feature #4199 Do not hide unnecessary escape characters (ruudk)

This PR was squashed before being merged into the 4.x branch.

Discussion
----------

Do not hide unnecessary escape characters

Follow up of #4176, #4123 and #2712.

Now that we have deprecated unnecessary escape in v3, we can change the behavior in v4.

With this change, unnecessary will no longer be ignored, but handled like any other character.

This allows for writing fully qualified class names like this:
```twig
{{ constant('App\Entity\User::SOME_CONSTANT') }}
```

Instead of having to escape the `\` in v3:
```twig
{{ constant('App\\Entity\\User::SOME_CONSTANT') }}
```

/cc `@fabpot` `@stof`

Commits
-------

53c24bf Do not hide unnecessary escape characters

CHANGELOG

@@ -7,3 +7,4 @@
  * Change the compilation of `for` loops to throw an exception when a `loop.*` variable is not defined
  * Make `Environment::getGlobals()` private
  * Drop support for PHP < 8.2
+ * Escape characters are no longer ignored

src/Lexer.php

@@ -428,12 +428,7 @@ private function stripcslashes(string $str, string $quoteType): string
 
             if (isset(self::SPECIAL_CHARS[$nextChar])) {
                 $result .= self::SPECIAL_CHARS[$nextChar];
-            } elseif ('\\' === $nextChar) {
-                $result .= $nextChar;
-            } elseif ("'" === $nextChar || '"' === $nextChar) {
-                if ($nextChar !== $quoteType) {
-                    trigger_deprecation('twig/twig', '3.12', 'Character "%s" at position %d should not be escaped; the "\" character is ignored in Twig v3 but will not be in v4. Please remove the extra "\" character.', $nextChar, $i + 1);
-                }
+            } elseif ($nextChar === '\\' || $nextChar === $quoteType) {
                 $result .= $nextChar;
             } elseif ('#' === $nextChar && $i + 1 < $length && '{' === $str[$i + 1]) {
                 $result .= '#{';
@@ -451,8 +446,7 @@ private function stripcslashes(string $str, string $quoteType): string
                 }
                 $result .= \chr(octdec($octal));
             } else {
-                trigger_deprecation('twig/twig', '3.12', 'Character "%s" at position %d should not be escaped; the "\" character is ignored in Twig v3 but will not be in v4. Please remove the extra "\" character.', $nextChar, $i + 1);
-                $result .= $nextChar;
+                $result .= '\\'.$nextChar;
             }
 
             ++$i;

tests/Fixtures/escape_characters.test

@@ -0,0 +1,14 @@
+--TEST--
+Exception with bad line number
+--TEMPLATE--
+{{ 'Foo\Bar' }}
+{{ 'Foo\\Bar' }}
+{{ 'Foo\\\Bar' }}
+{{ 'Foo\\\\Bar' }}
+--DATA--
+return []
+--EXPECT--
+Foo\Bar
+Foo\Bar
+Foo\\Bar
+Foo\\Bar

tests/Fixtures/functions/enum_cases/valid.test

@@ -6,10 +6,13 @@
 {% for c in enum_cases('Twig\\Tests\\DummyBackedEnum') %}
     {{~ c.name }}: {{ c.value }}
 {% endfor %}
-{% for c in enum_cases('Twig\\Tests\\DummyUnitEnum') %}
+{% for c in enum_cases('Twig\Tests\DummyBackedEnum') %}
+    {{~ c.name }}: {{ c.value }}
+{% endfor %}
+{% for c in enum_cases('Twig\Tests\DummyUnitEnum') %}
     {{~ c.name }}
 {% endfor %}
-{% set from_variable='Twig\\Tests\\DummyUnitEnum' %}
+{% set from_variable='Twig\Tests\DummyUnitEnum' %}
 {% for c in enum_cases(from_variable) %}
     {{~ c.name }}
 {% endfor %}
@@ -18,6 +21,8 @@ return []
 --EXPECT--
 FOO: foo
 BAR: bar
+FOO: foo
+BAR: bar
 BAR
 BAZ
 BAR

tests/LexerTest.php

@@ -12,7 +12,6 @@
  */
 
 use PHPUnit\Framework\TestCase;
-use Symfony\Bridge\PhpUnit\ExpectDeprecationTrait;
 use Twig\Environment;
 use Twig\Error\SyntaxError;
 use Twig\Lexer;
@@ -22,8 +21,6 @@
 
 class LexerTest extends TestCase
 {
-    use ExpectDeprecationTrait;
-
     public function testNameLabelForTag()
     {
         $template = '{% § %}';
@@ -195,6 +192,18 @@ public function testStringWithEscapedDelimiter(string $template, string $expecte
 
     public function getStringWithEscapedDelimiter()
     {
+        yield '{{ \'App\Test\' }} => App\Test' => [
+            '{{ \'App\\Test\' }}',
+            'App\Test',
+        ];
+        yield '{{ "foo \\\' bar" }} => foo \' bar' => [
+            '{{ "foo \\\' bar" }}',
+            "foo \' bar",
+        ];
+        yield '{{ \'foo \" bar\' }} => foo \" bar' => [
+            '{{ \'foo \\" bar\' }}',
+            'foo \" bar',
+        ];
         yield '{{ \'\x6\' }} => \x6' => [
             '{{ \'\x6\' }}',
             "\x6",
@@ -229,43 +238,6 @@ public function getStringWithEscapedDelimiter()
         ];
     }
 
-    /**
-     * @group legacy
-     * @dataProvider getStringWithEscapedDelimiterProducingDeprecation
-     */
-    public function testStringWithEscapedDelimiterProducingDeprecation(string $template, string $expected, string $expectedDeprecation)
-    {
-        $this->expectDeprecation($expectedDeprecation);
-
-        $lexer = new Lexer(new Environment(new ArrayLoader()));
-        $stream = $lexer->tokenize(new Source($template, 'index'));
-        $stream->expect(Token::VAR_START_TYPE);
-        $stream->expect(Token::STRING_TYPE, $expected);
-
-        // add a dummy assertion here to satisfy PHPUnit, the only thing we want to test is that the code above
-        // can be executed without throwing any exceptions
-        $this->addToAssertionCount(1);
-    }
-
-    public function getStringWithEscapedDelimiterProducingDeprecation()
-    {
-        yield '{{ \'App\Test\' }} => AppTest' => [
-            '{{ \'App\\Test\' }}',
-            'AppTest',
-            'Since twig/twig 3.12: Character "T" at position 5 should not be escaped; the "\" character is ignored in Twig v3 but will not be in v4. Please remove the extra "\" character.',
-        ];
-        yield '{{ "foo \\\' bar" }} => foo \' bar' => [
-            '{{ "foo \\\' bar" }}',
-            'foo \' bar',
-            'Since twig/twig 3.12: Character "\'" at position 6 should not be escaped; the "\" character is ignored in Twig v3 but will not be in v4. Please remove the extra "\" character.',
-        ];
-        yield '{{ \'foo \" bar\' }} => foo " bar' => [
-            '{{ \'foo \\" bar\' }}',
-            'foo " bar',
-            'Since twig/twig 3.12: Character """ at position 6 should not be escaped; the "\" character is ignored in Twig v3 but will not be in v4. Please remove the extra "\" character.',
-        ];
-    }
-
     public function testStringWithInterpolation()
     {
         $template = 'foo {{ "bar #{ baz + 1 }" }}';