Merge branch '2.8' into 3.2

* 2.8:
  don't keep internal state between parser runs
  Add \Traversable typehint to phpdoc
  [ExpressionLanguage] Avoid dependency on ctype
  [Debug] Fix php notice
  [VarDumper] Relax tests to adapt for php 7.1rc4

Author: xabbuh

Parser.php

@@ -87,23 +87,51 @@ public function parse($value, $flags = 0)
         if (false === preg_match('//u', $value)) {
             throw new ParseException('The YAML value does not appear to be valid UTF-8.');
         }
+
+        $this->refs = array();
+
+        $mbEncoding = null;
+        $e = null;
+        $data = null;
+
+        if (2 /* MB_OVERLOAD_STRING */ & (int) ini_get('mbstring.func_overload')) {
+            $mbEncoding = mb_internal_encoding();
+            mb_internal_encoding('UTF-8');
+        }
+
+        try {
+            $data = $this->doParse($value, $flags);
+        } catch (\Exception $e) {
+        } catch (\Throwable $e) {
+        }
+
+        if (null !== $mbEncoding) {
+            mb_internal_encoding($mbEncoding);
+        }
+
+        if (null !== $e) {
+            throw $e;
+        }
+
+        return $data;
+    }
+
+    private function doParse($value, $flags)
+    {
         $this->currentLineNb = -1;
         $this->currentLine = '';
         $value = $this->cleanup($value);
         $this->lines = explode("\n", $value);
+        $this->locallySkippedLineNumbers = array();
 
         if (null === $this->totalNumberOfLines) {
             $this->totalNumberOfLines = count($this->lines);
         }
 
-        if (2 /* MB_OVERLOAD_STRING */ & (int) ini_get('mbstring.func_overload')) {
-            $mbEncoding = mb_internal_encoding();
-            mb_internal_encoding('UTF-8');
-        }
-
         $data = array();
         $context = null;
         $allowOverwrite = false;
+
         while ($this->moveToNextLine()) {
             if ($this->isCurrentLineEmpty()) {
                 continue;
@@ -279,21 +307,13 @@ public function parse($value, $flags = 0)
                         throw $e;
                     }
 
-                    if (isset($mbEncoding)) {
-                        mb_internal_encoding($mbEncoding);
-                    }
-
                     return $value;
                 }
 
                 throw new ParseException('Unable to parse.', $this->getRealCurrentLineNb() + 1, $this->currentLine);
             }
         }
 
-        if (isset($mbEncoding)) {
-            mb_internal_encoding($mbEncoding);
-        }
-
         if (Yaml::PARSE_OBJECT_FOR_MAP & $flags && !is_object($data) && 'mapping' === $context) {
             $object = new \stdClass();
 
@@ -322,7 +342,7 @@ private function parseBlock($offset, $yaml, $flags)
         $parser = new self($offset, $this->totalNumberOfLines, $skippedLineNumbers);
         $parser->refs = &$this->refs;
 
-        return $parser->parse($yaml, $flags);
+        return $parser->doParse($yaml, $flags);
     }
 
     /**

Tests/ParserTest.php

@@ -1490,6 +1490,27 @@ public function testCanParseVeryLongValue()
 
         $this->assertEquals($trickyVal, $arrayFromYaml);
     }
+
+    /**
+     * @expectedException \Symfony\Component\Yaml\Exception\ParseException
+     * @expectedExceptionMessage Reference "foo" does not exist at line 2
+     */
+    public function testParserCleansUpReferencesBetweenRuns()
+    {
+        $yaml = <<<YAML
+foo: &foo
+    baz: foobar
+bar:
+    <<: *foo
+YAML;
+        $this->parser->parse($yaml);
+
+        $yaml = <<<YAML
+bar:
+    <<: *foo
+YAML;
+        $this->parser->parse($yaml);
+    }
 }
 
 class B