[ExpressionLanguage] Add enum expression function

Author: alexandre-daubois

components/expression_language/syntax.rst

@@ -127,18 +127,55 @@ Working with Functions
 ----------------------
 
 You can also use registered functions in the expression by using the same
-syntax as PHP and JavaScript. The ExpressionLanguage component comes with one
-function by default: ``constant()``, which will return the value of the PHP
-constant::
+syntax as PHP and JavaScript. The ExpressionLanguage component comes with the
+following functions by default:
+
+* ``constant()``
+* ``enum()``
+
+Constant function
+~~~~~~~~~~~~~~~~~
+
+This function will return the value of a PHP constant::
 
     define('DB_USER', 'root');
 
     var_dump($expressionLanguage->evaluate(
         'constant("DB_USER")'
     ));
 
+    // This also works with class constants
+    class Foo
+    {
+        public const DB_USER = 'root';
+    }
+
+    var_dump($expressionLanguage->evaluate(
+        'constant("App\\\SomeNamespace\\\Foo::DB_USER")'
+    ));
+
 This will print out ``root``.
 
+Enum function
+~~~~~~~~~~~~~
+
+This function will return the case of an enumeration::
+
+    enum Foo
+    {
+        case Bar;
+    }
+
+    var_dump(App\Enum\Foo::Bar === $expressionLanguage->evaluate(
+        'enum("App\\\Enum\\\Foo::Bar")'
+    ));
+
+This will print out ``true``.
+
+.. versionadded:: 6.3
+
+    The ``enum()`` function was introduced in Symfony 6.3.
+
 .. tip::
 
     To read how to register your own functions to use in an expression, see