Initial Drupal 11 with DDEV setup

web/core/modules/system/config/install/core.date_format.fallback.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: fallback
+label: 'Fallback date format'
+locked: true
+pattern: 'D, j M Y - H:i'

web/core/modules/system/config/install/core.date_format.html_date.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: html_date
+label: 'HTML Date'
+locked: true
+pattern: Y-m-d

web/core/modules/system/config/install/core.date_format.html_datetime.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: html_datetime
+label: 'HTML Datetime'
+locked: true
+pattern: 'Y-m-d\TH:i:sO'

web/core/modules/system/config/install/core.date_format.html_month.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: html_month
+label: 'HTML Month'
+locked: true
+pattern: Y-m

web/core/modules/system/config/install/core.date_format.html_time.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: html_time
+label: 'HTML Time'
+locked: true
+pattern: 'H:i:s'

web/core/modules/system/config/install/core.date_format.html_week.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: html_week
+label: 'HTML Week'
+locked: true
+pattern: Y-\WW

web/core/modules/system/config/install/core.date_format.html_year.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: html_year
+label: 'HTML Year'
+locked: true
+pattern: 'Y'

web/core/modules/system/config/install/core.date_format.html_yearless_date.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: html_yearless_date
+label: 'HTML Yearless date'
+locked: true
+pattern: m-d

web/core/modules/system/config/install/core.date_format.long.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: long
+label: 'Default long date'
+locked: false
+pattern: 'l, j F Y - H:i'

web/core/modules/system/config/install/core.date_format.medium.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: medium
+label: 'Default medium date'
+locked: false
+pattern: 'D, j M Y - H:i'

web/core/modules/system/config/install/core.date_format.short.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: short
+label: 'Default short date'
+locked: false
+pattern: 'j M Y - H:i'

web/core/modules/system/config/install/system.advisories.yml

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+enabled: true
+interval_hours: 6

web/core/modules/system/config/install/system.cron.yml

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+threshold:
+  requirements_warning: 172800
+  requirements_error: 1209600
+logging: true

web/core/modules/system/config/install/system.date.yml

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+first_day: 0
+country:
+  default: null
+timezone:
+  default: null
+  user:
+    configurable: true
+    default: 0
+    warn: false

web/core/modules/system/config/install/system.diff.yml

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+context:
+  lines_leading: 2
+  lines_trailing: 2

web/core/modules/system/config/install/system.feature_flags.yml

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+linkset_endpoint: false

web/core/modules/system/config/install/system.file.yml

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+allow_insecure_uploads: false
+default_scheme: 'public'
+temporary_maximum_age: 21600

web/core/modules/system/config/install/system.image.gd.yml

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+jpeg_quality: 75

web/core/modules/system/config/install/system.image.yml

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+toolkit: gd

web/core/modules/system/config/install/system.logging.yml

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+error_level: hide

web/core/modules/system/config/install/system.mail.yml

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+interface:
+  default: 'php_mail'
+mailer_dsn:
+  scheme: 'sendmail'
+  host: 'default'
+  user: null
+  password: null
+  port: null
+  options: []

web/core/modules/system/config/install/system.maintenance.yml

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+langcode: en
+message: '@site is currently under maintenance. We should be back shortly. Thank you for your patience.'

web/core/modules/system/config/install/system.menu.account.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: account
+label: 'User account menu'
+description: 'Links related to the active user account'
+locked: true

web/core/modules/system/config/install/system.menu.admin.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: admin
+label: Administration
+description: 'Administrative task links'
+locked: true

web/core/modules/system/config/install/system.menu.footer.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: footer
+label: Footer
+description: 'Site information links'
+locked: true

web/core/modules/system/config/install/system.menu.main.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: main
+label: 'Main navigation'
+description: 'Site section links'
+locked: true

web/core/modules/system/config/install/system.menu.tools.yml

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+langcode: en
+status: true
+dependencies: {  }
+id: tools
+label: Tools
+description: 'User tool links, often added by modules'
+locked: true

web/core/modules/system/config/install/system.performance.yml

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+cache:
+  page:
+    max_age: 0
+css:
+  preprocess: true
+  gzip: true
+fast_404:
+  enabled: true
+  paths: '/\.(?:txt|png|gif|jpe?g|css|js|ico|swf|flv|cgi|bat|pl|dll|exe|asp)$/i'
+  exclude_paths: '/\/(?:styles|imagecache)\//'
+  html: '<!DOCTYPE html><html><head><title>404 Not Found</title></head><body><h1>Not Found</h1><p>The requested URL "@path" was not found on this server.</p></body></html>'
+js:
+  preprocess: true
+  gzip: true

web/core/modules/system/config/install/system.rss.yml

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+items:
+  view_mode: rss

web/core/modules/system/config/install/system.site.yml

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+langcode: en
+uuid: ''
+name: ''
+mail: ''
+slogan: ''
+page:
+  403: ''
+  404: ''
+  front: /user/login
+admin_compact_mode: false
+weight_select_max: 100
+default_langcode: en
+mail_notification: null

web/core/modules/system/config/install/system.theme.global.yml

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+favicon:
+  mimetype: image/vnd.microsoft.icon
+  path: ''
+  url: ''
+  use_default: true
+features:
+  comment_user_picture: true
+  comment_user_verification: true
+  favicon: true
+  node_user_picture: true
+logo:
+  path: ''
+  url: ~
+  use_default: true

web/core/modules/system/config/install/system.theme.yml

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+admin: ''
+default: stark

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

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+# Schema for the configuration files of the System module.
+
+system.site:
+  type: config_object
+  label: 'Site information'
+  mapping:
+    uuid:
+      type: uuid
+      label: 'Site UUID'
+      constraints:
+        Uuid: []
+        NotNull: []
+    name:
+      type: label
+      label: 'Site name'
+    mail:
+      type: email
+      label: 'Email address'
+    slogan:
+      type: label
+      label: 'Slogan'
+    page:
+      type: mapping
+      label: 'Pages'
+      mapping:
+        403:
+          type: path
+          label: 'Default 403 (access denied) page'
+        404:
+          type: path
+          label: 'Default 404 (not found) page'
+        front:
+          type: path
+          label: 'Default front page'
+    admin_compact_mode:
+      type: boolean
+      label: 'Compact mode'
+    weight_select_max:
+      type: integer
+      label: 'Weight element maximum value'
+    default_langcode:
+      type: langcode
+      label: 'Site default language code'
+    mail_notification:
+      type: string
+      label: 'Notification email address'
+
+system.maintenance:
+  type: config_object
+  label: 'Maintenance mode'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    message:
+      type: text
+      label: 'Message to display when in maintenance mode'
+
+system.cron:
+  type: config_object
+  label: 'Cron settings'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    threshold:
+      type: mapping
+      label: 'Thresholds'
+      mapping:
+        requirements_warning:
+          type: integer
+          label: 'Requirements warning period'
+          constraints:
+            # @see system_requirements()
+            Range:
+              min: 60
+        requirements_error:
+          type: integer
+          label: 'Requirements error period'
+          constraints:
+            # @see system_requirements()
+            Range:
+              min: 300
+    logging:
+      type: boolean
+      label: 'Detailed cron logging'
+
+system.date:
+  type: config_object
+  label: 'Date settings'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    first_day:
+      type: integer
+      label: 'First day of week'
+      constraints:
+        Range:
+          # @see \Drupal\system\Form\RegionalForm::buildForm()
+          min: 0
+          max: 6
+    country:
+      type: mapping
+      label: 'Country'
+      mapping:
+        default:
+          nullable: true
+          type: string
+          label: 'Default country'
+          constraints:
+            # @see \Drupal\system\Form\RegionalForm::buildForm()
+            CountryCode: []
+    timezone:
+      type: mapping
+      label: 'Time zone settings'
+      mapping:
+        default:
+          type: string
+          label: 'Default time zone'
+          nullable: true
+          constraints:
+            # @see \Drupal\system\Form\RegionalForm::buildForm()
+            Choice:
+              callback: 'DateTimeZone::listIdentifiers'
+        user:
+          type: mapping
+          label: 'User'
+          mapping:
+            configurable:
+              type: boolean
+              label: 'Users may set their own time zone'
+            default:
+              type: integer
+              label: 'Time zone for new users'
+              constraints:
+                # Time zone for new users can have one of the following values:
+                # - UserInterface::TIMEZONE_DEFAULT
+                # - UserInterface::TIMEZONE_EMPTY
+                # - UserInterface::TIMEZONE_SELECT
+                # @see \Drupal\user\UserInterface::TIMEZONE_*
+                # @todo Update this to use enum in https://www.drupal.org/project/drupal/issues/3402178
+                Choice: [0, 1, 2]
+            warn:
+              type: boolean
+              label: 'Remind users at login if their time zone is not set'
+
+system.diff:
+  type: config_object
+  label: 'Diff settings'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    context:
+      type: mapping
+      label: 'Context'
+      mapping:
+        lines_leading:
+          type: integer
+          label: 'Number of leading lines in a diff'
+          constraints:
+            # @see \Drupal\Component\Diff\DiffFormatter
+            Range:
+              min: 0
+        lines_trailing:
+          type: integer
+          label: 'Number of trailing lines in a diff'
+          constraints:
+            # @see \Drupal\Component\Diff\DiffFormatter
+            Range:
+              min: 0
+
+system.logging:
+  type: config_object
+  label: 'Logging settings'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    error_level:
+      type: string
+      label: 'Error messages to display'
+      # @see core/includes/bootstrap.inc
+      # @todo Update this to use enum in https://www.drupal.org/project/drupal/issues/2951046
+      constraints:
+        Choice:
+          choices:
+            - 'hide'
+            - 'some'
+            - 'all'
+            - 'verbose'
+
+system.performance:
+  type: config_object
+  label: 'Performance settings'
+  mapping:
+    cache:
+      type: mapping
+      label: 'Caching'
+      mapping:
+        page:
+          type: mapping
+          label: 'Page caching'
+          mapping:
+            max_age:
+              type: integer
+              label: 'Max age'
+    css:
+      type: mapping
+      label: 'CSS performance settings'
+      mapping:
+        preprocess:
+          type: boolean
+          label: 'Aggregate CSS files'
+        gzip:
+          type: boolean
+          label: 'Compress CSS files'
+    fast_404:
+      type: mapping
+      label: 'Fast 404 settings'
+      mapping:
+        enabled:
+          type: boolean
+          label: 'Fast 404 enabled'
+        paths:
+          type: string
+          label: 'Regular expression to match'
+        exclude_paths:
+          type: string
+          label: 'Regular expression to not match'
+        html:
+          type: string
+          label: 'Fast 404 page html'
+    js:
+      type: mapping
+      label: 'JavaScript performance settings'
+      mapping:
+        preprocess:
+          type: boolean
+          label: 'JavaScript preprocess'
+        gzip:
+          type: boolean
+          label: 'Compress JavaScript files.'
+
+system.rss:
+  type: config_object
+  label: 'Feed settings'
+  mapping:
+    items:
+      type: mapping
+      label: 'Feed items'
+      mapping:
+        view_mode:
+          type: string
+          label: 'Feed content'
+
+system.theme:
+  type: config_object
+  label: 'Theme settings'
+  mapping:
+    admin:
+      type: string
+      label: 'Administration theme'
+    default:
+      type: string
+      label: 'Default theme'
+
+system.menu.*:
+  type: config_entity
+  label: 'Menu'
+  mapping:
+    id:
+      type: machine_name
+      label: 'ID'
+      # Menu IDs are specifically limited to 32 characters, and allow dashes but not
+      # underscores.
+      # @see \Drupal\menu_ui\MenuForm::form()
+      constraints:
+        Regex:
+          pattern: '/^[a-z0-9-]+$/'
+          message: "The %value machine name is not valid."
+        Length:
+          max: 32
+    label:
+      type: required_label
+      label: 'Label'
+    description:
+      type: label
+      label: 'Menu description'
+      # @see \Drupal\menu_ui\MenuForm::form()
+      nullable: true
+      constraints:
+        Length:
+          max: 512
+    locked:
+      type: boolean
+      label: 'Locked'
+  constraints:
+    FullyValidatable: ~
+
+system.action.*:
+  type: config_entity
+  label: 'System action'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    id:
+      type: machine_name
+      label: 'ID'
+      constraints:
+        # Action IDs also allow periods.
+        # @see user_user_role_insert()
+        Regex:
+          pattern: '/^[a-z0-9_\.]+$/'
+          message: "The %value machine name is not valid."
+    label:
+      type: required_label
+      label: 'Label'
+    type:
+      type: string
+      label: 'Type'
+      # Action can be specified without type.
+      # @see \Drupal\action_test\Plugin\Action\NoType
+      nullable: true
+      constraints:
+        NotBlank:
+          allowNull: true
+    plugin:
+      type: string
+      label: 'Plugin'
+      constraints:
+        PluginExists:
+          manager: plugin.manager.action
+          interface: 'Drupal\Core\Action\ActionInterface'
+    configuration:
+      type: action.configuration.[%parent.plugin]
+
+system.file:
+  type: config_object
+  label: 'File system'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    allow_insecure_uploads:
+      type: boolean
+      label: 'Allow insecure uploads'
+    default_scheme:
+      type: string
+      label: 'Default download method'
+      constraints:
+        ClassResolver:
+          classOrService: 'stream_wrapper_manager'
+          method: 'isValidScheme'
+    path:
+      type: mapping
+      label: 'Path settings'
+      deprecated: "The 'path' config schema is deprecated in drupal:11.2.0 and will be removed from drupal 12.0.0. Use 'file_temp_path' key in settings.php instead. See https://www.drupal.org/node/3039255."
+    temporary_maximum_age:
+      type: integer
+      label: 'Maximum age for temporary files'
+      constraints:
+        Range:
+          min: 0
+
+system.image:
+  type: config_object
+  label: 'Image settings'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    toolkit:
+      type: string
+      label: 'Toolkit'
+      constraints:
+        PluginExists:
+          manager: 'image.toolkit.manager'
+          interface: '\Drupal\Core\ImageToolkit\ImageToolkitInterface'
+
+system.image.gd:
+  type: config_object
+  label: 'Image settings'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    jpeg_quality:
+      type: integer
+      label: 'JPEG quality'
+      constraints:
+        # @see \Drupal\system\Plugin\ImageToolkit\GDToolkit::buildConfigurationForm()
+        Range:
+          min: 0
+          max: 100
+
+system.mail:
+  type: config_object
+  label: 'Mail system'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    interface:
+      type: sequence
+      label: 'Interfaces'
+      sequence:
+        type: string
+        label: 'Interface'
+        constraints:
+          PluginExists:
+            manager: plugin.manager.mail
+            interface: 'Drupal\Core\Mail\MailInterface'
+    mailer_dsn:
+      type: mailer_dsn
+      label: 'Symfony mailer transport DSN'
+
+system.theme.global:
+  type: theme_settings
+  label: 'Theme global settings'
+
+system.advisories:
+  type: config_object
+  label: 'Security advisory settings'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    enabled:
+      type: boolean
+      label: 'Display critical security advisories'
+    interval_hours:
+      type: integer
+      label: 'How often to check for security advisories, in hours'
+      # Minimum can be set to 0 as it just means the advisories will be retrieved on every call.
+      # @see \Drupal\system\SecurityAdvisories\SecurityAdvisoriesFetcher::getSecurityAdvisories
+      constraints:
+        Range:
+          min: 0
+
+block.settings.system_branding_block:
+  type: block_settings
+  label: 'Branding block'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    use_site_logo:
+      type: boolean
+      label: 'Use site logo'
+    use_site_name:
+      type: boolean
+      label: 'Use site name'
+    use_site_slogan:
+      type: boolean
+      label: 'Use site slogan'
+
+block.settings.system_menu_block:*:
+  type: block_settings
+  label: 'Menu block'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    level:
+      type: integer
+      label: 'Starting level'
+      constraints:
+        MenuLinkDepth:
+          min: 0
+    depth:
+      type: integer
+      label: 'Maximum number of levels'
+      nullable: true
+      constraints:
+        MenuLinkDepth:
+          baseLevel: '[%parent.level]'
+          min: 1
+    expand_all_items:
+      type: boolean
+      label: 'Expand all items'
+
+block.settings.local_tasks_block:
+  type: block_settings
+  label: 'Tabs block'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    primary:
+      type: boolean
+      label: 'Whether primary tabs are shown'
+    secondary:
+      type: boolean
+      label: 'Whether secondary tabs are shown'
+
+condition.plugin.request_path:
+  type: condition.plugin
+  mapping:
+    pages:
+      type: string
+
+condition.plugin.response_status:
+  type: condition.plugin
+  mapping:
+    status_codes:
+      type: sequence
+      sequence:
+        type: integer
+
+system.feature_flags:
+  type: config_object
+  label: 'System Feature Flags'
+  constraints:
+    FullyValidatable: ~
+  mapping:
+    linkset_endpoint:
+      type: boolean
+      label: 'Enable the menu linkset endpoint'
+
+condition.plugin.current_theme:
+  type: condition.plugin
+  mapping:
+    theme:
+      type: string
+      label: Theme

web/core/modules/system/css/components/align.module.css

@@ -0,0 +1,32 @@
+/**
+ * @file
+ * Alignment classes for text and block level elements.
+ */
+
+.text-align-left {
+  text-align: left;
+}
+.text-align-right {
+  text-align: right;
+}
+.text-align-center {
+  text-align: center;
+}
+.text-align-justify {
+  text-align: justify;
+}
+
+/**
+ * Alignment classes for block level elements (images, videos, blockquotes, etc.)
+ */
+.align-left {
+  float: left;
+}
+.align-right {
+  float: right;
+}
+.align-center {
+  display: block;
+  margin-right: auto;
+  margin-left: auto;
+}

web/core/modules/system/css/components/clearfix.module.css

@@ -0,0 +1,15 @@
+/**
+ * @file
+ * Float clearing.
+ *
+ * Based on the micro clearfix hack by Nicolas Gallagher, with the :before
+ * pseudo selector removed to allow normal top margin collapse.
+ *
+ * @see http://nicolasgallagher.com/micro-clearfix-hack
+ */
+
+.clearfix::after {
+  display: table;
+  clear: both;
+  content: "";
+}

web/core/modules/system/css/components/container-inline.module.css

@@ -0,0 +1,16 @@
+/**
+ * @file
+ * Inline items.
+ */
+
+.container-inline div,
+.container-inline label {
+  display: inline-block;
+}
+/* Details contents always need to be rendered as block. */
+.container-inline .details-wrapper {
+  display: block;
+}
+.container-inline .hidden {
+  display: none;
+}

web/core/modules/system/css/components/hidden.module.css

@@ -0,0 +1,53 @@
+/**
+ * @file
+ * Utility classes to hide elements in different ways.
+ */
+
+/**
+ * Hide elements from all users.
+ *
+ * Used for elements which should not be immediately displayed to any user. An
+ * example would be collapsible details that will be expanded with a click
+ * from a user. The effect of this class can be toggled with the jQuery show()
+ * and hide() functions.
+ */
+.hidden {
+  display: none;
+}
+
+/**
+ * Hide elements visually, but keep them available for screen readers.
+ *
+ * Used for information required for screen reader users to understand and use
+ * the site where visual display is undesirable. Information provided in this
+ * manner should be kept concise, to avoid unnecessary burden on the user.
+ * "!important" is used to prevent unintentional overrides.
+ */
+.visually-hidden {
+  position: absolute !important;
+  overflow: hidden;
+  clip: rect(1px, 1px, 1px, 1px);
+  width: 1px;
+  height: 1px;
+  word-wrap: normal;
+}
+
+/**
+ * The .focusable class extends the .visually-hidden class to allow
+ * the element to be focusable when navigated to via the keyboard.
+ */
+.visually-hidden.focusable:active,
+.visually-hidden.focusable:focus-within {
+  position: static !important;
+  overflow: visible;
+  clip: auto;
+  width: auto;
+  height: auto;
+}
+
+/**
+ * Hide visually and from screen readers, but maintain layout.
+ */
+.invisible {
+  visibility: hidden;
+}

web/core/modules/system/css/components/item-list.module.css

@@ -0,0 +1,19 @@
+/**
+ * @file
+ * Styles for item list.
+ */
+
+.item-list__comma-list,
+.item-list__comma-list li {
+  display: inline;
+}
+.item-list__comma-list {
+  margin: 0;
+  padding: 0;
+}
+.item-list__comma-list li::after {
+  content: ", ";
+}
+.item-list__comma-list li:last-child::after {
+  content: "";
+}

web/core/modules/system/css/components/js.module.css

@@ -0,0 +1,35 @@
+/**
+ * @file
+ * Utility classes to assist with JavaScript functionality.
+ */
+
+/**
+ * For anything you want to hide on page load when JS is enabled, so
+ * that you can use the JS to control visibility and avoid flicker.
+ */
+.js .js-hide {
+  display: none;
+}
+
+/**
+ * For anything you want to show on page load only when JS is enabled.
+ */
+.js-show {
+  display: none;
+}
+.js .js-show {
+  display: block;
+}
+
+/**
+ * Use the scripting media features for modern browsers to reduce layout shifts.
+ */
+@media (scripting: enabled) {
+  /* Extra specificity to override previous selector. */
+  .js-hide.js-hide {
+    display: none;
+  }
+  .js-show {
+    display: block;
+  }
+}

web/core/modules/system/css/components/position-container.module.css

@@ -0,0 +1,8 @@
+/*
+ * @file
+ * Contain positioned elements.
+ */
+
+.position-container {
+  position: relative;
+}

web/core/modules/system/css/components/reset-appearance.module.css

@@ -0,0 +1,14 @@
+/*
+ * @file
+ * Utility class to remove browser styles, especially for button.
+ */
+
+.reset-appearance {
+  margin: 0;
+  padding: 0;
+  border: 0 none;
+  background: transparent;
+  line-height: inherit;
+  -webkit-appearance: none;
+  appearance: none;
+}

web/core/modules/system/css/components/system-status-counter.css

@@ -0,0 +1,30 @@
+/**
+ * @file
+ * Styles for the system status counter component.
+ */
+
+.system-status-counter__status-icon {
+  display: inline-block;
+  width: 25px;
+  height: 25px;
+  vertical-align: middle;
+}
+.system-status-counter__status-icon::before {
+  display: block;
+  width: 100%;
+  height: 100%;
+  content: "";
+  background-repeat: no-repeat;
+  background-position: center 2px;
+  background-size: 16px;
+}
+
+.system-status-counter__status-icon--error::before {
+  background-image: url(../../../../misc/icons/e32700/error.svg);
+}
+.system-status-counter__status-icon--warning::before {
+  background-image: url(../../../../misc/icons/e29700/warning.svg);
+}
+.system-status-counter__status-icon--checked::before {
+  background-image: url(../../../../misc/icons/73b355/check.svg);
+}

web/core/modules/system/css/components/system-status-report-counters.css

@@ -0,0 +1,27 @@
+/**
+ * @file
+ * Styles for the system status report counters.
+ */
+
+.system-status-report-counters__item {
+  width: 100%;
+  margin-bottom: 0.5em;
+  padding: 0.5em 0;
+  text-align: center;
+  white-space: nowrap;
+  background-color: rgb(0, 0, 0, 0.063);
+}
+
+@media screen and (min-width: 60em) {
+  .system-status-report-counters {
+    display: flex;
+    flex-wrap: wrap;
+    justify-content: space-between;
+  }
+  .system-status-report-counters__item--half-width {
+    width: 49%;
+  }
+  .system-status-report-counters__item--third-width {
+    width: 33%;
+  }
+}

web/core/modules/system/css/components/system-status-report-general-info.css

@@ -0,0 +1,14 @@
+/**
+ * @file
+ * Default styles for the System Status general info.
+ */
+
+.system-status-general-info__item {
+  margin-top: 1em;
+  padding: 0 1em 1em;
+  border: 1px solid #ccc;
+}
+
+.system-status-general-info__item-title {
+  border-bottom: 1px solid #ccc;
+}

web/core/modules/system/css/system.admin.css

@@ -0,0 +1,408 @@
+/**
+ * @file
+ * Styles for administration pages.
+ */
+
+/**
+ * Reusable layout styles.
+ */
+.layout-container {
+  margin: 0 1.5em;
+}
+.layout-container::after {
+  display: table;
+  clear: both;
+  content: "";
+}
+
+@media screen and (min-width: 38em) {
+  .layout-container {
+    margin: 0 2.5em;
+  }
+  .layout-column {
+    float: left; /* LTR */
+    box-sizing: border-box;
+  }
+  [dir="rtl"] .layout-column {
+    float: right;
+  }
+  .layout-column + .layout-column {
+    padding-left: 10px; /* LTR */
+  }
+  [dir="rtl"] .layout-column + .layout-column {
+    padding-right: 10px;
+    padding-left: 0;
+  }
+  .layout-column--half {
+    width: 50%;
+  }
+  .layout-column--quarter {
+    width: 25%;
+  }
+  .layout-column--three-quarter {
+    width: 75%;
+  }
+}
+
+/**
+ * Panel.
+ * Used to visually group items together.
+ */
+.panel {
+  padding: 5px 5px 15px;
+}
+.panel__description {
+  margin: 0 0 3px;
+  padding: 2px 0 3px 0;
+}
+
+/**
+ * System compact link: to toggle the display of description text.
+ */
+.compact-link {
+  margin: 0 0 0.5em 0;
+}
+
+/**
+ * Quick inline admin links.
+ */
+small .admin-link::before {
+  content: " [";
+}
+small .admin-link::after {
+  content: "]";
+}
+
+/**
+ * Modules page.
+ */
+.system-modules thead > tr {
+  border: 0;
+}
+.system-modules div.incompatible {
+  font-weight: bold;
+}
+.system-modules td.checkbox {
+  width: 4%;
+  min-width: 25px;
+}
+.system-modules td.module {
+  width: 25%;
+}
+.system-modules td {
+  vertical-align: top;
+}
+.system-modules label,
+.system-modules-uninstall label {
+  color: #1d1d1d;
+  font-size: 1.15em;
+}
+.system-modules details {
+  color: #5c5c5b;
+  line-height: 20px;
+}
+.system-modules details[open] {
+  overflow: visible;
+  height: auto;
+  white-space: normal;
+}
+.system-modules details[open] summary .text {
+  text-transform: none;
+  -webkit-hyphens: auto;
+  hyphens: auto;
+}
+.system-modules td details a {
+  color: #5c5c5b;
+  border: 0;
+}
+.system-modules td details {
+  margin: 0;
+  border: 0;
+}
+.system-modules td details summary {
+  padding: 0;
+  cursor: default;
+  text-transform: none;
+  font-weight: normal;
+}
+.system-modules td {
+  padding-left: 0; /* LTR */
+}
+[dir="rtl"] .system-modules td {
+  padding-right: 0;
+  padding-left: 12px;
+}
+
+@media screen and (max-width: 40em) {
+  .system-modules td.name {
+    width: 20%;
+  }
+  .system-modules td.description {
+    width: 40%;
+  }
+}
+.system-modules .requirements {
+  max-width: 490px;
+  padding: 5px 0;
+}
+.system-modules .links {
+  overflow: hidden; /* prevents collapse */
+}
+.system-modules .checkbox {
+  margin: 0 5px;
+}
+.system-modules .checkbox .form-item {
+  margin-bottom: 0;
+}
+.admin-requirements,
+.admin-required {
+  color: #666;
+  font-size: 0.9em;
+}
+.admin-enabled {
+  color: #080;
+}
+.admin-missing {
+  color: #f00;
+}
+.module-link {
+  display: block;
+  float: left; /* LTR */
+  margin-top: 2px;
+  padding: 2px 20px;
+  white-space: nowrap;
+}
+[dir="rtl"] .module-link {
+  float: right;
+}
+.module-link-help {
+  background: url(../../../misc/icons/787878/questionmark-disc.svg) 0 50% no-repeat; /* LTR */
+}
+[dir="rtl"] .module-link-help {
+  background-position: top 50% right 0;
+}
+.module-link-permissions {
+  background: url(../../../misc/icons/787878/key.svg) 0 50% no-repeat; /* LTR */
+}
+[dir="rtl"] .module-link-permissions {
+  background-position: top 50% right 0;
+}
+.module-link-configure {
+  background: url(../../../misc/icons/787878/cog.svg) 0 50% no-repeat; /* LTR */
+}
+[dir="rtl"] .module-link-configure {
+  background-position: top 50% right 0;
+}
+.module-link--non-stable {
+  padding-left: 18px;
+  background: url(../../../misc/icons/e29700/warning.svg) 0 50% no-repeat; /* LTR */
+}
+[dir="rtl"] .module-link--non-stable {
+  padding-right: 18px;
+  padding-left: 0;
+  background-position: top 50% right 0;
+}
+
+/* Status report. */
+.system-status-report__status-title {
+  position: relative;
+  box-sizing: border-box;
+  width: 100%;
+  padding: 10px 6px 10px 40px; /* LTR */
+  vertical-align: top;
+  background-color: transparent;
+  font-weight: normal;
+}
+[dir="rtl"] .system-status-report__status-title {
+  padding: 10px 40px 10px 6px;
+}
+.system-status-report__status-icon::before {
+  position: absolute;
+  top: 12px;
+  left: 12px; /* LTR */
+  display: block;
+  width: 16px;
+  height: 16px;
+  content: "";
+  background-repeat: no-repeat;
+}
+[dir="rtl"] .system-status-report__status-icon::before {
+  right: 12px;
+  left: auto;
+}
+.system-status-report__status-icon--error::before {
+  background-image: url(../../../misc/icons/e32700/error.svg);
+}
+.system-status-report__status-icon--warning::before {
+  background-image: url(../../../misc/icons/e29700/warning.svg);
+}
+.system-status-report__entry__value {
+  padding: 1em 0.5em;
+}
+
+/**
+ * Appearance page.
+ */
+.theme-info__header {
+  margin-bottom: 0;
+  font-weight: normal;
+}
+.theme-default .theme-info__header {
+  font-weight: bold;
+}
+.theme-info__description {
+  margin-top: 0;
+}
+.theme-link--non-stable {
+  padding-left: 18px;
+  background: url(../../../misc/icons/e29700/warning.svg) 0 50% no-repeat; /* LTR */
+}
+.system-themes-list {
+  margin-bottom: 20px;
+}
+.system-themes-list-uninstalled {
+  padding-top: 20px;
+  border-top: 1px solid #cdcdcd;
+}
+.system-themes-list__header {
+  margin: 0;
+}
+
+.theme-selector {
+  padding-top: 20px;
+}
+.theme-selector .screenshot,
+.theme-selector .no-screenshot {
+  max-width: 100%;
+  height: auto;
+  padding: 2px;
+  text-align: center;
+  vertical-align: bottom;
+  border: 1px solid #e0e0d8;
+}
+.theme-default .screenshot {
+  border: 1px solid #aaa;
+}
+.system-themes-list-uninstalled .screenshot,
+.system-themes-list-uninstalled .no-screenshot {
+  max-width: 194px;
+  height: auto;
+}
+
+/**
+ * Theme display without vertical toolbar.
+ */
+@media screen and (min-width: 45em) {
+  body:not(.toolbar-vertical) .system-themes-list-installed .screenshot,
+  body:not(.toolbar-vertical) .system-themes-list-installed .no-screenshot {
+    float: left; /* LTR */
+    width: 294px;
+    margin: 0 20px 0 0; /* LTR */
+  }
+  [dir="rtl"] body:not(.toolbar-vertical) .system-themes-list-installed .screenshot,
+  [dir="rtl"] body:not(.toolbar-vertical) .system-themes-list-installed .no-screenshot {
+    float: right;
+    margin: 0 0 0 20px;
+  }
+  body:not(.toolbar-vertical) .system-themes-list-installed .system-themes-list__header {
+    margin-top: 0;
+  }
+  body:not(.toolbar-vertical) .system-themes-list-uninstalled .theme-selector {
+    float: left; /* LTR */
+    box-sizing: border-box;
+    width: 31.25%;
+    padding: 20px 20px 20px 0; /* LTR */
+  }
+  [dir="rtl"] body:not(.toolbar-vertical) .system-themes-list-uninstalled .theme-selector {
+    float: right;
+    padding: 20px 0 20px 20px;
+  }
+  body:not(.toolbar-vertical) .system-themes-list-uninstalled .theme-info {
+    min-height: 170px;
+  }
+}
+
+/**
+ * Theme display with vertical toolbar.
+ */
+@media screen and (min-width: 60em) {
+  .toolbar-vertical .system-themes-list-installed .screenshot,
+  .toolbar-vertical .system-themes-list-installed .no-screenshot {
+    float: left; /* LTR */
+    width: 294px;
+    margin: 0 20px 0 0; /* LTR */
+  }
+  [dir="rtl"] .toolbar-vertical .system-themes-list-installed .screenshot,
+  [dir="rtl"] .toolbar-vertical .system-themes-list-installed .no-screenshot {
+    float: right;
+    margin: 0 0 0 20px;
+  }
+  .toolbar-vertical .system-themes-list-installed .theme-info__header {
+    margin-top: 0;
+  }
+  .toolbar-vertical .system-themes-list-uninstalled .theme-selector {
+    float: left; /* LTR */
+    box-sizing: border-box;
+    width: 31.25%;
+    padding: 20px 20px 20px 0; /* LTR */
+  }
+  [dir="rtl"] .toolbar-vertical .system-themes-list-uninstalled .theme-selector {
+    float: right;
+    padding: 20px 0 20px 20px;
+  }
+  .toolbar-vertical .system-themes-list-uninstalled .theme-info {
+    min-height: 170px;
+  }
+}
+.system-themes-list-installed .theme-info {
+  max-width: 940px;
+}
+
+.theme-selector .incompatible {
+  margin-top: 10px;
+  font-weight: bold;
+}
+.theme-selector .operations {
+  margin: 10px 0 0 0;
+  padding: 0;
+}
+.theme-selector .operations li {
+  float: left; /* LTR */
+  margin: 0;
+  padding: 0 0.7em;
+  list-style-type: none;
+  border-right: 1px solid #cdcdcd; /* LTR */
+}
+[dir="rtl"] .theme-selector .operations li {
+  float: right;
+  border-right: none;
+  border-left: 1px solid #cdcdcd;
+}
+.theme-selector .operations li:last-child {
+  padding: 0 0 0 0.7em; /* LTR */
+  border-right: none; /* LTR */
+}
+[dir="rtl"] .theme-selector .operations li:last-child {
+  padding: 0 0.7em 0 0;
+  border-left: none;
+}
+.theme-selector .operations li:first-child {
+  padding: 0 0.7em 0 0; /* LTR */
+}
+[dir="rtl"] .theme-selector .operations li:first-child {
+  padding: 0 0 0 0.7em;
+}
+.system-themes-admin-form {
+  clear: left; /* LTR */
+}
+[dir="rtl"] .system-themes-admin-form {
+  clear: right;
+}
+.cron-description__run-cron {
+  display: block;
+}
+
+.system-cron-settings__link {
+  overflow-wrap: break-word;
+  word-wrap: break-word;
+}

web/core/modules/system/css/system.diff.css

@@ -0,0 +1,41 @@
+/**
+ * Traditional split diff theming
+ */
+table.diff {
+  width: 100%;
+  margin-bottom: 20px;
+  border-spacing: 4px;
+}
+table.diff .diff-context {
+  background-color: #fafafa;
+}
+table.diff .diff-deletedline {
+  width: 50%;
+  background-color: #ffa;
+}
+table.diff .diff-addedline {
+  width: 50%;
+  background-color: #afa;
+}
+table.diff .diffchange {
+  color: #f00;
+  font-weight: bold;
+}
+table.diff .diff-marker {
+  width: 1.4em;
+}
+table.diff th {
+  padding-right: inherit; /* LTR */
+}
+[dir="rtl"] table.diff th {
+  padding-right: 0;
+  padding-left: inherit;
+}
+table.diff td div {
+  overflow: auto;
+  padding: 0.1ex 0.5em;
+  word-wrap: break-word;
+}
+table.diff td {
+  padding: 0.1ex 0.4em;
+}

web/core/modules/system/css/system.maintenance.css

@@ -0,0 +1,56 @@
+/**
+ * Update styles
+ */
+.update-results {
+  margin-top: 3em;
+  padding: 0.25em;
+  border: 1px solid #ccc;
+  background: #eee;
+  font-size: smaller;
+}
+.update-results h2 {
+  margin-top: 0.25em;
+}
+.update-results h4 {
+  margin-bottom: 0.25em;
+}
+.update-results .none {
+  color: #888;
+  font-style: italic;
+}
+.update-results .failure strong {
+  color: #b63300;
+}
+
+/**
+ * Authorize.php styles
+ */
+#edit-submit-connection {
+  clear: both;
+}
+#edit-submit-process,
+.filetransfer {
+  display: none;
+  clear: both;
+}
+.js #edit-submit-connection {
+  display: none;
+}
+.js #edit-submit-process {
+  display: block;
+}
+
+#edit-connection-settings-change-connection-type {
+  margin: 2.6em 0.5em 0 1em; /* LTR */
+}
+[dir="rtl"] #edit-connection-settings-change-connection-type {
+  margin-right: 1em;
+  margin-left: 0.5em;
+}
+
+/**
+ * Theme maintenance styles
+ */
+.authorize-results__failure {
+  font-weight: bold;
+}

web/core/modules/system/help_topics/system.cache.html.twig

@@ -0,0 +1,20 @@
+---
+label: 'Clearing the site cache'
+related:
+  - core.maintenance
+---
+{% set performance_link_text %}{% trans %}Performance{% endtrans %}{% endset %}
+{% set performance_link = render_var(help_route_link(performance_link_text, 'system.performance_settings')) %}
+<h2>{% trans %}Goal{% endtrans %}</h2>
+<p>{% trans %}Clear the data in the site cache.{% endtrans %}</p>
+<h2>{% trans %}What is the cache?{% endtrans %}</h2>
+<p>{% trans %}Some of the calculations that are done when your site loads a page take a long time to run. To save time when these calculations would need to be done again, their results can be <em>cached</em> in your site's database. There are internal mechanisms to <em>clear</em> cached data when the conditions or assumptions that went into the calculation have changed, but you can also clear cached data manually. When your site is misbehaving, a good first step is to clear the cache and see if the problem goes away.{% endtrans %}</p>
+<h2>{% trans %}Steps{% endtrans %}</h2>
+<ol>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Configuration</em> &gt; <em>Development</em> &gt; <em>{{ performance_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}Click <em>Clear all caches</em>. Your site's cached data will be cleared.{% endtrans %}</li>
+</ol>
+<h2>{% trans %}Additional resources{% endtrans %}</h2>
+<ul>
+    <li>{% trans %}<a href="https://www.drupal.org/docs/user_guide/en/prevent-cache.html">Concept: Cache (Drupal User Guide)</a>{% endtrans %}</li>
+</ul>

web/core/modules/system/help_topics/system.config_basic.html.twig

@@ -0,0 +1,30 @@
+---
+label: 'Changing basic site settings'
+top_level: true
+related:
+  - user.security_account_settings
+---
+{% set regional_link_text %}{% trans %}Regional settings{% endtrans %}{% endset %}
+{% set regional_link = render_var(help_route_link(regional_link_text, 'system.regional_settings')) %}
+{% set information_link_text %}{% trans %}Basic site settings{% endtrans %}{% endset %}
+{% set information_link = render_var(help_route_link(information_link_text, 'system.site_information_settings')) %}
+{% set datetime_link_text %}{% trans %}Date and time formats{% endtrans %}{% endset %}
+{% set datetime_link = render_var(help_route_link(datetime_link_text, 'entity.date_format.collection')) %}
+<h2>{% trans %}Goal{% endtrans %}</h2>
+<p>{% trans %}Configure the basic settings of your site, including the site name, slogan, main email address, default time zone, default country, and the date formats to use.{% endtrans %}</p>
+<h2>{% trans %}Steps{% endtrans %}</h2>
+<ol>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Configuration</em> &gt; <em>System</em> &gt; <em>{{ information_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}Enter the site name, slogan, and main email address for your site. {% endtrans %}</li>
+  <li>{% trans %}Click <em>Save configuration</em>. You should see a message indicating that the settings were saved.{% endtrans %}</li>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Configuration</em> &gt; <em>Region and language</em> &gt; <em>{{ regional_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}Select the default country and default time zone for your site.{% endtrans %}</li>
+  <li>{% trans %}Click <em>Save configuration</em>. You should see a message indicating that the settings were saved.{% endtrans %}</li>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Configuration</em> &gt; <em>Region and language</em> &gt; <em>{{ datetime_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}Look at the <em>Patterns</em> for the Default long, medium, and short date formats. If any of them does not match the date format you want to use on your site, click <em>Edit</em> in that row to edit the format.{% endtrans %}</li>
+  <li>{% trans %}Adjust the <em>Format string</em> until the <em>Displayed</em> format matches what you want. (Date format strings are composed of PHP date format codes.){% endtrans %}</li>
+  <li>{% trans %}Click <em>Save format</em>. You should see a message indicating that the format was saved.{% endtrans %}</li>
+  <li>{% trans %}Repeat the previous three steps for any other date formats that need to be changed.{% endtrans %}</li>
+</ol>
+<h2>{% trans %}Additional resources{% endtrans %}</h2>
+<p>{% trans %}<a href="https://www.php.net/manual/datetime.format.php#refsect1-datetime.format-parameters">PHP date format codes reference</a>{% endtrans %}</p>

web/core/modules/system/help_topics/system.config_error.html.twig

@@ -0,0 +1,26 @@
+---
+label: 'Configuring error responses, including 403/404 pages'
+related:
+  - system.config_basic
+  - core.maintenance
+---
+{% set log_settings_link_text %}{% trans %}Logging and errors{% endtrans %}{% endset %}
+{% set log_settings_link = render_var(help_route_link(log_settings_link_text, 'system.logging_settings')) %}
+{% set information_link_text %}{% trans %}Basic site settings{% endtrans %}{% endset %}
+{% set information_link = render_var(help_route_link(information_link_text, 'system.site_information_settings')) %}
+<h2>{% trans %}Goal{% endtrans %}</h2>
+<p>{% trans %}Set up your site to respond appropriately to site errors, including 403 and 404 page responses.{% endtrans %}</p>
+<h2>{% trans %}What are 403 and 404 responses?{% endtrans %}</h2>
+<p>{% trans %}When a user visits a web page, the web server sends a response code in addition to the page content. A normal, non-error response has code 200. If the page does not exist on the site, the response code is 404. If the page exists, but the user is not authorized to visit the page, the response code is 403. The core software provides default responses for both 403 and 404 codes, but if you prefer, you can create your own pages for each.{% endtrans %}</p>
+<h2>{% trans %}What other errors can occur?{% endtrans %}</h2>
+<p>{% trans %}Under some situations, your site can generate error messages. These can be due to user errors (such as entering invalid values in a form, or incorrect configuration), PHP runtime errors, or software bugs. Some errors may result in a <em>white screen of death</em> (a totally blank web page response); less drastic errors will generate error messages. You can configure what happens when an error message is generated.{% endtrans %}</p>
+<h2>{% trans %}Steps {% endtrans %}</h2>
+<ol>
+  <li>{% trans %}If desired, create pages to use for 403 and 404 responses. Note the URLs for these pages.{% endtrans %}</li>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Configuration</em> &gt; <em>System</em> &gt; <em>{{ information_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}In the <em>Error pages</em> section, enter the URL for your 403/404 pages, starting after the site home page URL. For example, if your site URL is <em>https://example.com</em> and your 404 page is <em>https://example.com/not-found</em>, you would enter <em>/not-found</em>.{% endtrans %}</li>
+  <li>{% trans %}Click <em>Save configuration</em>. You should see a message indicating that the settings were saved.{% endtrans %}</li>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Configuration</em> &gt; <em>Development</em> &gt; <em>{{ log_settings_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}For a production site, select <em>None</em> under <em>Error messages to display</em>. For a site that is in development, select one of the other options, so that you are more aware of the errors the site is generating.{% endtrans %}</li>
+  <li>{% trans %}Click <em>Save configuration</em>. You should see a message indicating that the settings were saved.{% endtrans %}</li>
+</ol>

web/core/modules/system/help_topics/system.maintenance_mode.html.twig

@@ -0,0 +1,22 @@
+---
+label: 'Enabling and disabling maintenance mode'
+related:
+  - core.maintenance
+  - system.cache
+---
+{% set cache_topic = render_var(help_topic_link('system.cache')) %}
+{% set maintenance_link_text %}{% trans %}Maintenance mode{% endtrans %}{% endset %}
+{% set maintenance_link = render_var(help_route_link(maintenance_link_text, 'system.site_maintenance_mode')) %}
+<h2>{% trans %}Goal{% endtrans %}</h2>
+<p>{% trans %}Put your site in maintenance mode to perform maintenance operations, and then return to normal mode when finished.{% endtrans %}</p>
+<h2>{% trans %}What is maintenance mode?{% endtrans %}</h2>
+<p>{% trans %}When your site is in maintenance mode, most site visitors will see a simple maintenance mode message page, rather than being able to use the full functionality of the site. Users with <em>Use the site in maintenance mode</em> permission who are already logged in will be able to use the full site, and the log in page at <em>/user</em> will also be accessible to anyone.{% endtrans %}</p>
+<h2>{% trans %}Steps{% endtrans %}</h2>
+<ol>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Configuration</em> &gt; <em>Development</em> &gt; <em>{{ maintenance_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}Check <em>Put site into maintenance mode</em>, optionally change the <em>Message to display when in maintenance mode</em>, and click <em>Save configuration</em>. Your site will be in maintenance mode.{% endtrans %}</li>
+  <li>{% trans %}Perform your maintenance operations.{% endtrans %}</li>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Configuration</em> &gt; <em>Development</em> &gt; <em>{{ maintenance_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}Uncheck <em>Put site into maintenance mode</em> and click <em>Save configuration</em>. Your site will be back in normal operation mode.{% endtrans %}</li>
+  <li>{% trans %}Clear the site cache. See {{ cache_topic }} for instructions.{% endtrans %}</li>
+</ol>

web/core/modules/system/help_topics/system.module_install.html.twig

@@ -0,0 +1,18 @@
+---
+label: 'Installing a module'
+related:
+  - core.extending
+  - system.module_uninstall
+---
+{% set extend_link_text %}{% trans %}Extend{% endtrans %}{% endset %}
+{% set extend_link = render_var(help_route_link(extend_link_text, 'system.modules_list')) %}
+<h2>{% trans %}Goal{% endtrans %}</h2>
+<p>{% trans %}Install a core module, or a contributed module that has already been downloaded.{% endtrans %}</p>
+<h2>{% trans %}Steps{% endtrans %}</h2>
+<ol>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>{{ extend_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}Enter a word from the module name or description into the filter box, to make the list of modules smaller. Locate the module you want to install.{% endtrans %}</li>
+  <li>{% trans %}Check the box next to the name of the module you want to install; you can also check more than one box to install multiple modules at the same time. If the checkbox is disabled for the module you are trying to install, expand the information to see why -- you may need to download an additional module that your module requires.{% endtrans %}</li>
+  <li>{% trans %}Click <em>Install</em> at the bottom of the page. If you chose to install a module with dependencies that were not already installed, or if you chose an Experimental module, confirm your choice on the next page.{% endtrans %}</li>
+  <li>{% trans %}Wait for the module (or modules) to be installed. You should be returned to the <em>Extend</em> page with a message saying the module or modules were installed.{% endtrans %}</li>
+</ol>

web/core/modules/system/help_topics/system.module_uninstall.html.twig

@@ -0,0 +1,21 @@
+---
+label: 'Uninstalling a module'
+related:
+  - core.extending
+  - system.module_install
+  - system.maintenance_mode
+---
+{% set uninstall_link_text %}{% trans %}Uninstall{% endtrans %}{% endset %}
+{% set uninstall_link = render_var(help_route_link(uninstall_link_text, 'system.modules_uninstall')) %}
+{% set maintenance_topic = render_var(help_topic_link('system.maintenance_mode')) %}
+<h2>{% trans %}Goal{% endtrans %}</h2>
+<p>{% trans %}Uninstall a module. Your site should be in <em>maintenance mode</em> when you uninstall modules. See {{ maintenance_topic }} for details.{% endtrans %}</p>
+<h2>{% trans %}Steps{% endtrans %}</h2>
+<ol>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Extend</em> &gt; <em>{{ uninstall_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}Enter a word from the module name or description into the filter box, to make the list of modules smaller. Locate the module you want to uninstall.{% endtrans %}</li>
+  <li>{% trans %}In the <em>Description</em> column, see if there are reasons that this module cannot be uninstalled. For example, you may have created content using this module (which you would need to delete first), or there may be another module installed that requires this module to be installed (you would need to uninstall the other module first).{% endtrans %}</li>
+  <li>{% trans %}If there are no reasons listed, the module can be uninstalled. Check the box in the <em>Uninstall</em> column, next to the module's name.{% endtrans %}</li>
+  <li>{% trans %}Click <em>Uninstall</em> at the bottom of the page. Verify the list of modules to be uninstalled and configuration to be deleted on the confirmation page, and click <em>Uninstall</em>.{% endtrans %}</li>
+  <li>{% trans %}Wait for the module to be uninstalled. You should be returned to the <em>Uninstall</em> page with a message saying the module was uninstalled.{% endtrans %}</li>
+</ol>

web/core/modules/system/help_topics/system.reports.html.twig

@@ -0,0 +1,21 @@
+---
+label: 'Running reports on your site'
+related:
+  - core.maintenance
+  - core.security
+  - system.config_error
+---
+{% set status_link_text %}{% trans %}Status report{% endtrans %}{% endset %}
+{% set status_link = render_var(help_route_link(status_link_text, 'system.status')) %}
+<h2>{% trans %}Goal{% endtrans %}</h2>
+<p>{% trans %}Run reports to learn about the status and health of your site.{% endtrans %}</p>
+<h2>{% trans %}Steps{% endtrans %}</h2>
+<ol>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>Reports</em> &gt; <em>{{ status_link }}</em> to see a report that summarizes the health and status of your site. If there are any warnings or errors, you will need to fix them. Take note of any upcoming highly critical security releases that may impact your site.{% endtrans %}</li>
+  <li>{% trans %}If you have the core Database Logging module installed, in the <em>Manage</em> administrative menu, navigate to <em>Reports</em> &gt; <em>Recent log messages</em> to see a report of the error and informational messages your site has generated. You can filter the report by <em>Severity</em> to see only the most critical messages, if desired.{% endtrans %}</li>
+  <li>{% trans %}If you have the core Update Status module installed, in the <em>Manage</em> administrative menu, navigate to <em>Reports</em> &gt; <em>Available updates</em> to see a report of the updates that are available for your site software. If <em>Last checked</em> is far in the past, click <em>Check manually</em> to update the report. Scan the report; if the core software or any modules or themes have security updates available, you should update them as soon as possible.{% endtrans %}</li>
+</ol>
+<h2>{% trans %}Additional resources{% endtrans %}</h2>
+<ul>
+    <li>{% trans %}<a href="https://www.drupal.org/docs/user_guide/en/security-chapter.html">Security and Maintenance (Drupal User Guide)</a>, which includes information on how to update your site's core software, modules, and themes.{% endtrans %}</li>
+</ul>

web/core/modules/system/help_topics/system.theme_install.html.twig

@@ -0,0 +1,19 @@
+---
+label: 'Installing a theme and setting default themes'
+related:
+  - core.appearance
+  - system.theme_uninstall
+---
+{% set themes_link_text %}{% trans %}Appearance{% endtrans %}{% endset %}
+{% set themes_link = render_var(help_route_link(themes_link_text, 'system.themes_page')) %}
+<h2>{% trans %}Goal{% endtrans %}</h2>
+<p>{% trans %}Install a core theme, or a contributed theme that has already been downloaded. Choose the default themes to use for the site and for administrative pages.{% endtrans %}</p>
+<h2>{% trans %}Steps{% endtrans %}</h2>
+<ol>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>{{ themes_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}Locate the themes that you want to use as the site default theme and for administrative pages.{% endtrans %}</li>
+  <li>{% trans %}For each of these themes, if the theme is in the <em>Uninstalled themes</em> section, click the <em>Install</em> link to install the theme. Wait for the theme to be installed (translations might be downloaded). You should be returned to the <em>Appearance</em> page.{% endtrans %}</li>
+  <li>{% trans %}Locate the theme that you want to be your default theme, which should now be in the <em>Installed themes</em> section. If it is not already labeled as the <em>default theme</em>, click the <em>Set as default</em> link.{% endtrans %}</li>
+  <li>{% trans %}At the bottom of the page, select the <em>Administration theme</em> that you want to use on administrative pages. Click <em>Save configuration</em> if you selected a new theme.{% endtrans %}</li>
+  <li>{% trans %}If you changed the default theme for your site, visit the site home page or another page on the non-administration part of your site and verify that the site is using the new theme. If you changed the administration theme, verify that the new theme is used on administrative pages.{% endtrans %}</li>
+</ol>

web/core/modules/system/help_topics/system.theme_uninstall.html.twig

@@ -0,0 +1,16 @@
+---
+label: 'Uninstalling an unused theme'
+related:
+  - core.appearance
+  - system.theme_install
+---
+{% set themes_link_text %}{% trans %}Appearance{% endtrans %}{% endset %}
+{% set themes_link = render_var(help_route_link(themes_link_text, 'system.themes_page')) %}
+<h2>{% trans %}Goal{% endtrans %}</h2>
+<p>{% trans %}Uninstall a theme that was previously installed, but is no longer being used on the site.{% endtrans %}</p>
+<h2>{% trans %}Steps{% endtrans %}</h2>
+<ol>
+  <li>{% trans %}In the <em>Manage</em> administrative menu, navigate to <em>{{ themes_link }}</em>.{% endtrans %}</li>
+  <li>{% trans %}Locate the theme that you want to uninstall, in the <em>Installed themes</em> section.{% endtrans %}</li>
+  <li>{% trans %}Click the <em>Uninstall</em> link to uninstall the theme. If there is not an <em>Uninstall</em> link, the theme cannot be uninstalled because it is either being used as the site default theme, being used as the <em>Administration theme</em>, or is the base theme for another installed theme.{% endtrans %}</li>
+</ol>

web/core/modules/system/js/system.date.js

@@ -0,0 +1,69 @@
+/**
+ * @file
+ * Provides date format preview feature.
+ */
+
+(function ($, Drupal, drupalSettings) {
+  const dateFormats = drupalSettings.dateFormats;
+
+  /**
+   * Display the preview for date format entered.
+   *
+   * @type {Drupal~behavior}
+   *
+   * @prop {Drupal~behaviorAttach} attach
+   *   Attach behavior for previewing date formats on input elements.
+   */
+  Drupal.behaviors.dateFormat = {
+    attach(context) {
+      const source = once(
+        'dateFormat',
+        '[data-drupal-date-formatter="source"]',
+        context,
+      );
+      const target = once(
+        'dateFormat',
+        '[data-drupal-date-formatter="preview"]',
+        context,
+      );
+
+      // All elements have to exist.
+      if (!source.length || !target.length) {
+        return;
+      }
+
+      /**
+       * Event handler that replaces date characters with value.
+       *
+       * @param {jQuery.Event} e
+       *   The jQuery event triggered.
+       */
+      function dateFormatHandler(e) {
+        const baseValue = e.target.value || '';
+        const dateString = baseValue.replace(/\\?(.?)/gi, (key, value) =>
+          dateFormats[key] ? dateFormats[key] : value,
+        );
+
+        // Set date preview.
+        target.forEach((item) => {
+          item.querySelectorAll('em').forEach((em) => {
+            em.textContent = dateString;
+          });
+        });
+
+        $(target).toggleClass('js-hide', !dateString.length);
+      }
+
+      /**
+       * On given event triggers the date character replacement.
+       */
+      $(source)
+        .on(
+          'keyup.dateFormat change.dateFormat input.dateFormat',
+          dateFormatHandler,
+        )
+        // Initialize preview.
+        .trigger('keyup');
+    },
+  };
+})(jQuery, Drupal, drupalSettings);

web/core/modules/system/js/system.js

@@ -0,0 +1,82 @@
+/**
+ * @file
+ * System behaviors.
+ */
+
+(function ($, Drupal, drupalSettings) {
+  // Cache IDs in an array for ease of use.
+  const ids = [];
+
+  /**
+   * Attaches field copy behavior from input fields to other input fields.
+   *
+   * When a field is filled out, apply its value to other fields that will
+   * likely use the same value. In the installer this is used to populate the
+   * administrator email address with the same value as the site email address.
+   *
+   * @type {Drupal~behavior}
+   *
+   * @prop {Drupal~behaviorAttach} attach
+   *   Attaches the field copy behavior to an input field.
+   */
+  Drupal.behaviors.copyFieldValue = {
+    attach(context) {
+      // List of fields IDs on which to bind the event listener.
+      // Create an array of IDs to use with jQuery.
+      Object.keys(drupalSettings.copyFieldValue || {}).forEach((element) => {
+        ids.push(element);
+      });
+
+      if (ids.length) {
+        // Listen to value:copy events on all dependent fields.
+        // We have to use body and not document because of the way jQuery events
+        // bubble up the DOM tree.
+        $(once('copy-field-values', 'body')).on(
+          'value:copy',
+          this.valueTargetCopyHandler,
+        );
+        // Listen on all source elements.
+        $(once('copy-field-values', `#${ids.join(', #')}`)).on(
+          'blur',
+          this.valueSourceBlurHandler,
+        );
+      }
+    },
+    detach(context, settings, trigger) {
+      if (trigger === 'unload' && ids.length) {
+        $(once.remove('copy-field-values', 'body')).off('value:copy');
+        $(once.remove('copy-field-values', `#${ids.join(', #')}`)).off('blur');
+      }
+    },
+
+    /**
+     * Event handler that fill the target element with the specified value.
+     *
+     * @param {jQuery.Event} e
+     *   Event object.
+     * @param {string} value
+     *   Custom value from jQuery trigger.
+     */
+    valueTargetCopyHandler(e, value) {
+      const { target } = e;
+      if (target.value === '') {
+        target.value = value;
+      }
+    },
+
+    /**
+     * Handler for a Blur event on a source field.
+     *
+     * This event handler will trigger a 'value:copy' event on all dependent
+     * fields.
+     *
+     * @param {jQuery.Event} e
+     *   The event triggered.
+     */
+    valueSourceBlurHandler(e) {
+      const { value } = e.target;
+      const targetIds = drupalSettings.copyFieldValue[e.target.id];
+      $(`#${targetIds.join(', #')}`).trigger('value:copy', value);
+    },
+  };
+})(jQuery, Drupal, drupalSettings);

web/core/modules/system/js/system.modules.js

@@ -0,0 +1,112 @@
+/**
+ * @file
+ * Module page behaviors.
+ */
+
+(function ($, Drupal, debounce) {
+  /**
+   * Filters the module list table by a text input search string.
+   *
+   * Additionally accounts for multiple tables being wrapped in "package" details
+   * elements.
+   *
+   * Text search input: input.table-filter-text
+   * Target table:      input.table-filter-text[data-table]
+   * Source text:       .table-filter-text-source, .module-name, .module-description
+   *
+   * @type {Drupal~behavior}
+   */
+  Drupal.behaviors.tableFilterByText = {
+    attach(context, settings) {
+      const [input] = once('table-filter-text', 'input.table-filter-text');
+      if (!input) {
+        return;
+      }
+      const $table = $(input.getAttribute('data-table'));
+      let $rowsAndDetails;
+      let $rows;
+      let $details;
+      let searching = false;
+
+      function hidePackageDetails(index, element) {
+        const $packDetails = $(element);
+        const $visibleRows = $packDetails.find('tbody tr:visible');
+        $packDetails.toggle($visibleRows.length > 0);
+      }
+
+      function filterModuleList(e) {
+        const query = e.target.value;
+        // Case insensitive expression to find query at the beginning of a word.
+        const re = new RegExp(`\\b${query}`, 'i');
+
+        function showModuleRow(index, row) {
+          const sources = row.querySelectorAll(
+            '.table-filter-text-source, .module-name, .module-description',
+          );
+          let sourcesConcat = '';
+          // Concatenate the textContent of the elements in the row, with a
+          // space in between.
+          sources.forEach((item) => {
+            sourcesConcat += ` ${item.textContent}`;
+          });
+          const textMatch = sourcesConcat.search(re) !== -1;
+          $(row).closest('tr').toggle(textMatch);
+        }
+        // Search over all rows and packages.
+        $rowsAndDetails.show();
+
+        // Filter if the length of the query is at least 2 characters.
+        if (query.length >= 2) {
+          searching = true;
+          $rows.each(showModuleRow);
+
+          // Note that we first open all <details> to be able to use ':visible'.
+          // Mark the <details> elements that were closed before filtering, so
+          // they can be closed again when filtering is removed.
+          $details
+            .not('[open]')
+            .attr('data-drupal-system-state', 'forced-open');
+
+          // Hide the package <details> if they don't have any visible rows.
+          // Note that we first show() all <details> to be able to use ':visible'.
+          $details.attr('open', true).each(hidePackageDetails);
+
+          Drupal.announce(
+            Drupal.formatPlural(
+              $rowsAndDetails.filter('tbody tr:visible').length,
+              '1 module is available in the modified list.',
+              '@count modules are available in the modified list.',
+            ),
+          );
+        } else if (searching) {
+          searching = false;
+          $rowsAndDetails.show();
+          // Return <details> elements that had been closed before filtering
+          // to a closed state.
+          $details
+            .filter('[data-drupal-system-state="forced-open"]')
+            .removeAttr('data-drupal-system-state')
+            .attr('open', false);
+        }
+      }
+
+      function preventEnterKey(event) {
+        if (event.which === 13) {
+          event.preventDefault();
+          event.stopPropagation();
+        }
+      }
+
+      if ($table.length) {
+        $rowsAndDetails = $table.find('tr, details');
+        $rows = $table.find('tbody tr');
+        $details = $rowsAndDetails.filter('.package-listing');
+
+        $(input).on({
+          input: debounce(filterModuleList, 200),
+          keydown: preventEnterKey,
+        });
+      }
+    },
+  };
+})(jQuery, Drupal, Drupal.debounce);

web/core/modules/system/migrations/action_settings.yml

@@ -0,0 +1,20 @@
+id: action_settings
+label: Action configuration
+migration_tags:
+  - Drupal 6
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - actions_max_stack
+  source_module: system
+process:
+  recursion_limit:
+    plugin: skip_on_empty
+    method: row
+    source: empty
+destination:
+  plugin: config
+  config_name: null
+  destination_module: system

web/core/modules/system/migrations/d6_action.yml

@@ -0,0 +1,50 @@
+# cspell:ignore imagecache
+id: d6_action
+label: Actions
+migration_tags:
+  - Drupal 6
+  - Configuration
+source:
+  plugin: action
+process:
+  id:
+    -
+      plugin: machine_name
+      source: aid
+  label: description
+  type: type
+  plugin:
+    -
+      plugin: static_map
+      source: callback
+      map:
+        system_goto_action: action_goto_action
+        system_send_email_action: action_send_email_action
+        system_message_action: action_message_action
+        user_block_ip_action: 0
+        imagecache_flush_action: 0
+        imagecache_generate_all_action: 0
+        imagecache_generate_action: 0
+        comment_publish_action: entity:publish_action:comment
+        comment_unpublish_action: entity:unpublish_action:comment
+        comment_save_action: entity:save_action:comment
+        node_publish_action: entity:publish_action:node
+        node_unpublish_action: entity:unpublish_action:node
+        node_save_action: entity:save_action:node
+        comment_unpublish_by_keyword_action: 0
+        node_unpublish_by_keyword_action: 0
+        node_assign_owner_action: 0
+      bypass: true
+    -
+      plugin: skip_on_empty
+      method: row
+  configuration:
+    -
+      plugin: default_value
+      source: parameters
+      default_value: "a:0:{}"
+    -
+      plugin: callback
+      callable: unserialize
+destination:
+  plugin: entity:action

web/core/modules/system/migrations/d6_date_formats.yml

@@ -0,0 +1,24 @@
+# cspell:ignore multirow
+id: d6_date_formats
+label: Date format configuration
+migration_tags:
+  - Drupal 6
+  - Configuration
+source:
+  plugin: variable_multirow
+  variables:
+    - date_format_long
+    - date_format_medium
+    - date_format_short
+  source_module: system
+process:
+  id:
+    plugin: static_map
+    source: name
+    map:
+      date_format_long: long
+      date_format_short: short
+      date_format_medium: medium
+  pattern: value
+destination:
+  plugin: entity:date_format

web/core/modules/system/migrations/d6_menu.yml

@@ -0,0 +1,14 @@
+# The menu_settings migration is in the menu_ui module.
+id: d6_menu
+label: Menus
+migration_tags:
+  - Drupal 6
+  - Configuration
+source:
+  plugin: menu
+process:
+  id: menu_name
+  label: title
+  description: description
+destination:
+  plugin: entity:menu

web/core/modules/system/migrations/d6_system_cron.yml

@@ -0,0 +1,18 @@
+id: d6_system_cron
+label: Cron settings
+migration_tags:
+  - Drupal 6
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - cron_threshold_warning
+    - cron_threshold_error
+    - cron_last
+  source_module: system
+process:
+  'threshold/requirements_warning': cron_threshold_warning
+  'threshold/requirements_error': cron_threshold_error
+destination:
+  plugin: config
+  config_name: system.cron

web/core/modules/system/migrations/d6_system_date.yml

@@ -0,0 +1,21 @@
+id: d6_system_date
+label: System date configuration
+migration_tags:
+  - Drupal 6
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - configurable_timezones
+    - date_first_day
+    - date_default_timezone
+  source_module: system
+process:
+  'timezone/user/configurable': configurable_timezones
+  first_day: date_first_day
+  'timezone/default':
+    plugin: timezone
+    source: date_default_timezone
+destination:
+  plugin: config
+  config_name: system.date

web/core/modules/system/migrations/d6_system_file.yml

@@ -0,0 +1,20 @@
+id: d6_system_file
+label: File system configuration
+migration_tags:
+  - Drupal 6
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - allow_insecure_uploads
+  source_module: system
+process:
+  allow_insecure_uploads:
+    plugin: static_map
+    source: allow_insecure_uploads
+    map:
+      0: FALSE
+      1: TRUE
+destination:
+  plugin: config
+  config_name: system.file

web/core/modules/system/migrations/d6_system_performance.yml

@@ -0,0 +1,21 @@
+id: d6_system_performance
+label: Performance configuration
+migration_tags:
+  - Drupal 6
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - preprocess_css
+    - preprocess_js
+    - cache_lifetime
+    - cache
+    - page_compression
+  source_module: system
+process:
+  'css/preprocess': preprocess_css
+  'js/preprocess': preprocess_js
+  'cache/page/max_age': cache_lifetime
+destination:
+  plugin: config
+  config_name: system.performance

web/core/modules/system/migrations/d7_action.yml

@@ -0,0 +1,46 @@
+id: d7_action
+label: Actions
+migration_tags:
+  - Drupal 7
+  - Configuration
+source:
+  plugin: action
+process:
+  id:
+    -
+      plugin: machine_name
+      source: aid
+  label: label
+  type: type
+  plugin:
+    -
+      plugin: static_map
+      source: callback
+      map:
+        system_goto_action: action_goto_action
+        system_send_email_action: action_send_email_action
+        system_message_action: action_message_action
+        system_block_ip_action: 0
+        comment_publish_action: entity:publish_action:comment
+        comment_unpublish_action: entity:unpublish_action:comment
+        comment_save_action: entity:save_action:comment
+        node_publish_action: entity:publish_action:node
+        node_unpublish_action: entity:unpublish_action:node
+        node_save_action: entity:save_action:node
+        comment_unpublish_by_keyword_action: 0
+        node_unpublish_by_keyword_action: 0
+        node_assign_owner_action: 0
+      bypass: true
+    -
+      plugin: skip_on_empty
+      method: row
+  configuration:
+    -
+      plugin: default_value
+      source: parameters
+      default_value: "a:0:{}"
+    -
+      plugin: callback
+      callable: unserialize
+destination:
+  plugin: entity:action

web/core/modules/system/migrations/d7_global_theme_settings.yml

@@ -0,0 +1,31 @@
+id: d7_global_theme_settings
+label: D7 global theme settings
+migration_tags:
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - theme_settings
+  source_module: system
+process:
+  'features/logo': theme_settings/toggle_logo
+  'features/name': theme_settings/toggle_name
+  'features/slogan': theme_settings/toggle_slogan
+  'features/node_user_picture': theme_settings/toggle_node_user_picture
+  'features/comment_user_picture': theme_settings/toggle_comment_user_picture
+  'features/comment_user_verification': theme_settings/toggle_comment_user_verification
+  'features/favicon': theme_settings/toggle_favicon
+  'logo/use_default': theme_settings/default_logo
+  'logo/path': theme_settings/logo_path
+  'favicon/use_default': theme_settings/default_favicon
+  'favicon/path': theme_settings/favicon_path
+  'favicon/mimetype': theme_settings/favicon_mimetype
+# Ignore settings not present in Drupal 8
+#  theme_settings/logo_upload
+#  theme_settings/favicon_upload
+#  theme_settings/toggle_main_menu
+#  theme_settings/toggle_secondary_menu
+destination:
+  plugin: config
+  config_name: system.theme.global

web/core/modules/system/migrations/d7_menu.yml

@@ -0,0 +1,25 @@
+id: d7_menu
+label: Menus
+migration_tags:
+  - Drupal 7
+  - Configuration
+source:
+  plugin: menu
+process:
+  id:
+    plugin: static_map
+    bypass: true
+    source: menu_name
+    map:
+      main-menu: main
+      management: admin
+      navigation: tools
+      user-menu: account
+  label: title
+  description: description
+  langcode:
+    plugin: default_value
+    source: language
+    default_value: en
+destination:
+  plugin: entity:menu

web/core/modules/system/migrations/d7_system_authorize.yml

@@ -0,0 +1,19 @@
+id: d7_system_authorize
+label: Drupal 7 file transfer authorize configuration
+migration_tags:
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - authorize_filetransfer_default
+  source_module: system
+process:
+  filetransfer_default:
+    plugin: skip_on_empty
+    method: row
+    source: empty
+destination:
+  plugin: config
+  config_name: null
+  destination_module: system

web/core/modules/system/migrations/d7_system_cron.yml

@@ -0,0 +1,17 @@
+id: d7_system_cron
+label: Drupal 7 cron settings
+migration_tags:
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - cron_threshold_warning
+    - cron_threshold_error
+  source_module: system
+process:
+  'threshold/requirements_warning': cron_threshold_warning
+  'threshold/requirements_error': cron_threshold_error
+destination:
+  plugin: config
+  config_name: system.cron

web/core/modules/system/migrations/d7_system_date.yml

@@ -0,0 +1,25 @@
+id: d7_system_date
+label: Drupal 7 system date configuration
+migration_tags:
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - site_default_country
+    - date_first_day
+    - date_default_timezone
+    - configurable_timezones
+    - empty_timezone_message
+    - user_default_timezone
+  source_module: system
+process:
+  'country/default': site_default_country
+  first_day: date_first_day
+  'timezone/default': date_default_timezone
+  'timezone/user/configurable': configurable_timezones
+  'timezone/user/warn': empty_timezone_message
+  'timezone/user/default': user_default_timezone
+destination:
+  plugin: config
+  config_name: system.date

web/core/modules/system/migrations/d7_system_file.yml

@@ -0,0 +1,20 @@
+id: d7_system_file
+label: Drupal 7 file system configuration
+migration_tags:
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - allow_insecure_uploads
+  source_module: system
+process:
+  allow_insecure_uploads:
+    plugin: static_map
+    source: allow_insecure_uploads
+    map:
+      0: FALSE
+      1: TRUE
+destination:
+  plugin: config
+  config_name: system.file

web/core/modules/system/migrations/d7_system_mail.yml

@@ -0,0 +1,38 @@
+id: d7_system_mail
+label: Drupal 7 system mail configuration
+migration_tags:
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables_no_row_if_missing:
+    - mail_system
+  source_module: system
+process:
+  'interface/default':
+    plugin: static_map
+    source: 'mail_system/default-system'
+    map:
+      DefaultMailSystem: php_mail
+      MailTestCase: test_mail_collector
+  'mailer_dsn':
+    plugin: static_map
+    source: 'mail_system/default-system'
+    map:
+      DefaultMailSystem:
+        scheme: 'sendmail'
+        host: 'default'
+        user: null
+        password: null
+        port: null
+        options: []
+      MailTestCase:
+        scheme: 'null'
+        host: 'null'
+        user: null
+        password: null
+        port: null
+        options: []
+destination:
+  plugin: config
+  config_name: system.mail

web/core/modules/system/migrations/d7_system_performance.yml

@@ -0,0 +1,20 @@
+id: d7_system_performance
+label: Drupal 7 performance configuration
+migration_tags:
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - preprocess_css
+    - preprocess_js
+    - cache_lifetime
+    - page_compression
+  source_module: system
+process:
+  'css/preprocess': preprocess_css
+  'js/preprocess': preprocess_js
+  'cache/page/max_age': cache_lifetime
+destination:
+  plugin: config
+  config_name: system.performance

web/core/modules/system/migrations/d7_theme_settings.yml

@@ -0,0 +1,52 @@
+id: d7_theme_settings
+label: D7 theme settings
+migration_tags:
+  - Drupal 7
+  - Configuration
+source:
+  plugin: d7_theme_settings
+  constants:
+    config_suffix: '.settings'
+process:
+  # Build the configuration name from the variable name, i.e.
+  # theme_bartik_settings becomes bartik.settings.
+  legacy_theme_name:
+    -
+      plugin: explode
+      source: name
+      delimiter: _
+    -
+      plugin: extract
+      index:
+        - 1
+  theme_name:
+    plugin: static_map
+    source: '@legacy_theme_name'
+    bypass: true
+    map:
+      bartik: olivero
+      seven: claro
+  configuration_name:
+    plugin: concat
+    source:
+      - '@theme_name'
+      - constants/config_suffix
+  toggle_logo: theme_settings/toggle_logo
+  toggle_name: value/toggle_name
+  toggle_slogan: value/toggle_slogan
+  toggle_node_user_picture: value/toggle_node_user_picture
+  toggle_comment_user_picture: value/toggle_comment_user_picture
+  toggle_comment_user_verification: value/toggle_comment_user_verification
+  toggle_favicon: value/toggle_favicon
+  default_logo: value/default_logo
+  logo_path: value/logo_path
+  logo_upload: value/logo_upload
+  default_favicon: value/default_favicon
+  favicon_path: value/favicon_path
+  favicon_mimetype: value/favicon_mimetype
+# Ignore settings not present in Drupal 8.
+#  value/favicon_upload
+#  value/toggle_main_menu
+#  value/toggle_secondary_menu
+destination:
+  plugin: d7_theme_settings

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

@@ -0,0 +1,15 @@
+finished:
+  6:
+    menu:
+      - system
+      - menu_link_content
+      - menu_ui
+    system: system
+    # An upgrade path is not needed for jquery_ui.
+    jquery_ui: core
+  7:
+    menu:
+      - system
+      - menu_link_content
+      - menu_ui
+    system: system

web/core/modules/system/migrations/system_image.yml

@@ -0,0 +1,16 @@
+id: system_image
+label: Image toolkit configuration
+migration_tags:
+  - Drupal 6
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - image_toolkit
+  source_module: system
+process:
+  toolkit: image_toolkit
+destination:
+  plugin: config
+  config_name: system.image

web/core/modules/system/migrations/system_image_gd.yml

@@ -0,0 +1,16 @@
+id: system_image_gd
+label: Image quality configuration
+migration_tags:
+  - Drupal 6
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - image_jpeg_quality
+  source_module: system
+process:
+  jpeg_quality: image_jpeg_quality
+destination:
+  plugin: config
+  config_name: system.image.gd

web/core/modules/system/migrations/system_logging.yml

@@ -0,0 +1,24 @@
+id: system_logging
+label: System logging
+migration_tags:
+  - Drupal 6
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - error_level
+  source_module: system
+process:
+  error_level:
+    plugin: static_map
+    source: error_level
+    default_value: all
+    map:
+      0: hide
+      1: some
+      2: all
+      3: verbose
+destination:
+  plugin: config
+  config_name: system.logging

web/core/modules/system/migrations/system_maintenance.yml

@@ -0,0 +1,26 @@
+id: system_maintenance
+label: Maintenance page configuration
+migration_tags:
+  - Drupal 6
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - maintenance_mode_message
+    - site_offline_message
+  source_module: system
+process:
+  message:
+    -
+      plugin: callback
+      callable: array_filter
+      source:
+        - maintenance_mode_message
+        - site_offline_message
+    -
+      plugin: callback
+      callable: current
+destination:
+  plugin: config
+  config_name: system.maintenance

web/core/modules/system/migrations/system_rss.yml

@@ -0,0 +1,16 @@
+id: system_rss
+label: RSS configuration
+migration_tags:
+  - Drupal 6
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  variables:
+    - feed_item_length
+  source_module: system
+process:
+  'items/view_mode': feed_item_length
+destination:
+  plugin: config
+  config_name: system.rss

web/core/modules/system/migrations/system_site.yml

@@ -0,0 +1,70 @@
+id: system_site
+label: Site configuration
+migration_tags:
+  - Drupal 6
+  - Drupal 7
+  - Configuration
+source:
+  plugin: variable
+  constants:
+    slash: '/'
+  variables:
+    - site_name
+    - site_mail
+    - site_slogan
+    - site_frontpage
+    - site_403
+    - site_404
+    - drupal_weight_select_max
+    - admin_compact_mode
+  source_module: system
+process:
+  name: site_name
+  mail: site_mail
+  slogan: site_slogan
+  'page/front':
+    -
+      plugin: concat
+      source:
+        - constants/slash
+        - site_frontpage
+    -
+      plugin: static_map
+      map:
+        # Drupal 6 and Drupal 7 default site_frontpage is 'node'. If this
+        # variable is set to 'node', to an empty string, or it is completely
+        # missing, we want to migrate the equivalent Drupal 9 value, which is
+        # '/node'.
+        '/': '/node'
+      bypass: true
+  'page/403':
+    -
+      plugin: concat
+      source:
+        - constants/slash
+        - site_403
+    -
+      plugin: static_map
+      map:
+        '/': ''
+      bypass: true
+  'page/404':
+    -
+      plugin: concat
+      source:
+        - constants/slash
+        - site_404
+    -
+      plugin: static_map
+      map:
+        '/': ''
+      bypass: true
+  weight_select_max:
+    plugin: default_value
+    source: drupal_weight_select_max
+    strict: true
+    default_value: 100
+  admin_compact_mode: admin_compact_mode
+destination:
+  plugin: config
+  config_name: system.site

web/core/modules/system/src/Access/CronAccessCheck.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace Drupal\system\Access;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Routing\Access\AccessInterface;
+
+/**
+ * Access check for cron routes.
+ */
+class CronAccessCheck implements AccessInterface {
+
+  /**
+   * Checks access.
+   *
+   * @param string $key
+   *   The cron key.
+   *
+   * @return \Drupal\Core\Access\AccessResultInterface
+   *   The access result.
+   */
+  public function access($key) {
+    if ($key != \Drupal::state()->get('system.cron_key')) {
+      \Drupal::logger('cron')->notice('Cron could not run because an invalid key was used.');
+      return AccessResult::forbidden()->setCacheMaxAge(0);
+    }
+    elseif (\Drupal::state()->get('system.maintenance_mode')) {
+      \Drupal::logger('cron')->notice('Cron could not run because the site is in maintenance mode.');
+      return AccessResult::forbidden()->setCacheMaxAge(0);
+    }
+    return AccessResult::allowed()->setCacheMaxAge(0);
+  }
+
+}

web/core/modules/system/src/Access/DbUpdateAccessCheck.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Drupal\system\Access;
+
+use Drupal\Core\Routing\Access\AccessInterface;
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\Site\Settings;
+
+/**
+ * Access check for database update routes.
+ */
+class DbUpdateAccessCheck implements AccessInterface {
+
+  /**
+   * Checks access for update routes.
+   *
+   * @param \Drupal\Core\Session\AccountInterface $account
+   *   The currently logged in account.
+   *
+   * @return \Drupal\Core\Access\AccessResultInterface
+   *   The access result.
+   */
+  public function access(AccountInterface $account) {
+    // Allow the global variable in settings.php to override the access check.
+    if (Settings::get('update_free_access')) {
+      return AccessResult::allowed()->setCacheMaxAge(0);
+    }
+
+    if ($account->hasPermission('administer software updates')) {
+      return AccessResult::allowed()->cachePerPermissions();
+    }
+    else {
+      return AccessResult::forbidden()->cachePerPermissions();
+    }
+  }
+
+}

web/core/modules/system/src/Access/SystemAdminMenuBlockAccessCheck.php

@@ -0,0 +1,122 @@
+<?php
+
+namespace Drupal\system\Access;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Access\AccessResultInterface;
+use Drupal\Core\Menu\MenuLinkInterface;
+use Drupal\Core\Menu\MenuLinkManagerInterface;
+use Drupal\Core\Menu\MenuLinkTreeInterface;
+use Drupal\Core\Menu\MenuTreeParameters;
+use Drupal\Core\Routing\Access\AccessInterface;
+use Drupal\Core\Routing\AccessAwareRouter;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Access check for routes implementing _access_admin_menu_block_page.
+ *
+ * @see \Drupal\system\EventSubscriber\AccessRouteAlterSubscriber
+ * @see \Drupal\system\Controller\SystemController::systemAdminMenuBlockPage()
+ */
+class SystemAdminMenuBlockAccessCheck implements AccessInterface {
+
+  /**
+   * Constructs a new SystemAdminMenuBlockAccessCheck.
+   *
+   * @param \Drupal\Core\Menu\MenuLinkTreeInterface $menuLinkTree
+   *   The menu link tree service.
+   * @param \Drupal\Core\Routing\AccessAwareRouter $router
+   *   The router service.
+   * @param \Drupal\Core\Menu\MenuLinkManagerInterface $menuLinkManager
+   *   The menu link manager service.
+   */
+  public function __construct(
+    private readonly MenuLinkTreeInterface $menuLinkTree,
+    private readonly AccessAwareRouter $router,
+    private readonly MenuLinkManagerInterface $menuLinkManager,
+  ) {
+  }
+
+  /**
+   * Checks access.
+   *
+   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
+   *   The cron key.
+   * @param \Drupal\Core\Session\AccountInterface $account
+   *   The current user.
+   *
+   * @return \Drupal\Core\Access\AccessResultInterface
+   *   The access result.
+   */
+  public function access(RouteMatchInterface $route_match, AccountInterface $account): AccessResultInterface {
+    $parameters = $route_match->getParameters()->all();
+    $route = $route_match->getRouteObject();
+    // Load links in the 'admin' menu matching this route. First, try to find
+    // the menu link using all specified parameters.
+    $links = $this->menuLinkManager->loadLinksByRoute($route_match->getRouteName(), $parameters, 'admin');
+    // If the menu link was not found, try finding it without the parameters
+    // that match the route defaults. Depending on whether the parameter is
+    // specified in the menu item with a value matching the default, or not
+    // specified at all, will change how it is stored in the menu_tree table. In
+    // both cases the route match parameters will always include the default
+    // parameters. This fallback method of finding the menu item is needed so
+    // that menu items will work in either case.
+    // @todo Remove this fallback in https://drupal.org/i/3359511.
+    if (empty($links)) {
+
+      $parameters_without_defaults = array_filter($parameters, fn ($key) => !$route->hasDefault($key) || $route->getDefault($key) !== $parameters[$key], ARRAY_FILTER_USE_KEY);
+      $links = $this->menuLinkManager->loadLinksByRoute($route_match->getRouteName(), $parameters_without_defaults, 'admin');
+    }
+    if (empty($links)) {
+      // If we did not find a link then we have no opinion on access.
+      return AccessResult::neutral();
+    }
+    return $this->hasAccessToChildMenuItems(reset($links), $account)->cachePerPermissions();
+  }
+
+  /**
+   * Check that the given route has access to child routes.
+   *
+   * @param \Drupal\Core\Menu\MenuLinkInterface $link
+   *   The menu link.
+   * @param \Drupal\Core\Session\AccountInterface $account
+   *   The account.
+   *
+   * @return \Drupal\Core\Access\AccessResultInterface
+   *   The access result.
+   */
+  protected function hasAccessToChildMenuItems(MenuLinkInterface $link, AccountInterface $account): AccessResultInterface {
+    $parameters = new MenuTreeParameters();
+    $parameters->setRoot($link->getPluginId())
+      ->excludeRoot()
+      ->setTopLevelOnly()
+      ->onlyEnabledLinks();
+
+    $link_url = $link->getUrlObject();
+    if (!$link_url->isRouted()) {
+      // If the link is not routed, we cannot check access to it.
+      return AccessResult::neutral();
+    }
+
+    $route = $this->router->getRouteCollection()->get($link_url->getRouteName());
+    if ($route && empty($route->getRequirement('_access_admin_menu_block_page')) && empty($route->getRequirement('_access_admin_overview_page'))) {
+      return AccessResult::allowed();
+    }
+
+    foreach ($this->menuLinkTree->load(NULL, $parameters) as $element) {
+      // Skip the link if the user does not have access.
+      if (!$element->link->getUrlObject()->access($account)) {
+        continue;
+      }
+
+      // If access is allowed to this element in the tree, check for access to
+      // any of its own children.
+      if ($this->hasAccessToChildMenuItems($element->link, $account)->isAllowed()) {
+        return AccessResult::allowed();
+      }
+    }
+    return AccessResult::neutral();
+  }
+
+}

web/core/modules/system/src/ActionConfigEntityInterface.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Drupal\system;
+
+use Drupal\Core\Config\Entity\ConfigEntityInterface;
+
+/**
+ * Provides an interface defining an action entity.
+ */
+interface ActionConfigEntityInterface extends ConfigEntityInterface {
+
+  /**
+   * Returns whether or not this action is configurable.
+   *
+   * @return bool
+   *   TRUE if the action is configurable, FALSE otherwise.
+   */
+  public function isConfigurable();
+
+  /**
+   * Returns the operation type.
+   *
+   * The operation type can be NULL if no type is specified.
+   *
+   * @return string|null
+   *   The operation type, or NULL if no type is specified.
+   */
+  public function getType();
+
+  /**
+   * Returns the operation plugin.
+   *
+   * @return \Drupal\Core\Action\ActionInterface
+   *   The action plugin instance.
+   */
+  public function getPlugin();
+
+}

web/core/modules/system/src/Controller/AdminController.php

@@ -0,0 +1,66 @@
+<?php
+
+namespace Drupal\system\Controller;
+
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\Extension\ModuleExtensionList;
+use Drupal\system\ModuleAdminLinksHelper;
+use Drupal\user\ModulePermissionsLinkHelper;
+
+/**
+ * Controller for admin section.
+ */
+class AdminController extends ControllerBase {
+
+  /**
+   * AdminController constructor.
+   */
+  public function __construct(
+    protected ModuleExtensionList $moduleExtensionList,
+    protected ModuleAdminLinksHelper $moduleAdminLinks,
+    protected ModulePermissionsLinkHelper $modulePermissionsLinks,
+  ) {
+  }
+
+  /**
+   * Prints a listing of admin tasks, organized by module.
+   *
+   * @return array
+   *   A render array containing the listing.
+   */
+  public function index() {
+    $extensions = array_intersect_key($this->moduleExtensionList->getList(), $this->moduleHandler()->getModuleList());
+
+    uasort($extensions, [ModuleExtensionList::class, 'sortByName']);
+    $menu_items = [];
+
+    foreach ($extensions as $module => $extension) {
+      // Only display a section if there are any available tasks.
+      $admin_tasks = $this->moduleAdminLinks->getModuleAdminLinks($module);
+      if ($module_permissions_link = $this->modulePermissionsLinks->getModulePermissionsLink($module, $extension->info['name'])) {
+        $admin_tasks["user.admin_permissions.{$module}"] = $module_permissions_link;
+      }
+      if (!empty($admin_tasks)) {
+        // Sort links by title.
+        uasort($admin_tasks, ['\Drupal\Component\Utility\SortArray', 'sortByTitleElement']);
+        // Move 'Configure permissions' links to the bottom of each section.
+        $permission_key = "user.admin_permissions.$module";
+        if (isset($admin_tasks[$permission_key])) {
+          $permission_task = $admin_tasks[$permission_key];
+          unset($admin_tasks[$permission_key]);
+          $admin_tasks[$permission_key] = $permission_task;
+        }
+
+        $menu_items[$extension->info['name']] = [$extension->info['description'], $admin_tasks];
+      }
+    }
+
+    $output = [
+      '#theme' => 'system_admin_index',
+      '#menu_items' => $menu_items,
+    ];
+
+    return $output;
+  }
+
+}

web/core/modules/system/src/Controller/AssetControllerBase.php

@@ -0,0 +1,255 @@
+<?php
+
+namespace Drupal\system\Controller;
+
+use Drupal\Component\Utility\UrlHelper;
+use Drupal\Core\Asset\AssetCollectionGrouperInterface;
+use Drupal\Core\Asset\AssetCollectionOptimizerInterface;
+use Drupal\Core\Asset\AssetDumperUriInterface;
+use Drupal\Core\Asset\AssetGroupSetHashTrait;
+use Drupal\Core\Asset\AssetResolverInterface;
+use Drupal\Core\Asset\AttachedAssets;
+use Drupal\Core\Asset\AttachedAssetsInterface;
+use Drupal\Core\Asset\LibraryDependencyResolverInterface;
+use Drupal\Core\StreamWrapper\StreamWrapperManagerInterface;
+use Drupal\Core\Theme\ThemeInitializationInterface;
+use Drupal\Core\Theme\ThemeManagerInterface;
+use Drupal\system\FileDownloadController;
+use Symfony\Component\HttpFoundation\BinaryFileResponse;
+use Symfony\Component\HttpFoundation\RedirectResponse;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\HttpKernel\Exception\BadRequestHttpException;
+
+/**
+ * Defines a controller to serve asset aggregates.
+ */
+abstract class AssetControllerBase extends FileDownloadController {
+
+  use AssetGroupSetHashTrait;
+
+  /**
+   * The asset type.
+   *
+   * @var string
+   */
+  protected string $assetType;
+
+  /**
+   * The aggregate file extension.
+   *
+   * @var string
+   */
+  protected string $fileExtension;
+
+  /**
+   * The asset aggregate content type to send as Content-Type header.
+   *
+   * @var string
+   */
+  protected string $contentType;
+
+  /**
+   * The cache control header to use.
+   *
+   * Headers sent from PHP can never perfectly match those sent when the
+   * file is served by the filesystem, so ensure this request does not get
+   * cached in either the browser or reverse proxies. Subsequent requests
+   * for the file will be served from disk and be cached. This is done to
+   * avoid situations such as where one CDN endpoint is serving a version
+   * cached from PHP, while another is serving a version cached from disk.
+   * Should there be any discrepancy in behavior between those files, this
+   * can make debugging very difficult.
+   */
+  protected const CACHE_CONTROL = 'private, no-store';
+
+  /**
+   * Constructs an object derived from AssetControllerBase.
+   *
+   * @param \Drupal\Core\StreamWrapper\StreamWrapperManagerInterface $streamWrapperManager
+   *   The stream wrapper manager.
+   * @param \Drupal\Core\Asset\LibraryDependencyResolverInterface $libraryDependencyResolver
+   *   The library dependency resolver.
+   * @param \Drupal\Core\Asset\AssetResolverInterface $assetResolver
+   *   The asset resolver.
+   * @param \Drupal\Core\Theme\ThemeInitializationInterface $themeInitialization
+   *   The theme initializer.
+   * @param \Drupal\Core\Theme\ThemeManagerInterface $themeManager
+   *   The theme manager.
+   * @param \Drupal\Core\Asset\AssetCollectionGrouperInterface $grouper
+   *   The asset grouper.
+   * @param \Drupal\Core\Asset\AssetCollectionOptimizerInterface $optimizer
+   *   The asset collection optimizer.
+   * @param \Drupal\Core\Asset\AssetDumperUriInterface $dumper
+   *   The asset dumper.
+   */
+  public function __construct(
+    StreamWrapperManagerInterface $streamWrapperManager,
+    protected readonly LibraryDependencyResolverInterface $libraryDependencyResolver,
+    protected readonly AssetResolverInterface $assetResolver,
+    protected readonly ThemeInitializationInterface $themeInitialization,
+    protected readonly ThemeManagerInterface $themeManager,
+    protected readonly AssetCollectionGrouperInterface $grouper,
+    protected readonly AssetCollectionOptimizerInterface $optimizer,
+    protected readonly AssetDumperUriInterface $dumper,
+  ) {
+    parent::__construct($streamWrapperManager);
+    $this->fileExtension = $this->assetType;
+  }
+
+  /**
+   * Generates an aggregate, given a filename.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The request object.
+   * @param string $file_name
+   *   The file to deliver.
+   *
+   * @return \Symfony\Component\HttpFoundation\BinaryFileResponse|\Symfony\Component\HttpFoundation\Response
+   *   The transferred file as response.
+   *
+   * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
+   *   Thrown when the filename is invalid or an invalid query argument is
+   *   supplied.
+   */
+  public function deliver(Request $request, string $file_name) {
+    $uri = 'assets://' . $this->assetType . '/' . $file_name;
+
+    // Check to see whether a file matching the $uri already exists, this can
+    // happen if it was created while this request was in progress.
+    if (file_exists($uri)) {
+      return new BinaryFileResponse($uri, 200, [
+        'Cache-control' => static::CACHE_CONTROL,
+      ]);
+    }
+
+    // First validate that the request is valid enough to produce an asset group
+    // aggregate. The theme must be passed as a query parameter, since assets
+    // always depend on the current theme.
+    if (!$request->query->has('theme')) {
+      throw new BadRequestHttpException('The theme must be passed as a query argument');
+    }
+    if (!$request->query->has('delta') || !is_numeric($request->query->get('delta'))) {
+      throw new BadRequestHttpException('The numeric delta must be passed as a query argument');
+    }
+    if (!$request->query->has('language')) {
+      throw new BadRequestHttpException('The language must be passed as a query argument');
+    }
+    if (!$request->query->has('include')) {
+      throw new BadRequestHttpException('The libraries to include must be passed as a query argument');
+    }
+    $file_parts = explode('_', basename($file_name, '.' . $this->fileExtension), 2);
+    // Ensure the filename is correctly prefixed.
+    if ($file_parts[0] !== $this->fileExtension) {
+      throw new BadRequestHttpException('The filename prefix must match the file extension');
+    }
+
+    // The hash is the second segment of the filename.
+    if (!isset($file_parts[1])) {
+      throw new BadRequestHttpException('Invalid filename');
+    }
+    $received_hash = $file_parts[1];
+
+    // Now build the asset groups based on the libraries.  It requires the full
+    // set of asset groups to extract and build the aggregate for the group we
+    // want, since libraries may be split across different asset groups.
+    $theme = $request->query->get('theme');
+    $active_theme = $this->themeInitialization->initTheme($theme);
+    $this->themeManager->setActiveTheme($active_theme);
+
+    $attached_assets = new AttachedAssets();
+    $include_libraries = explode(',', UrlHelper::uncompressQueryParameter($request->query->get('include')));
+
+    // Check that library names are in the correct format.
+    $validate = function ($libraries_to_check) {
+      foreach ($libraries_to_check as $library) {
+        if (substr_count($library, '/') === 0) {
+          throw new BadRequestHttpException(sprintf('The "%s" library name must include at least one slash.', $library));
+        }
+      }
+    };
+    $validate($include_libraries);
+    $attached_assets->setLibraries($include_libraries);
+
+    if ($request->query->has('exclude')) {
+      $exclude_libraries = explode(',', UrlHelper::uncompressQueryParameter($request->query->get('exclude')));
+      $validate($exclude_libraries);
+      $attached_assets->setAlreadyLoadedLibraries($exclude_libraries);
+    }
+    $groups = $this->getGroups($attached_assets, $request);
+
+    $group = $this->getGroup($groups, $request->query->get('delta'));
+    // Generate a hash based on the asset group, this uses the same method as
+    // the collection optimizer does to create the filename, so it should match.
+    $generated_hash = $this->generateHash($group);
+    $data = $this->optimizer->optimizeGroup($group);
+
+    $response = new Response($data, 200, [
+      'Cache-control' => static::CACHE_CONTROL,
+      'Content-Type' => $this->contentType,
+    ]);
+
+    // However, the hash from the library definitions in code may not match the
+    // hash from the URL. This can be for three reasons:
+    // 1. Someone has requested an outdated URL, i.e. from a cached page, which
+    // matches a different version of the code base.
+    // 2. Someone has requested an outdated URL during a deployment. This is
+    // the same case as #1 but a much shorter window.
+    // 3. Someone is attempting to craft an invalid URL in order to conduct a
+    // denial of service attack on the site.
+    // Dump the optimized group into an aggregate file, but only if the
+    // received hash and generated hash match. This prevents invalid filenames
+    // from filling the disk, while still serving aggregates that may be
+    // referenced in cached HTML.
+    if (hash_equals($generated_hash, $received_hash)) {
+      $this->dumper->dumpToUri($data, $this->assetType, $uri);
+    }
+    else {
+      $expected_filename = $this->fileExtension . '_' . $generated_hash . '.' . $this->fileExtension;
+      $response = new RedirectResponse(
+        str_replace($file_name, $expected_filename, $request->getRequestUri()),
+        301,
+        ['Cache-Control' => 'public, max-age=3600, must-revalidate'],
+      );
+    }
+    return $response;
+  }
+
+  /**
+   * Gets a group.
+   *
+   * @param array $groups
+   *   An array of asset groups.
+   * @param int $group_delta
+   *   The group delta.
+   *
+   * @return array
+   *   The correct asset group matching $group_delta.
+   *
+   * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
+   *   Thrown when the filename is invalid.
+   */
+  protected function getGroup(array $groups, int $group_delta): array {
+    if (isset($groups[$group_delta])) {
+      return $groups[$group_delta];
+    }
+    throw new BadRequestHttpException('Invalid filename.');
+  }
+
+  /**
+   * Get grouped assets.
+   *
+   * @param \Drupal\Core\Asset\AttachedAssetsInterface $attached_assets
+   *   The attached assets.
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request.
+   *
+   * @return array
+   *   The grouped assets.
+   *
+   * @throws \Symfony\Component\HttpKernel\Exception\BadRequestHttpException
+   *   Thrown when the query argument is omitted.
+   */
+  abstract protected function getGroups(AttachedAssetsInterface $attached_assets, Request $request): array;
+
+}

web/core/modules/system/src/Controller/BatchController.php

@@ -0,0 +1,107 @@
+<?php
+
+namespace Drupal\system\Controller;
+
+use Drupal\Core\Batch\BatchStorageInterface;
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException;
+
+/**
+ * Controller routines for batch routes.
+ */
+class BatchController implements ContainerInjectionInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * Constructs a new BatchController.
+   */
+  public function __construct(
+    protected string $root,
+    protected BatchStorageInterface $batchStorage,
+  ) {
+    require_once $this->root . '/core/includes/batch.inc';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->getParameter('app.root'),
+      $container->get('batch.storage'),
+    );
+  }
+
+  /**
+   * Returns a system batch page.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request object.
+   *
+   * @return \Symfony\Component\HttpFoundation\Response|array
+   *   A \Symfony\Component\HttpFoundation\Response object or render array.
+   *
+   * @throws \Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException
+   */
+  public function batchPage(Request $request) {
+    $output = _batch_page($request);
+
+    if ($output === FALSE) {
+      throw new AccessDeniedHttpException();
+    }
+    elseif ($output instanceof Response) {
+      return $output;
+    }
+    elseif (isset($output)) {
+      $title = $output['#title'] ?? NULL;
+      $page = [
+        '#type' => 'page',
+        '#title' => $title,
+        '#show_messages' => FALSE,
+        'content' => $output,
+      ];
+
+      // Also inject title as a page header (if available).
+      if ($title) {
+        $page['header'] = [
+          '#type' => 'page_title',
+          '#title' => $title,
+        ];
+      }
+
+      return $page;
+    }
+  }
+
+  /**
+   * The _title_callback for the system.batch_page.html route.
+   *
+   * @return string
+   *   The page title.
+   */
+  public function batchPageTitle(Request $request) {
+    $batch = &batch_get();
+
+    if (!($request_id = $request->query->get('id'))) {
+      return '';
+    }
+
+    // Retrieve the current state of the batch.
+    if (!$batch) {
+      $batch = $this->batchStorage->load($request_id);
+    }
+
+    if (!$batch) {
+      return '';
+    }
+
+    $current_set = _batch_current_set();
+    return !empty($current_set['title']) ? $current_set['title'] : '';
+  }
+
+}

web/core/modules/system/src/Controller/CsrfTokenController.php

@@ -0,0 +1,52 @@
+<?php
+
+namespace Drupal\system\Controller;
+
+use Drupal\Core\Access\CsrfRequestHeaderAccessCheck;
+use Drupal\Core\Access\CsrfTokenGenerator;
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpFoundation\Response;
+
+/**
+ * Returns responses for CSRF token routes.
+ */
+class CsrfTokenController implements ContainerInjectionInterface {
+
+  /**
+   * The CSRF token generator.
+   *
+   * @var \Drupal\Core\Access\CsrfTokenGenerator
+   */
+  protected $tokenGenerator;
+
+  /**
+   * Constructs a new CsrfTokenController object.
+   *
+   * @param \Drupal\Core\Access\CsrfTokenGenerator $token_generator
+   *   The CSRF token generator.
+   */
+  public function __construct(CsrfTokenGenerator $token_generator) {
+    $this->tokenGenerator = $token_generator;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('csrf_token')
+    );
+  }
+
+  /**
+   * Returns a CSRF protecting session token.
+   *
+   * @return \Symfony\Component\HttpFoundation\Response
+   *   The response object.
+   */
+  public function csrfToken() {
+    return new Response($this->tokenGenerator->get(CsrfRequestHeaderAccessCheck::TOKEN_KEY), 200, ['Content-Type' => 'text/plain']);
+  }
+
+}

web/core/modules/system/src/Controller/CssAssetController.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace Drupal\system\Controller;
+
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpFoundation\Request;
+
+use Drupal\Core\Asset\AttachedAssetsInterface;
+use Drupal\Core\Asset\AssetGroupSetHashTrait;
+
+/**
+ * Defines a controller to serve CSS aggregates.
+ */
+class CssAssetController extends AssetControllerBase {
+
+  use AssetGroupSetHashTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected string $contentType = 'text/css';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected string $assetType = 'css';
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('stream_wrapper_manager'),
+      $container->get('library.dependency_resolver'),
+      $container->get('asset.resolver'),
+      $container->get('theme.initialization'),
+      $container->get('theme.manager'),
+      $container->get('asset.css.collection_grouper'),
+      $container->get('asset.css.collection_optimizer'),
+      $container->get('asset.css.dumper'),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getGroups(AttachedAssetsInterface $attached_assets, Request $request): array {
+    $language = $this->languageManager()->getLanguage($request->get('language'));
+    $assets = $this->assetResolver->getCssAssets($attached_assets, FALSE, $language);
+    return $this->grouper->group($assets);
+  }
+
+}

web/core/modules/system/src/Controller/DbUpdateController.php

@@ -0,0 +1,739 @@
+<?php
+
+namespace Drupal\system\Controller;
+
+use Drupal\Core\Asset\AssetQueryStringInterface;
+use Drupal\Core\Batch\BatchBuilder;
+use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Extension\Requirement\RequirementSeverity;
+use Drupal\Core\KeyValueStore\KeyValueExpirableFactoryInterface;
+use Drupal\Core\Render\BareHtmlPageRendererInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\Site\Settings;
+use Drupal\Core\State\StateInterface;
+use Drupal\Core\Update\UpdateRegistry;
+use Drupal\Core\Url;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+
+/**
+ * Controller routines for database update routes.
+ */
+class DbUpdateController extends ControllerBase {
+
+  /**
+   * The keyvalue expirable factory.
+   *
+   * @var \Drupal\Core\KeyValueStore\KeyValueExpirableFactoryInterface
+   */
+  protected $keyValueExpirableFactory;
+
+  /**
+   * A cache backend interface.
+   *
+   * @var \Drupal\Core\Cache\CacheBackendInterface
+   */
+  protected $cache;
+
+  /**
+   * The state service.
+   *
+   * @var \Drupal\Core\State\StateInterface
+   */
+  protected $state;
+
+  /**
+   * The module handler.
+   *
+   * @var \Drupal\Core\Extension\ModuleHandlerInterface
+   */
+  protected $moduleHandler;
+
+  /**
+   * The current user.
+   *
+   * @var \Drupal\Core\Session\AccountInterface
+   */
+  protected $account;
+
+  /**
+   * The bare HTML page renderer.
+   *
+   * @var \Drupal\Core\Render\BareHtmlPageRendererInterface
+   */
+  protected $bareHtmlPageRenderer;
+
+  /**
+   * The app root.
+   *
+   * @var string
+   */
+  protected $root;
+
+  /**
+   * The post update registry.
+   *
+   * @var \Drupal\Core\Update\UpdateRegistry
+   */
+  protected $postUpdateRegistry;
+
+  /**
+   * Constructs a new UpdateController.
+   *
+   * @param string $root
+   *   The app root.
+   * @param \Drupal\Core\KeyValueStore\KeyValueExpirableFactoryInterface $key_value_expirable_factory
+   *   The keyvalue expirable factory.
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache
+   *   A cache backend interface.
+   * @param \Drupal\Core\State\StateInterface $state
+   *   The state service.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   *   The module handler.
+   * @param \Drupal\Core\Session\AccountInterface $account
+   *   The current user.
+   * @param \Drupal\Core\Render\BareHtmlPageRendererInterface $bare_html_page_renderer
+   *   The bare HTML page renderer.
+   * @param \Drupal\Core\Update\UpdateRegistry $post_update_registry
+   *   The post update registry.
+   * @param \Drupal\Core\Asset\AssetQueryStringInterface $assetQueryString
+   *   The asset query string.
+   */
+  public function __construct(
+    $root,
+    KeyValueExpirableFactoryInterface $key_value_expirable_factory,
+    CacheBackendInterface $cache,
+    StateInterface $state,
+    ModuleHandlerInterface $module_handler,
+    AccountInterface $account,
+    BareHtmlPageRendererInterface $bare_html_page_renderer,
+    UpdateRegistry $post_update_registry,
+    protected AssetQueryStringInterface $assetQueryString,
+  ) {
+    $this->root = $root;
+    $this->keyValueExpirableFactory = $key_value_expirable_factory;
+    $this->cache = $cache;
+    $this->state = $state;
+    $this->moduleHandler = $module_handler;
+    $this->account = $account;
+    $this->bareHtmlPageRenderer = $bare_html_page_renderer;
+    $this->postUpdateRegistry = $post_update_registry;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->getParameter('app.root'),
+      $container->get('keyvalue.expirable'),
+      $container->get('cache.default'),
+      $container->get('state'),
+      $container->get('module_handler'),
+      $container->get('current_user'),
+      $container->get('bare_html_page_renderer'),
+      $container->get('update.post_update_registry'),
+      $container->get('asset.query_string')
+    );
+  }
+
+  /**
+   * Returns a database update page.
+   *
+   * @param string $op
+   *   The update operation to perform. Can be any of the below:
+   *    - "info".
+   *    - "selection".
+   *    - "run".
+   *    - "results".
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request object.
+   *
+   * @return \Symfony\Component\HttpFoundation\Response
+   *   A response object.
+   */
+  public function handle($op, Request $request) {
+    require_once $this->root . '/core/includes/install.inc';
+    require_once $this->root . '/core/includes/update.inc';
+
+    drupal_load_updates();
+
+    if ($request->query->get('continue')) {
+      $request->getSession()->set('update_ignore_warnings', TRUE);
+    }
+
+    $regions = [];
+    $requirements = update_check_requirements();
+    $severity = RequirementSeverity::maxSeverityFromRequirements($requirements);
+    if ($severity === RequirementSeverity::Error || ($severity === RequirementSeverity::Warning && !$request->getSession()->has('update_ignore_warnings'))) {
+      $regions['sidebar_first'] = $this->updateTasksList('requirements');
+      $output = $this->requirements($severity, $requirements, $request);
+    }
+    else {
+      switch ($op) {
+        case 'selection':
+          $regions['sidebar_first'] = $this->updateTasksList('selection');
+          $output = $this->selection($request);
+          break;
+
+        case 'run':
+          $regions['sidebar_first'] = $this->updateTasksList('run');
+          $output = $this->triggerBatch($request);
+          break;
+
+        case 'info':
+          $regions['sidebar_first'] = $this->updateTasksList('info');
+          $output = $this->info($request);
+          break;
+
+        case 'results':
+          $regions['sidebar_first'] = $this->updateTasksList('results');
+          $output = $this->results($request);
+          break;
+
+        // Regular batch ops : defer to batch processing API.
+        default:
+          require_once $this->root . '/core/includes/batch.inc';
+          $regions['sidebar_first'] = $this->updateTasksList('run');
+          $output = _batch_page($request);
+          break;
+      }
+    }
+
+    if ($output instanceof Response) {
+      return $output;
+    }
+    $title = $output['#title'] ?? $this->t('Drupal database update');
+
+    return $this->bareHtmlPageRenderer->renderBarePage($output, $title, 'maintenance_page', $regions);
+  }
+
+  /**
+   * Returns the info database update page.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request.
+   *
+   * @return array
+   *   A render array.
+   */
+  protected function info(Request $request) {
+    // Change query-strings on css/js files to enforce reload for all users.
+    $this->assetQueryString->reset();
+    // Flush the cache of all data for the update status module.
+    $this->keyValueExpirableFactory->get('update')->deleteAll();
+    $this->keyValueExpirableFactory->get('update_available_release')->deleteAll();
+
+    $build['info_header'] = [
+      '#markup' => '<p>' . $this->t('Use this utility to update your database whenever a module, theme, or the core software is updated.') . '</p><p>' . $this->t('For more detailed information, see the <a href="https://www.drupal.org/docs/updating-drupal">Updating Drupal guide</a>. If you are unsure what these terms mean you should probably contact your hosting provider.') . '</p>',
+    ];
+
+    $info[] = $this->t("<strong>Back up your code</strong>. Hint: when backing up module code, do not leave that backup in the 'modules' or 'sites/*/modules' directories as this may confuse Drupal's auto-discovery mechanism.");
+    // @todo Simplify with https://www.drupal.org/node/2548095
+    $base_url = str_replace('/update.php', '', $request->getBaseUrl());
+    $info[] = $this->t('Put your site into <a href=":url">maintenance mode</a>.', [
+      ':url' => Url::fromRoute('system.site_maintenance_mode')->setOption('base_url', $base_url)->toString(TRUE)->getGeneratedUrl(),
+    ]);
+    $info[] = $this->t('<strong>Back up your database</strong>. This process will change your database values and in case of emergency you may need to revert to a backup.');
+    $info[] = $this->t('Update your files (as described in the handbook page linked above).');
+    $build['info'] = [
+      '#theme' => 'item_list',
+      '#list_type' => 'ol',
+      '#items' => $info,
+    ];
+    $build['info_footer'] = [
+      '#markup' => '<p>' . $this->t('When you have performed the steps above, you may proceed.') . '</p>',
+    ];
+
+    $build['link'] = [
+      '#type' => 'link',
+      '#title' => $this->t('Continue'),
+      '#attributes' => ['class' => ['button', 'button--primary']],
+      // @todo Revisit once https://www.drupal.org/node/2548095 is in.
+      '#url' => Url::fromUri('base://selection'),
+    ];
+    return $build;
+  }
+
+  /**
+   * Renders a list of available database updates.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request.
+   *
+   * @return array
+   *   A render array.
+   */
+  protected function selection(Request $request) {
+    // Make sure there is no stale theme registry.
+    $this->cache->deleteAll();
+
+    $count = 0;
+    $incompatible_count = 0;
+    $build['start'] = [
+      '#tree' => TRUE,
+      '#type' => 'details',
+    ];
+
+    // Ensure system.module's updates appear first.
+    $build['start']['system'] = [];
+
+    $starting_updates = [];
+    $incompatible_updates_exist = FALSE;
+    $updates_per_extension = [];
+    foreach (['update', 'post_update'] as $update_type) {
+      switch ($update_type) {
+        case 'update':
+          $updates = update_get_update_list();
+          break;
+
+        case 'post_update':
+          $updates = $this->postUpdateRegistry->getPendingUpdateInformation();
+          break;
+      }
+      foreach ($updates as $extension => $update) {
+        if (!isset($update['start'])) {
+          $build['start'][$extension] = [
+            '#type' => 'item',
+            '#title' => $extension . ($this->moduleHandler->moduleExists($extension) ? ' module' : ' theme'),
+            '#markup' => $update['warning'],
+            '#prefix' => '<div class="messages messages--warning">',
+            '#suffix' => '</div>',
+          ];
+          $incompatible_updates_exist = TRUE;
+          continue;
+        }
+        if (!empty($update['pending'])) {
+          $updates_per_extension += [$extension => []];
+          $updates_per_extension[$extension] = array_merge($updates_per_extension[$extension], $update['pending']);
+          $build['start'][$extension] = [
+            '#type' => 'hidden',
+            '#value' => $update['start'],
+          ];
+          // Store the previous items in order to merge normal updates and
+          // post_update functions together.
+          $build['start'][$extension] = [
+            '#theme' => 'item_list',
+            '#items' => $updates_per_extension[$extension],
+            '#title' => $extension . ($this->moduleHandler->moduleExists($extension) ? ' module' : ' theme'),
+          ];
+
+          if ($update_type === 'update') {
+            $starting_updates[$extension] = $update['start'];
+          }
+        }
+        if (isset($update['pending'])) {
+          $count = $count + count($update['pending']);
+        }
+      }
+    }
+
+    // Find and label any incompatible updates.
+    foreach (update_resolve_dependencies($starting_updates) as $data) {
+      if (!$data['allowed']) {
+        $incompatible_updates_exist = TRUE;
+        $incompatible_count++;
+        $module_update_key = $data['module'] . '_updates';
+        if (isset($build['start'][$module_update_key]['#items'][$data['number']])) {
+          if ($data['missing_dependencies']) {
+            $text = $this->t('This update will been skipped due to the following missing dependencies:') . '<em>' . implode(', ', $data['missing_dependencies']) . '</em>';
+          }
+          else {
+            $text = $this->t("This update will be skipped due to an error in the module's code.");
+          }
+          $build['start'][$module_update_key]['#items'][$data['number']] .= '<div class="warning">' . $text . '</div>';
+        }
+        // Move the module containing this update to the top of the list.
+        $build['start'] = [$module_update_key => $build['start'][$module_update_key]] + $build['start'];
+      }
+    }
+
+    // Warn the user if any updates were incompatible.
+    if ($incompatible_updates_exist) {
+      $this->messenger()->addWarning($this->t('Some of the pending updates cannot be applied because their dependencies were not met.'));
+    }
+
+    if (empty($count)) {
+      $this->messenger()->addStatus($this->t('No pending updates.'));
+      unset($build);
+      $build['links'] = [
+        '#theme' => 'links',
+        '#links' => $this->helpfulLinks($request),
+      ];
+
+      // No updates to run, so caches won't get flushed later.  Clear them now.
+      drupal_flush_all_caches();
+    }
+    else {
+      $build['help'] = [
+        '#markup' => '<p>' . $this->t('The version of Drupal you are updating from has been automatically detected.') . '</p>',
+        '#weight' => -5,
+      ];
+      if ($incompatible_count) {
+        $build['start']['#title'] = $this->formatPlural(
+          $count,
+          '1 pending update (@number_applied to be applied, @number_incompatible skipped)',
+          '@count pending updates (@number_applied to be applied, @number_incompatible skipped)',
+          ['@number_applied' => $count - $incompatible_count, '@number_incompatible' => $incompatible_count]
+        );
+      }
+      else {
+        $build['start']['#title'] = $this->formatPlural($count, '1 pending update', '@count pending updates');
+      }
+      // @todo Simplify with https://www.drupal.org/node/2548095
+      $base_url = str_replace('/update.php', '', $request->getBaseUrl());
+      $url = (new Url('system.db_update', ['op' => 'run']))->setOption('base_url', $base_url);
+      $build['link'] = [
+        '#type' => 'link',
+        '#title' => $this->t('Apply pending updates'),
+        '#attributes' => ['class' => ['button', 'button--primary']],
+        '#weight' => 5,
+        '#url' => $url,
+        '#access' => $url->access($this->currentUser()),
+      ];
+    }
+
+    return $build;
+  }
+
+  /**
+   * Displays results of the update script with any accompanying errors.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request.
+   *
+   * @return array
+   *   A render array.
+   */
+  protected function results(Request $request) {
+    // @todo Simplify with https://www.drupal.org/node/2548095
+    $base_url = str_replace('/update.php', '', $request->getBaseUrl());
+
+    // Retrieve and remove session information.
+    $session = $request->getSession();
+    $update_results = $session->remove('update_results');
+    $update_success = $session->remove('update_success');
+    $session->remove('update_ignore_warnings');
+
+    // Report end result.
+    $dblog_exists = $this->moduleHandler->moduleExists('dblog');
+    if ($dblog_exists && $this->account->hasPermission('access site reports')) {
+      $log_message = $this->t('All errors have been <a href=":url">logged</a>.', [
+        ':url' => Url::fromRoute('dblog.overview')->setOption('base_url', $base_url)->toString(TRUE)->getGeneratedUrl(),
+      ]);
+    }
+    else {
+      $log_message = $this->t('All errors have been logged.');
+    }
+
+    if ($update_success) {
+      $message = '<p>' . $this->t('Updates were attempted. If you see no failures below, you may proceed happily back to your <a href=":url">site</a>. Otherwise, you may need to update your database manually.', [':url' => Url::fromRoute('<front>')->setOption('base_url', $base_url)->toString(TRUE)->getGeneratedUrl()]) . ' ' . $log_message . '</p>';
+    }
+    else {
+      $last = $session->get('updates_remaining');
+      $last = reset($last);
+      [$module, $version] = array_pop($last);
+      $message = '<p class="error">' . $this->t('The update process was aborted prematurely while running <strong>update #@version in @module.module</strong>.', [
+        '@version' => $version,
+        '@module' => $module,
+      ]) . ' ' . $log_message;
+      if ($dblog_exists) {
+        $message .= ' ' . $this->t('You may need to check the <code>watchdog</code> database table manually.');
+      }
+      $message .= '</p>';
+    }
+
+    if (Settings::get('update_free_access')) {
+      $message .= '<p>' . $this->t("<strong>Reminder: don't forget to set the <code>\$settings['update_free_access']</code> value in your <code>settings.php</code> file back to <code>FALSE</code>.</strong>") . '</p>';
+    }
+
+    $build['message'] = [
+      '#markup' => $message,
+    ];
+    $build['links'] = [
+      '#theme' => 'links',
+      '#links' => $this->helpfulLinks($request),
+    ];
+
+    // Output a list of info messages.
+    if (!empty($update_results)) {
+      $all_messages = [];
+      foreach ($update_results as $extension => $updates) {
+        if ($extension != '#abort') {
+          $extension_has_message = FALSE;
+          $info_messages = [];
+          foreach ($updates as $name => $queries) {
+            $messages = [];
+            foreach ($queries as $query) {
+              // If there is no message for this update, don't show anything.
+              if (empty($query['query'])) {
+                continue;
+              }
+
+              if ($query['success']) {
+                $messages[] = [
+                  '#wrapper_attributes' => ['class' => ['success']],
+                  '#markup' => $query['query'],
+                ];
+              }
+              else {
+                $messages[] = [
+                  '#wrapper_attributes' => ['class' => ['failure']],
+                  '#markup' => '<strong>' . $this->t('Failed:') . '</strong> ' . $query['query'],
+                ];
+              }
+            }
+
+            if ($messages) {
+              $extension_has_message = TRUE;
+              if (is_numeric($name)) {
+                $title = $this->t('Update #@count', ['@count' => $name]);
+              }
+              else {
+                $title = $this->t('Update @name', ['@name' => trim($name, '_')]);
+              }
+              $info_messages[] = [
+                '#theme' => 'item_list',
+                '#items' => $messages,
+                '#title' => $title,
+              ];
+            }
+          }
+
+          // If there were any messages then prefix them with the extension name
+          // and add it to the global message list.
+          if ($extension_has_message) {
+            $header = $this->moduleHandler->moduleExists($extension) ?
+              $this->t('@module module', ['@module' => $extension]) :
+              $this->t('@theme theme', ['@theme' => $extension]);
+            $all_messages[] = [
+              '#type' => 'container',
+              '#prefix' => '<h3>' . $header . '</h3>',
+              '#children' => $info_messages,
+            ];
+          }
+        }
+      }
+      if ($all_messages) {
+        $build['query_messages'] = [
+          '#type' => 'container',
+          '#children' => $all_messages,
+          '#attributes' => ['class' => ['update-results']],
+          '#prefix' => '<h2>' . $this->t('The following updates returned messages:') . '</h2>',
+        ];
+      }
+    }
+
+    return $build;
+  }
+
+  /**
+   * Renders a list of requirement errors or warnings.
+   *
+   * @param int $severity
+   *   The severity of the message, as per RFC 3164.
+   * @param array $requirements
+   *   The array of requirement values.
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request.
+   *
+   * @return array
+   *   A render array.
+   */
+  public function requirements($severity, array $requirements, Request $request) {
+    $options = $severity === RequirementSeverity::Warning ? ['continue' => 1] : [];
+    // @todo Revisit once https://www.drupal.org/node/2548095 is in. Something
+    // like Url::fromRoute('system.db_update')->setOptions() should then be
+    // possible.
+    $try_again_url = Url::fromUri($request->getUriForPath(''))->setOptions(['query' => $options])->toString(TRUE)->getGeneratedUrl();
+
+    $build['status_report'] = [
+      '#type' => 'status_report',
+      '#requirements' => $requirements,
+      '#suffix' => $this->t('Check the messages and <a href=":url">try again</a>.', [':url' => $try_again_url]),
+    ];
+
+    $build['#title'] = $this->t('Requirements problem');
+    return $build;
+  }
+
+  /**
+   * Provides the update task list render array.
+   *
+   * @param string $active
+   *   The active task.
+   *   Can be one of 'requirements', 'info', 'selection', 'run', 'results'.
+   *
+   * @return array
+   *   A render array.
+   */
+  protected function updateTasksList($active = NULL) {
+    // Default list of tasks.
+    $tasks = [
+      'requirements' => $this->t('Verify requirements'),
+      'info' => $this->t('Overview'),
+      'selection' => $this->t('Review updates'),
+      'run' => $this->t('Run updates'),
+      'results' => $this->t('Review log'),
+    ];
+
+    $task_list = [
+      '#theme' => 'maintenance_task_list',
+      '#items' => $tasks,
+      '#active' => $active,
+    ];
+    return $task_list;
+  }
+
+  /**
+   * Starts the database update batch process.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request object.
+   */
+  protected function triggerBatch(Request $request) {
+    $maintenance_mode = $this->state->get('system.maintenance_mode', FALSE);
+    // Store the current maintenance mode status in the session so that it can
+    // be restored at the end of the batch.
+    $request->getSession()->set('maintenance_mode', $maintenance_mode);
+    // During the update, always put the site into maintenance mode so that
+    // in-progress schema changes do not affect visiting users.
+    if (empty($maintenance_mode)) {
+      $this->state->set('system.maintenance_mode', TRUE);
+    }
+
+    /** @var \Drupal\Core\Batch\BatchBuilder $batch_builder */
+    $batch_builder = (new BatchBuilder())
+      ->setTitle($this->t('Updating'))
+      ->setInitMessage($this->t('Starting updates'))
+      ->setErrorMessage($this->t('An unrecoverable error has occurred. You can find the error message below. It is advised to copy it to the clipboard for reference.'))
+      ->setFinishCallback([DbUpdateController::class, 'batchFinished']);
+
+    // Resolve any update dependencies to determine the actual updates that will
+    // be run and the order they will be run in.
+    $start = $this->getModuleUpdates();
+    $updates = update_resolve_dependencies($start);
+
+    // Store the dependencies for each update function in an array which the
+    // batch API can pass in to the batch operation each time it is called. (We
+    // do not store the entire update dependency array here because it is
+    // potentially very large.)
+    $dependency_map = [];
+    foreach ($updates as $function => $update) {
+      $dependency_map[$function] = !empty($update['reverse_paths']) ? array_keys($update['reverse_paths']) : [];
+    }
+
+    // Determine updates to be performed.
+    foreach ($updates as $function => $update) {
+      if ($update['allowed']) {
+        // Set the installed version of each module so updates will start at the
+        // correct place. (The updates are already sorted, so we can simply base
+        // this on the first one we come across in the above foreach loop.)
+        if (isset($start[$update['module']])) {
+          \Drupal::service('update.update_hook_registry')->setInstalledVersion($update['module'], $update['number'] - 1);
+          unset($start[$update['module']]);
+        }
+        $batch_builder->addOperation('update_do_one', [$update['module'], $update['number'], $dependency_map[$function]]);
+      }
+    }
+
+    $post_updates = $this->postUpdateRegistry->getPendingUpdateFunctions();
+
+    if ($post_updates) {
+      // Now we rebuild all caches and after that execute the hook_post_update()
+      // functions.
+      $batch_builder->addOperation('drupal_flush_all_caches', []);
+      foreach ($post_updates as $function) {
+        $batch_builder->addOperation('update_invoke_post_update', [$function]);
+      }
+    }
+
+    batch_set($batch_builder->toArray());
+
+    // @todo Revisit once https://www.drupal.org/node/2548095 is in.
+    return batch_process(Url::fromUri('base://results'), Url::fromUri('base://start'));
+  }
+
+  /**
+   * Finishes the update process and stores the results for eventual display.
+   *
+   * After the updates run, all caches are flushed. The update results are
+   * stored into the session (for example, to be displayed on the update results
+   * page in update.php). Additionally, if the site was off-line, now that the
+   * update process is completed, the site is set back online.
+   *
+   * @param bool $success
+   *   Indicate that the batch API tasks were all completed successfully.
+   * @param array $results
+   *   An array of all the results that were updated in update_do_one().
+   * @param array $operations
+   *   A list of all the operations that had not been completed by the batch
+   *   API.
+   */
+  public static function batchFinished($success, $results, $operations) {
+    // No updates to run, so caches won't get flushed later.  Clear them now.
+    drupal_flush_all_caches();
+
+    $session = \Drupal::request()->getSession();
+    $session->set('update_results', $results);
+    $session->set('update_success', $success);
+    $session->set('updates_remaining', $operations);
+
+    // Now that the update is done, we can put the site back online if it was
+    // previously not in maintenance mode.
+    if (!$session->remove('maintenance_mode')) {
+      \Drupal::state()->set('system.maintenance_mode', FALSE);
+    }
+  }
+
+  /**
+   * Provides links to the homepage and administration pages.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request.
+   *
+   * @return array
+   *   An array of links.
+   */
+  protected function helpfulLinks(Request $request) {
+    // @todo Simplify with https://www.drupal.org/node/2548095
+    $base_url = str_replace('/update.php', '', $request->getBaseUrl());
+    $links['front'] = [
+      'title' => $this->t('Front page'),
+      'url' => Url::fromRoute('<front>')->setOption('base_url', $base_url),
+    ];
+    if ($this->account->hasPermission('access administration pages')) {
+      $links['admin-pages'] = [
+        'title' => $this->t('Administration pages'),
+        'url' => Url::fromRoute('system.admin')->setOption('base_url', $base_url),
+      ];
+    }
+    if ($this->account->hasPermission('administer site configuration')) {
+      $links['status-report'] = [
+        'title' => $this->t('Status report'),
+        'url' => Url::fromRoute('system.status')->setOption('base_url', $base_url),
+      ];
+    }
+    return $links;
+  }
+
+  /**
+   * Retrieves module updates.
+   *
+   * @return array
+   *   The module updates that can be performed.
+   */
+  protected function getModuleUpdates() {
+    $return = [];
+    $updates = update_get_update_list();
+    foreach ($updates as $module => $update) {
+      $return[$module] = $update['start'];
+    }
+
+    return $return;
+  }
+
+}

web/core/modules/system/src/Controller/EntityAutocompleteController.php

@@ -0,0 +1,123 @@
+<?php
+
+namespace Drupal\system\Controller;
+
+use Drupal\Component\Utility\Crypt;
+use Drupal\Component\Utility\Tags;
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\Entity\EntityAutocompleteMatcherInterface;
+use Drupal\Core\KeyValueStore\KeyValueStoreInterface;
+use Drupal\Core\Site\Settings;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpFoundation\JsonResponse;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException;
+
+/**
+ * Defines a route controller for entity autocomplete form elements.
+ */
+class EntityAutocompleteController extends ControllerBase {
+
+  /**
+   * The autocomplete matcher for entity references.
+   *
+   * @var \Drupal\Core\Entity\EntityAutocompleteMatcherInterface
+   */
+  protected $matcher;
+
+  /**
+   * The key value store.
+   *
+   * @var \Drupal\Core\KeyValueStore\KeyValueStoreInterface
+   */
+  protected $keyValue;
+
+  /**
+   * Constructs an EntityAutocompleteController object.
+   *
+   * @param \Drupal\Core\Entity\EntityAutocompleteMatcherInterface $matcher
+   *   The autocomplete matcher for entity references.
+   * @param \Drupal\Core\KeyValueStore\KeyValueStoreInterface $key_value
+   *   The key value factory.
+   */
+  public function __construct(EntityAutocompleteMatcherInterface $matcher, KeyValueStoreInterface $key_value) {
+    $this->matcher = $matcher;
+    $this->keyValue = $key_value;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity.autocomplete_matcher'),
+      $container->get('keyvalue')->get('entity_autocomplete')
+    );
+  }
+
+  /**
+   * Autocomplete the label of an entity.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The request object that contains the typed tags.
+   * @param string $target_type
+   *   The ID of the target entity type.
+   * @param string $selection_handler
+   *   The plugin ID of the entity reference selection handler.
+   * @param string $selection_settings_key
+   *   The hashed key of the key/value entry that holds the selection handler
+   *   settings.
+   *
+   * @return \Symfony\Component\HttpFoundation\JsonResponse
+   *   The matched entity labels as a JSON response.
+   *
+   * @throws \Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException
+   *   Thrown if the selection settings key is not found in the key/value store
+   *   or if it does not match the stored data.
+   */
+  public function handleAutocomplete(Request $request, $target_type, $selection_handler, $selection_settings_key) {
+    $matches = [];
+
+    // Get the typed string from the URL, if it exists.
+    $input = $request->query->get('q');
+
+    // Check this string for emptiness, but allow any non-empty string.
+    if (is_string($input) && strlen($input)) {
+      $tag_list = Tags::explode($input);
+      $typed_string = !empty($tag_list) ? mb_strtolower(array_pop($tag_list)) : '';
+
+      // Selection settings are passed in as a hashed key of a serialized array
+      // stored in the key/value store.
+      $selection_settings = $this->keyValue->get($selection_settings_key, FALSE);
+      if ($selection_settings !== FALSE) {
+        $selection_settings_hash = Crypt::hmacBase64(serialize($selection_settings) . $target_type . $selection_handler, Settings::getHashSalt());
+        if (!hash_equals($selection_settings_hash, $selection_settings_key)) {
+          // Disallow access when the selection settings hash does not match the
+          // passed-in key.
+          throw new AccessDeniedHttpException('Invalid selection settings key.');
+        }
+      }
+      else {
+        // Disallow access when the selection settings key is not found in the
+        // key/value store.
+        throw new AccessDeniedHttpException();
+      }
+
+      $entity_type_id = $request->query->get('entity_type');
+      if ($entity_type_id && $this->entityTypeManager()->hasDefinition($entity_type_id)) {
+        $entity_id = $request->query->get('entity_id');
+        if ($entity_id) {
+          $entity = $this->entityTypeManager()->getStorage($entity_type_id)->load($entity_id);
+          if ($entity->access('update')) {
+            $selection_settings['entity'] = $entity;
+          }
+        }
+      }
+
+      $matches = $this->matcher->getMatches($target_type, $selection_handler, $selection_settings, $typed_string);
+    }
+
+    return new JsonResponse($matches);
+  }
+
+}

web/core/modules/system/src/Controller/Http4xxController.php

@@ -0,0 +1,60 @@
+<?php
+
+namespace Drupal\system\Controller;
+
+use Drupal\Core\Controller\ControllerBase;
+
+/**
+ * Controller for default HTTP 4xx responses.
+ */
+class Http4xxController extends ControllerBase {
+
+  /**
+   * The default 4xx error content.
+   *
+   * @return array
+   *   A render array containing the message to display for 4xx errors.
+   */
+  public function on4xx() {
+    return [
+      '#markup' => $this->t('A client error happened'),
+    ];
+  }
+
+  /**
+   * The default 401 content.
+   *
+   * @return array
+   *   A render array containing the message to display for 401 pages.
+   */
+  public function on401() {
+    return [
+      '#markup' => $this->t('Log in to access this page.'),
+    ];
+  }
+
+  /**
+   * The default 403 content.
+   *
+   * @return array
+   *   A render array containing the message to display for 403 pages.
+   */
+  public function on403() {
+    return [
+      '#markup' => $this->t('You are not authorized to access this page.'),
+    ];
+  }
+
+  /**
+   * The default 404 content.
+   *
+   * @return array
+   *   A render array containing the message to display for 404 pages.
+   */
+  public function on404() {
+    return [
+      '#markup' => $this->t('The requested page could not be found.'),
+    ];
+  }
+
+}

web/core/modules/system/src/Controller/JsAssetController.php

@@ -0,0 +1,64 @@
+<?php
+
+namespace Drupal\system\Controller;
+
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpKernel\Exception\BadRequestHttpException;
+use Drupal\Core\Asset\AttachedAssetsInterface;
+use Drupal\Core\Asset\AssetGroupSetHashTrait;
+
+/**
+ * Defines a controller to serve Javascript aggregates.
+ */
+class JsAssetController extends AssetControllerBase {
+
+  use AssetGroupSetHashTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected string $contentType = 'text/javascript';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected string $assetType = 'js';
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('stream_wrapper_manager'),
+      $container->get('library.dependency_resolver'),
+      $container->get('asset.resolver'),
+      $container->get('theme.initialization'),
+      $container->get('theme.manager'),
+      $container->get('asset.js.collection_grouper'),
+      $container->get('asset.js.collection_optimizer'),
+      $container->get('asset.js.dumper'),
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getGroups(AttachedAssetsInterface $attached_assets, Request $request): array {
+    // The header and footer scripts are two distinct sets of asset groups. The
+    // $group_key is not sufficient to find the group, we also need to locate it
+    // within either the header or footer set.
+    $language = $this->languageManager()->getLanguage($request->get('language'));
+    [$js_assets_header, $js_assets_footer] = $this->assetResolver->getJsAssets($attached_assets, FALSE, $language);
+    $scope = $request->get('scope');
+    if (!isset($scope)) {
+      throw new BadRequestHttpException('The URL must have a scope query argument.');
+    }
+    $assets = $scope === 'header' ? $js_assets_header : $js_assets_footer;
+    // While the asset resolver will find settings, these are never aggregated,
+    // so filter them out.
+    unset($assets['drupalSettings']);
+    return $this->grouper->group($assets);
+  }
+
+}

web/core/modules/system/src/Controller/LinksetController.php

@@ -0,0 +1,282 @@
+<?php
+
+namespace Drupal\system\Controller;
+
+use Drupal\Core\Access\AccessResultInterface;
+use Drupal\Core\Cache\CacheableJsonResponse;
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Cache\RefinableCacheableDependencyInterface;
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\Menu\MenuLinkTreeInterface;
+use Drupal\Core\Menu\MenuTreeParameters;
+use Drupal\system\MenuInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Linkset controller.
+ *
+ * Provides a menu endpoint.
+ *
+ * @internal
+ *   This class's API is internal and it is not intended for extension.
+ */
+final class LinksetController extends ControllerBase {
+
+  /**
+   * Linkset constructor.
+   *
+   * @param \Drupal\Core\Menu\MenuLinkTreeInterface $menuTree
+   *   The menu tree loader service. This is used to load a menu's link
+   *   elements so that they can be serialized into a linkset response.
+   */
+  public function __construct(protected readonly MenuLinkTreeInterface $menuTree) {
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static($container->get('menu.link_tree'));
+  }
+
+  /**
+   * Serve linkset requests.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   An HTTP request.
+   * @param \Drupal\system\MenuInterface $menu
+   *   A menu for which to produce a linkset.
+   *
+   * @return \Drupal\Core\Cache\CacheableJsonResponse
+   *   A linkset response.
+   */
+  public function process(Request $request, MenuInterface $menu) {
+    // Load the given menu's tree of elements.
+    $tree = $this->loadMenuTree($menu);
+    // Get the incoming request URI and parse it so the linkset can use a
+    // relative URL for the linkset anchor.
+    ['path' => $path, 'query' => $query] = parse_url($request->getUri()) + ['query' => FALSE];
+    // Construct a relative URL.
+    $anchor = $path . (!empty($query) ? '?' . $query : '');
+    $cacheability = CacheableMetadata::createFromObject($menu);
+    // Encode the menu tree as links in the application/linkset+json media type
+    // and add the machine name of the menu to which they belong.
+    $menu_id = $menu->id();
+    $links = $this->toLinkTargetObjects($tree, $cacheability);
+    foreach ($links as $rel => $target_objects) {
+      $links[$rel] = array_map(function (array $target) use ($menu_id) {
+        // According to the Linkset specification, this member must be an array
+        // since the "machine-name" target attribute is non-standard.
+        // See https://tools.ietf.org/html/draft-ietf-httpapi-linkset-08#section-4.2.4.3
+        return $target + ['machine-name' => [$menu_id]];
+      }, $target_objects);
+    }
+    $linkset = !empty($tree)
+      ? [['anchor' => $anchor] + $links]
+      : [];
+    $data = ['linkset' => $linkset];
+    // Set the response content-type header.
+    $headers = ['content-type' => 'application/linkset+json'];
+    $response = new CacheableJsonResponse($data, 200, $headers);
+    // Attach cacheability metadata to the response.
+    $response->addCacheableDependency($cacheability);
+    return $response;
+  }
+
+  /**
+   * Encode a menu tree as link items and capture any cacheability metadata.
+   *
+   * This method recursively traverses the given menu tree to produce a flat
+   * array of link items encoded according the application/linkset+json
+   * media type.
+   *
+   * To preserve hierarchical information, the target attribute contains a
+   * `hierarchy` member. Its value is an array containing the position of a link
+   * within a particular sub-tree prepended by the positions of its ancestors,
+   * and can be used to reconstruct a hierarchical data structure.
+   *
+   * The reason that a `hierarchy` member is used instead of a `parent` or
+   * `children` member is because it is more compact, more suited to the linkset
+   * media type, and because it simplifies many menu operations. Specifically:
+   *
+   * 1. Creating a `parent` member would require each link to have an `id`
+   *    in order to have something referenceable by the `parent` member. Reusing
+   *    the link plugin IDs would not be viable because it would leak
+   *    information about which modules are installed on the site. Therefore,
+   *    this ID would have to be invented and would probably end up looking a
+   *    lot like the `hierarchy` value. Finally, link IDs would encourage
+   *    clients to hardcode the ID instead of using link relation types
+   *    appropriately.
+   * 2. The linkset media type is not itself hierarchical. This means that
+   *    `children` is infeasible without inventing our own Drupal-specific media
+   *    type.
+   * 3. The `hierarchy` member can be used to efficiently perform tree
+   *    operations that would otherwise be more complicated to implement. For
+   *    example, by comparing the first X amount of hierarchy levels, you can
+   *    find any subtree without writing recursive logic or complicated loops.
+   *    Visit the URL below for more examples.
+   *
+   * The structure of a `hierarchy` value is defined below.
+   *
+   * A link which is a child of another link will always be prefixed by the
+   * exact value of their parent's hierarchy member. For example, if a link /bar
+   * is a child of a link /foo and /foo has a hierarchy member with the value
+   * ["1"], then the link /bar might have a hierarchy member with the value
+   * ["1", "0"]. The link /foo can be said to have depth 1, while the link
+   * /bar can be said to have depth 2.
+   *
+   * Links which have the same parent (or no parent) have their relative order
+   * preserved in the final component of the hierarchy value.
+   *
+   * According to the Linkset specification, each value in the hierarchy array
+   * must be a string. See
+   * https://tools.ietf.org/html/draft-ietf-httpapi-linkset-08#section-4.2.4.3
+   *
+   * @param \Drupal\Core\Menu\MenuLinkTreeElement[] $tree
+   *   A tree of menu elements.
+   * @param \Drupal\Core\Cache\RefinableCacheableDependencyInterface $cacheability
+   *   An object to capture any cacheability metadata.
+   * @param array $hierarchy_ancestors
+   *   (Internal use only) The hierarchy value of the parent element
+   *   if $tree is a subtree. Do not pass this value.
+   *
+   * @return array
+   *   An array which can be JSON-encoded to represent the given link tree.
+   *
+   * @see https://www.drupal.org/project/decoupled_menus/issues/3204132#comment-14439385
+   */
+  protected function toLinkTargetObjects(array $tree, RefinableCacheableDependencyInterface $cacheability, $hierarchy_ancestors = []): array {
+    $links = [];
+    // Calling array_values() discards any key names so that $index will be
+    // numerical.
+    foreach (array_values($tree) as $index => $element) {
+      // Extract and preserve the access cacheability metadata.
+      $element_access = $element->access;
+      assert($element_access instanceof AccessResultInterface);
+      $cacheability->addCacheableDependency($element_access);
+      // If an element is not accessible, it should not be encoded. Its
+      // cacheability should be preserved regardless, which is why that is done
+      // outside of this conditional.
+      if ($element_access->isAllowed()) {
+        // Get and generate the URL of the link's target. This can create
+        // cacheability metadata also.
+        $url = $element->link->getUrlObject();
+        $generated_url = $url->toString(TRUE);
+        $cacheability = $cacheability->addCacheableDependency($generated_url);
+        // Take the hierarchy value for the current element and append it
+        // to the link element parent's hierarchy value. See this method's
+        // docblock for more context on why this value is the way it is.
+        $hierarchy = $hierarchy_ancestors;
+        array_push($hierarchy, strval($index));
+        $link_options = $element->link->getOptions();
+        $link_attributes = ($link_options['attributes'] ?? []);
+        $link_rel = $link_attributes['rel'] ?? 'item';
+        // Encode the link.
+        $link = [
+          'href' => $generated_url->getGeneratedUrl(),
+          // @todo should this use the "title*" key if it is internationalized?
+          // Follow up issue:
+          // https://www.drupal.org/project/decoupled_menus/issues/3280735
+          'title' => $element->link->getTitle(),
+          'hierarchy' => $hierarchy,
+        ];
+        $this->processCustomLinkAttributes($link, $link_attributes);
+        $links[$link_rel][] = $link;
+        // Recurse into the element's subtree.
+        if (!empty($element->subtree)) {
+          // Recursion!
+          $links = array_merge_recursive($links, $this->toLinkTargetObjects($element->subtree, $cacheability, $hierarchy));
+        }
+      }
+    }
+
+    return $links;
+  }
+
+  /**
+   * Process custom link parameters.
+   *
+   * Since the values for attributes are dynamic and we can't
+   * guarantee that they adhere to the linkset specification,
+   * we do some custom processing as follows,
+   * 1. Transform all of them into an array if
+   *    they are not already an array.
+   * 2. Transform all non-string values into strings
+   *    (e.g. ["42"] instead of [42])
+   * 3. Ignore (for now) any keys that are already specified.
+   *    Namely: hreflang, media, type, title, and title*.
+   * 4. Ensure that custom names do not contain an
+   *    asterisk and ignore them if they do.
+   * 5. These attributes require special handling. For instance,
+   *    these parameters must be strings instead of an array of strings.
+   *
+   * NOTE: Values which are not object/array are cast to string.
+   *
+   * @param array $link
+   *   Link structure.
+   * @param array $attributes
+   *   Attributes available for the link.
+   */
+  private function processCustomLinkAttributes(array &$link, array $attributes = []) {
+    $attribute_keys_to_ignore = [
+      'hreflang',
+      'media',
+      'type',
+      'title',
+      'title*',
+    ];
+
+    foreach ($attributes as $key => $value) {
+      if (in_array($key, $attribute_keys_to_ignore, TRUE)) {
+        continue;
+      }
+      // Skip the attribute key if it has an asterisk (*).
+      if (str_contains($key, '*')) {
+        continue;
+      }
+      // Skip the value if it is an object.
+      if (is_object($value)) {
+        continue;
+      }
+      // See https://datatracker.ietf.org/doc/html/draft-ietf-httpapi-linkset-03#section-4.2.4.3
+      // Values for custom attributes must follow these rules,
+      // - Values MUST be array.
+      // - Each item in the array MUST be a string.
+      if (is_array($value)) {
+        $link[$key] = [];
+        foreach ($value as $val) {
+          if (is_object($val) || is_array($val)) {
+            continue;
+          }
+          $link[$key][] = (string) $val;
+        }
+      }
+      else {
+        $link[$key] = [(string) $value];
+      }
+    }
+  }
+
+  /**
+   * Loads a menu tree.
+   *
+   * @param \Drupal\system\MenuInterface $menu
+   *   A menu for which a tree should be loaded.
+   *
+   * @return \Drupal\Core\Menu\MenuLinkTreeElement[]
+   *   A menu link tree.
+   */
+  protected function loadMenuTree(MenuInterface $menu) : array {
+    $parameters = new MenuTreeParameters();
+    $parameters->onlyEnabledLinks();
+    $parameters->setMinDepth(0);
+    $tree = $this->menuTree->load($menu->id(), $parameters);
+    $manipulators = [
+      ['callable' => 'menu.default_tree_manipulators:checkAccess'],
+      ['callable' => 'menu.default_tree_manipulators:generateIndexAndSort'],
+    ];
+    return $this->menuTree->transform($tree, $manipulators);
+  }
+
+}

web/core/modules/system/src/Controller/PerformanceController.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace Drupal\system\Controller;
+
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\system\Form\ClearCacheForm;
+use Drupal\system\Form\PerformanceForm;
+
+/**
+ * Controller for performance admin.
+ */
+class PerformanceController extends ControllerBase {
+
+  /**
+   * Displays the system performance page.
+   *
+   * @return array
+   *   A render array containing the cache-clear form and performance
+   *   configuration form.
+   */
+  public function build(): array {
+    // Load the cache form and embed it in a details element.
+    $cache_clear = $this->formBuilder()->getForm(ClearCacheForm::class);
+    $cache_clear['clear_cache'] = [
+      '#type' => 'details',
+      '#title' => $this->t('Clear cache'),
+      '#open' => TRUE,
+      'clear' => $cache_clear['clear'],
+    ];
+    unset($cache_clear['clear']);
+    return [
+      'cache_clear' => $cache_clear,
+      'performance' => $this->formBuilder()->getForm(PerformanceForm::class),
+    ];
+  }
+
+}