The debug class loader is always loaded by Debug::enable().

* 2.7:
  [Security] Fix logout
  #27250 limiting GET_LOCK key up to 64 char due to changes in MySQL 5.7.5 and later
  [Profiler] Remove propel & event_listener_loading category identifiers
  [Filesystem] Fix usages of error_get_last()
  [Debug] Fix populating error_get_last() for handled silent errors
  Suppress warnings when open_basedir is non-empty

Debug.php

@@ -23,10 +23,7 @@ class Debug
     /**
      * Enables the debug tools.
      *
-     * This method registers an error handler and an exception handler.
-     *
-     * If the Symfony ClassLoader component is available, a special
-     * class loader is also registered.
+     * This method registers an error handler, an exception handler and a special class loader.
      *
      * @param int  $errorReportingLevel The level of error reporting you want
      * @param bool $displayErrors       Whether to display errors (for development) or just log them (for production)

ErrorHandler.php

@@ -403,13 +403,15 @@ class ErrorHandler
      */
     public function handleError($type, $message, $file, $line)
     {
-        $level = error_reporting() | E_RECOVERABLE_ERROR | E_USER_ERROR | E_DEPRECATED | E_USER_DEPRECATED;
+        $level = error_reporting();
+        $silenced = 0 === ($level & $type);
+        $level |= E_RECOVERABLE_ERROR | E_USER_ERROR | E_DEPRECATED | E_USER_DEPRECATED;
         $log = $this->loggedErrors & $type;
         $throw = $this->thrownErrors & $type & $level;
         $type &= $level | $this->screamedErrors;
 
         if (!$type || (!$log && !$throw)) {
-            return $type && $log;
+            return !$silenced && $type && $log;
         }
         $scope = $this->scopedErrors & $type;
 
@@ -549,7 +551,7 @@ class ErrorHandler
             }
         }
 
-        return $type && $log;
+        return !$silenced && $type && $log;
     }
 
     /**

Exception/ClassNotFoundException.php

@@ -26,6 +26,9 @@ class ClassNotFoundException extends FatalErrorException
             $previous->getSeverity(),
             $previous->getFile(),
             $previous->getLine(),
+            null,
+            true,
+            null,
             $previous->getPrevious()
         );
         $this->setTrace($previous->getTrace());

Exception/FatalErrorException.php

@@ -35,9 +35,9 @@ use Symfony\Component\HttpKernel\Exception\FatalErrorException as LegacyFatalErr
  */
 class FatalErrorException extends LegacyFatalErrorException
 {
-    public function __construct($message, $code, $severity, $filename, $lineno, $traceOffset = null, $traceArgs = true, array $trace = null)
+    public function __construct($message, $code, $severity, $filename, $lineno, $traceOffset = null, $traceArgs = true, array $trace = null, $previous = null)
     {
-        parent::__construct($message, $code, $severity, $filename, $lineno);
+        parent::__construct($message, $code, $severity, $filename, $lineno, $previous);
 
         if (null !== $trace) {
             if (!$traceArgs) {

Exception/UndefinedFunctionException.php

@@ -26,6 +26,9 @@ class UndefinedFunctionException extends FatalErrorException
             $previous->getSeverity(),
             $previous->getFile(),
             $previous->getLine(),
+            null,
+            true,
+            null,
             $previous->getPrevious()
         );
         $this->setTrace($previous->getTrace());

Exception/UndefinedMethodException.php

@@ -26,6 +26,9 @@ class UndefinedMethodException extends FatalErrorException
             $previous->getSeverity(),
             $previous->getFile(),
             $previous->getLine(),
+            null,
+            true,
+            null,
             $previous->getPrevious()
         );
         $this->setTrace($previous->getTrace());

Tests/ErrorHandlerTest.php

@@ -65,6 +65,30 @@ class ErrorHandlerTest extends TestCase
         }
     }
 
+    public function testErrorGetLast()
+    {
+        $handler = ErrorHandler::register();
+        $logger = $this->getMockBuilder('Psr\Log\LoggerInterface')->getMock();
+        $handler->setDefaultLogger($logger);
+        $handler->screamAt(E_ALL);
+
+        try {
+            @trigger_error('Hello', E_USER_WARNING);
+            $expected = array(
+                'type' => E_USER_WARNING,
+                'message' => 'Hello',
+                'file' => __FILE__,
+                'line' => __LINE__ - 5,
+            );
+            $this->assertSame($expected, error_get_last());
+        } catch (\Exception $e) {
+            restore_error_handler();
+            restore_exception_handler();
+
+            throw $e;
+        }
+    }
+
     public function testNotice()
     {
         ErrorHandler::register();