diff -u b/core/modules/views/src/Plugin/views/filter/Compare.php b/core/modules/views/src/Plugin/views/filter/Compare.php
--- b/core/modules/views/src/Plugin/views/filter/Compare.php
+++ b/core/modules/views/src/Plugin/views/filter/Compare.php
@@ -101,7 +101,12 @@
    * {@inheritdoc}
    */
   public function adminSummary() {
-    return new FormattableMarkup('@left_field @operator @right_field', ['@left_field' => $this->options['left_field'], '@operator' => $this->options['operator'], '@right_field' => $this->options['right_field']]);
+    return new FormattableMarkup('@left_field @operator @right_field', [
+      '@left_field' => $this->options['left_field'],
+      '@operator' => $this->options['operator'],
+      '@right_field' => $this->options['right_field'],
+    ]
+    );
   }
 
   /**
@@ -122,13 +127,13 @@
     }
 
     // Get the left table and field.
-    /** @var \Drupal\views\Plugin\views\filter\FilterPluginBase $left_handler */
+    /** @var FilterPluginBase $left_handler */
     $left_handler = $field_handlers[$left];
     $left_handler->setRelationship();
     $left_table_alias = $this->query->ensureTable($left_handler->table, $left_handler->relationship);
 
     // Get the right table and field.
-    /** @var \Drupal\views\Plugin\views\filter\FilterPluginBase $right_handler */
+    /** @var FilterPluginBase $right_handler */
     $right_handler = $field_handlers[$right];
     $right_handler->setRelationship();
     $right_table_alias = $this->query->ensureTable($right_handler->table, $right_handler->relationship);
diff -u b/core/modules/views/tests/src/Kernel/Handler/FilterCompareTest.php b/core/modules/views/tests/src/Kernel/Handler/FilterCompareTest.php
--- b/core/modules/views/tests/src/Kernel/Handler/FilterCompareTest.php
+++ b/core/modules/views/tests/src/Kernel/Handler/FilterCompareTest.php
@@ -16,7 +16,7 @@
   /**
    * The column map used in the test.
    *
-   * @var array
+   * @var array|string[]
    */
   protected $columnMap = [
     'views_test_data_name' => 'name',
@@ -25,12 +25,15 @@
   /**
    * Views used by this test.
    *
-   * @var array
+   * @var array|string[]
    */
   public static $testViews = ['test_filter_compare'];
 
   /**
-   * {@inheritdoc}
+   * Returns a very simple test dataset.
+   *
+   * @returns array
+   *  dataset value array.
    */
   protected function dataSet() {
     // Setup age/created so comparing fields can be tested.
@@ -48,7 +51,7 @@
   /**
    * Tests the compare handler.
    */
-  public function testCompare() {
+  public function testCompare() : void {
     $view = Views::getView('test_filter_compare');
 
     // Test the equality operator.
@@ -103,7 +106,7 @@
     ];
 
     foreach ($tests as $parts) {
-      list($operator, $expected) = $parts;
+      [$operator, $expected] = $parts;
 
       $view->initDisplay();
       $item = $view->getHandler('default', 'filter', 'fields_compare');
diff -u b/core/modules/views/views.views.inc b/core/modules/views/views.views.inc
--- b/core/modules/views/views.views.inc
+++ b/core/modules/views/views.views.inc
@@ -1,10 +1,12 @@
 <?php
 
+use Drupal\views\EntityViewsDataInterface;
 /**
  * @file
  * Provide views data that isn't tied to any other module.
  */
 
+use Drupal\Core\Entity\Sql\DefaultTableMapping;
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Entity\ContentEntityTypeInterface;
 use Drupal\Core\Entity\EntityStorageInterface;
@@ -22,14 +24,14 @@
   $data['views']['table']['group'] = t('Global');
   $data['views']['table']['join'] = [
   // #global is a special flag which allows a table to appear all the time.
-  '#global' => [],
+    '#global' => [],
   ];
 
   $data['views']['random'] = [
-  'title' => t('Random'),
-  'help' => t('Randomize the display order.'),
-  'sort' => [
-    'id' => 'random',
+    'title' => t('Random'),
+    'help' => t('Randomize the display order.'),
+    'sort' => [
+      'id' => 'random',
     ],
   ];
 
@@ -116,7 +118,7 @@
   ];
 
   $data['views']['combine'] = [
-   'title' => t('Combine fields filter'),
+    'title' => t('Combine fields filter'),
     'help' => t('Combine multiple fields together and search by them.'),
     'filter' => [
       'id' => 'combine',
@@ -183,7 +185,7 @@
   // Registers views data for the entity itself.
   foreach (\Drupal::entityTypeManager()->getDefinitions() as $entity_type_id => $entity_type) {
     if ($entity_type->hasHandlerClass('views_data')) {
-      /** @var \Drupal\views\EntityViewsDataInterface $views_data */
+      /** @var EntityViewsDataInterface $views_data */
       $views_data = \Drupal::entityTypeManager()->getHandler($entity_type_id, 'views_data');
       $data = NestedArray::mergeDeep($data, $views_data->getViewsData());
     }
@@ -195,7 +197,7 @@
 
   $entity_type_manager = \Drupal::entityTypeManager();
   if ($entity_type_manager->hasDefinition('field_storage_config')) {
-    /** @var \Drupal\field\FieldStorageConfigInterface $field_storage */
+    /** @var FieldStorageConfigInterface $field_storage */
     foreach ($entity_type_manager->getStorage('field_storage_config')->loadMultiple() as $field_storage) {
       if (_views_field_get_entity_type_storage($field_storage)) {
         $result = (array) $module_handler->invoke($field_storage->getTypeProvider(), 'field_views_data', [$field_storage]);
@@ -227,7 +229,7 @@
   if (!$entity_type_manager->hasDefinition('field_storage_config')) {
     return;
   }
-  /** @var \Drupal\field\FieldStorageConfigInterface $field_storage */
+  /** @var FieldStorageConfigInterface $field_storage */
   foreach ($entity_type_manager->getStorage('field_storage_config')->loadMultiple() as $field_storage) {
     if (_views_field_get_entity_type_storage($field_storage)) {
       $function = $field_storage->getTypeProvider() . '_field_views_data_views_data_alter';
@@ -241,10 +243,10 @@
 /**
  * Determines whether the entity type the field appears in is SQL based.
  *
- * @param \Drupal\field\FieldStorageConfigInterface $field_storage
+ * @param FieldStorageConfigInterface $field_storage
  *   The field storage definition.
  *
- * @return \Drupal\Core\Entity\Sql\SqlContentEntityStorage
+ * @return SqlContentEntityStorage
  *   Returns the entity type storage if supported.
  */
 function _views_field_get_entity_type_storage(FieldStorageConfigInterface $field_storage) {
@@ -297,7 +299,7 @@
 /**
  * Default views data implementation for a field.
  *
- * @param \Drupal\field\FieldStorageConfigInterface $field_storage
+ * @param FieldStorageConfigInterface $field_storage
  *   The field definition.
  *
  * @return array
@@ -358,6 +360,7 @@
   // @todo Generalize this code to make it work with any table layout. See
   //   https://www.drupal.org/node/2079019.
   $table_mapping = $storage->getTableMapping();
+  assert($table_mapping instanceof DefaultTableMapping);
   $field_tables = [
     EntityStorageInterface::FIELD_LOAD_CURRENT => [
       'table' => $table_mapping->getDedicatedDataTableName($field_storage),
@@ -549,9 +552,17 @@
             'base' => $base_table,
             'group' => $group_name,
             'title' => $label_name,
-            'help' => t('This is an alias of @group: @field.', ['@group' => $group_name, '@field' => $label]),
+            'help' => t('This is an alias of @group: @field.', [
+              '@group' => $group_name,
+              '@field' => $label,
+            ]
+            ),
           ];
-          $also_known[] = t('@group: @field', ['@group' => $group_name, '@field' => $label_name]);
+          $also_known[] = t('@group: @field', [
+            '@group' => $group_name,
+            '@field' => $label_name,
+          ]
+          );
         }
       }
       elseif ($supports_revisions && $label != $label_name) {
@@ -559,9 +570,17 @@
           'base' => $table,
           'group' => t('@group (historical data)', ['@group' => $group_name]),
           'title' => $label_name,
-          'help' => t('This is an alias of @group: @field.', ['@group' => $group_name, '@field' => $label]),
+          'help' => t('This is an alias of @group: @field.', [
+            '@group' => $group_name,
+            '@field' => $label,
+          ]
+          ),
         ];
-        $also_known[] = t('@group (historical data): @field', ['@group' => $group_name, '@field' => $label_name]);
+        $also_known[] = t('@group (historical data): @field', [
+          '@group' => $group_name,
+          '@field' => $label_name,
+        ]
+        );
       }
     }
     if ($aliases) {
@@ -598,7 +617,7 @@
   foreach ($field_columns as $column => $attributes) {
     $allow_sort = TRUE;
 
-    // Identify likely filters and arguments for each column based on field type.
+    // Identify likely filters & arguments for each column based on field type.
     switch ($attributes['type']) {
       case 'int':
       case 'mediumint':
@@ -630,8 +649,17 @@
       $title_short = $label;
     }
     else {
-      $title = t('@label (@name:@column)', ['@label' => $label, '@name' => $field_name, '@column' => $column]);
-      $title_short = t('@label:@column', ['@label' => $label, '@column' => $column]);
+      $title = t('@label (@name:@column)', [
+        '@label' => $label,
+        '@name' => $field_name,
+        '@column' => $column,
+      ]
+      );
+      $title_short = t('@label:@column', [
+        '@label' => $label,
+        '@column' => $column,
+      ]
+      );
     }
 
     // Expose data for the property.
@@ -657,24 +685,41 @@
         'help' => t('Appears in: @bundles.', ['@bundles' => implode(', ', $bundles_names)]),
       ];
 
-      // Go through and create a list of aliases for all possible combinations of
-      // entity type + name.
+      // Go through and create a list of aliases for all possible
+      // combinations of entity type + name.
       $aliases = [];
       $also_known = [];
       foreach ($all_labels as $label_name => $true) {
         if ($label != $label_name) {
           if (count($field_columns) == 1 || $column == 'value') {
-            $alias_title = t('@label (@name)', ['@label' => $label_name, '@name' => $field_name]);
+            $alias_title = t('@label (@name)', [
+              '@label' => $label_name,
+              '@name' => $field_name,
+            ]
+            );
           }
           else {
-            $alias_title = t('@label (@name:@column)', ['@label' => $label_name, '@name' => $field_name, '@column' => $column]);
+            $alias_title = t('@label (@name:@column)', [
+              '@label' => $label_name,
+              '@name' => $field_name,
+              '@column' => $column,
+            ]
+            );
           }
           $aliases[] = [
             'group' => $group_name,
             'title' => $alias_title,
-            'help' => t('This is an alias of @group: @field.', ['@group' => $group_name, '@field' => $title]),
+            'help' => t('This is an alias of @group: @field.', [
+              '@group' => $group_name,
+              '@field' => $title,
+            ]
+            ),
           ];
-          $also_known[] = t('@group: @field', ['@group' => $group_name, '@field' => $title]);
+          $also_known[] = t('@group: @field', [
+            '@group' => $group_name,
+            '@field' => $title,
+          ]
+          );
         }
       }
       if ($aliases) {
@@ -727,7 +772,11 @@
 
       // Expose additional delta column for multiple value fields.
       if ($field_storage->isMultiple()) {
-        $title_delta = t('@label (@name:delta)', ['@label' => $label, '@name' => $field_name]);
+        $title_delta = t('@label (@name:delta)', [
+          '@label' => $label,
+          '@name' => $field_name,
+        ]
+        );
         $title_short_delta = t('@label:delta', ['@label' => $label]);
 
         $data[$table_alias]['delta'] = [
@@ -789,7 +838,7 @@
 
   $entity_type_manager = \Drupal::entityTypeManager();
   $entity_type_id = $field_storage->getTargetEntityTypeId();
-  /** @var \Drupal\Core\Entity\Sql\DefaultTableMapping $table_mapping */
+  /** @var DefaultTableMapping $table_mapping */
   $table_mapping = $entity_type_manager->getStorage($entity_type_id)->getTableMapping();
 
   foreach ($data as $table_name => $table_data) {
@@ -820,8 +869,8 @@
         'relationship field' => $field_name . '_target_id',
       ];
 
-      // Provide a reverse relationship for the entity type that is referenced by
-      // the field.
+      // Provide a reverse relationship for the entity type that is referenced
+      // by the field.
       $args['@entity'] = $entity_type->getLabel();
       $args['@label'] = $target_entity_type->getSingularLabel();
       $pseudo_field_name = 'reverse__' . $entity_type_id . '__' . $field_name;