symfony · fabpot · Oct 5, 2017 · Oct 3, 2017
diff --git a/src/Symfony/Component/Yaml/Parser.php b/src/Symfony/Component/Yaml/Parser.php
@@ -181,7 +181,7 @@ private function doParse($value, $exceptionOnInvalidType = false, $objectSupport
                    $key = (string) $key;
                }

-                if ('<<' === $key) {
+                if ('<<' === $key && (!isset($values['value']) || !self::preg_match('#^&(?P<ref>[^ ]+)#u', $values['value'], $refMatches))) {
                    $mergeNode = true;
                    $allowOverwrite = true;
                    if (isset($values['value']) && 0 === strpos($values['value'], '*')) {
@@ -226,14 +226,14 @@ private function doParse($value, $exceptionOnInvalidType = false, $objectSupport
                            $data += $parsed; // array union
                        }
                    }
-                } elseif (isset($values['value']) && self::preg_match('#^&(?P<ref>[^ ]+) *(?P<value>.*)#u', $values['value'], $matches)) {
+                } elseif ('<<' !== $key && isset($values['value']) && self::preg_match('#^&(?P<ref>[^ ]+) *(?P<value>.*)#u', $values['value'], $matches)) {
                    $isRef = $matches['ref'];
                    $values['value'] = $matches['value'];
                }

                if ($mergeNode) {
                    // Merge keys
-                } elseif (!isset($values['value']) || '' == trim($values['value'], ' ') || 0 === strpos(ltrim($values['value'], ' '), '#')) {
+                } elseif (!isset($values['value']) || '' == trim($values['value'], ' ') || 0 === strpos(ltrim($values['value'], ' '), '#') || '<<' === $key) {
                    // hash
                    // if next line is less indented or equal, then it means that the current value is null
                    if (!$this->isNextLineIndented() && !$this->isNextLineUnIndentedCollection()) {
@@ -244,9 +244,13 @@ private function doParse($value, $exceptionOnInvalidType = false, $objectSupport
                        }
                    } else {
                        $value = $this->parseBlock($this->getRealCurrentLineNb() + 1, $this->getNextEmbedBlock(), $exceptionOnInvalidType, $objectSupport, $objectForMap);
-                        // Spec: Keys MUST be unique; first one wins.
-                        // But overwriting is allowed when a merge node is used in current block.
-                        if ($allowOverwrite || !isset($data[$key])) {
+
+                        if ('<<' === $key) {
+                            $this->refs[$refMatches['ref']] = $value;
+                            $data += $value;
+                        } elseif ($allowOverwrite || !isset($data[$key])) {
+                            // Spec: Keys MUST be unique; first one wins.
+                            // But overwriting is allowed when a merge node is used in current block.
                            $data[$key] = $value;
                        }
                    }

diff --git a/src/Symfony/Component/Yaml/Tests/ParserTest.php b/src/Symfony/Component/Yaml/Tests/ParserTest.php
@@ -1179,6 +1179,34 @@ public function testParserCleansUpReferencesBetweenRuns()
 YAML;
        $this->parser->parse($yaml);
    }
+
+    public function testParseReferencesOnMergeKeys()
+    {
+        $yaml = <<<YAML
+mergekeyrefdef:
+    a: foo
+    <<: &quux
+        b: bar
+        c: baz
+mergekeyderef:
+    d: quux
+    <<: *quux
+YAML;
+        $expected = array(
+            'mergekeyrefdef' => array(
+                'a' => 'foo',
+                'b' => 'bar',
+                'c' => 'baz',
+            ),
+            'mergekeyderef' => array(
+                'd' => 'quux',
+                'b' => 'bar',
+                'c' => 'baz',
+            ),
+        );
+
+        $this->assertSame($expected, $this->parser->parse($yaml));
+    }
 }

 class B