[#2570593]: Add special case to EntityStorageBase::postLoad() for which entities to pass.

- If there's only a single class involved, pass the original $entities array.
- If there are multiple bundle classes, pass each one the matching entities from $items.
- Reverts the test coverage changes from the previous commit so we test the else case.
- Existing tests of role weights are excercising the if() case.

core/lib/Drupal/Core/Entity/EntityStorageBase.php

@@ -363,14 +363,21 @@ protected function preLoad(array &$ids = NULL) {
   protected function postLoad(array &$entities) {
     $entities_by_class = $this->getEntitiesByClass($entities);
 
-    // Invoke entity class specific postLoad() methods.
-    foreach (array_keys($entities_by_class) as $entity_class) {
-      // We must pass the full $entities array each time, so that if a
-      // postLoad() method is trying to reorder the array (for example,
-      // \Drupal\user\Entity\Role::postLoad()), it can actually manipulate the
-      // final array, not a subarray.
+    // Invoke entity class specific postLoad() methods. If there's only a single
+    // class involved, we want to pass in the original $entities array. For
+    // example, \Drupal\user\Entity\Role::postLoad() sorts the array to enforce
+    // role weights. We have to let it manipulate the final array, not a
+    // subarray. However if there are multiple bundle classes involved, we only
+    // want to pass each one the entities that match.
+    if (count($entities_by_class) === 1) {
+      $entity_class = array_key_first($entities_by_class);
       $entity_class::postLoad($this, $entities);
     }
+    else {
+      foreach ($entities_by_class as $entity_class => &$items) {
+        $entity_class::postLoad($this, $items);
+      }
+    }
     // Call hook_entity_load().
     foreach ($this->moduleHandler()->getImplementations('entity_load') as $module) {
       $function = $module . '_entity_load';

core/tests/Drupal/KernelTests/Core/Entity/BundleClassTest.php

@@ -146,11 +146,11 @@ public function testEntitySubclass() {
     $this->assertEquals(2, EntityTestBundleClass::$postLoadCount);
     $this->assertCount(2, EntityTestBundleClass::$postLoadEntitiesCount);
 
-    // Only 4 of the 5 requested entities need to be loaded. The other ($entity)
-    // has already been loaded and we're getting the cached entity without
-    // re-invoking postLoad(). So the custom postLoad() method should only have
-    // been invoked with 4 entities.
-    $this->assertEquals(4, EntityTestBundleClass::$postLoadEntitiesCount[1]);
+    // Only 3 of the 5 entities we just loaded use the bundle class. However,
+    // one of them has already been loaded and we're getting the cached entity
+    // without re-invoking postLoad(). So the custom postLoad() method should
+    // only have been invoked with 2 entities.
+    $this->assertEquals(2, EntityTestBundleClass::$postLoadEntitiesCount[1]);
 
     // Reset the storage cache and try loading again.
     $this->storage->resetCache();
@@ -158,8 +158,8 @@ public function testEntitySubclass() {
     $entities = $this->storage->loadMultiple($entity_ids);
     $this->assertEquals(3, EntityTestBundleClass::$postLoadCount);
     $this->assertCount(3, EntityTestBundleClass::$postLoadEntitiesCount);
-    // This time, all 5 entities should be included.
-    $this->assertEquals(5, EntityTestBundleClass::$postLoadEntitiesCount[2]);
+    // This time, all 3 bundle_class entities should be included.
+    $this->assertEquals(3, EntityTestBundleClass::$postLoadEntitiesCount[2]);
 
     // Start deleting things and count delete-related method invocations.
     $entity_test_1->delete();