[Backport]Magento should create log if an observer not implement ObserverInterface

lib/internal/Magento/Framework/Event/Invoker/InvokerDefault.php

@@ -9,7 +9,12 @@
 namespace Magento\Framework\Event\Invoker;
 
 use Magento\Framework\Event\Observer;
+use Psr\Log\LoggerInterface;
+use Magento\Framework\App\State;
 
+/**
+ * Default Invoker.
+ */
 class InvokerDefault implements \Magento\Framework\Event\InvokerInterface
 {
     /**
@@ -22,20 +27,29 @@ class InvokerDefault implements \Magento\Framework\Event\InvokerInterface
     /**
      * Application state
      *
-     * @var \Magento\Framework\App\State
+     * @var State
      */
     protected $_appState;
 
+    /**
+     * @var LoggerInterface
+     */
+    private $logger;
+
     /**
      * @param \Magento\Framework\Event\ObserverFactory $observerFactory
-     * @param \Magento\Framework\App\State $appState
+     * @param State $appState
+     * @param LoggerInterface $logger
      */
     public function __construct(
         \Magento\Framework\Event\ObserverFactory $observerFactory,
-        \Magento\Framework\App\State $appState
+        State $appState,
+        LoggerInterface $logger = null
     ) {
         $this->_observerFactory = $observerFactory;
         $this->_appState = $appState;
+        $this->logger = $logger ?: \Magento\Framework\App\ObjectManager::getInstance()
+            ->get(LoggerInterface::class);
     }
 
     /**
@@ -61,6 +75,8 @@ public function dispatch(array $configuration, Observer $observer)
     }
 
     /**
+     * Execute Observer.
+     *
      * @param \Magento\Framework\Event\ObserverInterface $object
      * @param Observer $observer
      * @return $this
@@ -70,14 +86,20 @@ protected function _callObserverMethod($object, $observer)
     {
         if ($object instanceof \Magento\Framework\Event\ObserverInterface) {
             $object->execute($observer);
-        } elseif ($this->_appState->getMode() == \Magento\Framework\App\State::MODE_DEVELOPER) {
+        } elseif ($this->_appState->getMode() == State::MODE_DEVELOPER) {
             throw new \LogicException(
                 sprintf(
                     'Observer "%s" must implement interface "%s"',
                     get_class($object),
                     \Magento\Framework\Event\ObserverInterface::class
                 )
             );
+        } else {
+            $this->logger->warning(sprintf(
+                'Observer "%s" must implement interface "%s"',
+                get_class($object),
+                \Magento\Framework\Event\ObserverInterface::class
+            ));
         }
         return $this;
     }

lib/internal/Magento/Framework/Event/Test/Unit/Invoker/InvokerDefaultTest.php

@@ -5,6 +5,9 @@
  */
 namespace Magento\Framework\Event\Test\Unit\Invoker;
 
+/**
+ * Test for Magento\Framework\Event\Invoker\InvokerDefault.
+ */
 class InvokerDefaultTest extends \PHPUnit\Framework\TestCase
 {
     /**
@@ -32,6 +35,11 @@ class InvokerDefaultTest extends \PHPUnit\Framework\TestCase
      */
     protected $_invokerDefault;
 
+    /**
+     * @var |Psr\Log|LoggerInterface
+     */
+    private $loggerMock;
+
     protected function setUp()
     {
         $this->_observerFactoryMock = $this->createMock(\Magento\Framework\Event\ObserverFactory::class);
@@ -41,10 +49,12 @@ protected function setUp()
             ['execute']
         );
         $this->_appStateMock = $this->createMock(\Magento\Framework\App\State::class);
+        $this->loggerMock = $this->createMock(\Psr\Log\LoggerInterface::class);
 
         $this->_invokerDefault = new \Magento\Framework\Event\Invoker\InvokerDefault(
             $this->_observerFactoryMock,
-            $this->_appStateMock
+            $this->_appStateMock,
+            $this->loggerMock
         );
     }
 
@@ -166,13 +176,15 @@ public function testWrongInterfaceCallWithDisabledDeveloperMode($shared)
             $this->returnValue($notObserver)
         );
         $this->_appStateMock->expects(
-            $this->once()
+            $this->exactly(1)
         )->method(
             'getMode'
         )->will(
             $this->returnValue(\Magento\Framework\App\State::MODE_PRODUCTION)
         );
 
+        $this->loggerMock->expects($this->once())->method('warning');
+
         $this->_invokerDefault->dispatch(
             [
                 'shared' => $shared,