feature #22059 [Yaml] deprecate "? " starting unquoted strings (xabbuh)

This PR was merged into the 3.3-dev branch.

Discussion
----------

[Yaml] deprecate "? " starting unquoted strings

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #20579
| License       | MIT
| Doc PR        |

Commits
-------

731a74e79c [Yaml] deprecate "? " starting unquoted strings

Author: fabpot

CHANGELOG.md

@@ -4,8 +4,12 @@ CHANGELOG
 3.3.0
 -----
 
- * Deprecated support for implicitly parsing non-string mapping keys as strings. Mapping keys that are no strings will
-   lead to a `ParseException` in Symfony 4.0. Use the `PARSE_KEYS_AS_STRINGS` flag to opt-in for keys to be parsed as
+ * Starting an unquoted string with a question mark followed by a space is
+   deprecated and will throw a `ParseException` in Symfony 4.0.
+
+ * Deprecated support for implicitly parsing non-string mapping keys as strings.
+   Mapping keys that are no strings will lead to a `ParseException` in Symfony
+   4.0. Use the `PARSE_KEYS_AS_STRINGS` flag to opt-in for keys to be parsed as
    strings.
 
    Before:

Parser.php

@@ -144,6 +144,10 @@ public function parse($value, $flags = 0)
                     $values['value'] = $matches['value'];
                 }
 
+                if (isset($values['value'][1]) && '?' === $values['value'][0] && ' ' === $values['value'][1]) {
+                    @trigger_error('Starting an unquoted string with a question mark followed by a space is deprecated since version 3.3 and will throw \Symfony\Component\Yaml\Exception\ParseException in 4.0.', E_USER_DEPRECATED);
+                }
+
                 // array
                 if (!isset($values['value']) || '' == trim($values['value'], ' ') || 0 === strpos(ltrim($values['value'], ' '), '#')) {
                     $data[] = $this->parseBlock($this->getRealCurrentLineNb() + 1, $this->getNextEmbedBlock(null, true), $flags);
@@ -304,6 +308,10 @@ public function parse($value, $flags = 0)
                     throw new ParseException('Multiple documents are not supported.', $this->currentLineNb + 1, $this->currentLine);
                 }
 
+                if (isset($this->currentLine[1]) && '?' === $this->currentLine[0] && ' ' === $this->currentLine[1]) {
+                    @trigger_error('Starting an unquoted string with a question mark followed by a space is deprecated since version 3.3 and will throw \Symfony\Component\Yaml\Exception\ParseException in 4.0.', E_USER_DEPRECATED);
+                }
+
                 // 1-liner optionally followed by newline(s)
                 if (is_string($value) && $this->lines[0] === trim($value)) {
                     try {

Tests/ParserTest.php

@@ -1641,6 +1641,52 @@ public function testExceptionWhenUsingUnsuportedBuiltInTags()
         $this->parser->parse('!!foo');
     }
 
+    /**
+     * @group legacy
+     * @expectedDeprecation Starting an unquoted string with a question mark followed by a space is deprecated since version 3.3 and will throw \Symfony\Component\Yaml\Exception\ParseException in 4.0.
+     */
+    public function testComplexMappingThrowsParseException()
+    {
+        $yaml = <<<YAML
+? "1"
+:
+  name: végétalien
+YAML;
+
+        $this->parser->parse($yaml);
+    }
+
+    /**
+     * @group legacy
+     * @expectedDeprecation Starting an unquoted string with a question mark followed by a space is deprecated since version 3.3 and will throw \Symfony\Component\Yaml\Exception\ParseException in 4.0.
+     */
+    public function testComplexMappingNestedInMappingThrowsParseException()
+    {
+        $yaml = <<<YAML
+diet:
+  ? "1"
+  :
+    name: végétalien
+YAML;
+
+        $this->parser->parse($yaml);
+    }
+
+    /**
+     * @group legacy
+     * @expectedDeprecation Starting an unquoted string with a question mark followed by a space is deprecated since version 3.3 and will throw \Symfony\Component\Yaml\Exception\ParseException in 4.0.
+     */
+    public function testComplexMappingNestedInSequenceThrowsParseException()
+    {
+        $yaml = <<<YAML
+- ? "1"
+  :
+    name: végétalien
+YAML;
+
+        $this->parser->parse($yaml);
+    }
+
     private function loadTestsFromFixtureFiles($testsFile)
     {
         $parser = new Parser();