bug #18899 [Yaml] search for colons in strings only (xabbuh)

This PR was merged into the 3.1 branch.

Discussion
----------

[Yaml] search for colons in strings only

| Q             | A
| ------------- | ---
| Branch?       | 3.1
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #18897
| License       | MIT
| Doc PR        |

Since the parser is able to return `\DateTime` instances when the
`Yaml::PARSE_DATETIME` flag is passed, we need to ensure that the parsed
value actually is a string before passing the parsed value to string
functions.

Commits
-------

0ea2228 [Yaml] search for colons in strings only

src/Symfony/Component/Yaml/Parser.php

@@ -539,7 +539,7 @@ private function parseValue($value, $flags, $context)
         try {
             $parsedValue = Inline::parse($value, $flags, $this->refs);
 
-            if ('mapping' === $context && '"' !== $value[0] && "'" !== $value[0] && '[' !== $value[0] && '{' !== $value[0] && '!' !== $value[0] && false !== strpos($parsedValue, ': ')) {
+            if ('mapping' === $context && is_string($parsedValue) && '"' !== $value[0] && "'" !== $value[0] && '[' !== $value[0] && '{' !== $value[0] && '!' !== $value[0] && false !== strpos($parsedValue, ': ')) {
                 throw new ParseException('A colon cannot be used in an unquoted mapping value.');
             }
 

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

@@ -1230,6 +1230,19 @@ public function getInvalidBinaryData()
             ),
         );
     }
+
+    public function testParseDateAsMappingValue()
+    {
+        $yaml = <<<EOT
+date: 2002-12-14
+EOT;
+        $expectedDate = new \DateTime();
+        $expectedDate->setTimeZone(new \DateTimeZone('UTC'));
+        $expectedDate->setDate(2002, 12, 14);
+        $expectedDate->setTime(0, 0, 0);
+
+        $this->assertEquals(array('date' => $expectedDate), $this->parser->parse($yaml, Yaml::PARSE_DATETIME));
+    }
 }
 
 class B