minor #10351 [Validator] Add new json Validator Documentation (zairigimad)

This PR was squashed before being merged into the master branch (closes #10351).

Discussion
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[Validator] Add new json Validator Documentation

Hi,

introduce ~~IsJson~~ `Json` Constraint .
this is a documentation for the new feature in the pull request symfony/symfony#28477

cordially,

Commits
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01ea746 [Validator] Add new json Validator Documentation

Author: javiereguiluz

reference/constraints.rst

@@ -19,6 +19,7 @@ Validation Constraints Reference
    constraints/Regex
    constraints/Ip
    constraints/Uuid
+   constraints/Json
 
    constraints/EqualTo
    constraints/NotEqualTo

reference/constraints/Json.rst

@@ -0,0 +1,99 @@
+Json
+
+Validates that a value is valid ``json``. Specifically, this checks to see if
+the value is a valid ``json`` or not.
+
++----------------+-----------------------------------------------------------------------+
+| Applies to     | :ref:`property or method <validation-property-target>`                |
++----------------+-----------------------------------------------------------------------+
+| Options        | - `message`_                                                          |
+|                | - `payload`_                                                          |
++----------------+-----------------------------------------------------------------------+
+| Class          | :class:`Symfony\\Component\\Validator\\Constraints\\Json`             |
++----------------+-----------------------------------------------------------------------+
+| Validator      | :class:`Symfony\\Component\\Validator\\Constraints\\JsonValidator`    |
++----------------+-----------------------------------------------------------------------+
+
+Basic Usage
+-----------
+
+The ``Json`` constraint can be applied to a property or a "getter" method,
+but is most commonly useful in the latter case. For example, suppose that
+you want to guarantee that some ``jsonString`` property is valid JSON.
+
+.. configuration-block::
+
+    .. code-block:: php-annotations
+
+        // src/Entity/Book.php
+        namespace App\Entity;
+
+        use Symfony\Component\Validator\Constraints as Assert;
+
+        class Book
+        {
+            /**
+             * @Assert\Json(
+             *     message = "You've entered an invalid Json."
+             * )
+             */
+             private $chapters;
+        }
+
+    .. code-block:: yaml
+
+        # config/validator/validation.yaml
+        App\Entity\Book:
+            properties:
+                chapters:
+                    - Json:
+                        message: You've entered an invalid Json.
+
+    .. code-block:: xml
+
+        <!-- config/validator/validation.xml -->
+        <?xml version="1.0" encoding="UTF-8" ?>
+        <constraint-mapping xmlns="http://symfony.com/schema/dic/constraint-mapping"
+            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xsi:schemaLocation="http://symfony.com/schema/dic/constraint-mapping http://symfony.com/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd">
+
+            <class name="App\Entity\Book">
+                <property name="chapters">
+                    <constraint name="Json">
+                        <option name"message">You've entered an invalid Json.</option>
+                    </constraint>
+                </property>
+            </class>
+        </constraint-mapping>
+
+    .. code-block:: php
+
+        // src/Entity/Book.php
+        namespace App\Entity;
+
+        use Symfony\Component\Validator\Mapping\ClassMetadata;
+        use Symfony\Component\Validator\Constraints as Assert;
+
+        class Book
+        {
+            private $chapters;
+
+            public static function loadValidatorMetadata(ClassMetadata $metadata)
+            {
+                $metadata->addPropertyConstraint('chapters', new Assert\Json(array(
+                    'message' => 'You\'ve entered an invalid Json.',
+                )));
+            }
+        }
+
+Options
+-------
+
+message
+~~~~~~~
+
+**type**: ``string`` **default**: ``This value should be valid JSON.``
+
+This message is shown if the underlying data is not a valid JSON.
+
+.. include:: /reference/constraints/_payload-option.rst.inc

reference/constraints/map.rst.inc

@@ -21,6 +21,7 @@ String Constraints
 * :doc:`Regex </reference/constraints/Regex>`
 * :doc:`Ip </reference/constraints/Ip>`
 * :doc:`Uuid</reference/constraints/Uuid>`
+* :doc:`Json</reference/constraints/Json>`
 
 Comparison Constraints
 ~~~~~~~~~~~~~~~~~~~~~~