Add always used method extension

conf/config.neon

@@ -984,6 +984,9 @@ services:
 	-
 		class: PHPStan\Rules\Constants\LazyAlwaysUsedClassConstantsExtensionProvider
 
+	-
+		class: PHPStan\Rules\Methods\LazyAlwaysUsedMethodExtensionProvider
+
 	-
 		class: PHPStan\Rules\PhpDoc\ConditionalReturnTypeRuleHelper
 

src/Rules/DeadCode/UnusedPrivateMethodRule.php

@@ -7,6 +7,7 @@
 use PHPStan\Analyser\Scope;
 use PHPStan\Node\ClassMethodsNode;
 use PHPStan\Reflection\MethodReflection;
+use PHPStan\Rules\Methods\AlwaysUsedMethodExtensionProvider;
 use PHPStan\Rules\Rule;
 use PHPStan\Rules\RuleErrorBuilder;
 use PHPStan\Type\Constant\ConstantStringType;
@@ -22,6 +23,10 @@
 class UnusedPrivateMethodRule implements Rule
 {
 
+	public function __construct(private AlwaysUsedMethodExtensionProvider $extensionProvider)
+	{
+	}
+
 	public function getNodeType(): string
 	{
 		return ClassMethodsNode::class;
@@ -54,6 +59,14 @@ public function processNode(Node $node, Scope $scope): array
 			if (strtolower($methodName) === '__clone') {
 				continue;
 			}
+
+			$methodReflection = $classType->getMethod($methodName, $scope);
+			foreach ($this->extensionProvider->getExtensions() as $extension) {
+				if ($extension->isAlwaysUsed($methodReflection)) {
+					continue 2;
+				}
+			}
+
 			$methods[strtolower($methodName)] = $method;
 		}
 

src/Rules/Methods/AlwaysUsedMethodExtension.php

@@ -0,0 +1,27 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Methods;
+
+use PHPStan\Reflection\MethodReflection;
+
+/**
+ * This is the extension interface to implement if you want to describe an always-used class method.
+ *
+ * To register it in the configuration file use the `phpstan.methods.alwaysUsedMethodExtension` service tag:
+ *
+ * ```
+ * services:
+ * 	-
+ *		class: App\PHPStan\MyExtension
+ *		tags:
+ *			- phpstan.methods.alwaysUsedMethodExtension
+ * ```
+ *
+ * @api
+ */
+interface AlwaysUsedMethodExtension
+{
+
+	public function isAlwaysUsed(MethodReflection $methodReflection): bool;
+
+}

src/Rules/Methods/AlwaysUsedMethodExtensionProvider.php

@@ -0,0 +1,15 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Methods;
+
+interface AlwaysUsedMethodExtensionProvider
+{
+
+	public const EXTENSION_TAG = 'phpstan.methods.alwaysUsedMethodExtension';
+
+	/**
+	 * @return AlwaysUsedMethodExtension[]
+	 */
+	public function getExtensions(): array;
+
+}

src/Rules/Methods/DirectAlwaysUsedMethodExtensionProvider.php

@@ -0,0 +1,20 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Methods;
+
+class DirectAlwaysUsedMethodExtensionProvider implements AlwaysUsedMethodExtensionProvider
+{
+
+	/**
+	 * @param AlwaysUsedMethodExtension[] $extensions
+	 */
+	public function __construct(private array $extensions)
+	{
+	}
+
+	public function getExtensions(): array
+	{
+		return $this->extensions;
+	}
+
+}

src/Rules/Methods/LazyAlwaysUsedMethodExtensionProvider.php

@@ -0,0 +1,22 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Methods;
+
+use PHPStan\DependencyInjection\Container;
+
+class LazyAlwaysUsedMethodExtensionProvider implements AlwaysUsedMethodExtensionProvider
+{
+
+	/** @var AlwaysUsedMethodExtension[]|null */
+	private ?array $extensions = null;
+
+	public function __construct(private Container $container)
+	{
+	}
+
+	public function getExtensions(): array
+	{
+		return $this->extensions ??= $this->container->getServicesByTag(static::EXTENSION_TAG);
+	}
+
+}

tests/PHPStan/Rules/DeadCode/UnusedPrivateMethodRuleTest.php

@@ -2,6 +2,9 @@
 
 namespace PHPStan\Rules\DeadCode;
 
+use PHPStan\Reflection\MethodReflection;
+use PHPStan\Rules\Methods\AlwaysUsedMethodExtension;
+use PHPStan\Rules\Methods\DirectAlwaysUsedMethodExtensionProvider;
 use PHPStan\Rules\Rule;
 use PHPStan\Testing\RuleTestCase;
 use const PHP_VERSION_ID;
@@ -14,7 +17,19 @@ class UnusedPrivateMethodRuleTest extends RuleTestCase
 
 	protected function getRule(): Rule
 	{
-		return new UnusedPrivateMethodRule();
+		return new UnusedPrivateMethodRule(
+			new DirectAlwaysUsedMethodExtensionProvider([
+				new class() implements AlwaysUsedMethodExtension {
+
+					public function isAlwaysUsed(MethodReflection $methodReflection): bool
+					{
+						return $methodReflection->getDeclaringClass()->is('UnusedPrivateMethod\IgnoredByExtension')
+							&& $methodReflection->getName() === 'foo';
+					}
+
+				},
+			]),
+		);
 	}
 
 	public function testRule(): void
@@ -40,6 +55,10 @@ public function testRule(): void
 				'Method UnusedPrivateMethod\Lorem::doBaz() is unused.',
 				99,
 			],
+			[
+				'Method UnusedPrivateMethod\IgnoredByExtension::bar() is unused.',
+				181,
+			],
 		]);
 	}
 

tests/PHPStan/Rules/DeadCode/data/unused-private-method.php

@@ -171,3 +171,14 @@ public function doTest(): void
 	}
 
 }
+
+class IgnoredByExtension
+{
+	private function foo(): void
+	{
+	}
+
+	private function bar(): void
+	{
+	}
+}