[Yaml] Fixed symfony#10597: Improved Yaml directive parsing

Author: VictoriaQ

src/Symfony/Component/Yaml/Parser.php

@@ -586,7 +586,7 @@ private function cleanup($value)
 
         // strip YAML header
         $count = 0;
-        $value = preg_replace('#^\%YAML[: ][\d\.]+.*\n#su', '', $value, -1, $count);
+        $value = preg_replace('#^\%YAML[: ][\d\.]+.*\n#u', '', $value, -1, $count);
         $this->offset += $count;
 
         // remove leading comments

src/Symfony/Component/Yaml/Tests/ParserTest.php

@@ -650,6 +650,17 @@ public function testReferenceResolvingInInlineStrings()
 EOF
         ));
     }
+
+    public function testYamlDirective()
+    {
+        $yaml = <<<EOF
+%YAML 1.2
+---
+foo: 1
+bar: 2
+EOF;
+        $this->assertEquals(array('foo' => 1, 'bar' => 2), $this->parser->parse($yaml));
+    }
 }
 
 class B