feature: Introduce NullableTypeDeclarationFixer (#7002)

doc/list.rst

@@ -1869,6 +1869,19 @@ List of Available Rules
    Part of rule sets `@PER <./ruleSets/PER.rst>`_ `@PER-CS1.0 <./ruleSets/PER-CS1.0.rst>`_ `@PSR12 <./ruleSets/PSR12.rst>`_ `@PhpCsFixer <./ruleSets/PhpCsFixer.rst>`_ `@Symfony <./ruleSets/Symfony.rst>`_
 
    `Source PhpCsFixer\\Fixer\\Whitespace\\NoWhitespaceInBlankLineFixer <./../src/Fixer/Whitespace/NoWhitespaceInBlankLineFixer.php>`_
+-  `nullable_type_declaration <./rules/language_construct/nullable_type_declaration.rst>`_
+
+   Nullable single type declaration should be standardised using configured syntax.
+
+   Configuration options:
+
+   - | ``syntax``
+     | Whether to use question mark (`?`) or explicit `null` union for nullable type.
+     | Allowed values: ``'question_mark'`` and ``'union'``
+     | Default value: ``'question_mark'``
+
+
+   `Source PhpCsFixer\\Fixer\\LanguageConstruct\\NullableTypeDeclarationFixer <./../src/Fixer/LanguageConstruct/NullableTypeDeclarationFixer.php>`_
 -  `nullable_type_declaration_for_default_null_value <./rules/function_notation/nullable_type_declaration_for_default_null_value.rst>`_
 
    Adds or removes ``?`` before single type declarations or ``|null`` at the end of union types when parameters have a default ``null`` value.

doc/rules/index.rst

@@ -471,6 +471,9 @@ Language Construct
 - `no_unset_on_property <./language_construct/no_unset_on_property.rst>`_ *(risky)*
 
   Properties should be set to ``null`` instead of using ``unset``.
+- `nullable_type_declaration <./language_construct/nullable_type_declaration.rst>`_
+
+  Nullable single type declaration should be standardised using configured syntax.
 - `single_space_after_construct <./language_construct/single_space_after_construct.rst>`_ *(deprecated)*
 
   Ensures a single space after language constructs.

doc/rules/language_construct/nullable_type_declaration.rst

@@ -0,0 +1,68 @@
+==================================
+Rule ``nullable_type_declaration``
+==================================
+
+Nullable single type declaration should be standardised using configured syntax.
+
+Configuration
+-------------
+
+``syntax``
+~~~~~~~~~~
+
+Whether to use question mark (``?``) or explicit ``null`` union for nullable
+type.
+
+Allowed values: ``'question_mark'`` and ``'union'``
+
+Default value: ``'question_mark'``
+
+Examples
+--------
+
+Example #1
+~~~~~~~~~~
+
+*Default* configuration.
+
+.. code-block:: diff
+
+   --- Original
+   +++ New
+    <?php
+   -function bar(null|int $value, null|\Closure $callable): void {}
+   +function bar(?int $value, ?\Closure $callable): void {}
+
+Example #2
+~~~~~~~~~~
+
+With configuration: ``['syntax' => 'union']``.
+
+.. code-block:: diff
+
+   --- Original
+   +++ New
+    <?php
+   -function baz(?int $value, ?\stdClass $obj, ?array $config): ?int {}
+   +function baz(null|int $value, null|\stdClass $obj, null|array $config): null|int {}
+
+Example #3
+~~~~~~~~~~
+
+With configuration: ``['syntax' => 'question_mark']``.
+
+.. code-block:: diff
+
+   --- Original
+   +++ New
+    <?php
+    class ValueObject
+    {
+   -    public null|string $name;
+   +    public ?string $name;
+        public ?int $count;
+   -    public null|bool $internal;
+   -    public null|\Closure $callback;
+   +    public ?bool $internal;
+   +    public ?\Closure $callback;
+    }

src/Fixer/ClassNotation/OrderedTypesFixer.php

@@ -86,7 +86,7 @@ public function bar(null|string|int $foo): string|int;
      * {@inheritdoc}
      *
      * Must run before TypesSpacesFixer.
-     * Must run after NullableTypeDeclarationForDefaultNullValueFixer.
+     * Must run after NullableTypeDeclarationFixer, NullableTypeDeclarationForDefaultNullValueFixer.
      */
     public function getPriority(): int
     {

src/Fixer/FunctionNotation/NullableTypeDeclarationForDefaultNullValueFixer.php

@@ -79,11 +79,11 @@ public function isCandidate(Tokens $tokens): bool
     /**
      * {@inheritdoc}
      *
-     * Must run before NoUnreachableDefaultArgumentValueFixer, OrderedTypesFixer.
+     * Must run before NoUnreachableDefaultArgumentValueFixer, NullableTypeDeclarationFixer, OrderedTypesFixer.
      */
     public function getPriority(): int
     {
-        return 1;
+        return 3;
     }
 
     protected function createConfigurationDefinition(): FixerConfigurationResolverInterface