[Yaml] fix parse error when unindented collections contain a comment

src/Symfony/Component/Yaml/Parser.php

@@ -619,8 +619,14 @@ class Parser
         }
 
         $isItUnindentedCollection = $this->isStringUnIndentedCollectionItem();
+        $isItComment = $this->isCurrentLineComment();
 
         while ($this->moveToNextLine()) {
+            if ($isItComment && !$isItUnindentedCollection) {
+                $isItUnindentedCollection = $this->isStringUnIndentedCollectionItem();
+                $isItComment = $this->isCurrentLineComment();
+            }
+
             $indent = $this->getCurrentLineIndentation();
 
             if ($isItUnindentedCollection && !$this->isCurrentLineEmpty() && !$this->isStringUnIndentedCollectionItem() && $newIndent === $indent) {

src/Symfony/Component/Yaml/Tests/Fixtures/sfComments.yml

@@ -74,3 +74,17 @@ yaml: |
     'foo #': baz
 php: |
     ['foo #' => 'baz']
+---
+test: Comment before first item in unindented collection
+brief: >
+    Comment directly before unindented collection is allowed
+yaml: |
+    collection1:
+    # comment
+    - a
+    - b
+    collection2:
+    - a
+    - b
+php: |
+    ['collection1' => ['a', 'b'], 'collection2' => ['a', 'b']]