[ExpressionLanguage] Add enum expression function

Author: alexandre-daubois

components/expression_language/syntax.rst

@@ -127,9 +127,16 @@ 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 the PHP constant::
 
     define('DB_USER', 'root');
 
@@ -139,6 +146,26 @@ constant::
 
 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