minor #14865 [Validator] Use PHP attributes when creating custom validation constraints (yoannrenard)

This PR was squashed before being merged into the 5.2 branch.

Discussion
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[Validator] Use PHP attributes when creating custom validation constraints

Describe how to use PHP attributes when creating custom validation constraints

Commits
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55c5676 [Validator] Use PHP attributes when creating custom validation constraints

Author: OskarStark

validation/custom_constraint.rst

@@ -12,20 +12,43 @@ alphanumeric characters.
 Creating the Constraint Class
 -----------------------------
 
-First you need to create a Constraint class and extend :class:`Symfony\\Component\\Validator\\Constraint`::
+First you need to create a Constraint class and extend :class:`Symfony\\Component\\Validator\\Constraint`:
 
-    // src/Validator/ContainsAlphanumeric.php
-    namespace App\Validator;
+.. configuration-block::
 
-    use Symfony\Component\Validator\Constraint;
+    .. code-block:: php-annotations
 
-    /**
-     * @Annotation
-     */
-    class ContainsAlphanumeric extends Constraint
-    {
-        public $message = 'The string "{{ string }}" contains an illegal character: it can only contain letters or numbers.';
-    }
+        // src/Validator/ContainsAlphanumeric.php
+        namespace App\Validator;
+
+        use Symfony\Component\Validator\Constraint;
+
+        /**
+         * @Annotation
+         */
+        class ContainsAlphanumeric extends Constraint
+        {
+            public $message = 'The string "{{ string }}" contains an illegal character: it can only contain letters or numbers.';
+        }
+
+    .. code-block:: php-attributes
+
+        // src/Validator/ContainsAlphanumeric.php
+        namespace App\Validator;
+
+        use Symfony\Component\Validator\Constraint;
+
+        #[\Attribute]
+        class ContainsAlphanumeric extends Constraint
+        {
+            public $message = 'The string "{{ string }}" contains an illegal character: it can only contain letters or numbers.';
+        }
+
+.. versionadded:: 5.2
+
+    The ability to use PHP attributes to configure constraints was introduced in
+    Symfony 5.2. Prior to this, Doctrine Annotations were the only way to
+    annotate constraints.
 
 .. note::
 
@@ -128,6 +151,25 @@ You can use custom validators like the ones provided by Symfony itself:
             // ...
         }
 
+    .. code-block:: php-attributes
+
+        // src/Entity/AcmeEntity.php
+        namespace App\Entity;
+
+        use App\Validator as AcmeAssert;
+        use Symfony\Component\Validator\Constraints as Assert;
+
+        class AcmeEntity
+        {
+            // ...
+
+            #[Assert\NotBlank]
+            #[AcmeAssert\ContainsAlphanumeric]
+            protected $name;
+
+            // ...
+        }
+
     .. code-block:: yaml
 
         # config/validator/validation.yaml
@@ -241,6 +283,14 @@ not to the property:
             // ...
         }
 
+    .. code-block:: php-attributes
+
+        #[AcmeAssert\ProtocolClass]
+        class AcmeEntity
+        {
+            // ...
+        }
+
     .. code-block:: yaml
 
         # config/validator/validation.yaml