateProcess;
+use Drupal\migrate\MigrateLookupInterface;
+use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Row;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Determines the block plugin ID.
+ */
+#[MigrateProcess('block_plugin_id')]
+class BlockPluginId extends ProcessPluginBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The migrate lookup service.
+   *
+   * @var \Drupal\migrate\MigrateLookupInterface
+   */
+  protected $migrateLookup;
+
+  /**
+   * The block_content entity storage handler.
+   *
+   * @var \Drupal\Core\Entity\EntityStorageInterface|null
+   */
+  protected $blockContentStorage;
+
+  /**
+   * Constructs a BlockPluginId object.
+   *
+   * @param array $configuration
+   *   The plugin configuration.
+   * @param string $plugin_id
+   *   The plugin ID.
+   * @param array $plugin_definition
+   *   The plugin definition.
+   * @param \Drupal\Core\Entity\EntityStorageInterface|null $storage
+   *   The block content storage object. NULL if the block_content module is
+   *   not installed.
+   * @param \Drupal\migrate\MigrateLookupInterface $migrate_lookup
+   *   The migrate lookup service.
+   */
+  public function __construct(array $configuration, $plugin_id, array $plugin_definition, ?EntityStorageInterface $storage, MigrateLookupInterface $migrate_lookup) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->blockContentStorage = $storage;
+    $this->migrateLookup = $migrate_lookup;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, ?MigrationInterface $migration = NULL) {
+    $entity_type_manager = $container->get('entity_type.manager');
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $entity_type_manager->hasDefinition('block_content') ? $entity_type_manager->getStorage('block_content') : NULL,
+      $container->get('migrate.lookup')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   *
+   * Set the block plugin id.
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    if (is_array($value)) {
+      [$module, $delta] = $value;
+      switch ($module) {
+        case 'aggregator':
+          [$type] = explode('-', $delta);
+          if ($type == 'feed') {
+            return 'aggregator_feed_block';
+          }
+          break;
+
+        case 'menu':
+          return "system_menu_block:$delta";
+
+        case 'block':
+          if ($this->blockContentStorage) {
+            $block_id = $row->getDestinationProperty('_block_module_plugin_id');
+            // Legacy generated migrations will not have the destination
+            // property '_block_module_plugin_id'.
+            if (!$block_id) {
+              $lookup_result = $this->migrateLookup->lookup(['d6_custom_block', 'd7_custom_block'], [$delta]);
+              if ($lookup_result) {
+                $block_id = $lookup_result[0]['id'];
+              }
+            }
+            if ($block_id) {
+              return 'block_content:' . $this->blockContentStorage->load($block_id)->uuid();
+            }
+          }
+          break;
+
+        default:
+          break;
+      }
+    }
+    else {
+      return $value;
+    }
+  }
+
+}

web/core/modules/block/src/Plugin/migrate/process/BlockRegion.php

@@ -0,0 +1,73 @@
+<?php
+
+namespace Drupal\block\Plugin\migrate\process;
+
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\migrate\Attribute\MigrateProcess;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\Plugin\migrate\process\StaticMap;
+use Drupal\migrate\Row;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Determines the region for a block.
+ */
+#[MigrateProcess('block_region')]
+class BlockRegion extends StaticMap implements ContainerFactoryPluginInterface {
+
+  /**
+   * List of regions, keyed by theme.
+   *
+   * @var array[]
+   */
+  protected $regions;
+
+  /**
+   * Constructs a BlockRegion plugin instance.
+   *
+   * @param array $configuration
+   *   The plugin configuration.
+   * @param string $plugin_id
+   *   The plugin ID.
+   * @param mixed $plugin_definition
+   *   The plugin definition.
+   * @param array $regions
+   *   Array of region maps, keyed by theme.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, array $regions) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->regions = $regions;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    $regions = [];
+    foreach ($container->get('theme_handler')->listInfo() as $key => $theme) {
+      $regions[$key] = $theme->info['regions'];
+    }
+    return new static($configuration, $plugin_id, $plugin_definition, $regions);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    // Set the destination region, based on the source region and theme as well
+    // as the current destination default theme.
+    [$source_theme, $destination_theme, $region] = $value;
+
+    // Theme is the same on both source and destination, so ensure that the
+    // region exists in the destination theme.
+    if (strtolower($source_theme) == strtolower($destination_theme)) {
+      if (isset($this->regions[$destination_theme][$region])) {
+        return $region;
+      }
+    }
+
+    // Fall back to static mapping.
+    return parent::transform($value, $migrate_executable, $row, $destination_property);
+  }
+
+}

web/core/modules/block/src/Plugin/migrate/process/BlockSettings.php

@@ -0,0 +1,104 @@
+<?php
+
+namespace Drupal\block\Plugin\migrate\process;
+
+use Drupal\Core\Block\BlockManagerInterface;
+use Drupal\Core\Block\BlockPluginInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\migrate\Attribute\MigrateProcess;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Row;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+// cspell:ignore whois
+
+/**
+ * Determines the block settings.
+ */
+#[MigrateProcess('block_settings')]
+class BlockSettings extends ProcessPluginBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The block manager service.
+   *
+   * @var \Drupal\Core\Block\BlockManagerInterface
+   */
+  protected readonly BlockManagerInterface $blockManager;
+
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, ?BlockManagerInterface $blockManager = NULL) {
+    if (empty($blockManager)) {
+      @trigger_error('Calling ' . __METHOD__ . '() without the $blockManager parameter is deprecated in drupal:11.2.0 and must be provided in drupal:12.0.0. See https://www.drupal.org/node/3522023', E_USER_DEPRECATED);
+      $blockManager = \Drupal::service(BlockManagerInterface::class);
+    }
+    $this->blockManager = $blockManager;
+
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition): static {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get(BlockManagerInterface::class),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   *
+   * Set the block configuration.
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    [$plugin, $delta, $old_settings, $title] = $value;
+    $settings = [];
+    $settings['label'] = $title;
+    if ($title && $title !== '<none>') {
+      $settings['label_display'] = BlockPluginInterface::BLOCK_LABEL_VISIBLE;
+    }
+    else {
+      $settings['label_display'] = '0';
+    }
+    switch ($plugin) {
+      case 'aggregator_feed_block':
+        [, $id] = explode('-', $delta);
+        $settings['block_count'] = $old_settings['aggregator']['item_count'];
+        $settings['feed'] = $id;
+        break;
+
+      case 'book_navigation':
+        $settings['block_mode'] = $old_settings['book']['block_mode'];
+        break;
+
+      case 'forum_active_block':
+      case 'forum_new_block':
+        $settings['block_count'] = $old_settings['forum']['block_num'];
+        break;
+
+      case 'statistics_popular_block':
+        $settings['top_day_num'] = $old_settings['statistics']['statistics_block_top_day_num'];
+        $settings['top_all_num'] = $old_settings['statistics']['statistics_block_top_all_num'];
+        $settings['top_last_num'] = $old_settings['statistics']['statistics_block_top_last_num'];
+        break;
+
+      case 'views_block:who_s_new-block_1':
+        $settings['items_per_page'] = $old_settings['user']['block_whois_new_count'];
+        break;
+
+      case 'views_block:who_s_online-who_s_online_block':
+        $settings['items_per_page'] = $old_settings['user']['max_list_count'];
+        break;
+    }
+
+    // Let the block plugin fill in any missing settings.
+    $settings = $this->blockManager->createInstance($plugin, $settings)
+      ->getConfiguration();
+
+    return $settings;
+  }
+
+}

web/core/modules/block/src/Plugin/migrate/process/BlockTheme.php

@@ -0,0 +1,91 @@
+<?php
+
+namespace Drupal\block\Plugin\migrate\process;
+
+use Drupal\Core\Config\Config;
+use Drupal\migrate\Attribute\MigrateProcess;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Row;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Determines the theme to use for a block.
+ */
+#[MigrateProcess('block_theme')]
+class BlockTheme extends ProcessPluginBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * Contains the system.theme configuration object.
+   */
+  protected Config $themeConfig;
+
+  /**
+   * List of themes available on the destination.
+   *
+   * @var string[]
+   */
+  protected array $themes;
+
+  /**
+   * Constructs a BlockTheme object.
+   *
+   * @param array $configuration
+   *   A configuration array containing information about the plugin instance.
+   * @param string $plugin_id
+   *   The plugin ID for the plugin instance.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\Core\Config\Config $theme_config
+   *   The system.theme configuration factory object.
+   * @param array $themes
+   *   The list of themes available on the destination.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, Config $theme_config, array $themes) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->themeConfig = $theme_config;
+    $this->themes = $themes;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('config.factory')->get('system.theme'),
+      $container->get('theme_handler')->listInfo()
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    [$theme, $default_theme, $admin_theme] = $value;
+
+    // If the source theme exists on the destination, we're good.
+    if (isset($this->themes[$theme])) {
+      return $theme;
+    }
+
+    // If the source block is assigned to a region in the source default theme,
+    // then assign it to the destination default theme.
+    if (strtolower($theme) == strtolower($default_theme)) {
+      return $this->themeConfig->get('default');
+    }
+
+    // If the source block is assigned to a region in the source admin theme,
+    // then assign it to the destination admin theme.
+    if ($admin_theme && strtolower($theme) == strtolower($admin_theme)) {
+      return $this->themeConfig->get('admin');
+    }
+
+    // We couldn't map it to a D8 theme so just return the incoming theme.
+    return $theme;
+  }
+
+}

web/core/modules/block/src/Plugin/migrate/process/BlockVisibility.php

@@ -0,0 +1,154 @@
+<?php
+
+namespace Drupal\block\Plugin\migrate\process;
+
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\migrate\Attribute\MigrateProcess;
+use Drupal\migrate\MigrateLookupInterface;
+use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\MigrateSkipRowException;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Row;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Determines the visibility for a block.
+ */
+#[MigrateProcess('block_visibility')]
+class BlockVisibility extends ProcessPluginBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The module handler.
+   *
+   * @var \Drupal\Core\Extension\ModuleHandlerInterface
+   */
+  protected $moduleHandler;
+
+  /**
+   * The migrate lookup service.
+   *
+   * @var \Drupal\migrate\MigrateLookupInterface
+   */
+  protected $migrateLookup;
+
+  /**
+   * Whether or not to skip blocks that use PHP for visibility.
+   *
+   * Only applies if the PHP module is not enabled.
+   *
+   * @var bool
+   */
+  protected $skipPHP = FALSE;
+
+  /**
+   * Constructs a BlockVisibility object.
+   *
+   * @param array $configuration
+   *   The plugin configuration.
+   * @param string $plugin_id
+   *   The plugin ID.
+   * @param mixed $plugin_definition
+   *   The plugin definition.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   *   The module handler service.
+   * @param \Drupal\migrate\MigrateLookupInterface $migrate_lookup
+   *   The migrate lookup service.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, ModuleHandlerInterface $module_handler, MigrateLookupInterface $migrate_lookup) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->moduleHandler = $module_handler;
+    $this->migrateLookup = $migrate_lookup;
+
+    if (isset($configuration['skip_php'])) {
+      $this->skipPHP = $configuration['skip_php'];
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, ?MigrationInterface $migration = NULL) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('module_handler'),
+      $container->get('migrate.lookup')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    [$old_visibility, $pages, $roles] = $value;
+
+    $visibility = [];
+
+    // If the block is assigned to specific roles, add the user_role condition.
+    if ($roles) {
+      $visibility['user_role'] = [
+        'id' => 'user_role',
+        'roles' => [],
+        'context_mapping' => [
+          'user' => '@user.current_user_context:current_user',
+        ],
+        'negate' => FALSE,
+      ];
+      // Legacy generated migrations will not have the destination property
+      // '_role_ids'.
+      $role_ids = $row->getDestinationProperty('_role_ids');
+      foreach ($roles as $key => $role_id) {
+        if (!$role_ids) {
+          $lookup = $this->migrateLookup->lookup(['d6_user_role', 'd7_user_role'], [$role_id]);
+          $lookup_result = $lookup[0]['id'];
+        }
+        else {
+          $lookup_result = $role_ids[$role_id] ?? NULL;
+        }
+        if ($lookup_result) {
+          $roles[$key] = $lookup_result;
+        }
+      }
+
+      $visibility['user_role']['roles'] = array_combine($roles, $roles);
+    }
+
+    if ($pages) {
+      // 2 == BLOCK_VISIBILITY_PHP in Drupal 6 and 7.
+      if ($old_visibility == 2) {
+        // If the PHP module is present, migrate the visibility code unaltered.
+        if ($this->moduleHandler->moduleExists('php')) {
+          $visibility['php'] = [
+            'id' => 'php',
+            // PHP code visibility could not be negated in Drupal 6 or 7.
+            'negate' => FALSE,
+            'php' => $pages,
+          ];
+        }
+        // Skip the row if we're configured to. If not, we don't need to do
+        // anything else -- the block will simply have no PHP or request_path
+        // visibility configuration.
+        elseif ($this->skipPHP) {
+          throw new MigrateSkipRowException(sprintf("The block with bid '%d' from module '%s' will have no PHP or request_path visibility configuration.", $row->getSourceProperty('bid'), $row->getSourceProperty('module')));
+        }
+      }
+      else {
+        $paths = preg_split("(\r\n?|\n)", $pages);
+        foreach ($paths as $key => $path) {
+          $paths[$key] = $path === '<front>' ? $path : '/' . ltrim($path, '/');
+        }
+        $visibility['request_path'] = [
+          'id' => 'request_path',
+          'negate' => !$old_visibility,
+          'pages' => implode("\n", $paths),
+        ];
+      }
+    }
+
+    return $visibility;
+  }
+
+}

web/core/modules/block/src/Plugin/migrate/process/RolesLookup.php

@@ -0,0 +1,103 @@
+<?php
+
+namespace Drupal\block\Plugin\migrate\process;
+
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\migrate\Attribute\MigrateProcess;
+use Drupal\migrate\MigrateLookupInterface;
+use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Row;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Gets the destination roles ID for an array of source roles IDs.
+ *
+ * The roles_lookup plugin is used to get the destination roles for roles that
+ * are assigned to a block. It always uses the 'roles' value on the row as the
+ * source value.
+ *
+ *  Examples
+ *
+ * @code
+ *  process:
+ *    roles:
+ *      plugin: roles_lookup
+ *      migration: d7_user_role
+ * @endcode
+ *
+ * This will get the destination role ID for each role in the 'roles' value on
+ * the source row.
+ *
+ * @see \Drupal\migrate\Plugin\MigrateProcessInterface
+ */
+#[MigrateProcess('roles_lookup')]
+class RolesLookup extends ProcessPluginBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The migrate lookup service.
+   *
+   * @var \Drupal\migrate\MigrateLookupInterface
+   */
+  protected $migrateLookup;
+
+  /**
+   * The migration for user role lookup.
+   *
+   * @var string
+   */
+  protected $migration;
+
+  /**
+   * Constructs a BlockVisibility object.
+   *
+   * @param array $configuration
+   *   The plugin configuration.
+   * @param string $plugin_id
+   *   The plugin ID.
+   * @param mixed $plugin_definition
+   *   The plugin definition.
+   * @param \Drupal\migrate\MigrateLookupInterface $migrate_lookup
+   *   The migrate lookup service.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, MigrateLookupInterface $migrate_lookup) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->migrateLookup = $migrate_lookup;
+
+    if (isset($configuration['migration'])) {
+      $this->migration = $configuration['migration'];
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, ?MigrationInterface $migration = NULL) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('migrate.lookup')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
+    $roles = $row->get('roles');
+    $roles_result = [];
+    // If the block is assigned to specific roles, add the user_role condition.
+    if ($roles) {
+      foreach ($roles as $role_id) {
+        $lookup_result = $this->migrateLookup->lookup([$this->migration], [$role_id]);
+        if ($lookup_result) {
+          $roles_result[$role_id] = $lookup_result[0]['id'];
+        }
+      }
+    }
+    return $roles_result;
+  }
+
+}

web/core/modules/block/src/Plugin/migrate/source/Block.php

@@ -0,0 +1,189 @@
+<?php
+
+namespace Drupal\block\Plugin\migrate\source;
+
+use Drupal\migrate\Row;
+use Drupal\migrate_drupal\Plugin\migrate\source\DrupalSqlBase;
+
+// cspell:ignore whois
+
+/**
+ * Drupal 6/7 block source from database.
+ *
+ * For available configuration keys, refer to the parent classes.
+ *
+ * @see \Drupal\migrate\Plugin\migrate\source\SqlBase
+ * @see \Drupal\migrate\Plugin\migrate\source\SourcePluginBase
+ *
+ * @MigrateSource(
+ *   id = "block",
+ *   source_module = "block"
+ * )
+ */
+class Block extends DrupalSqlBase {
+
+  /**
+   * The default theme name.
+   *
+   * @var string
+   */
+  protected $defaultTheme;
+
+  /**
+   * The admin theme name.
+   *
+   * @var string
+   */
+  protected $adminTheme;
+
+  /**
+   * Table containing block configuration.
+   *
+   * @var string
+   */
+  protected $blockTable;
+
+  /**
+   * Table mapping blocks to user roles.
+   *
+   * @var string
+   */
+  protected $blockRoleTable;
+
+  /**
+   * Table listing user roles.
+   *
+   * @var string
+   */
+  protected $userRoleTable;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function query() {
+    if ($this->getModuleSchemaVersion('system') >= 7000) {
+      $this->blockTable = 'block';
+      $this->blockRoleTable = 'block_role';
+    }
+    else {
+      $this->blockTable = 'blocks';
+      $this->blockRoleTable = 'blocks_roles';
+    }
+    // Drupal 6 & 7 both use the same name for the user roles table.
+    $this->userRoleTable = 'role';
+
+    return $this->select($this->blockTable, 'b')->fields('b');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function initializeIterator() {
+    $this->defaultTheme = $this->variableGet('theme_default', 'Garland');
+    $this->adminTheme = $this->variableGet('admin_theme', NULL);
+    return parent::initializeIterator();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function fields() {
+    return [
+      'bid' => $this->t('The block numeric identifier.'),
+      'module' => $this->t('The module providing the block.'),
+      'delta' => $this->t("The block's delta."),
+      'theme' => $this->t('Which theme the block is placed in.'),
+      'status' => $this->t('Whether or not the block is enabled.'),
+      'weight' => $this->t('Weight of the block for ordering within regions.'),
+      'region' => $this->t('Region the block is placed in.'),
+      'visibility' => $this->t('Visibility expression.'),
+      'pages' => $this->t('Pages list.'),
+      'title' => $this->t('Block title.'),
+      'cache' => $this->t('Cache rule.'),
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getIds() {
+    $ids['module']['type'] = 'string';
+    $ids['delta']['type'] = 'string';
+    $ids['theme']['type'] = 'string';
+    return $ids;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function prepareRow(Row $row) {
+    $row->setSourceProperty('default_theme', $this->defaultTheme);
+    $row->setSourceProperty('admin_theme', $this->adminTheme);
+
+    $module = $row->getSourceProperty('module');
+    $delta = $row->getSourceProperty('delta');
+
+    $query = $this->select($this->blockRoleTable, 'br')
+      ->fields('br', ['rid'])
+      ->condition('module', $module)
+      ->condition('delta', $delta);
+    $query->join($this->userRoleTable, 'ur', '[br].[rid] = [ur].[rid]');
+    $roles = $query->execute()
+      ->fetchCol();
+    $row->setSourceProperty('roles', $roles);
+
+    $settings = [];
+    switch ($module) {
+      case 'aggregator':
+        [$type, $id] = explode('-', $delta);
+        if ($type == 'feed') {
+          $item_count = $this->select('aggregator_feed', 'af')
+            ->fields('af', ['block'])
+            ->condition('fid', $id)
+            ->execute()
+            ->fetchField();
+        }
+        else {
+          $item_count = $this->select('aggregator_category', 'ac')
+            ->fields('ac', ['block'])
+            ->condition('cid', $id)
+            ->execute()
+            ->fetchField();
+        }
+        $settings['aggregator']['item_count'] = $item_count;
+        break;
+
+      case 'book':
+        $settings['book']['block_mode'] = $this->variableGet('book_block_mode', 'all pages');
+        break;
+
+      case 'forum':
+        $settings['forum']['block_num'] = $this->variableGet('forum_block_num_' . $delta, 5);
+        break;
+
+      case 'statistics':
+        foreach (['statistics_block_top_day_num', 'statistics_block_top_all_num', 'statistics_block_top_last_num'] as $name) {
+          $settings['statistics'][$name] = $this->variableGet($name, 0);
+        }
+        break;
+
+      case 'user':
+        switch ($delta) {
+          case 2:
+          case 'new':
+            $settings['user']['block_whois_new_count'] = $this->variableGet('user_block_whois_new_count', 5);
+            break;
+
+          case 3:
+          case 'online':
+            $settings['user']['block_seconds_online'] = $this->variableGet('user_block_seconds_online', 900);
+            $settings['user']['max_list_count'] = $this->variableGet('user_block_max_list_count', 10);
+            break;
+        }
+        break;
+    }
+    $row->setSourceProperty('settings', $settings);
+    return parent::prepareRow($row);
+  }
+
+}

web/core/modules/block/src/Plugin/migrate/source/d6/BlockTranslation.php

@@ -0,0 +1,76 @@
+<?php
+
+namespace Drupal\block\Plugin\migrate\source\d6;
+
+use Drupal\block\Plugin\migrate\source\Block;
+use Drupal\migrate\Plugin\migrate\source\SourcePluginBase;
+use Drupal\migrate\Row;
+
+/**
+ * Drupal 6 i18n block data from database.
+ *
+ * For available configuration keys, refer to the parent classes.
+ *
+ * @see \Drupal\migrate\Plugin\migrate\source\SqlBase
+ * @see \Drupal\migrate\Plugin\migrate\source\SourcePluginBase
+ *
+ * @MigrateSource(
+ *   id = "d6_block_translation",
+ *   source_module = "i18nblocks"
+ * )
+ */
+class BlockTranslation extends Block {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function query() {
+    // Let the parent set the block table to use, but do not use the parent
+    // query. Instead build a query so can use an inner join to the selected
+    // block table.
+    parent::query();
+    $query = $this->select('i18n_blocks', 'i18n')
+      ->fields('i18n')
+      ->fields('b', ['bid', 'module', 'delta', 'theme', 'title']);
+    $query->innerJoin($this->blockTable, 'b', ('[b].[module] = [i18n].[module] AND [b].[delta] = [i18n].[delta]'));
+    return $query;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function fields() {
+    return [
+      'bid' => $this->t('The block numeric identifier.'),
+      'ibid' => $this->t('The i18n_blocks block numeric identifier.'),
+      'module' => $this->t('The module providing the block.'),
+      'delta' => $this->t("The block's delta."),
+      'type' => $this->t('Block type'),
+      'language' => $this->t('Language for this field.'),
+      'theme' => $this->t('Which theme the block is placed in.'),
+      'default_theme' => $this->t('The default theme.'),
+      'title' => $this->t('Block title.'),
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function prepareRow(Row $row) {
+    $row->setSourceProperty('default_theme', $this->defaultTheme);
+    return SourcePluginBase::prepareRow($row);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getIds() {
+    $ids = parent::getIds();
+    $ids['module']['alias'] = 'b';
+    $ids['delta']['alias'] = 'b';
+    $ids['theme']['alias'] = 'b';
+    $ids['language']['type'] = 'string';
+    return $ids;
+  }
+
+}

web/core/modules/block/src/Plugin/migrate/source/d7/BlockTranslation.php

@@ -0,0 +1,115 @@
+<?php
+
+namespace Drupal\block\Plugin\migrate\source\d7;
+
+use Drupal\block\Plugin\migrate\source\Block;
+
+// cspell:ignore objectid objectindex plid textgroup
+
+/**
+ * Drupal 7 i18n block data from database.
+ *
+ * For available configuration keys, refer to the parent classes.
+ *
+ * @see \Drupal\migrate\Plugin\migrate\source\SqlBase
+ * @see \Drupal\migrate\Plugin\migrate\source\SourcePluginBase
+ *
+ * @MigrateSource(
+ *   id = "d7_block_translation",
+ *   source_module = "i18n_block"
+ * )
+ */
+class BlockTranslation extends Block {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function query() {
+    // Let the parent set the block table to use, but do not use the parent
+    // query. Instead build a query so can use an inner join to the selected
+    // block table.
+    parent::query();
+    $query = $this->select('i18n_string', 'i18n')
+      ->fields('i18n')
+      ->fields('b', [
+        'bid',
+        'module',
+        'delta',
+        'theme',
+        'status',
+        'weight',
+        'region',
+        'custom',
+        'visibility',
+        'pages',
+        'title',
+        'cache',
+        'i18n_mode',
+      ])
+      ->fields('lt', [
+        'lid',
+        'translation',
+        'language',
+        'plid',
+        'plural',
+      ])
+      ->condition('i18n_mode', 1);
+    $query->leftJoin($this->blockTable, 'b', ('[b].[delta] = [i18n].[objectid]'));
+    $query->innerJoin('locales_target', 'lt', '[lt].[lid] = [i18n].[lid]');
+
+    // The i18n_string module adds a status column to locale_target. It was
+    // originally 'status' in a later revision it was named 'i18n_status'.
+    if ($this->getDatabase()->schema()->fieldExists('locales_target', 'status')) {
+      $query->addField('lt', 'status', 'i18n_status');
+    }
+    if ($this->getDatabase()->schema()->fieldExists('locales_target', 'i18n_status')) {
+      $query->addField('lt', 'i18n_status', 'i18n_status');
+    }
+
+    return $query;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function fields() {
+    return [
+      'bid' => $this->t('The block numeric identifier.'),
+      'module' => $this->t('The module providing the block.'),
+      'delta' => $this->t("The block's delta."),
+      'theme' => $this->t('Which theme the block is placed in.'),
+      'status' => $this->t('Block enabled status'),
+      'weight' => $this->t('Block weight within region'),
+      'region' => $this->t('Theme region within which the block is set'),
+      'visibility' => $this->t('Visibility'),
+      'pages' => $this->t('Pages list.'),
+      'title' => $this->t('Block title.'),
+      'cache' => $this->t('Cache rule.'),
+      'i18n_mode' => $this->t('Multilingual mode'),
+      'lid' => $this->t('Language string ID'),
+      'textgroup' => $this->t('A module defined group of translations'),
+      'context' => $this->t('Full string ID for quick search: type:objectid:property.'),
+      'objectid' => $this->t('Object ID'),
+      'type' => $this->t('Object type for this string'),
+      'property' => $this->t('Object property for this string'),
+      'objectindex' => $this->t('Integer value of Object ID'),
+      'format' => $this->t('The {filter_format}.format of the string'),
+      'translation' => $this->t('Translation'),
+      'language' => $this->t('Language code'),
+      'plid' => $this->t('Parent lid'),
+      'plural' => $this->t('Plural index number'),
+      'i18n_status' => $this->t('Translation needs update'),
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getIds() {
+    $ids['delta']['type'] = 'string';
+    $ids['delta']['alias'] = 'b';
+    $ids['language']['type'] = 'string';
+    return $ids;
+  }
+
+}

web/core/modules/block/src/Theme/AdminDemoNegotiator.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Drupal\block\Theme;
+
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Theme\ThemeNegotiatorInterface;
+
+/**
+ * Negotiates the theme for the block admin demo page via the URL.
+ */
+class AdminDemoNegotiator implements ThemeNegotiatorInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function applies(RouteMatchInterface $route_match) {
+    return $route_match->getRouteName() == 'block.admin_demo';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function determineActiveTheme(RouteMatchInterface $route_match) {
+    // We return exactly what was passed in, to guarantee that the page will
+    // always be displayed using the theme whose blocks are being configured.
+    return $route_match->getParameter('theme');
+  }
+
+}

web/core/modules/block/templates/block.html.twig

@@ -0,0 +1,40 @@
+{#
+/**
+ * @file
+ * Default theme implementation to display a block.
+ *
+ * Available variables:
+ * - plugin_id: The ID of the block implementation.
+ * - label: The configured label of the block if visible.
+ * - configuration: A list of the block's configuration values.
+ *   - label: The configured label for the block.
+ *   - label_display: The display settings for the label.
+ *   - provider: The module or other provider that provided this block plugin.
+ *   - Block plugin specific settings will also be stored here.
+ * - in_preview: Whether the plugin is being rendered in preview mode.
+ * - content: The content of this block.
+ * - attributes: array of HTML attributes populated by modules, intended to
+ *   be added to the main container tag of this template.
+ *   - id: A valid HTML ID and guaranteed unique.
+ * - title_attributes: Same as attributes, except applied to the main title
+ *   tag that appears in the template.
+ * - title_prefix: Additional output populated by modules, intended to be
+ *   displayed in front of the main title tag that appears in the template.
+ * - title_suffix: Additional output populated by modules, intended to be
+ *   displayed after the main title tag that appears in the template.
+ *
+ * @see template_preprocess_block()
+ *
+ * @ingroup themeable
+ */
+#}
+<div{{ attributes }}>
+  {{ title_prefix }}
+  {% if label %}
+    <h2{{ title_attributes }}>{{ label }}</h2>
+  {% endif %}
+  {{ title_suffix }}
+  {% block content %}
+    {{ content }}
+  {% endblock %}
+</div>

web/core/modules/block/tests/fixtures/update/add-menu-block-with-zero-depth.php

@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * @file
+ * Adds a menu block with a `depth` setting of 0.
+ */
+
+use Drupal\Core\Database\Database;
+
+$connection = Database::getConnection();
+
+$data = $connection->select('config')
+  ->condition('name', 'block.block.olivero_account_menu')
+  ->fields('config', ['data'])
+  ->execute()
+  ->fetchField();
+$data = unserialize($data);
+// Change the depth setting to 0, which the update hook should change to NULL.
+// @see system_post_update_set_menu_block_depth_to_null_if_zero().
+$data['settings']['depth'] = 0;
+$connection->update('config')
+  ->condition('name', 'block.block.olivero_account_menu')
+  ->fields([
+    'data' => serialize($data),
+  ])
+  ->execute();

web/core/modules/block/tests/modules/block_test/block_test.info.yml

@@ -0,0 +1,7 @@
+name: 'Block test'
+type: module
+description: 'Provides test blocks.'
+package: Testing
+version: VERSION
+dependencies:
+  - drupal:block

web/core/modules/block/tests/modules/block_test/block_test.routing.yml

@@ -0,0 +1,7 @@
+block_test.test_multiple_forms:
+  path: '/test-multiple-forms'
+  defaults:
+    _controller: '\Drupal\block_test\Controller\TestMultipleFormController::testMultipleForms'
+    _title: 'Multiple forms'
+  requirements:
+    _access: 'TRUE'

web/core/modules/block/tests/modules/block_test/block_test.services.yml

@@ -0,0 +1,6 @@
+services:
+  block_test.multiple_static_context:
+    class: Drupal\block_test\ContextProvider\MultipleStaticContext
+    arguments: ['@current_user', '@entity_type.manager']
+    tags:
+      - { name: 'context_provider' }

web/core/modules/block/tests/modules/block_test/config/install/block.block.test_block.yml

@@ -0,0 +1,17 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - block_test
+  theme:
+    - stark
+id: test_block
+theme: stark
+region: '-1'
+weight: 0
+plugin: test_html
+settings:
+  label: 'Test HTML block'
+  label_display: hidden
+  provider: block_test
+visibility: {  }

web/core/modules/block/tests/modules/block_test/config/schema/block_test.schema.yml

@@ -0,0 +1,10 @@
+block.settings.test_block_instantiation:
+  type: block_settings
+  label: 'Test block instantiation settings'
+  mapping:
+    display_message:
+      type: string
+      label: 'Message text'
+
+condition.plugin.baloney_spam:
+  type: condition.plugin

web/core/modules/block/tests/modules/block_test/src/BlockRenderAlterContent.php

@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test;
+
+use Drupal\Core\Render\Element\RenderCallbackInterface;
+
+/**
+ * Implements a trusted preRender callback.
+ */
+class BlockRenderAlterContent implements RenderCallbackInterface {
+
+  /**
+   * Render API callback: Alters the content of a block.
+   *
+   * This function is assigned as a #pre_render callback.
+   */
+  public static function preRender(array $build) {
+    $build['#prefix'] = 'Hiya!<br>';
+    return $build;
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/ContextProvider/MultipleStaticContext.php

@@ -0,0 +1,73 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\ContextProvider;
+
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Plugin\Context\ContextProviderInterface;
+use Drupal\Core\Plugin\Context\EntityContext;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Sets multiple contexts for a static value.
+ */
+class MultipleStaticContext implements ContextProviderInterface {
+
+  /**
+   * The current user.
+   *
+   * @var \Drupal\Core\Session\AccountInterface
+   */
+  protected $account;
+
+  /**
+   * The user storage.
+   *
+   * @var \Drupal\user\UserStorageInterface
+   */
+  protected $userStorage;
+
+  /**
+   * Constructs a new MultipleStaticContext.
+   *
+   * @param \Drupal\Core\Session\AccountInterface $account
+   *   The current user.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   */
+  public function __construct(AccountInterface $account, EntityTypeManagerInterface $entity_type_manager) {
+    $this->account = $account;
+    $this->userStorage = $entity_type_manager->getStorage('user');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getRuntimeContexts(array $unqualified_context_ids) {
+    $current_user = $this->userStorage->load($this->account->id());
+
+    $context1 = EntityContext::fromEntity($current_user, 'User A');
+    $context2 = EntityContext::fromEntity($current_user, 'User B');
+
+    $cacheability = new CacheableMetadata();
+    $cacheability->setCacheContexts(['user']);
+
+    $context1->addCacheableDependency($cacheability);
+    $context2->addCacheableDependency($cacheability);
+
+    return [
+      'userA' => $context1,
+      'userB' => $context2,
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getAvailableContexts() {
+    return $this->getRuntimeContexts([]);
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Controller/TestMultipleFormController.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Controller;
+
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\Form\FormState;
+
+/**
+ * Controller for block_test module.
+ */
+class TestMultipleFormController extends ControllerBase {
+
+  public function testMultipleForms() {
+    $form_state = new FormState();
+    $build = [
+      'form1' => $this->formBuilder()->buildForm('\Drupal\block_test\Form\TestForm', $form_state),
+      'form2' => $this->formBuilder()->buildForm('\Drupal\block_test\Form\FavoriteAnimalTestForm', $form_state),
+    ];
+
+    // Output all attached placeholders trough
+    // \Drupal\Core\Messenger\MessengerInterface::addMessage(), so we can
+    // see if there's only one in the tests.
+    $post_render_callable = function ($elements) {
+      $matches = [];
+      preg_match_all('<form\s(.*?)action="(.*?)"(.*)>', (string) $elements, $matches);
+
+      $action_values = $matches[2];
+
+      foreach ($action_values as $action_value) {
+        $this->messenger()->addStatus('Form action: ' . $action_value);
+      }
+      return $elements;
+    };
+
+    $build['#post_render'] = [$post_render_callable];
+
+    return $build;
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Form/FavoriteAnimalTestForm.php

@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Form that performs favorite animal test.
+ *
+ * @internal
+ */
+class FavoriteAnimalTestForm extends FormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'block_test_form_favorite_animal_test';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form['favorite_animal'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Your favorite animal.'),
+    ];
+
+    $form['submit_animal'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Submit your chosen animal'),
+    ];
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $this->messenger()->addStatus($this->t('Your favorite animal is: @favorite_animal', ['@favorite_animal' => $form['favorite_animal']['#value']]));
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Form/TestForm.php

@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Form that performs base block form test.
+ *
+ * @internal
+ */
+class TestForm extends FormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'block_test_form_test';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form['email'] = [
+      '#type' => 'email',
+      '#title' => $this->t('Your .com email address.'),
+    ];
+
+    $form['show'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Submit'),
+    ];
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    if (!str_contains($form_state->getValue('email'), '.com')) {
+      $form_state->setErrorByName('email', $this->t('This is not a .com email address.'));
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $this->messenger()->addStatus($this->t('Your email address is @email', ['@email' => $form['email']['#value']]));
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Hook/BlockTestHooks.php

@@ -0,0 +1,73 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Hook;
+
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Block\BlockPluginInterface;
+use Drupal\Core\Hook\Attribute\Hook;
+
+/**
+ * Hook implementations for block_test.
+ */
+class BlockTestHooks {
+
+  /**
+   * Implements hook_block_alter().
+   */
+  #[Hook('block_alter')]
+  public function blockAlter(&$block_info): void {
+    if (\Drupal::state()->get('block_test_info_alter') && isset($block_info['test_block_instantiation'])) {
+      $block_info['test_block_instantiation']['category'] = 'Custom category';
+    }
+  }
+
+  /**
+   * Implements hook_block_view_BASE_BLOCK_ID_alter().
+   */
+  #[Hook('block_view_test_cache_alter')]
+  public function blockViewTestCacheAlter(array &$build, BlockPluginInterface $block): void {
+    if (\Drupal::state()->get('block_test_view_alter_suffix') !== NULL) {
+      $build['#attributes']['foo'] = 'bar';
+    }
+    if (\Drupal::state()->get('block_test_view_alter_append_pre_render_prefix') !== NULL) {
+      $build['#pre_render'][] = '\Drupal\block_test\BlockRenderAlterContent::preRender';
+    }
+  }
+
+  /**
+   * Implements hook_block_view_BASE_BLOCK_ID_alter().
+   *
+   * @see \Drupal\Tests\block\Kernel\BlockViewBuilderTest::testBlockViewBuilderCacheTitleBlock()
+   */
+  #[Hook('block_view_page_title_block_alter')]
+  public function blockViewPageTitleBlockAlter(array &$build, BlockPluginInterface $block): void {
+    $build['#cache']['tags'][] = 'custom_cache_tag';
+  }
+
+  /**
+   * Implements hook_block_build_BASE_BLOCK_ID_alter().
+   */
+  #[Hook('block_build_test_cache_alter')]
+  public function blockBuildTestCacheAlter(array &$build, BlockPluginInterface $block): void {
+    // Test altering cache keys, contexts, tags and max-age.
+    if (\Drupal::state()->get('block_test_block_alter_cache_key') !== NULL) {
+      $build['#cache']['keys'][] = \Drupal::state()->get('block_test_block_alter_cache_key');
+    }
+    if (\Drupal::state()->get('block_test_block_alter_cache_context') !== NULL) {
+      $build['#cache']['contexts'][] = \Drupal::state()->get('block_test_block_alter_cache_context');
+    }
+    if (\Drupal::state()->get('block_test_block_alter_cache_tag') !== NULL) {
+      $build['#cache']['tags'] = Cache::mergeTags($build['#cache']['tags'], [\Drupal::state()->get('block_test_block_alter_cache_tag')]);
+    }
+    if (\Drupal::state()->get('block_test_block_alter_cache_max_age') !== NULL) {
+      $build['#cache']['max-age'] = \Drupal::state()->get('block_test_block_alter_cache_max_age');
+    }
+    // Test setting #create_placeholder.
+    if (\Drupal::state()->get('block_test_block_alter_create_placeholder') !== NULL) {
+      $build['#create_placeholder'] = \Drupal::state()->get('block_test_block_alter_create_placeholder');
+    }
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestAccessBlock.php

@@ -0,0 +1,78 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\KeyValueStore\KeyValueStoreInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a block to test access.
+ */
+#[Block(
+  id: "test_access",
+  admin_label: new TranslatableMarkup("Test block access"),
+)]
+class TestAccessBlock extends BlockBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * Tests the test access block.
+   *
+   * @param array $configuration
+   *   The plugin configuration, i.e. an array with configuration values keyed
+   *   by configuration option name. The special key 'context' may be used to
+   *   initialize the defined contexts by setting it to an array of context
+   *   values keyed by context names.
+   * @param string $plugin_id
+   *   The plugin ID for the plugin instance.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\Core\KeyValueStore\KeyValueStoreInterface $keyValue
+   *   The key value store.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, protected KeyValueStoreInterface $keyValue) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('keyvalue')->get('block_test')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function blockAccess(AccountInterface $account) {
+    return $this->keyValue->get('access', FALSE) ? AccessResult::allowed()->setCacheMaxAge(0) : AccessResult::forbidden()->setCacheMaxAge(0);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return ['#markup' => 'Hello test world'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheMaxAge() {
+    return Cache::PERMANENT;
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestBlockInstantiation.php

@@ -0,0 +1,67 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a basic block for testing block instantiation and configuration.
+ */
+#[Block(
+  id: "test_block_instantiation",
+  admin_label: new TranslatableMarkup("Display message")
+)]
+class TestBlockInstantiation extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultConfiguration() {
+    return [
+      'display_message' => 'no message set',
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function blockAccess(AccountInterface $account) {
+    return AccessResult::allowedIfHasPermission($account, 'access content');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function blockForm($form, FormStateInterface $form_state) {
+    $form['display_message'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Display message'),
+      '#default_value' => $this->configuration['display_message'],
+    ];
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function blockSubmit($form, FormStateInterface $form_state) {
+    $this->configuration['display_message'] = $form_state->getValue('display_message');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [
+      '#children' => $this->configuration['display_message'],
+    ];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestCacheBlock.php

@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a block to test caching.
+ */
+#[Block(
+  id: "test_cache",
+  admin_label: new TranslatableMarkup("Test block caching")
+)]
+class TestCacheBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    $content = \Drupal::keyValue('block_test')->get('content');
+
+    $build = [];
+    if (!empty($content)) {
+      $build['#markup'] = $content;
+    }
+    return $build;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheContexts() {
+    return \Drupal::state()->get('block_test.cache_contexts', []);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheMaxAge() {
+    return \Drupal::state()->get('block_test.cache_max_age', parent::getCacheMaxAge());
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestContextAwareBlock.php

@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Plugin\Context\EntityContextDefinition;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\user\UserInterface;
+
+/**
+ * Provides a context-aware block.
+ */
+#[Block(
+  id: "test_context_aware",
+  admin_label: new TranslatableMarkup("Test context-aware block"),
+  context_definitions: [
+    'user' => new EntityContextDefinition(
+      data_type: 'entity:user',
+      label: new TranslatableMarkup("User Context"),
+      required: FALSE,
+      constraints: [
+        "NotNull" => [],
+      ]
+    ),
+  ]
+)]
+class TestContextAwareBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    /** @var \Drupal\user\UserInterface $user */
+    $user = $this->getContextValue('user');
+    return [
+      '#prefix' => '<div id="' . $this->getPluginId() . '--username">',
+      '#suffix' => '</div>',
+      '#markup' => $user ? $user->getAccountName() : 'No context mapping selected.',
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function blockAccess(AccountInterface $account) {
+    if ($this->getContextValue('user') instanceof UserInterface) {
+      $this->messenger()->addStatus('User context found.');
+    }
+
+    return parent::blockAccess($account);
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestContextAwareNoValidContextOptionsBlock.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Plugin\Context\ContextDefinition;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a context-aware block that uses a not-passed, non-required context.
+ */
+#[Block(
+  id: "test_context_aware_no_valid_context_options",
+  admin_label: new TranslatableMarkup("Test context-aware block - no valid context options"),
+  context_definitions: [
+    'user' => new ContextDefinition(data_type: 'email', required: FALSE),
+  ]
+)]
+class TestContextAwareNoValidContextOptionsBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [
+      '#markup' => 'Rendered block with no valid context options',
+    ];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestContextAwareUnsatisfiedBlock.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Plugin\Context\EntityContextDefinition;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a context-aware block.
+ */
+#[Block(
+  id: "test_context_aware_unsatisfied",
+  admin_label: new TranslatableMarkup("Test context-aware unsatisfied block"),
+  context_definitions: [
+    'user' => new EntityContextDefinition('entity:foobar'),
+  ]
+)]
+class TestContextAwareUnsatisfiedBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [
+      '#markup' => 'test',
+    ];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestEmptyBlock.php

@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a block that returns an empty array.
+ */
+#[Block(
+  id: "test_empty",
+  admin_label: new TranslatableMarkup("Test Empty block"),
+)]
+class TestEmptyBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestFormBlock.php

@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a block to test caching.
+ */
+#[Block(
+  id: "test_form_in_block",
+  admin_label: new TranslatableMarkup("Test form block caching"),
+)]
+class TestFormBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return \Drupal::formBuilder()->getForm('Drupal\block_test\Form\TestForm');
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestHtmlBlock.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a block to test HTML.
+ */
+#[Block(
+  id: "test_html",
+  admin_label: new TranslatableMarkup("Test HTML block"),
+)]
+class TestHtmlBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [
+      '#attributes' => \Drupal::keyvalue('block_test')->get('attributes'),
+      '#children' => \Drupal::keyValue('block_test')->get('content'),
+    ];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestMultipleFormsBlock.php

@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\block_test\PluginForm\EmptyBlockForm;
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a block with multiple forms.
+ */
+#[Block(
+  id: "test_multiple_forms_block",
+  forms: [
+    'secondary' => EmptyBlockForm::class,
+  ],
+  admin_label: new TranslatableMarkup("Multiple forms test block"),
+)]
+class TestMultipleFormsBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestSettingsValidationBlock.php

@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a test settings validation block.
+ */
+#[Block(
+  id: "test_settings_validation",
+  admin_label: new TranslatableMarkup("Test settings validation block"),
+)]
+class TestSettingsValidationBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function blockForm($form, FormStateInterface $form_state) {
+    return ['digits' => ['#type' => 'textfield']] + $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function blockValidate($form, FormStateInterface $form_state) {
+    if (!ctype_digit($form_state->getValue('digits'))) {
+      $form_state->setErrorByName('digits', $this->t('Only digits are allowed'));
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return ['#markup' => 'foo'];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Condition/BaloneySpam.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Condition;
+
+use Drupal\Core\Condition\Attribute\Condition;
+use Drupal\Core\Condition\ConditionPluginBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a 'baloney_spam' condition.
+ */
+#[Condition(
+  id: "baloney_spam",
+  label: new TranslatableMarkup("Baloney spam"),
+)]
+class BaloneySpam extends ConditionPluginBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function evaluate() {
+    return TRUE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function summary() {
+    return 'Summary';
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Condition/MissingSchema.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Condition;
+
+use Drupal\Core\Condition\Attribute\Condition;
+use Drupal\Core\Condition\ConditionPluginBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a 'missing_schema' condition.
+ */
+#[Condition(
+  id: "missing_schema",
+  label: new TranslatableMarkup("Missing schema"),
+)]
+class MissingSchema extends ConditionPluginBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function evaluate() {
+    return FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function summary() {
+    return 'Summary';
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/PluginForm/EmptyBlockForm.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\PluginForm;
+
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Plugin\PluginFormBase;
+
+/**
+ * Provides a form for a block that is empty.
+ */
+class EmptyBlockForm extends PluginFormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public $plugin;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
+    // Intentionally empty.
+  }
+
+}

web/core/modules/block/tests/modules/block_test/themes/block_test_special_chars_theme/block_test_special_chars_theme.info.yml

@@ -0,0 +1,7 @@
+name: '<"Cat" & ''Mouse''>'
+type: theme
+base theme: stable9
+description: 'Theme for testing special characters in block admin.'
+regions:
+  content: Content
+  help: Help

web/core/modules/block/tests/modules/block_test/themes/block_test_theme/block_test_theme.info.yml

@@ -0,0 +1,16 @@
+name: 'Block test theme'
+type: theme
+base theme: stable9
+description: 'Theme for testing the block system'
+version: VERSION
+regions:
+  sidebar_first: 'Left sidebar'
+  sidebar_second: 'Right sidebar'
+  content: Content
+  header: Header
+  footer: Footer
+  highlighted: Highlighted
+  help: Help
+regions_hidden:
+  - sidebar_first
+  - sidebar_second

web/core/modules/block/tests/modules/block_test_views/block_test_views.info.yml

@@ -0,0 +1,8 @@
+name: 'Block test views'
+type: module
+description: 'Provides a view and block to test block displays in views.'
+package: Testing
+version: VERSION
+dependencies:
+  - drupal:block
+  - drupal:views

web/core/modules/block/tests/modules/block_test_views/test_views/views.view.test_view_block.yml

@@ -0,0 +1,56 @@
+langcode: en
+status: true
+dependencies: {  }
+id: test_view_block
+label: test_view_block
+module: views
+description: ''
+tag: ''
+base_table: views_test_data
+base_field: id
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: null
+    display_options:
+      access:
+        type: none
+      cache:
+        type: tag
+      query:
+        type: views_query
+      exposed_form:
+        type: basic
+      pager:
+        type: some
+        options:
+          items_per_page: 5
+      style:
+        type: default
+      row:
+        type: fields
+      fields:
+        name:
+          id: name
+          table: views_test_data
+          field: name
+      title: test_view_block
+      footer:
+        area_text_custom:
+          id: area_text_custom
+          table: views
+          field: area_text_custom
+          relationship: none
+          group_type: group
+          admin_label: ''
+          plugin_id: text_custom
+          empty: false
+          content: '[view:title]'
+          tokenize: false
+  block_1:
+    display_plugin: block
+    id: block_1
+    display_title: Block
+    position: null

web/core/modules/block/tests/modules/block_test_views/test_views/views.view.test_view_block2.yml

@@ -0,0 +1,56 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - user
+id: test_view_block2
+label: test_view_block2
+module: views
+description: ''
+tag: ''
+base_table: views_test_data
+base_field: id
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: null
+    display_options:
+      access:
+        type: perm
+      cache:
+        type: tag
+      query:
+        type: views_query
+      exposed_form:
+        type: basic
+      pager:
+        type: some
+        options:
+          items_per_page: 5
+      style:
+        type: default
+      row:
+        type: fields
+      fields:
+        name:
+          id: name
+          table: views_test_data
+          field: name
+      title: test_view_block2
+  block_1:
+    display_plugin: block
+    id: block_1
+    display_title: Block
+    position: null
+  block_2:
+    display_plugin: block
+    id: block_2
+    display_title: Block
+    position: null
+  block_3:
+    display_plugin: block
+    id: block_3
+    display_title: Block
+    position: null

web/core/modules/block/tests/modules/block_test_views/test_views/views.view.test_view_block_with_context.yml

@@ -0,0 +1,426 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - node
+    - user
+id: test_view_block_with_context
+label: test_view_block_with_context
+module: views
+description: ''
+tag: ''
+base_table: node_field_data
+base_field: nid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: 0
+    display_options:
+      access:
+        type: perm
+        options:
+          perm: 'access content'
+      cache:
+        type: tag
+        options: {  }
+      query:
+        type: views_query
+        options:
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_comment: ''
+          query_tags: {  }
+      exposed_form:
+        type: basic
+        options:
+          submit_button: Apply
+          reset_button: false
+          reset_button_label: Reset
+          exposed_sorts_label: 'Sort by'
+          expose_sort_order: true
+          sort_asc_label: Asc
+          sort_desc_label: Desc
+      pager:
+        type: some
+        options:
+          items_per_page: 5
+          offset: 0
+      style:
+        type: default
+      row:
+        type: fields
+      fields:
+        title:
+          id: title
+          table: node_field_data
+          field: title
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: ''
+          exclude: false
+          alter:
+            alter_text: true
+            text: 'Test view row: {{ title }}'
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: value
+          type: string
+          settings:
+            link_to_entity: true
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+          plugin_id: field
+      filters:
+        status:
+          value: '1'
+          table: node_field_data
+          field: status
+          plugin_id: boolean
+          entity_type: node
+          entity_field: status
+          id: status
+          expose:
+            operator: ''
+          group: 1
+      sorts:
+        created:
+          id: created
+          table: node_field_data
+          field: created
+          order: DESC
+          entity_type: node
+          entity_field: created
+          plugin_id: date
+          relationship: none
+          group_type: group
+          admin_label: ''
+          exposed: false
+          expose:
+            label: ''
+          granularity: second
+      title: test_view_block_with_context
+      header: {  }
+      footer: {  }
+      empty:
+        area_text_custom:
+          id: area_text_custom
+          table: views
+          field: area_text_custom
+          relationship: none
+          group_type: group
+          admin_label: ''
+          empty: true
+          tokenize: false
+          content: 'Test view: No results found.'
+          plugin_id: text_custom
+      relationships: {  }
+      arguments:
+        'null':
+          id: 'null'
+          table: views
+          field: 'null'
+          relationship: none
+          group_type: group
+          admin_label: ''
+          default_action: default
+          exception:
+            value: all
+            title_enable: false
+            title: All
+          title_enable: false
+          title: ''
+          default_argument_type: fixed
+          default_argument_options:
+            argument: foo
+          summary_options:
+            base_path: ''
+            count: true
+            items_per_page: 25
+            override: false
+          summary:
+            sort_order: asc
+            number_of_records: 0
+            format: default_summary
+          specify_validation: false
+          validate:
+            type: none
+            fail: 'not found'
+          validate_options: {  }
+          must_not_be: false
+          plugin_id: 'null'
+        null_1:
+          id: null_1
+          table: views
+          field: 'null'
+          relationship: none
+          group_type: group
+          admin_label: ''
+          default_action: ignore
+          exception:
+            value: all
+            title_enable: false
+            title: All
+          title_enable: false
+          title: ''
+          default_argument_type: fixed
+          default_argument_options:
+            argument: ''
+          summary_options:
+            base_path: ''
+            count: true
+            items_per_page: 25
+            override: false
+          summary:
+            sort_order: asc
+            number_of_records: 0
+            format: default_summary
+          specify_validation: false
+          validate:
+            type: none
+            fail: 'not found'
+          validate_options: {  }
+          must_not_be: false
+          plugin_id: 'null'
+        nid:
+          id: nid
+          table: node_field_data
+          field: nid
+          relationship: none
+          group_type: group
+          admin_label: ''
+          default_action: empty
+          exception:
+            value: all
+            title_enable: false
+            title: All
+          title_enable: false
+          title: ''
+          default_argument_type: fixed
+          default_argument_options:
+            argument: ''
+          summary_options:
+            base_path: ''
+            count: true
+            items_per_page: 25
+            override: false
+          summary:
+            sort_order: asc
+            number_of_records: 0
+            format: default_summary
+          specify_validation: true
+          validate:
+            type: 'entity:node'
+            fail: 'not found'
+          validate_options:
+            operation: view
+            multiple: 0
+            bundles: {  }
+            access: false
+          break_phrase: false
+          not: false
+          entity_type: node
+          entity_field: nid
+          plugin_id: node_nid
+      display_extenders: {  }
+    cache_metadata:
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url
+        - 'user.node_grants:view'
+        - user.permissions
+      cacheable: false
+      max-age: -1
+      tags: {  }
+  block_1:
+    display_plugin: block
+    id: block_1
+    display_title: Block
+    position: 1
+    display_options:
+      display_extenders: {  }
+    cache_metadata:
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url
+        - 'user.node_grants:view'
+        - user.permissions
+      cacheable: false
+      max-age: -1
+      tags: {  }
+  block_2:
+    display_plugin: block
+    id: block_2
+    display_title: 'Block 2'
+    position: 2
+    display_options:
+      display_extenders: {  }
+      arguments:
+        created:
+          id: created
+          table: node_field_data
+          field: created
+          relationship: none
+          group_type: group
+          admin_label: ''
+          default_action: ignore
+          exception:
+            value: all
+            title_enable: false
+            title: All
+          title_enable: false
+          title: ''
+          default_argument_type: fixed
+          default_argument_options:
+            argument: ''
+          summary_options:
+            base_path: ''
+            count: true
+            items_per_page: 25
+            override: false
+          summary:
+            sort_order: asc
+            number_of_records: 0
+            format: default_summary
+          specify_validation: true
+          validate:
+            type: numeric
+            fail: 'not found'
+          validate_options: {  }
+          entity_type: node
+          entity_field: created
+          plugin_id: date
+        vid:
+          id: vid
+          table: node_field_data
+          field: vid
+          relationship: none
+          group_type: group
+          admin_label: ''
+          default_action: ignore
+          exception:
+            value: all
+            title_enable: false
+            title: All
+          title_enable: false
+          title: ''
+          default_argument_type: fixed
+          default_argument_options:
+            argument: ''
+          summary_options:
+            base_path: ''
+            count: true
+            items_per_page: 25
+            override: false
+          summary:
+            sort_order: asc
+            number_of_records: 0
+            format: default_summary
+          specify_validation: false
+          validate:
+            type: none
+            fail: 'not found'
+          validate_options: {  }
+          break_phrase: false
+          not: false
+          entity_type: node
+          entity_field: vid
+          plugin_id: numeric
+        title:
+          id: title
+          table: node_field_data
+          field: title
+          relationship: none
+          group_type: group
+          admin_label: ''
+          default_action: ignore
+          exception:
+            value: all
+            title_enable: false
+            title: All
+          title_enable: false
+          title: ''
+          default_argument_type: fixed
+          default_argument_options:
+            argument: ''
+          summary_options:
+            base_path: ''
+            count: true
+            items_per_page: 25
+            override: false
+          summary:
+            sort_order: asc
+            number_of_records: 0
+            format: default_summary
+          specify_validation: false
+          validate:
+            type: none
+            fail: 'not found'
+          validate_options: {  }
+          glossary: false
+          limit: 0
+          case: none
+          path_case: none
+          transform_dash: false
+          break_phrase: false
+          entity_type: node
+          entity_field: title
+          plugin_id: string
+      defaults:
+        arguments: false
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url
+        - 'user.node_grants:view'
+        - user.permissions
+      tags: {  }

web/core/modules/block/tests/src/Functional/AssertBlockAppearsTrait.php

@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\block\Entity\Block;
+
+/**
+ * Provides test assertions for testing block appearance.
+ *
+ * Can be used by test classes that extend \Drupal\Tests\BrowserTestBase.
+ */
+trait AssertBlockAppearsTrait {
+
+  /**
+   * Checks to see whether a block appears on the page.
+   *
+   * @param \Drupal\block\Entity\Block $block
+   *   The block entity to find on the page.
+   */
+  protected function assertBlockAppears(Block $block) {
+    $this->assertSession()->elementExists('xpath', "//div[@id = 'block-{$block->id()}']");
+  }
+
+  /**
+   * Checks to see whether a block does not appears on the page.
+   *
+   * @param \Drupal\block\Entity\Block $block
+   *   The block entity to find on the page.
+   */
+  protected function assertNoBlockAppears(Block $block) {
+    $this->assertSession()->elementNotExists('xpath', "//div[@id = 'block-{$block->id()}']");
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockAdminThemeTest.php

@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests the block system with admin themes.
+ *
+ * @group block
+ */
+class BlockAdminThemeTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'contextual'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Check for the accessibility of the admin theme on the block admin page.
+   */
+  public function testAdminTheme(): void {
+    // Create administrative user.
+    $admin_user = $this->drupalCreateUser([
+      'administer blocks',
+      'administer themes',
+    ]);
+    $this->drupalLogin($admin_user);
+
+    // Ensure that access to block admin page is denied when theme is not
+    // installed.
+    $this->drupalGet('admin/structure/block/list/olivero');
+    $this->assertSession()->statusCodeEquals(403);
+
+    // Install admin theme and confirm that tab is accessible.
+    \Drupal::service('theme_installer')->install(['olivero']);
+    $edit['admin_theme'] = 'olivero';
+    $this->drupalGet('admin/appearance');
+    $this->submitForm($edit, 'Save configuration');
+    $this->drupalGet('admin/structure/block/list/olivero');
+    $this->assertSession()->statusCodeEquals(200);
+  }
+
+  /**
+   * Ensure contextual links are disabled in Claro theme.
+   */
+  public function testClaroAdminTheme(): void {
+    // Create administrative user.
+    $admin_user = $this->drupalCreateUser([
+      'access administration pages',
+      'administer themes',
+      'access contextual links',
+      'view the administration theme',
+    ]);
+    $this->drupalLogin($admin_user);
+
+    // Install admin theme and confirm that tab is accessible.
+    \Drupal::service('theme_installer')->install(['claro']);
+    $edit['admin_theme'] = 'claro';
+    $this->drupalGet('admin/appearance');
+    $this->submitForm($edit, 'Save configuration');
+
+    // Define our block settings.
+    $settings = [
+      'theme' => 'claro',
+      'region' => 'header',
+    ];
+
+    // Place a block.
+    $block = $this->drupalPlaceBlock('local_tasks_block', $settings);
+
+    // Open admin page.
+    $this->drupalGet('admin');
+
+    // Check if contextual link classes are unavailable.
+    $this->assertSession()->responseNotContains('<div data-contextual-id="block:block=' . $block->id() . ':langcode=en"></div>');
+    $this->assertSession()->responseNotContains('contextual-region');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockCacheTest.php

@@ -0,0 +1,240 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Core\Cache\Cache;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests block caching.
+ *
+ * @group block
+ */
+class BlockCacheTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_test', 'test_page_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * A user with permission to administer blocks.
+   *
+   * @var object
+   */
+  protected $adminUser;
+
+  /**
+   * An authenticated user to test block caching.
+   *
+   * @var object
+   */
+  protected $normalUser;
+
+  /**
+   * Another authenticated user to test block caching.
+   *
+   * @var object
+   */
+  protected $normalUserAlt;
+
+  /**
+   * The block used by this test.
+   *
+   * @var \Drupal\block\BlockInterface
+   */
+  protected $block;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Create an admin user, log in and enable test blocks.
+    $this->adminUser = $this->drupalCreateUser([
+      'administer blocks',
+      'access administration pages',
+    ]);
+    $this->drupalLogin($this->adminUser);
+
+    // Create additional users to test caching modes.
+    $this->normalUser = $this->drupalCreateUser();
+    $this->normalUserAlt = $this->drupalCreateUser();
+    // Sync the roles, since drupalCreateUser() creates separate roles for
+    // the same permission sets.
+    $this->normalUserAlt->roles = $this->normalUser->getRoles();
+    $this->normalUserAlt->save();
+
+    // Enable our test block.
+    $this->block = $this->drupalPlaceBlock('test_cache');
+  }
+
+  /**
+   * Tests "user.roles" cache context.
+   */
+  public function testCachePerRole(): void {
+    \Drupal::state()->set('block_test.cache_contexts', ['user.roles']);
+
+    // Enable our test block. Set some content for it to display.
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+    $this->drupalLogin($this->normalUser);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($current_content);
+
+    // Change the content, but the cached copy should still be served.
+    $old_content = $current_content;
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($old_content);
+
+    // Clear the cache and verify that the stale data is no longer there.
+    Cache::invalidateTags(['block_view']);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextNotContains($old_content);
+    // Fresh block content is displayed after clearing the cache.
+    $this->assertSession()->pageTextContains($current_content);
+
+    // Test whether the cached data is served for the correct users.
+    $old_content = $current_content;
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+    $this->drupalLogout();
+    $this->drupalGet('');
+    // Anonymous user does not see content cached per-role for normal user.
+    $this->assertSession()->pageTextNotContains($old_content);
+
+    // User with the same roles sees per-role cached content.
+    $this->drupalLogin($this->normalUserAlt);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($old_content);
+
+    // Admin user does not see content cached per-role for normal user.
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextNotContains($old_content);
+
+    // Block is served from the per-role cache.
+    $this->drupalLogin($this->normalUser);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($old_content);
+  }
+
+  /**
+   * Tests a cacheable block without any additional cache context.
+   */
+  public function testCachePermissions(): void {
+    // user.permissions is a required context, so a user with different
+    // permissions will see a different version of the block.
+    \Drupal::state()->set('block_test.cache_contexts', []);
+
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($current_content);
+
+    $old_content = $current_content;
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+
+    // Block content served from cache.
+    $this->drupalGet('user');
+    $this->assertSession()->pageTextContains($old_content);
+
+    // Block content not served from cache.
+    $this->drupalLogout();
+    $this->drupalGet('user');
+    $this->assertSession()->pageTextContains($current_content);
+  }
+
+  /**
+   * Tests non-cacheable block.
+   */
+  public function testNoCache(): void {
+    \Drupal::state()->set('block_test.cache_max_age', 0);
+
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+
+    // If max_age = 0 has no effect, the next request would be cached.
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($current_content);
+
+    // A cached copy should not be served.
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+    $this->drupalGet('');
+    // Maximum age of zero prevents blocks from being cached.
+    $this->assertSession()->pageTextContains($current_content);
+  }
+
+  /**
+   * Tests "user" cache context.
+   */
+  public function testCachePerUser(): void {
+    \Drupal::state()->set('block_test.cache_contexts', ['user']);
+
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+    $this->drupalLogin($this->normalUser);
+
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($current_content);
+
+    $old_content = $current_content;
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+
+    // Block is served from per-user cache.
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($old_content);
+
+    // Per-user block cache is not served for other users.
+    $this->drupalLogin($this->normalUserAlt);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($current_content);
+
+    // Per-user block cache is persistent.
+    $this->drupalLogin($this->normalUser);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($old_content);
+  }
+
+  /**
+   * Tests "url" cache context.
+   */
+  public function testCachePerPage(): void {
+    \Drupal::state()->set('block_test.cache_contexts', ['url']);
+
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+
+    $this->drupalGet('test-page');
+    $this->assertSession()->pageTextContains($current_content);
+
+    $old_content = $current_content;
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+
+    $this->drupalGet('user');
+    $this->assertSession()->statusCodeEquals(200);
+    // Verify that block content cached for the test page does not show up
+    // for the user page.
+    $this->assertSession()->pageTextNotContains($old_content);
+    $this->drupalGet('test-page');
+    $this->assertSession()->statusCodeEquals(200);
+    // Verify that the block content is cached for the test page.
+    $this->assertSession()->pageTextContains($old_content);
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockDemoTest.php

@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests the block demo page with admin themes.
+ *
+ * @group block
+ */
+class BlockDemoTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Check for the accessibility of the admin block demo page.
+   */
+  public function testBlockDemo(): void {
+    // Create administrative user.
+    $admin_user = $this->drupalCreateUser([
+      'administer blocks',
+      'administer themes',
+    ]);
+    $this->drupalLogin($admin_user);
+
+    // Confirm we have access to the block demo page for the default theme.
+    $config = $this->container->get('config.factory')->get('system.theme');
+    $default_theme = $config->get('default');
+    $this->drupalGet('admin/structure/block/demo/' . $default_theme);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->linkByHrefExists('admin/structure/block');
+    $this->assertSession()->linkByHrefNotExists('admin/structure/block/list/' . $default_theme);
+
+    // All available themes in core.
+    $available_themes = [
+      'olivero',
+      'claro',
+      'stark',
+    ];
+
+    // All available themes minute minus the default theme.
+    $themes = array_diff($available_themes, [$default_theme]);
+
+    foreach ($themes as $theme) {
+      // Install theme.
+      $this->container->get('theme_installer')->install([$theme]);
+      // Confirm access to the block demo page for the theme.
+      $this->drupalGet('admin/structure/block/demo/' . $theme);
+      $this->assertSession()->statusCodeEquals(200);
+      // Confirm existence of link for "Exit block region demonstration".
+      $this->assertSession()->linkByHrefExists('admin/structure/block/list/' . $theme);
+    }
+
+    // Confirm access to the block demo page is denied for an invalid theme.
+    $this->drupalGet('admin/structure/block/demo/invalid_theme');
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockFormInBlockTest.php

@@ -0,0 +1,77 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Component\Utility\Crypt;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests form in block caching.
+ *
+ * @group block
+ */
+class BlockFormInBlockTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_test', 'test_page_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Enable our test block.
+    $this->drupalPlaceBlock('test_form_in_block');
+  }
+
+  /**
+   * Tests to see if form in block's redirect isn't cached.
+   */
+  public function testCachePerPage(): void {
+    $form_values = ['email' => 'test@example.com'];
+
+    // Go to "test-page" and test if the block is enabled.
+    $this->drupalGet('test-page');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Your .com email address.');
+
+    // Make sure that we're currently still on /test-page after submitting the
+    // form.
+    $this->submitForm($form_values, 'Submit');
+    $this->assertSession()->addressEquals('test-page');
+    $this->assertSession()->pageTextContains('Your email address is test@example.com');
+
+    // Go to a different page and see if the block is enabled there as well.
+    $this->drupalGet('test-render-title');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Your .com email address.');
+
+    // Make sure that submitting the form didn't redirect us to the first page
+    // we submitted the form from after submitting the form from
+    // /test-render-title.
+    $this->submitForm($form_values, 'Submit');
+    $this->assertSession()->addressEquals('test-render-title');
+    $this->assertSession()->pageTextContains('Your email address is test@example.com');
+  }
+
+  /**
+   * Tests the actual placeholders.
+   */
+  public function testPlaceholders(): void {
+    $this->drupalGet('test-multiple-forms');
+
+    $placeholder = 'form_action_' . Crypt::hashBase64('Drupal\Core\Form\FormBuilder::prepareForm');
+    $this->assertSession()->pageTextContains('Form action: ' . $placeholder);
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockHiddenRegionTest.php

@@ -0,0 +1,81 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests that blocks are not added to hidden regions on theme installation.
+ *
+ * @group block
+ */
+class BlockHiddenRegionTest extends BrowserTestBase {
+
+  /**
+   * An administrative user to configure the test environment.
+   *
+   * @var \Drupal\user\Entity\User|false
+   */
+  protected $adminUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_test', 'search'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Create administrative user.
+    $this->adminUser = $this->drupalCreateUser([
+      'administer blocks',
+      'administer themes',
+      'search content',
+    ]);
+
+    $this->drupalLogin($this->adminUser);
+    $this->drupalPlaceBlock('search_form_block');
+    $this->drupalPlaceBlock('local_tasks_block');
+  }
+
+  /**
+   * Tests that hidden regions do not inherit blocks when a theme is installed.
+   */
+  public function testBlockNotInHiddenRegion(): void {
+
+    // Ensure that the search form block is displayed.
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains('Search');
+
+    // Install "block_test_theme" and set it as the default theme.
+    $theme = 'block_test_theme';
+    // We need to install a non-hidden theme so that there is more than one
+    // local task.
+    \Drupal::service('theme_installer')->install([$theme, 'stark']);
+    $this->config('system.theme')
+      ->set('default', $theme)
+      ->save();
+    // Installing a theme will cause the kernel terminate event to rebuild the
+    // router. Simulate that here.
+    \Drupal::service('router.builder')->rebuildIfNeeded();
+
+    // Ensure that "block_test_theme" is set as the default theme.
+    $this->drupalGet('admin/structure/block');
+    $this->assertSession()->pageTextContains('Block test theme');
+
+    // Ensure that the search form block is displayed.
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains('Search');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockHookOperationTest.php

@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests for Block module regarding hook_entity_operations_alter().
+ *
+ * @group block
+ */
+class BlockHookOperationTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'entity_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $permissions = [
+      'administer blocks',
+    ];
+
+    // Create and log in user.
+    $admin_user = $this->drupalCreateUser($permissions);
+    $this->drupalLogin($admin_user);
+  }
+
+  /**
+   * Tests the block list to see if the test_operation link is added.
+   */
+  public function testBlockOperationAlter(): void {
+    // Add a test block, any block will do.
+    // Set the machine name so the test_operation link can be built later.
+    $block_id = $this->randomMachineName(16);
+    $this->drupalPlaceBlock('system_powered_by_block', ['id' => $block_id]);
+
+    // Get the Block listing.
+    $this->drupalGet('admin/structure/block');
+
+    $test_operation_link = 'admin/structure/block/manage/' . $block_id . '/test_operation';
+    // Test if the test_operation link is on the page.
+    $this->assertSession()->linkByHrefExists($test_operation_link);
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockHtmlTest.php

@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests block HTML ID validity.
+ *
+ * @group block
+ */
+class BlockHtmlTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer blocks',
+      'access administration pages',
+    ]));
+
+    // Enable the test_html block, to test HTML ID and attributes.
+    \Drupal::keyValue('block_test')->set('attributes', ['data-custom-attribute' => 'foo']);
+    \Drupal::keyValue('block_test')->set('content', $this->randomMachineName());
+    $this->drupalPlaceBlock('test_html', ['id' => 'test_html_block']);
+
+    // Enable a menu block, to test more complicated HTML.
+    $this->drupalPlaceBlock('system_menu_block:admin', ['id' => 'test_menu_block']);
+  }
+
+  /**
+   * Tests for valid HTML for a block.
+   */
+  public function testHtml(): void {
+    $this->drupalGet('');
+
+    // Ensure that a block's ID is converted to an HTML valid ID, and that
+    // block-specific attributes are added to the same DOM element.
+    $this->assertSession()->elementExists('xpath', '//div[@id="block-test-html-block" and @data-custom-attribute="foo"]');
+
+    // Ensure expected markup for a menu block.
+    $this->assertSession()->elementExists('xpath', '//nav[@id="block-test-menu-block"]/ul/li');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockInstallTest.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests block module's installation.
+ *
+ * @group block
+ */
+class BlockInstallTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests cache tag invalidation after installing the block module.
+   */
+  public function testCacheTagInvalidationUponInstallation(): void {
+    // Warm the page cache.
+    $this->drupalGet('');
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+    $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'config:block_list');
+
+    // Install the block module, and place the "Powered by Drupal" block.
+    $this->container->get('module_installer')->install(['block', 'shortcut']);
+    $this->rebuildContainer();
+    $this->drupalPlaceBlock('system_powered_by_block');
+
+    // Check the same page, block.module's hook_install() should have
+    // invalidated the 'rendered' cache tag to make blocks show up.
+    $this->drupalGet('');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:block_list');
+    $this->assertSession()->pageTextContains('Powered by Drupal');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockInvalidRegionTest.php

@@ -0,0 +1,83 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+use Drupal\block\Entity\Block;
+
+/**
+ * Tests that blocks assigned to invalid regions are disabled with a warning.
+ *
+ * @group block
+ */
+class BlockInvalidRegionTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $configSchemaCheckerExclusions = [
+    // This block is intentionally put in an invalid region, so it will violate
+    // config schema.
+    // @see ::testBlockInvalidRegion()
+    'block.block.invalid_region',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    // Create an admin user.
+    $admin_user = $this->drupalCreateUser([
+      'administer site configuration',
+      'access administration pages',
+      'administer blocks',
+    ]);
+    $this->drupalLogin($admin_user);
+  }
+
+  /**
+   * Tests that blocks assigned to invalid regions work correctly.
+   */
+  public function testBlockInInvalidRegion(): void {
+    // Enable a test block and place it in an invalid region.
+    $block = $this->drupalPlaceBlock('test_html', ['id' => 'invalid_region']);
+    \Drupal::configFactory()->getEditable('block.block.' . $block->id())->set('region', 'invalid_region')->save();
+    $block = Block::load($block->id());
+
+    $warning_message = 'The block ' . $block->id() . ' was assigned to the invalid region invalid_region and has been disabled.';
+
+    // Clearing the cache should disable the test block placed in the invalid
+    // region.
+    $this->drupalGet('admin/config/development/performance');
+    $this->submitForm([], 'Clear all caches');
+    $this->assertSession()->statusMessageContains($warning_message, 'warning');
+
+    // Clear the cache to check if the warning message is not triggered.
+    $this->drupalGet('admin/config/development/performance');
+    $this->submitForm([], 'Clear all caches');
+    $this->assertSession()->statusMessageNotContains($warning_message, 'warning');
+
+    // Place disabled test block in the invalid region of the default theme.
+    \Drupal::configFactory()->getEditable('block.block.' . $block->id())->set('region', 'invalid_region')->save();
+    $block = Block::load($block->id());
+
+    // Clear the cache to check if the warning message is not triggered.
+    $this->drupalGet('admin/config/development/performance');
+    $this->submitForm([], 'Clear all caches');
+    $this->assertSession()->statusMessageNotContains($warning_message, 'warning');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockLanguageCacheTest.php

@@ -0,0 +1,85 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\language\Entity\ConfigurableLanguage;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests display of menu blocks with multiple languages.
+ *
+ * @group block
+ */
+class BlockLanguageCacheTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'language', 'menu_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * List of langcodes.
+   *
+   * @var array
+   */
+  protected $langcodes = [];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Create test languages.
+    $this->langcodes = [ConfigurableLanguage::load('en')];
+    for ($i = 1; $i < 3; ++$i) {
+      $language = ConfigurableLanguage::create([
+        'id' => 'l' . $i,
+        'label' => $this->randomString(),
+      ]);
+      $language->save();
+      $this->langcodes[$i] = $language;
+    }
+  }
+
+  /**
+   * Creates a block in a language, check blocks page in all languages.
+   */
+  public function testBlockLinks(): void {
+    // Create admin user to be able to access block admin.
+    $admin_user = $this->drupalCreateUser([
+      'administer blocks',
+      'access administration pages',
+      'administer menu',
+    ]);
+    $this->drupalLogin($admin_user);
+
+    // Create the block cache for all languages.
+    foreach ($this->langcodes as $langcode) {
+      $this->drupalGet('admin/structure/block', ['language' => $langcode]);
+      $this->clickLink('Place block');
+    }
+
+    // Create a menu in the default language.
+    $edit['label'] = $this->randomMachineName();
+    $edit['id'] = mb_strtolower($edit['label']);
+    $this->drupalGet('admin/structure/menu/add');
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->pageTextContains('Menu ' . $edit['label'] . ' has been added.');
+
+    // Check that the block is listed for all languages.
+    foreach ($this->langcodes as $langcode) {
+      $this->drupalGet('admin/structure/block', ['language' => $langcode]);
+      $this->clickLink('Place block');
+      $this->assertSession()->pageTextContains($edit['label']);
+    }
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockLanguageTest.php

@@ -0,0 +1,224 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+use Drupal\block\Entity\Block;
+
+/**
+ * Tests per-language block configuration.
+ *
+ * @group block
+ */
+class BlockLanguageTest extends BrowserTestBase {
+
+  /**
+   * An administrative user to configure the test environment.
+   *
+   * @var \Drupal\user\Entity\User|false
+   */
+  protected $adminUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['language', 'block', 'content_translation', 'node'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->adminUser = $this->drupalCreateUser([
+      'administer blocks',
+      'administer languages',
+    ]);
+    $this->drupalLogin($this->adminUser);
+
+    // Add predefined language.
+    $edit = [
+      'predefined_langcode' => 'fr',
+    ];
+    $this->drupalGet('admin/config/regional/language/add');
+    $this->submitForm($edit, 'Add language');
+
+    // Verify that language was added successfully.
+    $this->assertSession()->pageTextContains('French');
+
+    // Set path prefixes for both languages.
+    $this->config('language.negotiation')->set('url', [
+      'source' => 'path_prefix',
+      'prefixes' => [
+        'en' => 'en',
+        'fr' => 'fr',
+      ],
+    ])->save();
+
+    $this->drupalCreateContentType(['type' => 'page']);
+    $this->drupalCreateNode();
+  }
+
+  /**
+   * Tests the visibility settings for the blocks based on language.
+   */
+  public function testLanguageBlockVisibility(): void {
+    // Check if the visibility setting is available.
+    $default_theme = $this->config('system.theme')->get('default');
+    $this->drupalGet('admin/structure/block/add/system_powered_by_block/' . $default_theme);
+    // Ensure that the language visibility field is visible without a type
+    // setting.
+    $this->assertSession()->fieldExists('visibility[language][langcodes][en]');
+    $this->assertSession()->fieldNotExists('visibility[language][context_mapping][language]');
+
+    // Enable a standard block and set the visibility setting for one language.
+    $edit = [
+      'visibility[language][langcodes][en]' => TRUE,
+      'id' => $this->randomMachineName(8),
+      'region' => 'sidebar_first',
+    ];
+    $this->drupalGet('admin/structure/block/add/system_powered_by_block/' . $default_theme);
+    $this->submitForm($edit, 'Save block');
+
+    // Change the default language.
+    $edit = [
+      'site_default_language' => 'fr',
+    ];
+    $this->drupalGet('admin/config/regional/language');
+    $this->submitForm($edit, 'Save configuration');
+
+    // Check that a page has a block.
+    $this->drupalGet('en');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Powered by Drupal');
+
+    // Check that a page doesn't has a block for the current language anymore.
+    $this->drupalGet('fr');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+  }
+
+  /**
+   * Tests if the visibility settings are removed if the language is deleted.
+   */
+  public function testLanguageBlockVisibilityLanguageDelete(): void {
+    // Enable a standard block and set the visibility setting for one language.
+    $edit = [
+      'visibility' => [
+        'language' => [
+          'langcodes' => [
+            'fr' => 'fr',
+          ],
+          'context_mapping' => ['language' => '@language.current_language_context:language_interface'],
+        ],
+      ],
+    ];
+    $block = $this->drupalPlaceBlock('system_powered_by_block', $edit);
+
+    // Check that we have the language in config after saving the setting.
+    $visibility = $block->getVisibility();
+    $this->assertEquals('fr', $visibility['language']['langcodes']['fr'], 'Language is set in the block configuration.');
+
+    // Delete the language.
+    $this->drupalGet('admin/config/regional/language/delete/fr');
+    $this->submitForm([], 'Delete');
+
+    // Check that the language is no longer stored in the configuration after
+    // it is deleted.
+    $block = Block::load($block->id());
+    $visibility = $block->getVisibility();
+    $this->assertArrayNotHasKey('language', $visibility, 'Language is no longer not set in the block configuration after deleting the block.');
+
+    // Ensure that the block visibility for language is gone from the UI.
+    $this->drupalGet('admin/structure/block');
+    $this->clickLink('Configure');
+    $this->assertSession()->elementNotExists('xpath', '//details[@id="edit-visibility-language"]');
+  }
+
+  /**
+   * Tests block language visibility with different language types.
+   */
+  public function testMultipleLanguageTypes(): void {
+    // Customize content language detection to be different from interface
+    // language detection.
+    $edit = [
+      // Interface language detection: only using session.
+      'language_interface[enabled][language-url]' => FALSE,
+      'language_interface[enabled][language-session]' => TRUE,
+      // Content language detection: only using URL.
+      'language_content[configurable]' => TRUE,
+      'language_content[enabled][language-url]' => TRUE,
+      'language_content[enabled][language-interface]' => FALSE,
+    ];
+    $this->drupalGet('admin/config/regional/language/detection');
+    $this->submitForm($edit, 'Save settings');
+
+    // Check if the visibility setting is available with a type setting.
+    $default_theme = $this->config('system.theme')->get('default');
+    $this->drupalGet('admin/structure/block/add/system_powered_by_block/' . $default_theme);
+    $this->assertSession()->fieldExists('visibility[language][langcodes][en]');
+    $this->assertSession()->fieldExists('visibility[language][context_mapping][language]');
+
+    // Enable a standard block and set visibility to French only.
+    $block_id = $this->randomMachineName(8);
+    $edit = [
+      'visibility[language][context_mapping][language]' => '@language.current_language_context:language_interface',
+      'visibility[language][langcodes][fr]' => TRUE,
+      'id' => $block_id,
+      'region' => 'sidebar_first',
+    ];
+    $this->drupalGet('admin/structure/block/add/system_powered_by_block/' . $default_theme);
+    $this->submitForm($edit, 'Save block');
+
+    // Interface negotiation depends on request arguments.
+    $this->drupalGet('node/1', ['query' => ['language' => 'en']]);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+    $this->drupalGet('node/1', ['query' => ['language' => 'fr']]);
+    $this->assertSession()->pageTextContains('Powered by Drupal');
+
+    // Log in again in order to clear the interface language stored in the
+    // session.
+    $this->drupalLogout();
+    $this->drupalLogin($this->adminUser);
+
+    // Content language does not depend on session/request arguments.
+    // It will fall back on English (site default) and not display the block.
+    $this->drupalGet('en');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+    $this->drupalGet('fr');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+
+    // Change visibility to now depend on content language for this block.
+    $edit = [
+      'visibility[language][context_mapping][language]' => '@language.current_language_context:language_content',
+    ];
+    $this->drupalGet('admin/structure/block/manage/' . $block_id);
+    $this->submitForm($edit, 'Save block');
+
+    // Content language negotiation does not depend on request arguments.
+    // It will fall back on English (site default) and not display the block.
+    $this->drupalGet('node/1', ['query' => ['language' => 'en']]);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+    $this->drupalGet('node/1', ['query' => ['language' => 'fr']]);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+
+    // Content language negotiation depends on path prefix.
+    $this->drupalGet('en');
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+    $this->drupalGet('fr');
+    $this->assertSession()->pageTextContains('Powered by Drupal');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockRenderOrderTest.php

@@ -0,0 +1,92 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Component\Utility\Html;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests blocks are being rendered in order by weight.
+ *
+ * @group block
+ */
+class BlockRenderOrderTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['node', 'block'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    // Create a test user.
+    $end_user = $this->drupalCreateUser([
+      'access content',
+    ]);
+    $this->drupalLogin($end_user);
+  }
+
+  /**
+   * Tests the render order of the blocks.
+   */
+  public function testBlockRenderOrder(): void {
+    // Enable test blocks and place them in the same region.
+    $region = 'header';
+    $test_blocks = [
+      'stark_powered' => [
+        'weight' => -3,
+        'id' => 'stark_powered',
+        'label' => 'Test block A',
+      ],
+      'stark_by' => [
+        'weight' => 3,
+        'id' => 'stark_by',
+        'label' => 'Test block C',
+      ],
+      'stark_drupal' => [
+        'weight' => 3,
+        'id' => 'stark_drupal',
+        'label' => 'Test block B',
+      ],
+    ];
+
+    // Place the test blocks.
+    foreach ($test_blocks as $test_block) {
+      $this->drupalPlaceBlock('system_powered_by_block', [
+        'label' => $test_block['label'],
+        'region' => $region,
+        'weight' => $test_block['weight'],
+        'id' => $test_block['id'],
+      ]);
+    }
+
+    $this->drupalGet('');
+    $test_content = $this->getSession()->getPage()->getContent();
+
+    $controller = $this->container->get('entity_type.manager')->getStorage('block');
+    foreach ($controller->loadMultiple() as $return_block) {
+      $id = $return_block->id();
+      if ($return_block_weight = $return_block->getWeight()) {
+        $this->assertSame((int) $test_blocks[$id]['weight'], $return_block_weight, 'Block weight is set as "' . $return_block_weight . '" for ' . $id . ' block.');
+        $position[$id] = strpos($test_content, Html::getClass('block-' . $test_blocks[$id]['id']));
+      }
+    }
+    // Verify that blocks with different weight are rendered in the correct
+    // order.
+    $this->assertLessThan($position['stark_by'], $position['stark_powered']);
+    // Verify that blocks with identical weight are rendered in alphabetical
+    // order.
+    $this->assertLessThan($position['stark_by'], $position['stark_drupal']);
+  }
+
+}