Initial Drupal 11 with DDEV setup

web/core/modules/link/tests/modules/link_test_base_field/link_test_base_field.info.yml

@@ -0,0 +1,7 @@
+name: Link test base field
+description: Tests link field as an optional base field
+type: module
+hidden: true
+dependencies:
+  - drupal:link
+  - drupal:entity_test

web/core/modules/link/tests/modules/link_test_base_field/src/Hook/LinkTestBaseFieldHooks.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\link_test_base_field\Hook;
+
+use Drupal\link\LinkItemInterface;
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+use Drupal\Core\Field\BaseFieldDefinition;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Hook\Attribute\Hook;
+
+/**
+ * Hook implementations for link_test_base_field.
+ */
+class LinkTestBaseFieldHooks {
+
+  /**
+   * Implements hook_entity_base_field_info().
+   */
+  #[Hook('entity_base_field_info')]
+  public function entityBaseFieldInfo(EntityTypeInterface $entity_type): array {
+    $fields = [];
+    if ($entity_type->id() === 'entity_test') {
+      $fields['links'] = BaseFieldDefinition::create('link')->setLabel('Links')->setRevisionable(TRUE)->setCardinality(FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED)->setDescription('Add links to the entity.')->setRequired(FALSE)->setSettings([
+        'link_type' => LinkItemInterface::LINK_GENERIC,
+        'title' => DRUPAL_REQUIRED,
+      ])->setDisplayOptions('form', ['type' => 'link_default', 'weight' => 49]);
+    }
+    return $fields;
+  }
+
+}

web/core/modules/link/tests/modules/link_test_views/link_test_views.info.yml

@@ -0,0 +1,9 @@
+name: 'Link test views'
+type: module
+description: 'Provides default views for views link tests.'
+package: Testing
+version: VERSION
+dependencies:
+  - drupal:node
+  - drupal:views
+  - drupal:link

web/core/modules/link/tests/modules/link_test_views/test_views/views.view.test_link_tokens.yml

@@ -0,0 +1,205 @@
+langcode: en
+status: true
+dependencies:
+  config:
+    - field.storage.node.field_link
+  module:
+    - link
+    - node
+    - user
+id: test_link_tokens
+label: link
+module: views
+description: ''
+tag: ''
+base_table: node_field_data
+base_field: nid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: 0
+    display_options:
+      access:
+        type: perm
+        options:
+          perm: 'access content'
+      cache:
+        type: tag
+        options: {  }
+      query:
+        type: views_query
+        options:
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_comment: ''
+          query_tags: {  }
+      exposed_form:
+        type: basic
+        options:
+          submit_button: Apply
+          reset_button: false
+          reset_button_label: Reset
+          exposed_sorts_label: 'Sort by'
+          expose_sort_order: true
+          sort_asc_label: Asc
+          sort_desc_label: Desc
+      pager:
+        type: full
+        options:
+          items_per_page: 10
+          offset: 0
+          id: 0
+          total_pages: null
+          expose:
+            items_per_page: false
+            items_per_page_label: 'Items per page'
+            items_per_page_options: '5, 10, 25, 50'
+            items_per_page_options_all: false
+            items_per_page_options_all_label: '- All -'
+            offset: false
+            offset_label: Offset
+          tags:
+            previous: '‹ previous'
+            next: 'next ›'
+            first: '« first'
+            last: 'last »'
+          quantity: 9
+      style:
+        type: default
+      row:
+        type: fields
+        options:
+          default_field_elements: true
+          inline: {  }
+          separator: ''
+          hide_empty: false
+      fields:
+        field_link:
+          id: field_link
+          table: node__field_link
+          field: field_link
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: ''
+          exclude: false
+          alter:
+            alter_text: true
+            text: "Formatted: {{ field_link }}<br />\nRaw uri: {{ field_link__uri }}<br />\nRaw title: {{ field_link__title }}<br />\nRaw options: {{ field_link__options }}."
+            make_link: false
+            path: '{{ field_link__uri }}'
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: uri
+          type: link
+          settings:
+            trim_length: 80
+            url_only: false
+            url_plain: false
+            rel: '0'
+            target: '0'
+          group_column: ''
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+          plugin_id: field
+      filters:
+        status:
+          value: '1'
+          table: node_field_data
+          field: status
+          plugin_id: boolean
+          entity_type: node
+          entity_field: status
+          id: status
+          expose:
+            operator: ''
+          group: 1
+      sorts:
+        created:
+          id: created
+          table: node_field_data
+          field: created
+          order: DESC
+          entity_type: node
+          entity_field: created
+          plugin_id: date
+          relationship: none
+          group_type: group
+          admin_label: ''
+          exposed: false
+          expose:
+            label: ''
+          granularity: second
+      title: link
+      header: {  }
+      footer: {  }
+      empty: {  }
+      relationships: {  }
+      arguments: {  }
+      display_extenders: {  }
+    cache_metadata:
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url.query_args
+        - 'user.node_grants:view'
+        - user.permissions
+      cacheable: false
+  page_1:
+    display_plugin: page
+    id: page_1
+    display_title: Page
+    position: 1
+    display_options:
+      display_extenders: {  }
+      path: test_link_tokens
+    cache_metadata:
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url.query_args
+        - 'user.node_grants:view'
+        - user.permissions
+      cacheable: false

web/core/modules/link/tests/src/Functional/GenericTest.php

@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Functional;
+
+use Drupal\Tests\system\Functional\Module\GenericModuleTestBase;
+
+/**
+ * Generic module test for link.
+ *
+ * @group link
+ */
+class GenericTest extends GenericModuleTestBase {}

web/core/modules/link/tests/src/Functional/LinkFieldTest.php

@@ -0,0 +1,555 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Functional;
+
+use Drupal\Core\Link;
+use Drupal\Core\Url;
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\link\LinkItemInterface;
+use Drupal\node\NodeInterface;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\Traits\Core\PathAliasTestTrait;
+
+/**
+ * Tests link field widgets and formatters.
+ *
+ * @group link
+ * @group #slow
+ */
+class LinkFieldTest extends BrowserTestBase {
+
+  use PathAliasTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'entity_test',
+    'link',
+    'node',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'link_test_theme';
+
+  /**
+   * A field to use in this test class.
+   *
+   * @var \Drupal\field\Entity\FieldStorageConfig
+   */
+  protected $fieldStorage;
+
+  /**
+   * The instance used in this test class.
+   *
+   * @var \Drupal\field\Entity\FieldConfig
+   */
+  protected $field;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->drupalLogin($this->drupalCreateUser([
+      'view test entity',
+      'administer entity_test content',
+      'link to any page',
+    ]));
+  }
+
+  /**
+   * Tests the functionality and rendering of the link field.
+   *
+   * This is being as one to avoid multiple Drupal install.
+   */
+  public function testLinkField(): void {
+    $this->doTestURLValidation();
+    $this->doTestLinkTitle();
+    $this->doTestEditNonNodeEntityLink();
+  }
+
+  /**
+   * Tests link field URL validation.
+   */
+  protected function doTestURLValidation(): void {
+    $field_name = $this->randomMachineName();
+    // Create a field with settings to validate.
+    $this->fieldStorage = FieldStorageConfig::create([
+      'field_name' => $field_name,
+      'entity_type' => 'entity_test',
+      'type' => 'link',
+    ]);
+    $this->fieldStorage->save();
+    $this->field = FieldConfig::create([
+      'field_storage' => $this->fieldStorage,
+      'bundle' => 'entity_test',
+      'settings' => [
+        'title' => DRUPAL_DISABLED,
+        'link_type' => LinkItemInterface::LINK_GENERIC,
+      ],
+    ]);
+    $this->field->save();
+    /** @var \Drupal\Core\Entity\EntityDisplayRepositoryInterface $display_repository */
+    $display_repository = \Drupal::service('entity_display.repository');
+    $display_repository->getFormDisplay('entity_test', 'entity_test')
+      ->setComponent($field_name, [
+        'type' => 'link_default',
+        'settings' => [
+          'placeholder_url' => 'http://example.com',
+        ],
+      ])
+      ->save();
+    $display_repository->getViewDisplay('entity_test', 'entity_test', 'full')
+      ->setComponent($field_name, [
+        'type' => 'link',
+      ])
+      ->save();
+
+    // Display creation form.
+    $this->drupalGet('entity_test/add');
+    $this->assertSession()->fieldValueEquals("{$field_name}[0][uri]", '');
+    $this->assertSession()->responseContains('placeholder="http://example.com"');
+
+    // Create a path alias.
+    $this->createPathAlias('/admin', '/a/path/alias');
+
+    // Create a node to test the link widget.
+    $node = $this->drupalCreateNode();
+
+    $restricted_node = $this->drupalCreateNode(['status' => NodeInterface::NOT_PUBLISHED]);
+
+    // Define some valid URLs (keys are the entered values, values are the
+    // strings displayed to the user).
+    $valid_external_entries = [
+      'http://www.example.com/' => 'http://www.example.com/',
+      // Strings within parenthesis without leading space char.
+      'http://www.example.com/strings_(string_within_parenthesis)' => 'http://www.example.com/strings_(string_within_parenthesis)',
+      // Numbers within parenthesis without leading space char.
+      'http://www.example.com/numbers_(9999)' => 'http://www.example.com/numbers_(9999)',
+    ];
+    $valid_internal_entries = [
+      '/entity_test/add' => '/entity_test/add',
+      '/a/path/alias' => '/a/path/alias',
+
+      // Front page, with query string and fragment.
+      '/' => '&lt;front&gt;',
+      '/?example=llama' => '&lt;front&gt;?example=llama',
+      '/#example' => '&lt;front&gt;#example',
+
+      // Trailing spaces should be ignored.
+      '/ ' => '&lt;front&gt;',
+      '/path with spaces ' => '/path with spaces',
+
+      // @todo '<front>' is valid input for BC reasons, may be removed by
+      //   https://www.drupal.org/node/2421941
+      '<front>' => '&lt;front&gt;',
+      '<front>#example' => '&lt;front&gt;#example',
+      '<front>?example=llama' => '&lt;front&gt;?example=llama',
+
+      // Text-only links.
+      '<nolink>' => '&lt;nolink&gt;',
+      'route:<nolink>' => '&lt;nolink&gt;',
+      '<none>' => '&lt;none&gt;',
+      '<button>' => '&lt;button&gt;',
+
+      // Query string and fragment.
+      '?example=llama' => '?example=llama',
+      '#example' => '#example',
+
+      // Complex query string. Similar to facet links.
+      '?a[]=1&a[]=2'     => '?a[]=1&amp;a[]=2',
+      '?b[0]=1&b[1]=2'   => '?b[0]=1&amp;b[1]=2',
+      '?c[]=1&d=3&c[]=2' => '?c[]=1&amp;d=3&amp;c[]=2',
+      '?e[f][g]=h'       => '?e[f][g]=h',
+      '?i[j[k]]=l'       => '?i[j[k]]=l',
+      '?x=1&x=2'         => '?x=1&amp;x=2',
+      '?z[0]=1&z[0]=2'   => '?z[0]=1&amp;z[0]=2',
+
+      // Entity reference autocomplete value.
+      $node->label() . ' (1)' => $node->label() . ' (1)',
+      // Entity URI displayed as ER autocomplete value when displayed in a form.
+      'entity:node/1' => $node->label() . ' (1)',
+      // URI for an entity that exists, but is not accessible by the user.
+      'entity:node/' . $restricted_node->id() => '- Restricted access - (' . $restricted_node->id() . ')',
+      // URI for an entity that doesn't exist, but with a valid ID.
+      'entity:user/999999' => 'entity:user/999999',
+    ];
+
+    // Define some invalid URLs.
+    $validation_error_1 = "The path '@link_path' is invalid.";
+    $validation_error_2 = 'Manually entered paths should start with one of the following characters: / ? #';
+    $validation_error_3 = "The path '@link_path' is inaccessible.";
+    $invalid_external_entries = [
+      // Invalid protocol
+      'invalid://not-a-valid-protocol' => $validation_error_1,
+      // Missing host name
+      'http://' => $validation_error_1,
+    ];
+    $invalid_internal_entries = [
+      'no-leading-slash' => $validation_error_2,
+      'entity:non_existing_entity_type/yar' => $validation_error_1,
+      // URI for an entity that doesn't exist, with an invalid ID.
+      'entity:user/invalid-parameter' => $validation_error_1,
+    ];
+
+    // Test external and internal URLs for
+    // 'link_type' = LinkItemInterface::LINK_GENERIC.
+    $this->assertValidEntries($field_name, $valid_external_entries + $valid_internal_entries);
+    $this->assertInvalidEntries($field_name, $invalid_external_entries + $invalid_internal_entries);
+
+    // Test external URLs for 'link_type' = LinkItemInterface::LINK_EXTERNAL.
+    $this->field->setSetting('link_type', LinkItemInterface::LINK_EXTERNAL);
+    $this->field->save();
+    $this->assertValidEntries($field_name, $valid_external_entries);
+    $this->assertInvalidEntries($field_name, $valid_internal_entries + $invalid_external_entries);
+
+    // Test external URLs for 'link_type' = LinkItemInterface::LINK_INTERNAL.
+    $this->field->setSetting('link_type', LinkItemInterface::LINK_INTERNAL);
+    $this->field->save();
+    $this->assertValidEntries($field_name, $valid_internal_entries);
+    $this->assertInvalidEntries($field_name, $valid_external_entries + $invalid_internal_entries);
+
+    // Ensure that users with 'link to any page', don't apply access checking.
+    $this->drupalLogin($this->drupalCreateUser([
+      'view test entity',
+      'administer entity_test content',
+    ]));
+    $this->assertValidEntries($field_name, ['/entity_test/add' => '/entity_test/add']);
+    $this->assertInValidEntries($field_name, ['/admin' => $validation_error_3]);
+  }
+
+  /**
+   * Asserts that valid URLs can be submitted.
+   *
+   * @param string $field_name
+   *   The field name.
+   * @param array $valid_entries
+   *   An array of valid URL entries.
+   *
+   * @internal
+   */
+  protected function assertValidEntries(string $field_name, array $valid_entries): void {
+    foreach ($valid_entries as $uri => $string) {
+      $edit = [
+        "{$field_name}[0][uri]" => $uri,
+      ];
+      $this->drupalGet('entity_test/add');
+      $this->submitForm($edit, 'Save');
+      preg_match('|entity_test/manage/(\d+)|', $this->getUrl(), $match);
+      $id = $match[1];
+      $this->assertSession()->statusMessageContains('entity_test ' . $id . ' has been created.', 'status');
+      $this->assertSession()->responseContains('"' . $string . '"');
+    }
+  }
+
+  /**
+   * Asserts that invalid URLs cannot be submitted.
+   *
+   * @param string $field_name
+   *   The field name.
+   * @param array $invalid_entries
+   *   An array of invalid URL entries.
+   *
+   * @internal
+   */
+  protected function assertInvalidEntries(string $field_name, array $invalid_entries): void {
+    foreach ($invalid_entries as $invalid_value => $error_message) {
+      $edit = [
+        "{$field_name}[0][uri]" => $invalid_value,
+      ];
+      $this->drupalGet('entity_test/add');
+      $this->submitForm($edit, 'Save');
+      $this->assertSession()->responseContains(strtr($error_message, ['@link_path' => $invalid_value]));
+    }
+  }
+
+  /**
+   * Tests the link title settings of a link field.
+   */
+  protected function doTestLinkTitle(): void {
+    $field_name = $this->randomMachineName();
+    // Create a field with settings to validate.
+    $this->fieldStorage = FieldStorageConfig::create([
+      'field_name' => $field_name,
+      'entity_type' => 'entity_test',
+      'type' => 'link',
+    ]);
+    $this->fieldStorage->save();
+    $this->field = FieldConfig::create([
+      'field_storage' => $this->fieldStorage,
+      'bundle' => 'entity_test',
+      'label' => 'Read more about this entity',
+      'settings' => [
+        'title' => DRUPAL_OPTIONAL,
+        'link_type' => LinkItemInterface::LINK_GENERIC,
+      ],
+    ]);
+    $this->field->save();
+    /** @var \Drupal\Core\Entity\EntityDisplayRepositoryInterface $display_repository */
+    $display_repository = \Drupal::service('entity_display.repository');
+    $display_repository->getFormDisplay('entity_test', 'entity_test')
+      ->setComponent($field_name, [
+        'type' => 'link_default',
+        'settings' => [
+          'placeholder_url' => 'http://example.com',
+          'placeholder_title' => 'Enter the text for this link',
+        ],
+      ])
+      ->save();
+    $display_repository->getViewDisplay('entity_test', 'entity_test', 'full')
+      ->setComponent($field_name, [
+        'type' => 'link',
+        'label' => 'hidden',
+      ])
+      ->save();
+
+    // Verify that the link text field works according to the field setting.
+    foreach ([DRUPAL_DISABLED, DRUPAL_REQUIRED, DRUPAL_OPTIONAL] as $title_setting) {
+      // Update the link title field setting.
+      $this->field->setSetting('title', $title_setting);
+      $this->field->save();
+
+      // Display creation form.
+      $this->drupalGet('entity_test/add');
+      // Assert label is shown.
+      $this->assertSession()->pageTextContains('Read more about this entity');
+      $this->assertSession()->fieldValueEquals("{$field_name}[0][uri]", '');
+      $this->assertSession()->responseContains('placeholder="http://example.com"');
+
+      if ($title_setting === DRUPAL_DISABLED) {
+        $this->assertSession()->fieldNotExists("{$field_name}[0][title]");
+        $this->assertSession()->responseNotContains('placeholder="Enter the text for this link"');
+      }
+      else {
+        $this->assertSession()->responseContains('placeholder="Enter the text for this link"');
+
+        $this->assertSession()->fieldValueEquals("{$field_name}[0][title]", '');
+        if ($title_setting === DRUPAL_OPTIONAL) {
+          // Verify that the URL is required, if the link text is non-empty.
+          $edit = [
+            "{$field_name}[0][title]" => 'Example',
+          ];
+          $this->submitForm($edit, 'Save');
+          $this->assertSession()->statusMessageContains('The URL field is required when the Link text field is specified.', 'error');
+        }
+        if ($title_setting === DRUPAL_REQUIRED) {
+          // Verify that the link text is required, if the URL is non-empty.
+          $edit = [
+            "{$field_name}[0][uri]" => 'http://www.example.com',
+          ];
+          $this->submitForm($edit, 'Save');
+          $this->assertSession()->statusMessageContains('Link text field is required if there is URL input.', 'error');
+
+          // Verify that the link text is not required, if the URL is empty.
+          $edit = [
+            "{$field_name}[0][uri]" => '',
+          ];
+          $this->submitForm($edit, 'Save');
+          $this->assertSession()->statusMessageNotContains('Link text field is required.');
+
+          // Verify that a URL and link text meets requirements.
+          $this->drupalGet('entity_test/add');
+          $edit = [
+            "{$field_name}[0][uri]" => 'http://www.example.com',
+            "{$field_name}[0][title]" => 'Example',
+          ];
+          $this->submitForm($edit, 'Save');
+          $this->assertSession()->statusMessageNotContains('Link text field is required.');
+        }
+      }
+    }
+
+    // Verify that a link without link text is rendered using the URL as text.
+    $value = 'http://www.example.com/';
+    $edit = [
+      "{$field_name}[0][uri]" => $value,
+      "{$field_name}[0][title]" => '',
+    ];
+    $this->submitForm($edit, 'Save');
+    preg_match('|entity_test/manage/(\d+)|', $this->getUrl(), $match);
+    $id = $match[1];
+    $this->assertSession()->statusMessageContains('entity_test ' . $id . ' has been created.', 'status');
+
+    $output = $this->renderTestEntity($id);
+    $expected_link = (string) Link::fromTextAndUrl($value, Url::fromUri($value))->toString();
+    $this->assertStringContainsString($expected_link, $output);
+
+    // Verify that a link with text is rendered using the link text.
+    $title = $this->randomMachineName();
+    $edit = [
+      "{$field_name}[0][title]" => $title,
+    ];
+    $this->drupalGet("entity_test/manage/{$id}/edit");
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->statusMessageContains('entity_test ' . $id . ' has been updated.', 'status');
+
+    $output = $this->renderTestEntity($id);
+    $expected_link = (string) Link::fromTextAndUrl($title, Url::fromUri($value))->toString();
+    $this->assertStringContainsString($expected_link, $output);
+  }
+
+  /**
+   * Tests editing a link to a non-node entity.
+   */
+  protected function doTestEditNonNodeEntityLink(): void {
+
+    $entity_type_manager = \Drupal::entityTypeManager();
+    $entity_test_storage = $entity_type_manager->getStorage('entity_test');
+
+    // Create a field with settings to validate.
+    $this->fieldStorage = FieldStorageConfig::create([
+      'field_name' => 'field_link',
+      'entity_type' => 'entity_test',
+      'type' => 'link',
+      'cardinality' => 1,
+    ]);
+    $this->fieldStorage->save();
+    FieldConfig::create([
+      'field_storage' => $this->fieldStorage,
+      'label' => 'Read more about this entity',
+      'bundle' => 'entity_test',
+      'settings' => [
+        'title' => DRUPAL_OPTIONAL,
+      ],
+    ])->save();
+
+    $entity_type_manager
+      ->getStorage('entity_form_display')
+      ->load('entity_test.entity_test.default')
+      ->setComponent('field_link', [
+        'type' => 'link_default',
+      ])
+      ->save();
+
+    // Create a node and a test entity to have a possibly valid reference for
+    // both. Create another test entity that references the first test entity.
+    $entity_test_link = $entity_test_storage->create(['name' => 'correct link target']);
+    $entity_test_link->save();
+
+    // Create a node with the same ID as the test entity to ensure that the link
+    // doesn't match incorrectly.
+    $this->drupalCreateNode(['title' => 'wrong link target']);
+
+    $correct_link = 'entity:entity_test/' . $entity_test_link->id();
+    $entity_test = $entity_test_storage->create([
+      'name' => 'correct link target',
+      'field_link' => $correct_link,
+    ]);
+    $entity_test->save();
+
+    // Edit the entity and save it, verify the correct link is kept and not
+    // changed to point to a node. Currently, widget does not support non-node
+    // autocomplete and therefore must show the link unaltered.
+    $this->drupalGet($entity_test->toUrl('edit-form'));
+    $this->assertSession()->fieldValueEquals('field_link[0][uri]', $correct_link);
+    $this->submitForm([], 'Save');
+
+    $entity_test_storage->resetCache();
+    $entity_test = $entity_test_storage->load($entity_test->id());
+
+    $this->assertEquals($correct_link, $entity_test->get('field_link')->uri);
+  }
+
+  /**
+   * Renders a test_entity and returns the output.
+   *
+   * @param int $id
+   *   The test_entity ID to render.
+   * @param string $view_mode
+   *   (optional) The view mode to use for rendering.
+   * @param bool $reset
+   *   (optional) Whether to reset the entity_test storage cache. Defaults to
+   *   TRUE to simplify testing.
+   *
+   * @return string
+   *   The rendered HTML output.
+   */
+  protected function renderTestEntity($id, $view_mode = 'full', $reset = TRUE): string {
+    if ($reset) {
+      $this->container->get('entity_type.manager')->getStorage('entity_test')->resetCache([$id]);
+    }
+    $entity = EntityTest::load($id);
+    $display = \Drupal::service('entity_display.repository')
+      ->getViewDisplay($entity->getEntityTypeId(), $entity->bundle(), $view_mode);
+    $content = $display->build($entity);
+    $output = \Drupal::service('renderer')->renderRoot($content);
+    return (string) $output;
+  }
+
+  /**
+   * Test link widget exception handled if link uri value is invalid.
+   */
+  public function testLinkWidgetCaughtExceptionEditingInvalidUrl(): void {
+    $field_name = $this->randomMachineName();
+    $this->fieldStorage = FieldStorageConfig::create([
+      'field_name' => $field_name,
+      'entity_type' => 'entity_test',
+      'type' => 'link',
+      'cardinality' => 1,
+    ]);
+    $this->fieldStorage->save();
+    FieldConfig::create([
+      'field_storage' => $this->fieldStorage,
+      'label' => 'Link',
+      'bundle' => 'entity_test',
+      'settings' => [
+        'title' => DRUPAL_OPTIONAL,
+        'link_type' => LinkItemInterface::LINK_GENERIC,
+      ],
+    ])->save();
+
+    $entityTypeManager = $this->container->get('entity_type.manager');
+    $entityTypeManager
+      ->getStorage('entity_form_display')
+      ->load('entity_test.entity_test.default')
+      ->setComponent($field_name, [
+        'type' => 'link_default',
+      ])
+      ->save();
+
+    $entityTypeManager
+      ->getStorage('entity_view_display')
+      ->create([
+        'targetEntityType' => 'entity_test',
+        'bundle' => 'entity_test',
+        'mode' => 'full',
+        'status' => TRUE,
+      ])
+      ->setComponent($field_name, [
+        'type' => 'link',
+      ])
+      ->save();
+
+    // Entities can be saved without validation, for example via migration.
+    // Link fields may contain invalid uris such as external URLs without
+    // scheme.
+    $invalidUri = 'www.example.com';
+    $invalidLinkUrlEntity = $entityTypeManager
+      ->getStorage('entity_test')
+      ->create([
+        'name' => 'Test entity with invalid link URL',
+        $field_name => ['uri' => $invalidUri],
+      ]);
+    $invalidLinkUrlEntity->save();
+
+    // If a user without 'link to any page' permission edits an entity, widget
+    // checks access by converting uri to Url object, which will throw an
+    // InvalidArgumentException if uri is invalid.
+    $this->drupalLogin($this->drupalCreateUser([
+      'view test entity',
+      'administer entity_test content',
+    ]));
+    $this->drupalGet("/entity_test/manage/{$invalidLinkUrlEntity->id()}/edit");
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->fieldValueEquals("{$field_name}[0][uri]", $invalidUri);
+  }
+
+}

web/core/modules/link/tests/src/Functional/LinkFieldUITest.php

@@ -0,0 +1,258 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Functional;
+
+use Drupal\Core\Url;
+use Drupal\Component\Utility\Html;
+use Drupal\Core\Entity\Entity\EntityFormDisplay;
+use Drupal\link\LinkItemInterface;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\Tests\field_ui\Traits\FieldUiTestTrait;
+
+/**
+ * Tests link field UI functionality.
+ *
+ * @group link
+ * @group #slow
+ */
+class LinkFieldUITest extends BrowserTestBase {
+
+  use FieldUiTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['node', 'link', 'field_ui', 'block'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * A user that can edit content types.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $adminUser;
+
+  /**
+   * A user that should see the help texts.
+   *
+   * @var \Drupal\user\Entity\User
+   */
+  protected $helpTextUser;
+
+  /**
+   * The content type to add fields to.
+   *
+   * @var \Drupal\node\Entity\NodeType
+   */
+  protected $contentType;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->contentType = $this->drupalCreateContentType();
+    $this->adminUser = $this->drupalCreateUser([
+      'administer content types',
+      'administer node fields',
+      'administer node display',
+    ]);
+    $this->helpTextUser = $this->drupalCreateUser([
+      'create ' . $this->contentType->id() . ' content',
+    ]);
+    $this->drupalPlaceBlock('system_breadcrumb_block');
+  }
+
+  /**
+   * Tests the link field UI.
+   */
+  public function testFieldUI(): void {
+    foreach ($this->providerTestFieldUI() as $item) {
+      [$cardinality, $link_type, $title, $label, $field_name, $default_uri] = $item;
+      $this->runFieldUIItem($cardinality, $link_type, $title, $label, $field_name, $default_uri);
+    }
+  }
+
+  /**
+   * Provides test data for ::testFieldUI().
+   */
+  protected function providerTestFieldUI() {
+    // There are many combinations of field settings: where the description
+    // should show: variation on internal, external, both; cardinality (where
+    // the fieldset is hidden or used); and link text shown (required or
+    // optional) or disabled. There are two descriptions: field and URL help
+    // text.
+    $cardinalities = [1, 2];
+    $title_settings = [
+      DRUPAL_DISABLED,
+      DRUPAL_OPTIONAL,
+    ];
+    $link_types = [
+      LinkItemInterface::LINK_EXTERNAL => 'https://example.com',
+      LinkItemInterface::LINK_GENERIC => '',
+      LinkItemInterface::LINK_INTERNAL => '<front>',
+    ];
+
+    // Test all variations of link types on all cardinalities.
+    foreach ($cardinalities as $cardinality) {
+      foreach ($link_types as $link_type => $default_uri) {
+        // Now, test this with both the title enabled and disabled.
+        foreach ($title_settings as $title_setting) {
+          // Test both empty and non-empty labels.
+          foreach ([TRUE, FALSE] as $label_provided) {
+            // Generate a unique machine name for the field so it can be
+            // identified in the test.
+            $id = implode('_', [
+              'link',
+              $cardinality,
+              $link_type,
+              $title_setting,
+              (int) $label_provided,
+            ]);
+
+            // Use a unique label that contains some HTML.
+            $label = '<img src="https://example.com">' . $id;
+
+            yield [
+              $cardinality,
+              $link_type,
+              $title_setting,
+              $label_provided ? $label : '',
+              $id,
+              $default_uri,
+            ];
+          }
+        }
+      }
+    }
+  }
+
+  /**
+   * Tests one link field UI item.
+   *
+   * @param int $cardinality
+   *   The field cardinality.
+   * @param int $link_type
+   *   Determine if the link is external, internal or both.
+   * @param int $title
+   *   Determine if the field will display the link text field.
+   * @param string $label
+   *   The field label.
+   * @param string $field_name
+   *   The unique machine name for the field.
+   * @param string $default_uri
+   *   The default URI value.
+   */
+  public function runFieldUIItem($cardinality, $link_type, $title, $label, $field_name, $default_uri): void {
+    $this->drupalLogin($this->adminUser);
+    $type_path = 'admin/structure/types/manage/' . $this->contentType->id();
+
+    // Add a link field to the newly-created type.
+    $description = 'link field description';
+    $field_edit = [
+      'description' => $description,
+      'settings[link_type]' => (int) $link_type,
+    ];
+    if (!empty($default_uri)) {
+      $field_edit['set_default_value'] = '1';
+      $field_edit['default_value_input[field_' . $field_name . '][0][uri]'] = $default_uri;
+      $field_edit['default_value_input[field_' . $field_name . '][0][title]'] = 'Default title';
+    }
+    $storage_edit = [
+      'cardinality_number' => $cardinality,
+    ];
+    $this->fieldUIAddNewField($type_path, $field_name, $label, 'link', $storage_edit, $field_edit);
+
+    // Load the formatter page to check that the settings summary does not
+    // generate warnings.
+    // @todo Mess with the formatter settings a bit here.
+    $this->drupalGet("$type_path/display");
+    $this->assertSession()->pageTextContains('Link text trimmed to 80 characters');
+
+    // Make the fields visible in the form display.
+    $form_display_id = implode('.', ['node', $this->contentType->id(), 'default']);
+    $form_display = EntityFormDisplay::load($form_display_id);
+    $form_display->setComponent($field_name, ['region' => 'content']);
+    $form_display->save();
+
+    // Log in a user that is allowed to create this content type, see if
+    // the user can see the expected help text.
+    $this->drupalLogin($this->helpTextUser);
+
+    $add_path = 'node/add/' . $this->contentType->id();
+    $this->drupalGet($add_path);
+
+    $expected_help_texts = [
+      LinkItemInterface::LINK_EXTERNAL => 'This must be an external URL such as <em class="placeholder">https://example.com</em>.',
+      LinkItemInterface::LINK_GENERIC => 'You can also enter an internal path such as <em class="placeholder">/node/add</em> or an external URL such as <em class="placeholder">https://example.com</em>. Enter <em class="placeholder">&lt;front&gt;</em> to link to the front page. Enter <em class="placeholder">&lt;nolink&gt;</em> to display link text only',
+      LinkItemInterface::LINK_INTERNAL => rtrim(Url::fromRoute('<front>', [], ['absolute' => TRUE])->toString(), '/'),
+    ];
+
+    // Check that the help texts we assume should be there, is there.
+    $this->assertFieldContainsRawText($field_name, $expected_help_texts[$link_type]);
+    if ($link_type === LinkItemInterface::LINK_INTERNAL) {
+      // Internal links have no "system" description. Test that none
+      // of the other help texts show here.
+      $this->assertNoFieldContainsRawText($field_name, $expected_help_texts[LinkItemInterface::LINK_EXTERNAL]);
+      $this->assertNoFieldContainsRawText($field_name, $expected_help_texts[LinkItemInterface::LINK_GENERIC]);
+    }
+    // Also assert that the description we made is here, no matter what the
+    // cardinality or link setting.
+    if (!empty($label)) {
+      $this->assertFieldContainsRawText($field_name, $label);
+    }
+
+    // Test the default field value is used as expected.
+    $this->assertSession()->fieldValueEquals('field_' . $field_name . '[0][uri]', $default_uri);
+  }
+
+  /**
+   * Checks that given field contains the given raw text.
+   *
+   * @param string $field_name
+   *   The name of the field to check.
+   * @param string $text
+   *   The text to check.
+   *
+   * @internal
+   */
+  protected function assertFieldContainsRawText(string $field_name, string $text): void {
+    $this->assertTrue((bool) preg_match('/' . preg_quote($text, '/') . '/ui', $this->getFieldHtml($field_name)));
+  }
+
+  /**
+   * Checks that given field does not contain the given raw text.
+   *
+   * @param string $field_name
+   *   The name of the field to check.
+   * @param string $text
+   *   The text to check.
+   *
+   * @internal
+   */
+  protected function assertNoFieldContainsRawText(string $field_name, string $text): void {
+    $this->assertFalse((bool) preg_match('/' . preg_quote($text, '/') . '/ui', $this->getFieldHtml($field_name)));
+  }
+
+  /**
+   * Returns the raw HTML for the given field.
+   *
+   * @param string $field_name
+   *   The name of the field for which to return the HTML.
+   *
+   * @return string
+   *   The raw HTML.
+   */
+  protected function getFieldHtml($field_name) {
+    $css_id = Html::cleanCssIdentifier('edit-field-' . $field_name . '-wrapper');
+    return $this->xpath('//*[@id=:id]', [':id' => $css_id])[0]->getHtml();
+  }
+
+}

web/core/modules/link/tests/src/Functional/Views/LinkViewsTokensTest.php

@@ -0,0 +1,104 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Functional\Views;
+
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\views\Functional\ViewTestBase;
+
+/**
+ * Tests the views integration for link tokens.
+ *
+ * @group link
+ */
+class LinkViewsTokensTest extends ViewTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['link_test_views'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Views used by this test.
+   *
+   * @var array
+   */
+  public static $testViews = ['test_link_tokens'];
+
+  /**
+   * The field name used for the link field.
+   *
+   * @var string
+   */
+  protected $fieldName = 'field_link';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp($import_test_views = TRUE, $modules = ['link_test_views']): void {
+    parent::setUp($import_test_views, $modules);
+
+    // Create Basic page node type.
+    $this->drupalCreateContentType([
+      'type' => 'page',
+      'name' => 'Basic page',
+    ]);
+
+    // Create a field.
+    FieldStorageConfig::create([
+      'field_name' => $this->fieldName,
+      'type' => 'link',
+      'entity_type' => 'node',
+      'cardinality' => 1,
+    ])->save();
+    FieldConfig::create([
+      'field_name' => $this->fieldName,
+      'entity_type' => 'node',
+      'bundle' => 'page',
+      'label' => 'link field',
+    ])->save();
+
+  }
+
+  /**
+   * Tests the link views tokens.
+   */
+  public function testLinkViewsTokens(): void {
+    // Array of URI's to test.
+    $uris = [
+      'http://www.example.com' => 'example.com',
+    ];
+
+    // Add nodes with the URI's and titles.
+    foreach ($uris as $uri => $title) {
+      $values = ['type' => 'page'];
+      $values[$this->fieldName][] = ['uri' => $uri, 'title' => $title, 'options' => ['attributes' => ['class' => 'test-link-class']]];
+      $this->drupalCreateNode($values);
+    }
+
+    $this->drupalGet('test_link_tokens');
+
+    foreach ($uris as $uri => $title) {
+      // Formatted link: {{ field_link }}<br />
+      $this->assertSession()->responseContains("Formatted: <a href=\"$uri\" class=\"test-link-class\">$title</a>");
+
+      // Raw uri: {{ field_link__uri }}<br />
+      $this->assertSession()->responseContains("Raw uri: $uri");
+
+      // Raw title: {{ field_link__title }}<br />
+      $this->assertSession()->responseContains("Raw title: $title");
+
+      // Raw options: {{ field_link__options }}<br />
+      // Options is an array and should return empty after token replace.
+      $this->assertSession()->responseContains("Raw options: .");
+    }
+  }
+
+}

web/core/modules/link/tests/src/FunctionalJavascript/LinkFieldFormStatesTest.php

@@ -0,0 +1,81 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\FunctionalJavascript;
+
+use Drupal\FunctionalJavascriptTests\WebDriverTestBase;
+
+/**
+ * Tests link field form states functionality.
+ *
+ * @group link
+ * @group #slow
+ */
+class LinkFieldFormStatesTest extends WebDriverTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'entity_test',
+    'link',
+    'node',
+    'link_test_base_field',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer entity_test content',
+    ]));
+  }
+
+  /**
+   * @dataProvider linkFieldFormStatesData
+   */
+  public function testLinkFieldFormStates(string $uri, string $title): void {
+    $this->drupalGet('entity_test/add');
+    $session = $this->assertSession();
+    $session->elementNotExists('css', '#edit-links-0-uri[required]');
+    $session->elementNotExists('css', '#edit-links-0-title[required]');
+
+    $page = $this->getSession()->getPage();
+
+    if ($uri !== '') {
+      $page->fillField('links[0][uri]', $uri);
+      $session->elementNotExists('css', '#edit-links-0-uri[required]');
+      $session->elementExists('css', '#edit-links-0-title[required]');
+    }
+    else {
+      $page->fillField('links[0][title]', $title);
+      $session->elementExists('css', '#edit-links-0-uri[required]');
+      $session->elementNotExists('css', '#edit-links-0-title[required]');
+    }
+  }
+
+  /**
+   * Provides data for ::testLinkFieldJSFormStates.
+   */
+  public static function linkFieldFormStatesData() {
+    return [
+      'Fill uri, keep title empty' => [
+        'https://example.com',
+        '',
+      ],
+      'Fill title, keep uri empty' => [
+        '',
+        'https://example.com',
+      ],
+    ];
+  }
+
+}

web/core/modules/link/tests/src/Kernel/LinkFieldWidgetTest.php

@@ -0,0 +1,66 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Kernel;
+
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\link\LinkItemInterface;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\field\Kernel\FieldKernelTestBase;
+
+/**
+ * Tests link field widgets.
+ *
+ * @group link
+ */
+class LinkFieldWidgetTest extends FieldKernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'link',
+  ];
+
+  /**
+   * Tests '#link_type' property exists on 'link_default' widget.
+   *
+   * Make sure the 'link_default' widget exposes a '#link_type' property on
+   * its element. Modules can use it to understand if a text form element is
+   * a link and also which LinkItemInterface::LINK_* is (EXTERNAL, GENERIC,
+   * INTERNAL).
+   */
+  public function testLinkTypeOnLinkWidget(): void {
+    $link_type = LinkItemInterface::LINK_EXTERNAL;
+    $field_name = $this->randomMachineName();
+
+    // Create a field with settings to validate.
+    $fieldStorage = FieldStorageConfig::create([
+      'field_name' => $field_name,
+      'entity_type' => 'entity_test',
+      'type' => 'link',
+      'cardinality' => 1,
+    ]);
+    $fieldStorage->save();
+    FieldConfig::create([
+      'field_storage' => $fieldStorage,
+      'label' => 'Read more about this entity',
+      'bundle' => 'entity_test',
+      'settings' => [
+        'title' => DRUPAL_OPTIONAL,
+        'link_type' => $link_type,
+      ],
+    ])->save();
+
+    \Drupal::service('entity_display.repository')
+      ->getFormDisplay('entity_test', 'entity_test')
+      ->setComponent($field_name, ['type' => 'link_default'])
+      ->save();
+
+    $form = \Drupal::service('entity.form_builder')->getForm(EntityTest::create());
+    $this->assertEquals($link_type, $form[$field_name]['widget'][0]['uri']['#link_type']);
+  }
+
+}

web/core/modules/link/tests/src/Kernel/LinkFormatterDisplayTest.php

@@ -0,0 +1,268 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Kernel;
+
+use Drupal\Tests\field\Kernel\FieldKernelTestBase;
+use Drupal\Tests\link\Traits\LinkInputValuesTraits;
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\link\LinkItemInterface;
+
+// cspell:ignore Fragm
+
+/**
+ * Tests the default 'link' field formatter.
+ *
+ * The formatter is tested with several forms of complex query parameters. And
+ * each form is tested with different display settings.
+ *
+ * @group link
+ */
+class LinkFormatterDisplayTest extends FieldKernelTestBase {
+
+  use LinkInputValuesTraits;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['link'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    FieldStorageConfig::create([
+      'entity_type' => 'entity_test',
+      'field_name' => 'field_test',
+      'type' => 'link',
+    ])->save();
+
+    FieldConfig::create([
+      'entity_type' => 'entity_test',
+      'field_name' => 'field_test',
+      'bundle' => 'entity_test',
+      'settings' => [
+        'title' => DRUPAL_OPTIONAL,
+        'link_type' => LinkItemInterface::LINK_GENERIC,
+      ],
+    ])->save();
+  }
+
+  /**
+   * Tests that links are rendered correctly.
+   *
+   * Run tests without dataProvider to improve speed.
+   *
+   * @see \Drupal\Tests\link\Traits\LinkInputValuesTraits::getLinkInputValues()
+   * @see self::getTestCases()
+   */
+  public function testLinkFormatter(): void {
+    // Create an entity with link field values provided.
+    $entity = EntityTest::create();
+    $entity->field_test->setValue($this->getLinkInputValues());
+
+    foreach ($this->getTestCases() as $case_name => $case_options) {
+      [$display_settings, $expected_results] = array_values($case_options);
+      $this->assertEquals(count($this->getLinkInputValues()), count($expected_results), "Each field delta have expected result. Case name: '$case_name'");
+
+      // Render link field with default 'link' formatter and custom
+      // display settings. Hide field label.
+      $render_array = $entity->field_test->view([
+        'label' => 'hidden',
+        'settings' => $display_settings,
+      ]);
+      $output = (string) \Drupal::service('renderer')->renderRoot($render_array);
+      // Convert each field delta value to separate array item.
+      $field_deltas_display = explode("\n", trim($output));
+
+      // Check results.
+      foreach ($expected_results as $delta => $expected_result) {
+        $rendered_delta = trim($field_deltas_display[$delta]);
+        $message = "Test case failed. Case name: '$case_name'. Delta: '$delta'. Uri: '{$this->getLinkInputValues()[$delta]['uri']}'";
+        $this->assertEquals($expected_result, $rendered_delta, $message);
+      }
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getTestCases(): \Generator {
+    $default = [
+      0 => '<div><a href="http://www.example.com/content/articles/archive?author=John&amp;year=2012#com">http://www.example.com/content/articles/archive?author=John&amp;year=2012#com</a></div>',
+      1 => '<div><a href="http://www.example.org/content/articles/archive?author=John&amp;year=2012#org">A very long &amp; strange example title that could break the nice layout of the site</a></div>',
+      2 => '<div><a href="#net">Fragment only</a></div>',
+      3 => '<div><a href="?a%5B0%5D=1&amp;a%5B1%5D=2">?a%5B0%5D=1&amp;a%5B1%5D=2</a></div>',
+      4 => '<div><a href="?b%5B0%5D=1&amp;b%5B1%5D=2">?b%5B0%5D=1&amp;b%5B1%5D=2</a></div>',
+      16 => '<div><a href="?b%5B0%5D=9&amp;b%5B1%5D=8">?b%5B0%5D=9&amp;b%5B1%5D=8</a></div>',
+      5 => '<div><a href="?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3">?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3</a></div>',
+      6 => '<div><a href="?e%5Bf%5D%5Bg%5D=h">?e%5Bf%5D%5Bg%5D=h</a></div>',
+      7 => '<div><a href="?i%5Bj%5Bk%5D=l">?i%5Bj%5Bk%5D=l</a></div>',
+      8 => '<div><a href="?x=2">?x=2</a></div>',
+      9 => '<div><a href="?z%5B0%5D=2">?z%5B0%5D=2</a></div>',
+      10 => '<div><a href=""></a></div>',
+      11 => '<div><a href="">Title, no link</a></div>',
+      12 => '<div><span></span></div>',
+      13 => '<div><span>Title, no link</span></div>',
+      14 => '<div><button type="button"></button></div>',
+      15 => '<div><button type="button">Title, button</button></div>',
+    ];
+
+    yield 'default settings' => [
+      'display settings' => [],
+      'expected_results' => $default,
+    ];
+
+    yield 'trim_length=null' => [
+      'display_settings' => ['trim_length' => NULL],
+      'expected_results' => $default,
+    ];
+
+    yield 'trim_length=6' => [
+      'display settings' => ['trim_length' => 6],
+      'expected_results' => [
+        0 => '<div><a href="http://www.example.com/content/articles/archive?author=John&amp;year=2012#com">http:…</a></div>',
+        1 => '<div><a href="http://www.example.org/content/articles/archive?author=John&amp;year=2012#org">A ver…</a></div>',
+        2 => '<div><a href="#net">Fragm…</a></div>',
+        3 => '<div><a href="?a%5B0%5D=1&amp;a%5B1%5D=2">?a%5B…</a></div>',
+        4 => '<div><a href="?b%5B0%5D=1&amp;b%5B1%5D=2">?b%5B…</a></div>',
+        16 => '<div><a href="?b%5B0%5D=9&amp;b%5B1%5D=8">?b%5B…</a></div>',
+        5 => '<div><a href="?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3">?c%5B…</a></div>',
+        6 => '<div><a href="?e%5Bf%5D%5Bg%5D=h">?e%5B…</a></div>',
+        7 => '<div><a href="?i%5Bj%5Bk%5D=l">?i%5B…</a></div>',
+        8 => '<div><a href="?x=2">?x=2</a></div>',
+        9 => '<div><a href="?z%5B0%5D=2">?z%5B…</a></div>',
+        10 => '<div><a href=""></a></div>',
+        11 => '<div><a href="">Title…</a></div>',
+        12 => '<div><span></span></div>',
+        13 => '<div><span>Title…</span></div>',
+        14 => '<div><button type="button"></button></div>',
+        15 => '<div><button type="button">Title…</button></div>',
+      ],
+    ];
+
+    yield 'attribute rel=null' => [
+      'display_settings' => ['rel' => NULL],
+      'expected_results' => $default,
+    ];
+
+    yield 'attribute rel=nofollow' => [
+      'display_settings' => ['rel' => 'nofollow'],
+      'expected_results' => [
+        0 => '<div><a href="http://www.example.com/content/articles/archive?author=John&amp;year=2012#com" rel="nofollow">http://www.example.com/content/articles/archive?author=John&amp;year=2012#com</a></div>',
+        1 => '<div><a href="http://www.example.org/content/articles/archive?author=John&amp;year=2012#org" rel="nofollow">A very long &amp; strange example title that could break the nice layout of the site</a></div>',
+        2 => '<div><a href="#net" rel="nofollow">Fragment only</a></div>',
+        3 => '<div><a href="?a%5B0%5D=1&amp;a%5B1%5D=2" rel="nofollow">?a%5B0%5D=1&amp;a%5B1%5D=2</a></div>',
+        4 => '<div><a href="?b%5B0%5D=1&amp;b%5B1%5D=2" rel="nofollow">?b%5B0%5D=1&amp;b%5B1%5D=2</a></div>',
+        16 => '<div><a href="?b%5B0%5D=9&amp;b%5B1%5D=8" rel="nofollow">?b%5B0%5D=9&amp;b%5B1%5D=8</a></div>',
+        5 => '<div><a href="?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3" rel="nofollow">?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3</a></div>',
+        6 => '<div><a href="?e%5Bf%5D%5Bg%5D=h" rel="nofollow">?e%5Bf%5D%5Bg%5D=h</a></div>',
+        7 => '<div><a href="?i%5Bj%5Bk%5D=l" rel="nofollow">?i%5Bj%5Bk%5D=l</a></div>',
+        8 => '<div><a href="?x=2" rel="nofollow">?x=2</a></div>',
+        9 => '<div><a href="?z%5B0%5D=2" rel="nofollow">?z%5B0%5D=2</a></div>',
+        10 => '<div><a href="" rel="nofollow"></a></div>',
+        11 => '<div><a href="" rel="nofollow">Title, no link</a></div>',
+        12 => '<div><span rel="nofollow"></span></div>',
+        13 => '<div><span rel="nofollow">Title, no link</span></div>',
+        14 => '<div><button rel="nofollow" type="button"></button></div>',
+        15 => '<div><button rel="nofollow" type="button">Title, button</button></div>',
+      ],
+    ];
+
+    yield 'attribute target=null' => [
+      'display_settings' => ['target' => NULL],
+      'expected_results' => $default,
+    ];
+
+    yield 'attribute target=_blank' => [
+      'display_settings' => ['target' => '_blank'],
+      'expected_results' => [
+        0 => '<div><a href="http://www.example.com/content/articles/archive?author=John&amp;year=2012#com" target="_blank">http://www.example.com/content/articles/archive?author=John&amp;year=2012#com</a></div>',
+        1 => '<div><a href="http://www.example.org/content/articles/archive?author=John&amp;year=2012#org" target="_blank">A very long &amp; strange example title that could break the nice layout of the site</a></div>',
+        2 => '<div><a href="#net" target="_blank">Fragment only</a></div>',
+        3 => '<div><a href="?a%5B0%5D=1&amp;a%5B1%5D=2" target="_blank">?a%5B0%5D=1&amp;a%5B1%5D=2</a></div>',
+        4 => '<div><a href="?b%5B0%5D=1&amp;b%5B1%5D=2" target="_blank">?b%5B0%5D=1&amp;b%5B1%5D=2</a></div>',
+        16 => '<div><a href="?b%5B0%5D=9&amp;b%5B1%5D=8" target="_blank">?b%5B0%5D=9&amp;b%5B1%5D=8</a></div>',
+        5 => '<div><a href="?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3" target="_blank">?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3</a></div>',
+        6 => '<div><a href="?e%5Bf%5D%5Bg%5D=h" target="_blank">?e%5Bf%5D%5Bg%5D=h</a></div>',
+        7 => '<div><a href="?i%5Bj%5Bk%5D=l" target="_blank">?i%5Bj%5Bk%5D=l</a></div>',
+        8 => '<div><a href="?x=2" target="_blank">?x=2</a></div>',
+        9 => '<div><a href="?z%5B0%5D=2" target="_blank">?z%5B0%5D=2</a></div>',
+        10 => '<div><a href="" target="_blank"></a></div>',
+        11 => '<div><a href="" target="_blank">Title, no link</a></div>',
+        12 => '<div><span target="_blank"></span></div>',
+        13 => '<div><span target="_blank">Title, no link</span></div>',
+        14 => '<div><button target="_blank" type="button"></button></div>',
+        15 => '<div><button target="_blank" type="button">Title, button</button></div>',
+      ],
+    ];
+
+    yield 'url_only=false' => [
+      'display_settings' => ['url_only' => FALSE],
+      'expected_results' => $default,
+    ];
+
+    yield 'url_only=true' => [
+      'display_settings' => ['url_only' => TRUE],
+      'expected_results' => [
+        0 => '<div><a href="http://www.example.com/content/articles/archive?author=John&amp;year=2012#com">http://www.example.com/content/articles/archive?author=John&amp;year=2012#com</a></div>',
+        1 => '<div><a href="http://www.example.org/content/articles/archive?author=John&amp;year=2012#org">http://www.example.org/content/articles/archive?author=John&amp;year=2012#org</a></div>',
+        2 => '<div><a href="#net">#net</a></div>',
+        3 => '<div><a href="?a%5B0%5D=1&amp;a%5B1%5D=2">?a%5B0%5D=1&amp;a%5B1%5D=2</a></div>',
+        4 => '<div><a href="?b%5B0%5D=1&amp;b%5B1%5D=2">?b%5B0%5D=1&amp;b%5B1%5D=2</a></div>',
+        16 => '<div><a href="?b%5B0%5D=9&amp;b%5B1%5D=8">?b%5B0%5D=9&amp;b%5B1%5D=8</a></div>',
+        5 => '<div><a href="?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3">?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3</a></div>',
+        6 => '<div><a href="?e%5Bf%5D%5Bg%5D=h">?e%5Bf%5D%5Bg%5D=h</a></div>',
+        7 => '<div><a href="?i%5Bj%5Bk%5D=l">?i%5Bj%5Bk%5D=l</a></div>',
+        8 => '<div><a href="?x=2">?x=2</a></div>',
+        9 => '<div><a href="?z%5B0%5D=2">?z%5B0%5D=2</a></div>',
+        10 => '<div><a href=""></a></div>',
+        11 => '<div><a href=""></a></div>',
+        12 => '<div><span></span></div>',
+        13 => '<div><span></span></div>',
+        14 => '<div><button type="button"></button></div>',
+        15 => '<div><button type="button"></button></div>',
+      ],
+    ];
+
+    yield 'url_only=false, url_plain=true' => [
+      'display_settings' => [
+        'url_only' => FALSE,
+        'url_plain' => TRUE,
+      ],
+      'expected_results' => $default,
+    ];
+
+    yield 'url_only=true, url_plain=true' => [
+      'display_settings' => [
+        'url_only' => TRUE,
+        'url_plain' => TRUE,
+      ],
+      'expected_results' => [
+        0 => '<div>http://www.example.com/content/articles/archive?author=John&amp;year=2012#com</div>',
+        1 => '<div>http://www.example.org/content/articles/archive?author=John&amp;year=2012#org</div>',
+        2 => '<div>#net</div>',
+        3 => '<div>?a%5B0%5D=1&amp;a%5B1%5D=2</div>',
+        4 => '<div>?b%5B0%5D=1&amp;b%5B1%5D=2</div>',
+        16 => '<div>?b%5B0%5D=9&amp;b%5B1%5D=8</div>',
+        5 => '<div>?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3</div>',
+        6 => '<div>?e%5Bf%5D%5Bg%5D=h</div>',
+        7 => '<div>?i%5Bj%5Bk%5D=l</div>',
+        8 => '<div>?x=2</div>',
+        9 => '<div>?z%5B0%5D=2</div>',
+        10 => '<div></div>',
+        11 => '<div></div>',
+        12 => '<div></div>',
+        13 => '<div></div>',
+        14 => '<div></div>',
+        15 => '<div></div>',
+      ],
+    ];
+  }
+
+}

web/core/modules/link/tests/src/Kernel/LinkFormatterTest.php

@@ -0,0 +1,132 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Kernel;
+
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
+use Drupal\user\Entity\Role;
+use Drupal\user\RoleInterface;
+
+/**
+ * Tests the Field Formatter for the link field type.
+ *
+ * @group link
+ */
+class LinkFormatterTest extends EntityKernelTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  protected static $modules = ['link'];
+
+  /**
+   * The entity type used in this test.
+   *
+   * @var string
+   */
+  protected string $entityType = 'entity_test';
+
+  /**
+   * The bundle used in this test.
+   *
+   * @var string
+   */
+  protected string $bundle = 'entity_test';
+
+  /**
+   * The name of the field used in this test.
+   *
+   * @var string
+   */
+  protected string $fieldName = 'field_test';
+
+  /**
+   * The entity to be tested.
+   *
+   * @var \Drupal\Core\Entity\EntityInterface
+   */
+  protected $entity;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Use Stark theme for testing markup output.
+    \Drupal::service('theme_installer')->install(['stark']);
+    $this->config('system.theme')->set('default', 'stark')->save();
+    $this->installEntitySchema('entity_test');
+    // Grant the 'view test entity' permission.
+    $this->installConfig(['user']);
+    Role::load(RoleInterface::ANONYMOUS_ID)
+      ->grantPermission('view test entity')
+      ->save();
+
+    FieldStorageConfig::create([
+      'field_name' => $this->fieldName,
+      'type' => 'link',
+      'entity_type' => $this->entityType,
+      'cardinality' => 1,
+    ])->save();
+
+    FieldConfig::create([
+      'field_name' => $this->fieldName,
+      'entity_type' => $this->entityType,
+      'bundle' => $this->bundle,
+      'label' => 'Field test',
+    ])->save();
+  }
+
+  /**
+   * Tests the link formatters.
+   *
+   * @param string $formatter
+   *   The name of the link formatter to test.
+   *
+   * @dataProvider providerLinkFormatter
+   */
+  public function testLinkFormatter(string $formatter): void {
+    $entity = $this->container->get('entity_type.manager')
+      ->getStorage($this->entityType)
+      ->create([
+        'name' => $this->randomMachineName(),
+        $this->fieldName => [
+          'uri' => 'https://www.drupal.org/',
+          'title' => 'Hello world',
+          'options' => [
+            'attributes' => [
+              'class' => 'classy',
+              'onmouseover' => 'alert(document.cookie)',
+            ],
+          ],
+        ],
+      ]);
+    $entity->save();
+
+    $build = $entity->get($this->fieldName)->view(['type' => $formatter]);
+
+    $renderer = $this->container->get('renderer');
+    $renderer->renderRoot($build[0]);
+
+    $output = (string) $build[0]['#markup'];
+    $this->assertStringContainsString('<a href="https://www.drupal.org/" class="classy">', $output);
+    $this->assertStringNotContainsString('onmouseover=', $output);
+  }
+
+  /**
+   * Data provider for ::testLinkFormatter.
+   */
+  public static function providerLinkFormatter(): array {
+    return [
+      'default formatter' => ['link'],
+      'separate link text and URL' => ['link_separate'],
+    ];
+  }
+
+}

web/core/modules/link/tests/src/Kernel/LinkItemSerializationTest.php

@@ -0,0 +1,107 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Kernel;
+
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\link\LinkItemInterface;
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\Component\Utility\UrlHelper;
+use Drupal\Tests\field\Kernel\FieldKernelTestBase;
+
+/**
+ * Tests link field serialization.
+ *
+ * @group link
+ */
+class LinkItemSerializationTest extends FieldKernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['link', 'serialization'];
+
+  /**
+   * The serializer service.
+   *
+   * @var \Symfony\Component\Serializer\SerializerInterface
+   */
+  protected $serializer;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->installEntitySchema('user');
+    $this->serializer = \Drupal::service('serializer');
+
+    // Create a generic, external, and internal link fields for validation.
+    FieldStorageConfig::create([
+      'entity_type' => 'entity_test',
+      'field_name' => 'field_test',
+      'type' => 'link',
+    ])->save();
+
+    FieldConfig::create([
+      'entity_type' => 'entity_test',
+      'field_name' => 'field_test',
+      'bundle' => 'entity_test',
+      'settings' => ['link_type' => LinkItemInterface::LINK_GENERIC],
+    ])->save();
+  }
+
+  /**
+   * Tests the serialization.
+   */
+  public function testLinkSerialization(): void {
+    // Create entity.
+    $entity = EntityTest::create();
+    $url = 'https://www.drupal.org?test_param=test_value';
+    $parsed_url = UrlHelper::parse($url);
+    $title = $this->randomMachineName();
+    $class = $this->randomMachineName();
+    $entity->field_test->uri = $parsed_url['path'];
+    $entity->field_test->title = $title;
+    $entity->field_test->first()
+      ->get('options')
+      ->set('query', $parsed_url['query']);
+    $entity->field_test->first()
+      ->get('options')
+      ->set('attributes', ['class' => $class]);
+    $entity->save();
+    $serialized = $this->serializer->serialize($entity, 'json');
+    $deserialized = $this->serializer->deserialize($serialized, EntityTest::class, 'json');
+    $options_expected = [
+      'query' => $parsed_url['query'],
+      'attributes' => ['class' => $class],
+    ];
+    $this->assertSame($options_expected, $deserialized->field_test->options);
+  }
+
+  /**
+   * Tests the deserialization.
+   */
+  public function testLinkDeserialization(): void {
+    // Create entity.
+    $entity = EntityTest::create();
+    $url = 'https://www.drupal.org?test_param=test_value';
+    $parsed_url = UrlHelper::parse($url);
+    $title = $this->randomMachineName();
+    $entity->field_test->uri = $parsed_url['path'];
+    $entity->field_test->title = $title;
+    $entity->field_test->first()
+      ->get('options')
+      ->set('query', $parsed_url['query']);
+    $json = json_decode($this->serializer->serialize($entity, 'json'), TRUE);
+    $json['field_test'][0]['options'] = 'string data';
+    $serialized = json_encode($json);
+    $this->expectException(\LogicException::class);
+    $this->expectExceptionMessage('The generic FieldItemNormalizer cannot denormalize string values for "options" properties of the "field_test" field (field item class: Drupal\link\Plugin\Field\FieldType\LinkItem).');
+    $this->serializer->deserialize($serialized, EntityTest::class, 'json');
+  }
+
+}

web/core/modules/link/tests/src/Kernel/LinkItemTest.php

@@ -0,0 +1,181 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Kernel;
+
+use Drupal\Component\Utility\UrlHelper;
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\Core\Field\FieldItemInterface;
+use Drupal\Core\Url;
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\field\Kernel\FieldKernelTestBase;
+use Drupal\link\LinkItemInterface;
+
+/**
+ * Tests the new entity API for the link field type.
+ *
+ * @group link
+ */
+class LinkItemTest extends FieldKernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['link'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Create a generic, external, and internal link fields for validation.
+    FieldStorageConfig::create([
+      'field_name' => 'field_test',
+      'entity_type' => 'entity_test',
+      'type' => 'link',
+    ])->save();
+    FieldConfig::create([
+      'entity_type' => 'entity_test',
+      'field_name' => 'field_test',
+      'bundle' => 'entity_test',
+      'settings' => ['link_type' => LinkItemInterface::LINK_GENERIC],
+    ])->save();
+    FieldStorageConfig::create([
+      'field_name' => 'field_test_external',
+      'entity_type' => 'entity_test',
+      'type' => 'link',
+    ])->save();
+    FieldConfig::create([
+      'entity_type' => 'entity_test',
+      'field_name' => 'field_test_external',
+      'bundle' => 'entity_test',
+      'settings' => ['link_type' => LinkItemInterface::LINK_EXTERNAL],
+    ])->save();
+    FieldStorageConfig::create([
+      'field_name' => 'field_test_internal',
+      'entity_type' => 'entity_test',
+      'type' => 'link',
+    ])->save();
+    FieldConfig::create([
+      'entity_type' => 'entity_test',
+      'field_name' => 'field_test_internal',
+      'bundle' => 'entity_test',
+      'settings' => ['link_type' => LinkItemInterface::LINK_INTERNAL],
+    ])->save();
+  }
+
+  /**
+   * Tests using entity fields of the link field type.
+   */
+  public function testLinkItem(): void {
+    // Create entity.
+    $entity = EntityTest::create();
+    $url = 'https://www.drupal.org?test_param=test_value';
+    $parsed_url = UrlHelper::parse($url);
+    $title = $this->randomMachineName();
+    $class = $this->randomMachineName();
+    $entity->field_test->uri = $parsed_url['path'];
+    $entity->field_test->title = $title;
+    $entity->field_test->first()->get('options')->set('query', $parsed_url['query']);
+    $entity->field_test->first()->get('options')->set('attributes', ['class' => $class]);
+    $this->assertEquals([
+      'query' => $parsed_url['query'],
+      'attributes' => [
+        'class' => $class,
+      ],
+      'external' => TRUE,
+    ], $entity->field_test->first()->getUrl()->getOptions());
+    $entity->name->value = $this->randomMachineName();
+    $entity->save();
+
+    // Verify that the field value is changed.
+    $id = $entity->id();
+    $entity = EntityTest::load($id);
+    $this->assertInstanceOf(FieldItemListInterface::class, $entity->field_test);
+    $this->assertInstanceOf(FieldItemInterface::class, $entity->field_test[0]);
+    $this->assertEquals($parsed_url['path'], $entity->field_test->uri);
+    $this->assertEquals($parsed_url['path'], $entity->field_test[0]->uri);
+    $this->assertEquals($title, $entity->field_test->title);
+    $this->assertEquals($title, $entity->field_test[0]->title);
+    $this->assertEquals($title, $entity->field_test[0]->getTitle());
+    $this->assertEquals($class, $entity->field_test->options['attributes']['class']);
+    $this->assertEquals($parsed_url['query'], $entity->field_test->options['query']);
+
+    // Update only the entity name property to check if the link field data will
+    // remain intact.
+    $entity->name->value = $this->randomMachineName();
+    $entity->save();
+    $id = $entity->id();
+    $entity = EntityTest::load($id);
+    $this->assertEquals($parsed_url['path'], $entity->field_test->uri);
+    $this->assertEquals($class, $entity->field_test->options['attributes']['class']);
+    $this->assertEquals($parsed_url['query'], $entity->field_test->options['query']);
+
+    // Verify changing the field value.
+    $new_url = 'https://www.drupal.org';
+    $new_title = $this->randomMachineName();
+    $new_class = $this->randomMachineName();
+    $entity->field_test->uri = $new_url;
+    $entity->field_test->title = $new_title;
+    $entity->field_test->first()->get('options')->set('query', NULL);
+    $entity->field_test->first()->get('options')->set('attributes', ['class' => $new_class]);
+    $this->assertEquals($new_url, $entity->field_test->uri);
+    $this->assertEquals($new_title, $entity->field_test->title);
+    $this->assertEquals($new_class, $entity->field_test->options['attributes']['class']);
+    $this->assertNull($entity->field_test->options['query']);
+
+    // Read changed entity and assert changed values.
+    $entity->save();
+    $entity = EntityTest::load($id);
+    $this->assertEquals($new_url, $entity->field_test->uri);
+    $this->assertEquals($new_title, $entity->field_test->title);
+    $this->assertEquals($new_class, $entity->field_test->options['attributes']['class']);
+
+    // Check that if we only set uri the default values for title and options
+    // are also initialized.
+    $entity->field_test = ['uri' => 'internal:/node/add'];
+    $this->assertEquals('internal:/node/add', $entity->field_test->uri);
+    $this->assertNull($entity->field_test->title);
+    $this->assertSame([], $entity->field_test->options);
+
+    // Check that if we set uri and options then the default values are properly
+    // initialized.
+    $entity->field_test = [
+      'uri' => 'internal:/node/add',
+      'options' => ['query' => NULL],
+    ];
+    $this->assertEquals('internal:/node/add', $entity->field_test->uri);
+    $this->assertNull($entity->field_test->title);
+    $this->assertNull($entity->field_test->options['query']);
+
+    // Check that if we set the direct value of link field it correctly set the
+    // uri and the default values of the field.
+    $entity->field_test = 'internal:/node/add';
+    $this->assertEquals('internal:/node/add', $entity->field_test->uri);
+    $this->assertNull($entity->field_test->title);
+    $this->assertSame([], $entity->field_test->options);
+
+    // Check that setting options to NULL does not trigger an error when
+    // calling getUrl();
+    $entity->field_test->options = NULL;
+    $this->assertInstanceOf(Url::class, $entity->field_test[0]->getUrl());
+
+    // Check that setting LinkItem value NULL doesn't generate any error or
+    // warning.
+    $entity->field_test[0] = NULL;
+    $this->assertNull($entity->field_test[0]->getValue());
+
+    // Test the generateSampleValue() method for generic, external, and internal
+    // link types.
+    $entity = EntityTest::create();
+    $entity->field_test->generateSampleItems();
+    $entity->field_test_external->generateSampleItems();
+    $entity->field_test_internal->generateSampleItems();
+    $this->entityValidateAndSave($entity);
+  }
+
+}

web/core/modules/link/tests/src/Kernel/LinkItemUrlValidationTest.php

@@ -0,0 +1,124 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Kernel;
+
+use Drupal\Tests\field\Kernel\FieldKernelTestBase;
+
+/**
+ * Tests link field validation.
+ *
+ * @group link
+ */
+class LinkItemUrlValidationTest extends FieldKernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['link'];
+
+  /**
+   * Tests link validation.
+   */
+  public function testExternalLinkValidation(): void {
+    $definition = \Drupal::typedDataManager()
+      ->createDataDefinition('field_item:link');
+    $link_item = \Drupal::typedDataManager()->create($definition);
+    $test_links = $this->getTestLinks();
+
+    foreach ($test_links as $data) {
+      [$value, $expected_violations] = $data;
+      $link_item->setValue($value);
+      $violations = $link_item->validate();
+      $expected_count = count($expected_violations);
+      $this->assertCount($expected_count, $violations, sprintf('Violation message count error for %s', $value));
+      if ($expected_count) {
+        $i = 0;
+        foreach ($expected_violations as $error_msg) {
+          // If the expected message contains a '%' add the current link value.
+          if (strpos($error_msg, '%')) {
+            $error_msg = sprintf($error_msg, $value);
+          }
+          $this->assertEquals($error_msg, $violations[$i++]->getMessage());
+        }
+      }
+    }
+  }
+
+  /**
+   * Builds an array of links to test.
+   *
+   * @return array
+   *   The first element of the array is the link value to test. The second
+   *   value is an array of expected violation messages.
+   */
+  protected function getTestLinks(): array {
+    $violation_0 = "The path '%s' is invalid.";
+    $violation_1 = 'This value should be of the correct primitive type.';
+    return [
+      ['invalid://not-a-valid-protocol', [$violation_0]],
+      ['http://www.example.com/', []],
+      // Strings within parenthesis without leading space char.
+      ['http://www.example.com/strings_(string_within_parenthesis)', []],
+      // Numbers within parenthesis without leading space char.
+      ['http://www.example.com/numbers_(9999)', []],
+      ['http://www.example.com/?name=ferret&color=purple', []],
+      ['http://www.example.com/page?name=ferret&color=purple', []],
+      ['http://www.example.com?a=&b[]=c&d[]=e&d[]=f&h==', []],
+      ['http://www.example.com#colors', []],
+      // Use list of valid URLS from],
+      // https://cran.r-project.org/web/packages/rex/vignettes/url_parsing.html.
+      ["http://foo.com/blah_blah", []],
+      ["http://foo.com/blah_blah/", []],
+      ["http://foo.com/blah_blah_(wikipedia)", []],
+      ["http://foo.com/blah_blah_(wikipedia)_(again)", []],
+      ["http://www.example.com/wpstyle/?p=364", []],
+      ["https://www.example.com/foo/?bar=baz&inga=42&quux", []],
+      ["http://✪df.ws/123", []],
+      ["http://userid:password@example.com:8080", []],
+      ["http://userid:password@example.com:8080/", []],
+      ["http://userid@example.com", []],
+      ["http://userid@example.com/", []],
+      ["http://userid@example.com:8080", []],
+      ["http://userid@example.com:8080/", []],
+      ["http://userid:password@example.com", []],
+      ["http://userid:password@example.com/", []],
+      ["http://➡.ws/䨹", []],
+      ["http://⌘.ws", []],
+      ["http://⌘.ws/", []],
+      ["http://foo.com/blah_(wikipedia)#cite-1", []],
+      ["http://foo.com/blah_(wikipedia)_blah#cite-1", []],
+      // The following invalid URLs produce false positives.
+      ["http://foo.com/unicode_(✪)_in_parens", []],
+      ["http://foo.com/(something)?after=parens", []],
+      ["http://☺.damowmow.com/", []],
+      ["http://code.google.com/events/#&product=browser", []],
+      ["http://j.mp", []],
+      ["ftp://foo.bar/baz", []],
+      ["http://foo.bar/?q=Test%20URL-encoded%20stuff", []],
+      ["http://مثال.إختبار", []],
+      ["http://例子.测试", []],
+      ["http://-.~_!$&'()*+,;=:%40:80%2f::::::@example.com", []],
+      ["http://1337.net", []],
+      ["http://a.b-c.de", []],
+      ["radar://1234", [$violation_0]],
+      ["h://test", [$violation_0]],
+      ["ftps://foo.bar/", [$violation_0]],
+      // Use invalid URLS from
+      // https://cran.r-project.org/web/packages/rex/vignettes/url_parsing.html.
+      ['http://', [$violation_0, $violation_1]],
+      ["http://?", [$violation_0, $violation_1]],
+      ["http://??", [$violation_0, $violation_1]],
+      ["http://??/", [$violation_0, $violation_1]],
+      ["http://#", [$violation_0, $violation_1]],
+      ["http://##", [$violation_0, $violation_1]],
+      ["http://##/", [$violation_0, $violation_1]],
+      ["//", [$violation_0, $violation_1]],
+      ["///a", [$violation_0, $violation_1]],
+      ["///", [$violation_0, $violation_1]],
+      ["http:///a", [$violation_0, $violation_1]],
+    ];
+  }
+
+}

web/core/modules/link/tests/src/Kernel/LinkSeparateFormatterDisplayTest.php

@@ -0,0 +1,339 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Kernel;
+
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\link\LinkItemInterface;
+use Drupal\Tests\field\Kernel\FieldKernelTestBase;
+use Drupal\Tests\link\Traits\LinkInputValuesTraits;
+
+// cspell:ignore Fragm
+
+/**
+ * Tests the 'link_separate' field formatter.
+ *
+ * The formatter is tested with several forms of complex query parameters. And
+ * each form is tested with different display settings.
+ *
+ * @group link
+ */
+class LinkSeparateFormatterDisplayTest extends FieldKernelTestBase {
+
+  use LinkInputValuesTraits;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['link'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    FieldStorageConfig::create([
+      'entity_type' => 'entity_test',
+      'field_name' => 'field_test',
+      'type' => 'link',
+    ])->save();
+
+    FieldConfig::create([
+      'entity_type' => 'entity_test',
+      'field_name' => 'field_test',
+      'bundle' => 'entity_test',
+      'settings' => [
+        'title' => DRUPAL_OPTIONAL,
+        'link_type' => LinkItemInterface::LINK_GENERIC,
+      ],
+    ])->save();
+  }
+
+  /**
+   * Tests that links are rendered correctly.
+   *
+   * Run tests without dataProvider to improve speed.
+   *
+   * @see \Drupal\Tests\link\Traits\LinkInputValuesTraits::getLinkInputValues()
+   * @see self::getTestCases()
+   */
+  public function testLinkSeparateFormatter(): void {
+    // Create an entity with link field values provided.
+    $entity = EntityTest::create();
+    $entity->field_test->setValue($this->getLinkInputValues());
+
+    foreach ($this->getTestCases() as $case_name => $case_options) {
+      [$display_settings, $expected_results] = array_values($case_options);
+      $this->assertEquals(count($this->getLinkInputValues()), count($expected_results), "Each field delta have expected result. Case name: '$case_name'");
+
+      // Render link field with 'link_separate' formatter and custom
+      // display settings. Hide field label.
+      $render_array = $entity->field_test->view([
+        'label' => 'hidden',
+        'settings' => $display_settings,
+        'type' => 'link_separate',
+      ]);
+      $output = (string) \Drupal::service('renderer')->renderRoot($render_array);
+      // Convert each field delta value to separate array item.
+      $field_deltas_display = explode("\n          ", trim($output));
+
+      // Check results.
+      foreach ($expected_results as $delta => $expected_result) {
+        $rendered_delta = trim($field_deltas_display[$delta]);
+        $this->assertEquals($expected_result, $rendered_delta, "Test case failed. Case name: '$case_name'. Delta: '$delta'. Uri: '{$this->getLinkInputValues()[$delta]['uri']}'");
+      }
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getTestCases(): \Generator {
+    $defaultExpectedResults = [
+      0 => '<div>
+<a href="http://www.example.com/content/articles/archive?author=John&amp;year=2012#com">http://www.example.com/content/articles/archive?author=John&amp;year=2012#com</a>
+</div>',
+      1 => '<div>A very long &amp; strange example title that could break the nice layout of the site
+<a href="http://www.example.org/content/articles/archive?author=John&amp;year=2012#org">http://www.example.org/content/articles/archive?author=John&amp;year=2012#org</a>
+</div>',
+      2 => '<div>Fragment only
+<a href="#net">#net</a>
+</div>',
+      3 => '<div>
+<a href="?a%5B0%5D=1&amp;a%5B1%5D=2">?a%5B0%5D=1&amp;a%5B1%5D=2</a>
+</div>',
+      4 => '<div>
+<a href="?b%5B0%5D=1&amp;b%5B1%5D=2">?b%5B0%5D=1&amp;b%5B1%5D=2</a>
+</div>',
+      16 => '<div>
+<a href="?b%5B0%5D=9&amp;b%5B1%5D=8">?b%5B0%5D=9&amp;b%5B1%5D=8</a>
+</div>',
+      5 => '<div>
+<a href="?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3">?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3</a>
+</div>',
+      6 => '<div>
+<a href="?e%5Bf%5D%5Bg%5D=h">?e%5Bf%5D%5Bg%5D=h</a>
+</div>',
+      7 => '<div>
+<a href="?i%5Bj%5Bk%5D=l">?i%5Bj%5Bk%5D=l</a>
+</div>',
+      8 => '<div>
+<a href="?x=2">?x=2</a>
+</div>',
+      9 => '<div>
+<a href="?z%5B0%5D=2">?z%5B0%5D=2</a>
+</div>',
+      10 => '<div>
+<a href=""></a>
+</div>',
+      11 => '<div>Title, no link
+<a href=""></a>
+</div>',
+      12 => '<div>
+<span></span>
+</div>',
+      13 => '<div>Title, no link
+<span></span>
+</div>',
+      14 => '<div>
+<button type="button"></button>
+</div>',
+      15 => '<div>Title, button
+<button type="button"></button>
+</div>',
+    ];
+
+    yield 'default settings' => [
+      'display settings' => [],
+      'expected_results' => $defaultExpectedResults,
+    ];
+
+    yield 'trim_length=null' => [
+      'display_settings' => ['trim_length' => NULL],
+      'expected_results' => $defaultExpectedResults,
+    ];
+
+    yield 'trim_length=6' => [
+      'display settings' => ['trim_length' => 6],
+      'expected_results' => [
+        0 => '<div>
+<a href="http://www.example.com/content/articles/archive?author=John&amp;year=2012#com">http:…</a>
+</div>',
+        1 => '<div>A ver…
+<a href="http://www.example.org/content/articles/archive?author=John&amp;year=2012#org">http:…</a>
+</div>',
+        2 => '<div>Fragm…
+<a href="#net">#net</a>
+</div>',
+        3 => '<div>
+<a href="?a%5B0%5D=1&amp;a%5B1%5D=2">?a%5B…</a>
+</div>',
+        4 => '<div>
+<a href="?b%5B0%5D=1&amp;b%5B1%5D=2">?b%5B…</a>
+</div>',
+        16 => '<div>
+<a href="?b%5B0%5D=9&amp;b%5B1%5D=8">?b%5B…</a>
+</div>',
+        5 => '<div>
+<a href="?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3">?c%5B…</a>
+</div>',
+        6 => '<div>
+<a href="?e%5Bf%5D%5Bg%5D=h">?e%5B…</a>
+</div>',
+        7 => '<div>
+<a href="?i%5Bj%5Bk%5D=l">?i%5B…</a>
+</div>',
+        8 => '<div>
+<a href="?x=2">?x=2</a>
+</div>',
+        9 => '<div>
+<a href="?z%5B0%5D=2">?z%5B…</a>
+</div>',
+        10 => '<div>
+<a href=""></a>
+</div>',
+        11 => '<div>Title…
+<a href=""></a>
+</div>',
+        12 => '<div>
+<span></span>
+</div>',
+        13 => '<div>Title…
+<span></span>
+</div>',
+        14 => '<div>
+<button type="button"></button>
+</div>',
+        15 => '<div>Title…
+<button type="button"></button>
+</div>',
+      ],
+    ];
+
+    yield 'attribute rel=null' => [
+      'display_settings' => ['rel' => NULL],
+      'expected_results' => $defaultExpectedResults,
+    ];
+    yield 'attribute rel=nofollow' => [
+      'display_settings' => ['rel' => 'nofollow'],
+      'expected_results' => [
+        0 => '<div>
+<a href="http://www.example.com/content/articles/archive?author=John&amp;year=2012#com" rel="nofollow">http://www.example.com/content/articles/archive?author=John&amp;year=2012#com</a>
+</div>',
+        1 => '<div>A very long &amp; strange example title that could break the nice layout of the site
+<a href="http://www.example.org/content/articles/archive?author=John&amp;year=2012#org" rel="nofollow">http://www.example.org/content/articles/archive?author=John&amp;year=2012#org</a>
+</div>',
+        2 => '<div>Fragment only
+<a href="#net" rel="nofollow">#net</a>
+</div>',
+        3 => '<div>
+<a href="?a%5B0%5D=1&amp;a%5B1%5D=2" rel="nofollow">?a%5B0%5D=1&amp;a%5B1%5D=2</a>
+</div>',
+        4 => '<div>
+<a href="?b%5B0%5D=1&amp;b%5B1%5D=2" rel="nofollow">?b%5B0%5D=1&amp;b%5B1%5D=2</a>
+</div>',
+        16 => '<div>
+<a href="?b%5B0%5D=9&amp;b%5B1%5D=8" rel="nofollow">?b%5B0%5D=9&amp;b%5B1%5D=8</a>
+</div>',
+        5 => '<div>
+<a href="?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3" rel="nofollow">?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3</a>
+</div>',
+        6 => '<div>
+<a href="?e%5Bf%5D%5Bg%5D=h" rel="nofollow">?e%5Bf%5D%5Bg%5D=h</a>
+</div>',
+        7 => '<div>
+<a href="?i%5Bj%5Bk%5D=l" rel="nofollow">?i%5Bj%5Bk%5D=l</a>
+</div>',
+        8 => '<div>
+<a href="?x=2" rel="nofollow">?x=2</a>
+</div>',
+        9 => '<div>
+<a href="?z%5B0%5D=2" rel="nofollow">?z%5B0%5D=2</a>
+</div>',
+        10 => '<div>
+<a href="" rel="nofollow"></a>
+</div>',
+        11 => '<div>Title, no link
+<a href="" rel="nofollow"></a>
+</div>',
+        12 => '<div>
+<span rel="nofollow"></span>
+</div>',
+        13 => '<div>Title, no link
+<span rel="nofollow"></span>
+</div>',
+        14 => '<div>
+<button rel="nofollow" type="button"></button>
+</div>',
+        15 => '<div>Title, button
+<button rel="nofollow" type="button"></button>
+</div>',
+      ],
+    ];
+    yield 'attribute target=null' => [
+      'display_settings' => ['target' => NULL],
+      'expected_results' => $defaultExpectedResults,
+    ];
+    yield 'attribute target=_blank' => [
+      'display_settings' => ['target' => '_blank'],
+      'expected_results' => [
+        0 => '<div>
+<a href="http://www.example.com/content/articles/archive?author=John&amp;year=2012#com" target="_blank">http://www.example.com/content/articles/archive?author=John&amp;year=2012#com</a>
+</div>',
+        1 => '<div>A very long &amp; strange example title that could break the nice layout of the site
+<a href="http://www.example.org/content/articles/archive?author=John&amp;year=2012#org" target="_blank">http://www.example.org/content/articles/archive?author=John&amp;year=2012#org</a>
+</div>',
+        2 => '<div>Fragment only
+<a href="#net" target="_blank">#net</a>
+</div>',
+        3 => '<div>
+<a href="?a%5B0%5D=1&amp;a%5B1%5D=2" target="_blank">?a%5B0%5D=1&amp;a%5B1%5D=2</a>
+</div>',
+        4 => '<div>
+<a href="?b%5B0%5D=1&amp;b%5B1%5D=2" target="_blank">?b%5B0%5D=1&amp;b%5B1%5D=2</a>
+</div>',
+        16 => '<div>
+<a href="?b%5B0%5D=9&amp;b%5B1%5D=8" target="_blank">?b%5B0%5D=9&amp;b%5B1%5D=8</a>
+</div>',
+        5 => '<div>
+<a href="?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3" target="_blank">?c%5B0%5D=1&amp;c%5B1%5D=2&amp;d=3</a>
+</div>',
+        6 => '<div>
+<a href="?e%5Bf%5D%5Bg%5D=h" target="_blank">?e%5Bf%5D%5Bg%5D=h</a>
+</div>',
+        7 => '<div>
+<a href="?i%5Bj%5Bk%5D=l" target="_blank">?i%5Bj%5Bk%5D=l</a>
+</div>',
+        8 => '<div>
+<a href="?x=2" target="_blank">?x=2</a>
+</div>',
+        9 => '<div>
+<a href="?z%5B0%5D=2" target="_blank">?z%5B0%5D=2</a>
+</div>',
+        10 => '<div>
+<a href="" target="_blank"></a>
+</div>',
+        11 => '<div>Title, no link
+<a href="" target="_blank"></a>
+</div>',
+        12 => '<div>
+<span target="_blank"></span>
+</div>',
+        13 => '<div>Title, no link
+<span target="_blank"></span>
+</div>',
+        14 => '<div>
+<button target="_blank" type="button"></button>
+</div>',
+        15 => '<div>Title, button
+<button target="_blank" type="button"></button>
+</div>',
+      ],
+    ];
+  }
+
+}

web/core/modules/link/tests/src/Kernel/Plugin/migrate/field/d7/LinkFieldTest.php

@@ -0,0 +1,74 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Kernel\Plugin\migrate\field\d7;
+
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\link\Plugin\migrate\field\d7\LinkField;
+use Prophecy\Argument;
+
+/**
+ * @coversDefaultClass \Drupal\link\Plugin\migrate\field\d7\LinkField
+ * @group link
+ */
+class LinkFieldTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['system'];
+
+  /**
+   * @var \Drupal\migrate_drupal\Plugin\MigrateFieldInterface
+   */
+  protected $plugin;
+
+  /**
+   * @var \Drupal\migrate\Plugin\MigrationInterface
+   */
+  protected $migration;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->plugin = new LinkField([], 'link', []);
+
+    $migration = $this->prophesize(MigrationInterface::class);
+
+    // The plugin's alterFieldInstanceMigration() method will call
+    // mergeProcessOfProperty() and return nothing. So, in order to examine the
+    // process pipeline created by the plugin, we need to ensure that
+    // getProcess() always returns the last input to mergeProcessOfProperty().
+    $migration->mergeProcessOfProperty(Argument::type('string'), Argument::type('array'))
+      ->will(function ($arguments) use ($migration) {
+        $migration->getProcess()->willReturn($arguments[1]);
+      });
+
+    $this->migration = $migration->reveal();
+  }
+
+  /**
+   * @covers ::alterFieldInstanceMigration
+   */
+  public function testAlterFieldInstanceMigration($method = 'alterFieldInstanceMigration'): void {
+    $this->plugin->$method($this->migration);
+
+    $expected = [
+      'plugin' => 'static_map',
+      'source' => 'settings/title',
+      'bypass' => TRUE,
+      'map' => [
+        'disabled' => DRUPAL_DISABLED,
+        'optional' => DRUPAL_OPTIONAL,
+        'required' => DRUPAL_REQUIRED,
+      ],
+    ];
+    $this->assertSame($expected, $this->migration->getProcess());
+  }
+
+}

web/core/modules/link/tests/src/Traits/LinkInputValuesTraits.php

@@ -0,0 +1,62 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Traits;
+
+/**
+ * Provides test values for the Link field.
+ */
+trait LinkInputValuesTraits {
+
+  /**
+   * Link field values use for test.
+   *
+   * @return array
+   *   Values to use at link field setter.
+   */
+  protected function getLinkInputValues(): array {
+    $test_values = [
+      // External links.
+      0 => [
+        'uri' => 'http://www.example.com/content/articles/archive?author=John&year=2012#com',
+      ],
+      1 => [
+        'uri' => 'http://www.example.org/content/articles/archive?author=John&year=2012#org',
+        'title' => 'A very long & strange example title that could break the nice layout of the site',
+      ],
+      2 => ['uri' => 'internal:#net', 'title' => 'Fragment only'],
+
+      // Complex internal links.
+      // Result link: '?a[0]=1&a[1]=2'.
+      3 => ['uri' => 'internal:?a[]=1&a[]=2'],
+      4 => ['uri' => 'internal:?b[0]=1&b[1]=2'],
+      // Injecting new test value in the middle of array.
+      16 => ['uri' => 'internal:?b[0]=9&b[1]=8'],
+      // UrlHelper::buildQuery will change order of params.
+      // Result link: '?c[0]=1&c[1]=2&d=3'.
+      5 => ['uri' => 'internal:?c[]=1&d=3&c[]=2'],
+      6 => ['uri' => 'internal:?e[f][g]=h'],
+      7 => ['uri' => 'internal:?i[j[k]]=l'],
+
+      // Query string replace value.
+      // Result link: '?x=1&x=2'.
+      8 => ['uri' => 'internal:?x=1&x=2'],
+      // Result link: '?z[0]=2'.
+      9 => ['uri' => 'internal:?z[0]=1&z[0]=2'],
+
+      // Special empty links.
+      10 => ['uri' => 'route:<none>'],
+      11 => ['uri' => 'route:<none>', 'title' => 'Title, no link'],
+      12 => ['uri' => 'route:<nolink>'],
+      13 => ['uri' => 'route:<nolink>', 'title' => 'Title, no link'],
+      14 => ['uri' => 'route:<button>'],
+      15 => ['uri' => 'route:<button>', 'title' => 'Title, button'],
+
+    ];
+    // Sort by keys, to be able to inject new test anywhere in the array.
+    ksort($test_values, SORT_NUMERIC);
+    return $test_values;
+  }
+
+}

web/core/modules/link/tests/src/Unit/AttributeXssTest.php

@@ -0,0 +1,126 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Unit;
+
+use Drupal\link\AttributeXss;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Tests AttributeXss.
+ *
+ * @group link
+ * @covers \Drupal\link\AttributeXss
+ */
+final class AttributeXssTest extends UnitTestCase {
+
+  /**
+   * Covers ::sanitizeAttributes.
+   *
+   * @dataProvider providerSanitizeAttributes
+   */
+  public function testSanitizeAttributes(array $attributes, array $expected): void {
+    self::assertSame($expected, AttributeXss::sanitizeAttributes($attributes));
+  }
+
+  /**
+   * Data provider for ::testSanitizeAttributes.
+   *
+   * @return \Generator
+   *   Test cases.
+   */
+  public static function providerSanitizeAttributes(): \Generator {
+    yield 'safe' => [
+      ['class' => ['foo', 'bar'], 'data-biscuit' => TRUE],
+      ['class' => ['foo', 'bar'], 'data-biscuit' => TRUE],
+    ];
+
+    yield 'valueless' => [
+      ['class' => ['foo', 'bar'], 'selected' => ''],
+      ['class' => ['foo', 'bar'], 'selected' => ''],
+    ];
+
+    yield 'empty names' => [
+      ['class' => ['foo', 'bar'], '' => 'live', '  ' => TRUE],
+      ['class' => ['foo', 'bar']],
+    ];
+
+    yield 'only empty names' => [
+      ['' => 'live', '  ' => TRUE],
+      [],
+    ];
+
+    yield 'valueless, mangled with a space' => [
+      ['class' => ['foo', 'bar'], 'selected href' => 'http://example.com'],
+      ['class' => ['foo', 'bar'], 'selected' => 'selected', 'href' => 'http://example.com'],
+    ];
+
+    yield 'valueless, mangled with a space, blocked' => [
+      ['class' => ['foo', 'bar'], 'selected onclick href' => 'http://example.com'],
+      ['class' => ['foo', 'bar'], 'selected' => 'selected', 'href' => 'http://example.com'],
+    ];
+
+    yield 'with encoding' => [
+      ['class' => ['foo', 'bar'], 'data-how-good' => "It's the bee's knees"],
+      ['class' => ['foo', 'bar'], 'data-how-good' => "It's the bee's knees"],
+    ];
+
+    yield 'valueless, mangled with multiple spaces, blocked' => [
+      ['class' => ['foo', 'bar'], 'selected  onclick href' => 'http://example.com'],
+      ['class' => ['foo', 'bar'], 'selected' => 'selected', 'href' => 'http://example.com'],
+    ];
+
+    yield 'valueless, mangled with multiple spaces, blocked, mangled first' => [
+      ['selected  onclick href' => 'http://example.com', 'class' => ['foo', 'bar']],
+      ['selected' => 'selected', 'href' => 'http://example.com', 'class' => ['foo', 'bar']],
+    ];
+
+    yield 'valueless but with value' => [
+      ['class' => ['foo', 'bar'], 'selected' => 'selected', 'href' => 'http://example.com'],
+      ['class' => ['foo', 'bar'], 'selected' => 'selected', 'href' => 'http://example.com'],
+    ];
+
+    yield 'valueless but with value, bad protocol' => [
+      ['class' => ['foo', 'bar'], 'selected' => 'selected', 'href' => 'javascript:alert()'],
+      ['class' => ['foo', 'bar'], 'selected' => 'selected', 'href' => 'alert()'],
+    ];
+
+    yield 'valueless, mangled with a space and bad protocol' => [
+      ['class' => ['foo', 'bar'], 'selected href' => 'javascript:alert()'],
+      ['class' => ['foo', 'bar'], 'selected' => 'selected', 'href' => 'alert()'],
+    ];
+
+    yield 'valueless, mangled with a space and bad protocol, repeated' => [
+      ['class' => ['foo', 'bar'], 'selected href' => 'javascript:alert()', 'href' => 'http://example.com'],
+      ['class' => ['foo', 'bar'], 'selected' => 'selected', 'href' => 'alert()'],
+    ];
+
+    yield 'with a space' => [
+      ['class' => ['foo', 'bar'], 'href' => \urlencode('some file.pdf')],
+      ['class' => ['foo', 'bar'], 'href' => 'some+file.pdf'],
+    ];
+
+    yield 'with an unencoded space' => [
+      ['class' => ['foo', 'bar'], 'href' => 'some file.pdf'],
+      ['class' => ['foo', 'bar'], 'href' => 'some file.pdf'],
+    ];
+
+    yield 'xss onclick' => [
+      ['class' => ['foo', 'bar'], 'onclick' => 'alert("whoop");'],
+      ['class' => ['foo', 'bar']],
+    ];
+
+    yield 'xss onclick, valueless, mangled with a space' => [
+      ['class' => ['foo', 'bar'], 'selected onclick href' => 'http://example.com'],
+      ['class' => ['foo', 'bar'], 'selected' => 'selected', 'href' => 'http://example.com'],
+    ];
+
+    yield 'xss protocol' => [
+      ['class' => ['foo', 'bar'], 'src' => 'javascript:alert("whoop");'],
+      ['class' => ['foo', 'bar'], 'src' => 'alert("whoop");'],
+    ];
+
+  }
+
+}

web/core/modules/link/tests/src/Unit/LinkFormatterTest.php

@@ -0,0 +1,155 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Unit;
+
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Field\FieldDefinitionInterface;
+use Drupal\Core\Field\FieldItemList;
+use Drupal\Core\Field\FieldTypePluginManagerInterface;
+use Drupal\Core\Path\PathValidatorInterface;
+use Drupal\Core\Routing\UrlGenerator;
+use Drupal\Core\Url;
+use Drupal\link\LinkItemInterface;
+use Drupal\link\Plugin\Field\FieldFormatter\LinkFormatter;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Tests the Field Formatter for the link field type.
+ *
+ * @group link
+ */
+class LinkFormatterTest extends UnitTestCase {
+
+  /**
+   * Tests when LinkItem::getUrl with malformed URL renders empty link.
+   *
+   * LinkItem::getUrl will throw \InvalidArgumentException.
+   */
+  public function testFormatterLinkItemUrlMalformed(): void {
+    $entity = $this->createMock(EntityInterface::class);
+
+    $linkItem = $this->createMock(LinkItemInterface::class);
+    $exception = new \InvalidArgumentException();
+    $linkItem->expects($this->any())
+      ->method('getParent')
+      ->willReturn($entity);
+    $linkItem->expects($this->once())
+      ->method('getUrl')
+      ->willThrowException($exception);
+    $linkItem->expects($this->any())
+      ->method('__get')
+      ->with('options')
+      ->willReturn([]);
+    $fieldDefinition = $this->createMock(FieldDefinitionInterface::class);
+    $fieldList = new FieldItemList($fieldDefinition, '', $linkItem);
+
+    $fieldTypePluginManager = $this->createMock(FieldTypePluginManagerInterface::class);
+    $fieldTypePluginManager->expects($this->once())
+      ->method('createFieldItem')
+      ->willReturn($linkItem);
+    $urlGenerator = $this->createMock(UrlGenerator::class);
+    $urlGenerator->expects($this->once())
+      ->method('generateFromRoute')
+      ->with('<none>', [], [], FALSE)
+      ->willReturn('http://example.com');
+    $container = new ContainerBuilder();
+    $container->set('plugin.manager.field.field_type', $fieldTypePluginManager);
+    $container->set('url_generator', $urlGenerator);
+    \Drupal::setContainer($container);
+    $fieldList->setValue([$linkItem]);
+
+    $pathValidator = $this->createMock(PathValidatorInterface::class);
+    $linkFormatter = new LinkFormatter('', [], $fieldDefinition, [], '', '', [], $pathValidator);
+    $elements = $linkFormatter->viewElements($fieldList, 'es');
+    $this->assertEquals('link', $elements[0]['#type']);
+  }
+
+  /**
+   * Tests when LinkItem::getUrl throws an unexpected exception.
+   */
+  public function testFormatterLinkItemUrlUnexpectedException(): void {
+    $exception = new \Exception('Unexpected!!!');
+
+    $linkItem = $this->createMock(LinkItemInterface::class);
+    $entity = $this->createMock(EntityInterface::class);
+    $linkItem->expects($this->any())
+      ->method('getParent')
+      ->willReturn($entity);
+    $linkItem->expects($this->once())
+      ->method('getUrl')
+      ->willThrowException($exception);
+    $linkItem->expects($this->any())
+      ->method('__get')
+      ->with('options')
+      ->willReturn([]);
+    $fieldDefinition = $this->createMock(FieldDefinitionInterface::class);
+    $fieldList = new FieldItemList($fieldDefinition, '', $linkItem);
+
+    $fieldTypePluginManager = $this->createMock(FieldTypePluginManagerInterface::class);
+    $fieldTypePluginManager->expects($this->once())
+      ->method('createFieldItem')
+      ->willReturn($linkItem);
+    $container = new ContainerBuilder();
+    $container->set('plugin.manager.field.field_type', $fieldTypePluginManager);
+    \Drupal::setContainer($container);
+    $fieldList->setValue([$linkItem]);
+
+    $pathValidator = $this->createMock(PathValidatorInterface::class);
+    $linkFormatter = new LinkFormatter('', [], $fieldDefinition, [], '', '', [], $pathValidator);
+    $this->expectException(\Exception::class);
+    $this->expectExceptionMessage('Unexpected!!!');
+    $linkFormatter->viewElements($fieldList, 'fr');
+  }
+
+  /**
+   * Tests when LinkItem::getUrl returns a functional URL.
+   */
+  public function testFormatterLinkItem(): void {
+    $expectedUrl = Url::fromUri('route:<front>');
+
+    $linkItem = $this->createMock(LinkItemInterface::class);
+    $entity = $this->createMock(EntityInterface::class);
+    $linkItem->expects($this->any())
+      ->method('getParent')
+      ->willReturn($entity);
+    $linkItem->expects($this->once())
+      ->method('getUrl')
+      ->willReturn($expectedUrl);
+    $linkItem->expects($this->any())
+      ->method('__get')
+      ->with('options')
+      ->willReturn([]);
+    $fieldDefinition = $this->createMock(FieldDefinitionInterface::class);
+    $fieldList = new FieldItemList($fieldDefinition, '', $linkItem);
+
+    $fieldTypePluginManager = $this->createMock(FieldTypePluginManagerInterface::class);
+    $fieldTypePluginManager->expects($this->once())
+      ->method('createFieldItem')
+      ->willReturn($linkItem);
+    $urlGenerator = $this->createMock(UrlGenerator::class);
+    $urlGenerator->expects($this->once())
+      ->method('generateFromRoute')
+      ->with('<front>', [], [], FALSE)
+      ->willReturn('http://example.com');
+    $container = new ContainerBuilder();
+    $container->set('plugin.manager.field.field_type', $fieldTypePluginManager);
+    $container->set('url_generator', $urlGenerator);
+    \Drupal::setContainer($container);
+    $fieldList->setValue([$linkItem]);
+
+    $pathValidator = $this->createMock(PathValidatorInterface::class);
+    $linkFormatter = new LinkFormatter('', [], $fieldDefinition, [], '', '', [], $pathValidator);
+    $elements = $linkFormatter->viewElements($fieldList, 'zh');
+    $this->assertEquals([
+      [
+        '#type' => 'link',
+        '#title' => 'http://example.com',
+        '#url' => $expectedUrl,
+      ],
+    ], $elements);
+  }
+
+}

web/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkAccessConstraintValidatorTest.php

@@ -0,0 +1,86 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Unit\Plugin\Validation\Constraint;
+
+use Drupal\link\Plugin\Validation\Constraint\LinkAccessConstraint;
+use Drupal\link\Plugin\Validation\Constraint\LinkAccessConstraintValidator;
+use Drupal\Tests\UnitTestCase;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
+
+/**
+ * Tests the LinkAccessConstraintValidator validator.
+ *
+ * @coversDefaultClass \Drupal\link\Plugin\Validation\Constraint\LinkAccessConstraintValidator
+ * @group validation
+ */
+class LinkAccessConstraintValidatorTest extends UnitTestCase {
+
+  /**
+   * Tests the access validation constraint for links.
+   *
+   * @covers ::validate
+   * @dataProvider providerValidate
+   */
+  public function testValidate(bool $mayLinkAnyPage, bool $urlAccess, bool $valid): void {
+    // Mock a Url object that returns a boolean indicating user access.
+    $url = $this->getMockBuilder('Drupal\Core\Url')
+      ->disableOriginalConstructor()
+      ->getMock();
+    if ($mayLinkAnyPage) {
+      $url->expects($this->never())
+        ->method('access');
+    }
+    else {
+      $url->expects($this->once())
+        ->method('access')
+        ->willReturn($urlAccess);
+    }
+
+    // Mock a link object that returns the URL object.
+    $link = $this->createMock('Drupal\link\LinkItemInterface');
+    $link->expects($this->any())
+      ->method('getUrl')
+      ->willReturn($url);
+
+    // Mock a user object that returns a boolean indicating user access to all
+    // links.
+    $user = $this->createMock('Drupal\Core\Session\AccountProxyInterface');
+    $user->expects($this->any())
+      ->method('hasPermission')
+      ->with($this->equalTo('link to any page'))
+      ->willReturn($mayLinkAnyPage);
+
+    $context = $this->createMock(ExecutionContextInterface::class);
+    if ($valid) {
+      $context->expects($this->never())
+        ->method('addViolation');
+    }
+    else {
+      $context->expects($this->once())
+        ->method('addViolation');
+    }
+
+    $constraint = new LinkAccessConstraint();
+    $validate = new LinkAccessConstraintValidator($user);
+    $validate->initialize($context);
+    $validate->validate($link, $constraint);
+  }
+
+  /**
+   * Data provider for LinkAccessConstraintValidator::validate().
+   *
+   * @return array
+   *   An array of tests, matching the parameter inputs for testValidate.
+   *
+   * @see \Drupal\Tests\link\LinkAccessConstraintValidatorTest::validate()
+   */
+  public static function providerValidate(): \Generator {
+    yield [TRUE, TRUE, TRUE];
+    yield [TRUE, FALSE, TRUE];
+    yield [FALSE, TRUE, TRUE];
+    yield [FALSE, FALSE, FALSE];
+  }
+
+}

web/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php

@@ -0,0 +1,111 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Unit\Plugin\Validation\Constraint;
+
+use Drupal\Component\Utility\UrlHelper;
+use Drupal\Core\Url;
+use Drupal\link\Plugin\Validation\Constraint\LinkExternalProtocolsConstraint;
+use Drupal\link\Plugin\Validation\Constraint\LinkExternalProtocolsConstraintValidator;
+use Drupal\Tests\UnitTestCase;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
+
+/**
+ * @coversDefaultClass \Drupal\link\Plugin\Validation\Constraint\LinkExternalProtocolsConstraintValidator
+ * @group Link
+ */
+class LinkExternalProtocolsConstraintValidatorTest extends UnitTestCase {
+
+  /**
+   * @covers ::validate
+   * @dataProvider providerValidate
+   * @runInSeparateProcess
+   */
+  public function testValidate($url, $valid): void {
+    $link = $this->createMock('Drupal\link\LinkItemInterface');
+    $link->expects($this->any())
+      ->method('getUrl')
+      ->willReturn(Url::fromUri($url));
+    $context = $this->createMock(ExecutionContextInterface::class);
+
+    if ($valid) {
+      $context->expects($this->never())
+        ->method('addViolation');
+    }
+    else {
+      $context->expects($this->once())
+        ->method('addViolation');
+    }
+
+    // Setup some more allowed protocols.
+    UrlHelper::setAllowedProtocols(['http', 'https', 'magnet']);
+
+    $constraint = new LinkExternalProtocolsConstraint();
+
+    $validator = new LinkExternalProtocolsConstraintValidator();
+    $validator->initialize($context);
+    $validator->validate($link, $constraint);
+  }
+
+  /**
+   * Data provider for ::testValidate.
+   */
+  public static function providerValidate() {
+    $data = [];
+
+    // Test allowed protocols.
+    $data[] = ['http://www.example.com', TRUE];
+    $data[] = ['https://www.example.com', TRUE];
+    // cSpell:disable-next-line
+    $data[] = ['magnet:?xt=urn:sha1:YNCKHTQCWBTRNJIV4WNAE52SJUQCZO5C', TRUE];
+
+    // Invalid protocols.
+    $data[] = ['ftp://ftp.funet.fi/pub/standards/RFC/rfc959.txt', FALSE];
+
+    return $data;
+  }
+
+  /**
+   * @covers ::validate
+   *
+   * @see \Drupal\Core\Url::fromUri
+   */
+  public function testValidateWithMalformedUri(): void {
+    $link = $this->createMock('Drupal\link\LinkItemInterface');
+    $link->expects($this->any())
+      ->method('getUrl')
+      ->willThrowException(new \InvalidArgumentException());
+
+    $context = $this->createMock(ExecutionContextInterface::class);
+    $context->expects($this->never())
+      ->method('addViolation');
+
+    $constraint = new LinkExternalProtocolsConstraint();
+
+    $validator = new LinkExternalProtocolsConstraintValidator();
+    $validator->initialize($context);
+    $validator->validate($link, $constraint);
+  }
+
+  /**
+   * @covers ::validate
+   */
+  public function testValidateIgnoresInternalUrls(): void {
+    $link = $this->createMock('Drupal\link\LinkItemInterface');
+    $link->expects($this->any())
+      ->method('getUrl')
+      ->willReturn(Url::fromRoute('example.test'));
+
+    $context = $this->createMock(ExecutionContextInterface::class);
+    $context->expects($this->never())
+      ->method('addViolation');
+
+    $constraint = new LinkExternalProtocolsConstraint();
+
+    $validator = new LinkExternalProtocolsConstraintValidator();
+    $validator->initialize($context);
+    $validator->validate($link, $constraint);
+  }
+
+}

web/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkNotExistingInternalConstraintValidatorTest.php

@@ -0,0 +1,118 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Unit\Plugin\Validation\Constraint;
+
+use Drupal\Core\Routing\UrlGeneratorInterface;
+use Drupal\Core\Url;
+use Drupal\link\LinkItemInterface;
+use Drupal\link\Plugin\Validation\Constraint\LinkNotExistingInternalConstraint;
+use Drupal\link\Plugin\Validation\Constraint\LinkNotExistingInternalConstraintValidator;
+use Drupal\Tests\UnitTestCase;
+use PHPUnit\Framework\MockObject\MockObject;
+use Symfony\Component\Routing\Exception\RouteNotFoundException;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
+
+/**
+ * @coversDefaultClass \Drupal\link\Plugin\Validation\Constraint\LinkNotExistingInternalConstraintValidator
+ * @group Link
+ */
+class LinkNotExistingInternalConstraintValidatorTest extends UnitTestCase {
+
+  /**
+   * @covers ::validate
+   */
+  public function testValidateFromUri(): void {
+    $url = Url::fromUri('https://www.drupal.org');
+
+    $link = $this->createMock(LinkItemInterface::class);
+    $link->expects($this->any())
+      ->method('getUrl')
+      ->willReturn($url);
+
+    $context = $this->createMock(ExecutionContextInterface::class);
+    $context->expects($this->never())
+      ->method('addViolation');
+
+    $this->validate($link, $context);
+  }
+
+  /**
+   * @covers ::validate
+   */
+  public function testValidateFromRoute(): void {
+    $url = Url::fromRoute('example.existing_route');
+
+    $urlGenerator = $this->createMock(UrlGeneratorInterface::class);
+    $urlGenerator->expects($this->any())
+      ->method('generateFromRoute')
+      ->with('example.existing_route', [], [])
+      ->willReturn('/example/existing');
+    $url->setUrlGenerator($urlGenerator);
+
+    $link = $this->createMock(LinkItemInterface::class);
+    $link->expects($this->any())
+      ->method('getUrl')
+      ->willReturn($url);
+
+    $context = $this->createMock(ExecutionContextInterface::class);
+    $context->expects($this->never())
+      ->method('addViolation');
+
+    $this->validate($link, $context);
+  }
+
+  /**
+   * @covers ::validate
+   */
+  public function testValidateFromNonExistingRoute(): void {
+    $url = Url::fromRoute('example.not_existing_route');
+
+    $urlGenerator = $this->createMock(UrlGeneratorInterface::class);
+    $urlGenerator->expects($this->any())
+      ->method('generateFromRoute')
+      ->with('example.not_existing_route', [], [])
+      ->willThrowException(new RouteNotFoundException());
+    $url->setUrlGenerator($urlGenerator);
+
+    $link = $this->createMock(LinkItemInterface::class);
+    $link->expects($this->any())
+      ->method('getUrl')
+      ->willReturn($url);
+
+    $context = $this->createMock(ExecutionContextInterface::class);
+    $context->expects($this->once())
+      ->method('addViolation');
+
+    $this->validate($link, $context);
+  }
+
+  /**
+   * @covers ::validate
+   *
+   * @see \Drupal\Core\Url::fromUri
+   */
+  public function testValidateWithMalformedUri(): void {
+    $link = $this->createMock(LinkItemInterface::class);
+    $link->expects($this->any())
+      ->method('getUrl')
+      ->willThrowException(new \InvalidArgumentException());
+
+    $context = $this->createMock(ExecutionContextInterface::class);
+    $context->expects($this->never())
+      ->method('addViolation');
+
+    $this->validate($link, $context);
+  }
+
+  /**
+   * Validate the link.
+   */
+  protected function validate(LinkItemInterface&MockObject $link, ExecutionContextInterface&MockObject $context): void {
+    $validator = new LinkNotExistingInternalConstraintValidator();
+    $validator->initialize($context);
+    $validator->validate($link, new LinkNotExistingInternalConstraint());
+  }
+
+}

web/core/modules/link/tests/src/Unit/Plugin/migrate/field/d6/LinkFieldTest.php

@@ -0,0 +1,67 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Unit\Plugin\migrate\field\d6;
+
+use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\Tests\UnitTestCase;
+use Drupal\link\Plugin\migrate\field\d6\LinkField;
+use Prophecy\Argument;
+
+/**
+ * @coversDefaultClass \Drupal\link\Plugin\migrate\field\d6\LinkField
+ * @group link
+ */
+class LinkFieldTest extends UnitTestCase {
+
+  /**
+   * The migrate field plugin.
+   *
+   * @var \Drupal\migrate_drupal\Plugin\MigrateFieldInterface
+   */
+  protected $plugin;
+
+  /**
+   * The migration.
+   *
+   * @var \Drupal\migrate\Plugin\MigrationInterface
+   */
+  protected $migration;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->plugin = new LinkField([], 'link', []);
+
+    $migration = $this->prophesize(MigrationInterface::class);
+
+    // The plugin's defineValueProcessPipeline() method will call
+    // mergeProcessOfProperty() and return nothing. So, in order to examine the
+    // process pipeline created by the plugin, we need to ensure that
+    // getProcess() always returns the last input to mergeProcessOfProperty().
+    $migration->mergeProcessOfProperty(Argument::type('string'), Argument::type('array'))
+      ->will(function ($arguments) use ($migration) {
+        $migration->getProcess()->willReturn($arguments[1]);
+      });
+
+    $this->migration = $migration->reveal();
+  }
+
+  /**
+   * @covers ::defineValueProcessPipeline
+   */
+  public function testDefineValueProcessPipeline($method = 'defineValueProcessPipeline'): void {
+    $this->plugin->$method($this->migration, 'field_name', []);
+
+    $expected = [
+      'plugin' => 'field_link',
+      'source' => 'field_name',
+    ];
+    $this->assertSame($expected, $this->migration->getProcess());
+  }
+
+}

web/core/modules/link/tests/src/Unit/Plugin/migrate/process/FieldLinkTest.php

@@ -0,0 +1,135 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\link\Unit\Plugin\migrate\process;
+
+use Drupal\link\Plugin\migrate\process\FieldLink;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\migrate\Row;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Tests the link field migrate process plugin.
+ *
+ * @group Link
+ */
+class FieldLinkTest extends UnitTestCase {
+
+  /**
+   * Tests the URL transformations in the FieldLink process plugin.
+   *
+   * @dataProvider canonicalizeUriDataProvider
+   */
+  public function testCanonicalizeUri($url, $expected, $configuration = []): void {
+    $link_plugin = new FieldLink($configuration, '', [], $this->createMock(MigrationInterface::class));
+    $transformed = $link_plugin->transform([
+      'url' => $url,
+      'title' => '',
+      'attributes' => serialize([]),
+    ], $this->createMock(MigrateExecutableInterface::class), $this->getMockBuilder(Row::class)->disableOriginalConstructor()->getMock(), NULL);
+    $this->assertEquals($expected, $transformed['uri']);
+  }
+
+  /**
+   * Data provider for testCanonicalizeUri.
+   */
+  public static function canonicalizeUriDataProvider() {
+    return [
+      'Simple front-page' => [
+        '<front>',
+        'internal:/',
+      ],
+      'Front page with query' => [
+        '<front>?query=1',
+        'internal:/?query=1',
+      ],
+      'No leading forward slash' => [
+        'node/10',
+        'internal:/node/10',
+      ],
+      'Leading forward slash' => [
+        '/node/10',
+        'internal:/node/10',
+      ],
+      'Existing scheme' => [
+        'scheme:test',
+        'scheme:test',
+      ],
+      'Absolute URL with protocol prefix' => [
+        'http://www.google.com',
+        'http://www.google.com',
+      ],
+      'Absolute URL without protocol prefix' => [
+        'www.yahoo.com',
+        'http://www.yahoo.com',
+      ],
+      'Absolute URL without protocol prefix nor www' => [
+        'yahoo.com',
+        'https://yahoo.com',
+        ['uri_scheme' => 'https://'],
+      ],
+      'Absolute URL without explicit protocol (protocol-relative)' => [
+        '//example.com',
+        'http://example.com',
+      ],
+      'Absolute URL with non-standard characters' => [
+        'http://www.ßÀÑÐ¥ƒå¢ë.com',
+        'http://www.ßÀÑÐ¥ƒå¢ë.com',
+      ],
+      'Absolute URL with non-standard characters, without protocol prefix' => [
+        'www.ÐØÑ¢åþë.com',
+        'http://www.ÐØÑ¢åþë.com',
+      ],
+      'Absolute URL with non-standard top level domain' => [
+        'http://www.example.xxx',
+        'http://www.example.xxx',
+      ],
+      'Internal link with fragment' => [
+        '/node/10#top',
+        'internal:/node/10#top',
+      ],
+      'External link with fragment' => [
+        'http://www.example.com/page#links',
+        'http://www.example.com/page#links',
+      ],
+      'empty' => [
+        '',
+        'route:<nolink>',
+      ],
+      'No link' => [
+        '<nolink>',
+        'route:<nolink>',
+      ],
+      'none' => [
+        '<none>',
+        'route:<nolink>',
+      ],
+    ];
+  }
+
+  /**
+   * Tests the attributes that are deeply serialized are discarded.
+   */
+  public function testCanonicalizeUriSerialized(): void {
+    $link_plugin = new FieldLink([], '', [], $this->createMock(MigrationInterface::class));
+    $migrate_executable = $this->createMock(MigrateExecutableInterface::class);
+    $row = new Row();
+
+    $transformed = $link_plugin->transform([
+      'url' => '',
+      'title' => '',
+      'attributes' => serialize(serialize(['not too deep'])),
+    ], $migrate_executable, $row, NULL);
+    $this->assertEquals(['not too deep'], $transformed['options']['attributes']);
+
+    $transformed = $link_plugin->transform([
+      'url' => '',
+      'title' => '',
+      'attributes' => serialize(serialize(serialize(['too deep']))),
+    ], $migrate_executable, $row, NULL);
+    $this->assertEmpty($transformed['options']['attributes']);
+  }
+
+}

web/core/modules/link/tests/themes/link_test_theme/link_test_theme.info.yml

@@ -0,0 +1,5 @@
+name: 'Link Test Theme'
+type: theme
+description: 'Theme for testing link module'
+version: VERSION
+base theme: stark

web/core/modules/link/tests/themes/link_test_theme/templates/link-formatter-link-separate.html.twig

@@ -0,0 +1,19 @@
+{#
+/**
+ * @file
+ * Theme override of a link with separate title and URL elements.
+ *
+ * Available variables:
+ * - link: The link that has already been formatted by l().
+ * - title: (optional) A descriptive or alternate title for the link, which may
+ *   be different than the actual link text.
+ *
+ * @see template_preprocess_link_formatter_link_separate()
+ */
+#}
+<div class="link-item">
+  {%- if title -%}
+    <div class="link-title">{{- title -}}</div>
+  {%- endif -%}
+  <div class="link-url">{{- link -}}</div>
+</div>