Use the registryAlias when setting entity source.

Refs #7187

src/ORM/ResultSet.php

@@ -507,7 +507,7 @@ class ResultSet implements ResultSetInterface
                 )
             );
             if ($this->_hydrate) {
-                $options['source'] = $alias;
+                $options['source'] = $matching['instance']->registryAlias();
                 $entity = new $matching['entityClass']($results['_matchingData'][$alias], $options);
                 $entity->clean();
                 $results['_matchingData'][$alias] = $entity;
@@ -546,7 +546,7 @@ class ResultSet implements ResultSetInterface
             }
 
             $target = $instance->target();
-            $options['source'] = $target->alias();
+            $options['source'] = $target->registryAlias();
             unset($presentAliases[$alias]);
 
             if ($assoc['canBeJoined']) {

tests/TestCase/ORM/ResultSetTest.php

@@ -15,6 +15,7 @@
 namespace Cake\Test\TestCase\ORM;
 
 use Cake\Core\Configure;
+use Cake\Core\Plugin;
 use Cake\Datasource\ConnectionManager;
 use Cake\ORM\Entity;
 use Cake\ORM\Query;
@@ -29,7 +30,7 @@ use Cake\TestSuite\TestCase;
 class ResultSetTest extends TestCase
 {
 
-    public $fixtures = ['core.articles', 'core.comments'];
+    public $fixtures = ['core.authors', 'core.articles', 'core.comments'];
 
     /**
      * setup
@@ -343,4 +344,28 @@ class ResultSetTest extends TestCase
         $result->valid();
         $data = $result->current();
     }
+
+    /**
+     * Test that associations have source() correctly set.
+     *
+     * @return void
+     */
+    public function testSourceOnContainAssociations()
+    {
+        Plugin::load('TestPlugin');
+        $comments = TableRegistry::get('TestPlugin.Comments');
+        $comments->belongsTo('Authors', [
+            'className' => 'TestPlugin.Authors',
+            'foreignKey' => 'user_id'
+        ]);
+        $result = $comments->find()->contain(['Authors'])->first();
+        $this->assertEquals('TestPlugin.Comments', $result->source());
+        $this->assertEquals('TestPlugin.Authors', $result->author->source());
+
+        $result = $comments->find()->matching('Authors', function ($q) {
+            return $q->where(['Authors.id' => 1]);
+        })->first();
+        $this->assertEquals('TestPlugin.Comments', $result->source());
+        $this->assertEquals('TestPlugin.Authors', $result->_matchingData['Authors']->source());
+    }
 }