Make ExpressionLanguageSyntax validator usable with annotation

Author: jderusse

Constraints/ExpressionLanguageSyntax.php

@@ -37,6 +37,6 @@ class ExpressionLanguageSyntax extends Constraint
      */
     public function validatedBy()
     {
-        return $this->service;
+        return $this->service ?? static::class.'Validator';
     }
 }

Constraints/ExpressionLanguageSyntaxValidator.php

@@ -24,7 +24,7 @@ class ExpressionLanguageSyntaxValidator extends ConstraintValidator
 {
     private $expressionLanguage;
 
-    public function __construct(ExpressionLanguage $expressionLanguage)
+    public function __construct(ExpressionLanguage $expressionLanguage = null)
     {
         $this->expressionLanguage = $expressionLanguage;
     }
@@ -42,6 +42,10 @@ public function validate($expression, Constraint $constraint): void
             throw new UnexpectedTypeException($expression, 'string');
         }
 
+        if (null === $this->expressionLanguage) {
+            $this->expressionLanguage = new ExpressionLanguage();
+        }
+
         try {
             $this->expressionLanguage->lint($expression, ($constraint->validateNames ? ($constraint->names ?? []) : null));
         } catch (SyntaxError $exception) {