feature #16201 [Yaml] deprecated non-escaped \ in double-quoted strings when parsing (fabpot)

This PR was merged into the 2.8 branch.

Discussion
----------

[Yaml] deprecated non-escaped \ in double-quoted strings when parsing

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

According to the YAML specs, backslashes must be escaped when used in a double-quoted string. So, `"Foo\Var"` is not valid, `"Foo\\Var"` is.

This PR deprecates the old ways so that we can throw an exception in 3.0 when parsing a non-compliant YAML string in 3.0.

ping @nicolas-grekas @tucksaun

Commits
-------

e599a72 [Yaml] deprecated non-escaped \ in double-quoted strings when parsing

src/Symfony/Component/Yaml/CHANGELOG.md

@@ -1,6 +1,12 @@
 CHANGELOG
 =========
 
+2.8.0
+-----
+
+ * Deprecated non-escaped \ in double-quoted strings when parsing Yaml
+   ("Foo\Var" is not valid whereas "Foo\\Var" is)
+
 2.1.0
 -----
 

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

@@ -145,3 +145,11 @@ php: |
     array(
         'double' => "some value\n \"some quoted string\" and 'some single quotes one'"
     )
+---
+test: Backslashes
+yaml: |
+    { single: 'foo\Var', no-quotes: foo\Var, double: "foo\\Var" }
+php: |
+    array(
+        'single' => 'foo\Var', 'no-quotes' => 'foo\Var', 'double' => 'foo\Var'
+    )

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

@@ -72,6 +72,23 @@ class InlineTest extends \PHPUnit_Framework_TestCase
         $this->assertSame($value, Inline::parse(Inline::dump($value)));
     }
 
+    /**
+     * @group legacy
+     * throws \Symfony\Component\Yaml\Exception\ParseException in 3.0
+     */
+    public function testParseScalarWithNonEscapedBlackslashShouldThrowException()
+    {
+        $this->assertSame('Foo\Var', Inline::parse('"Foo\Var"'));
+    }
+
+    /**
+     * @expectedException \Symfony\Component\Yaml\Exception\ParseException
+     */
+    public function testParseScalarWithNonEscapedBlackslashAtTheEndShouldThrowException()
+    {
+        Inline::parse('"Foo\\"');
+    }
+
     /**
      * @expectedException \Symfony\Component\Yaml\Exception\ParseException
      */

src/Symfony/Component/Yaml/Unescaper.php

@@ -32,7 +32,7 @@ class Unescaper
     /**
      * Regex fragment that matches an escaped character in a double quoted string.
      */
-    const REGEX_ESCAPED_CHARACTER = "\\\\([0abt\tnvfre \\\"\\/\\\\N_LP]|x[0-9a-fA-F]{2}|u[0-9a-fA-F]{4}|U[0-9a-fA-F]{8})";
+    const REGEX_ESCAPED_CHARACTER = "\\\\(x[0-9a-fA-F]{2}|u[0-9a-fA-F]{4}|U[0-9a-fA-F]{8}|.)";
 
     /**
      * Unescapes a single quoted string.
@@ -70,10 +70,13 @@ class Unescaper
      * @param string $value An escaped character
      *
      * @return string The unescaped character
+     *
+     * @internal This method is public to be usable as callback. It should not
+     *           be used in user code. Should be changed in 3.0.
      */
     public function unescapeCharacter($value)
     {
-        switch ($value{1}) {
+        switch ($value[1]) {
             case '0':
                 return "\x0";
             case 'a':
@@ -120,6 +123,10 @@ class Unescaper
                 return self::utf8chr(hexdec(substr($value, 2, 4)));
             case 'U':
                 return self::utf8chr(hexdec(substr($value, 2, 8)));
+            default:
+                @trigger_error('Not escaping a backslash in a double-quoted string is deprecated since Symfony 2.8 and will throw a ParseException in 3.0.', E_USER_DEPRECATED);
+
+                return $value;
         }
     }