Add rule to ensure Arrow Functions declaration format

Author: carusogabriel

lib/Doctrine/ruleset.xml

@@ -267,6 +267,14 @@
     <rule ref="SlevomatCodingStandard.Exceptions.DeadCatch"/>
     <!-- Require using Throwable instead of Exception -->
     <rule ref="SlevomatCodingStandard.Exceptions.ReferenceThrowableOnly"/>
+    <!-- Ensure Arrow Functions declaration format 9 -->
+    <rule ref="SlevomatCodingStandard.Functions.ArrowFunctionDeclaration">
+        <properties>
+            <property name="spacesCountAfterKeyword" value="1"/>
+            <property name="spacesCountBeforeArrow" value="1"/>
+            <property name="spacesCountAfterArrow" value="1"/>
+        </properties>
+    </rule>
     <!-- Require closures not referencing $this be static -->
     <rule ref="SlevomatCodingStandard.Functions.StaticClosure"/>
     <!-- Forbid unused variables passed to closures via `use` -->

tests/fixed/arrow-functions-format.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+$missingStatic = static fn ($a, $b) => $a + $b;
+
+$uselessParentheses = static fn ($x) => $x + $y;
+
+$withReturnType = static fn (): int => 1 + 2;
+
+$withTypesInArguments = static fn (int $a, int $b): int => $a + $b;
+
+$spacing = static fn (int $x) => $x * 2;
+
+$nested = static fn ($x) => static fn ($y) => $x * $y + $z;
+
+$returningObject = static fn () => new stdClass();
+
+Collection::from([1, 2])
+    ->map(static fn (int $v): int => $v * 2)
+    ->reduce(static fn (int $tmp, int $v): int => $tmp + $v, 0);
+
+$thisIsNotAnArrowFunction = [$this->fn => 'value'];
+
+$arrayWithArrowFunctions = [
+    'true' => static fn () => true,
+    'false' => static fn () => false,
+];

tests/input/arrow-functions-format.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+$missingStatic = fn ($a, $b) => $a + $b;
+
+$uselessParentheses = static fn ($x) => ($x + $y);
+
+$withReturnType = static fn () : int => 1 + 2;
+
+$withTypesInArguments = static fn (int $a , int $b): int => $a + $b;
+
+$spacing = static fn(int $x)  =>  $x * 2;
+
+$nested = static fn ($x)=>static fn ($y) => $x * $y + $z;
+
+$returningObject = static fn () => new stdClass();
+
+Collection::from([1, 2])
+    ->map(static fn (int $v): int => $v * 2)
+    ->reduce(static fn (int $tmp, int $v): int => $tmp + $v, 0);
+
+$thisIsNotAnArrowFunction = [$this->fn => 'value'];
+
+$arrayWithArrowFunctions = [
+    'true' => static fn () => true,
+    'false' => static fn () => false,
+];