Simplify property memoization for Flyweight pattern by replacing it with ??=

build/PHPStan/Build/MemoizationPropertyRule.php

@@ -0,0 +1,112 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Build;
+
+use PhpParser\Node;
+use PhpParser\Node\Expr\Assign;
+use PhpParser\Node\Expr\AssignOp\Coalesce;
+use PhpParser\Node\Expr\BinaryOp\Identical;
+use PhpParser\Node\Expr\ConstFetch;
+use PhpParser\Node\Expr\PropertyFetch;
+use PhpParser\Node\Expr\Variable;
+use PhpParser\Node\Identifier;
+use PhpParser\Node\Stmt\Expression;
+use PhpParser\Node\Stmt\If_;
+use PhpParser\Node\Stmt\Return_;
+use PHPStan\Analyser\Scope;
+use PHPStan\File\FileHelper;
+use PHPStan\Node\InClassMethodNode;
+use PHPStan\Rules\Rule;
+use PHPStan\Rules\RuleErrorBuilder;
+use function count;
+use function dirname;
+use function sprintf;
+use function str_starts_with;
+use function strcasecmp;
+
+/**
+ * @implements Rule<InClassMethodNode>
+ */
+final class MemoizationPropertyRule implements Rule
+{
+
+	public function __construct(private FileHelper $fileHelper, private bool $skipTests = true)
+	{
+	}
+
+	public function getNodeType(): string
+	{
+		return InClassMethodNode::class;
+	}
+
+	public function processNode(Node $node, Scope $scope): array
+	{
+		$methodNode = $node->getOriginalNode();
+		if (count($methodNode->params) !== 0) {
+			return [];
+		}
+
+		$stmts = $methodNode->getStmts();
+		if ($stmts === null || count($stmts) !== 2) {
+			return [];
+		}
+
+		[$ifNode, $returnNode] = $stmts;
+		if (!$returnNode instanceof Return_
+			|| !$returnNode->expr instanceof PropertyFetch
+			|| !$returnNode->expr->var instanceof Variable
+			|| !$returnNode->expr->name instanceof Identifier
+		) {
+			return [];
+		}
+
+		if (!$ifNode instanceof If_
+			|| count($ifNode->stmts) !== 1
+			|| !$ifNode->stmts[0] instanceof Expression
+			|| count($ifNode->elseifs) !== 0
+			|| $ifNode->else !== null
+			|| !$ifNode->cond instanceof Identical
+			|| !$ifNode->cond->left instanceof PropertyFetch
+			|| !$ifNode->cond->left->var instanceof Variable
+			|| !$ifNode->cond->left->name instanceof Identifier
+			|| !$ifNode->cond->right instanceof ConstFetch
+			|| strcasecmp($ifNode->cond->right->name->name, 'null') !== 0
+		) {
+			return [];
+		}
+
+		$ifThenNode = $ifNode->stmts[0]->expr;
+		if (!$ifThenNode instanceof Assign || !$ifThenNode->var instanceof PropertyFetch) {
+			return [];
+		}
+
+		if ($returnNode->expr->var->name !== $ifNode->cond->left->var->name
+			|| $returnNode->expr->name->name !== $ifNode->cond->left->name->name
+		) {
+			return [];
+		}
+
+		if ($this->skipTests && str_starts_with($this->fileHelper->normalizePath($scope->getFile()), $this->fileHelper->normalizePath(dirname(__DIR__, 3) . '/tests'))) {
+			return [];
+		}
+
+		$classReflection = $node->getClassReflection();
+		$methodName = $methodNode->name->name;
+		$errorBuilder = RuleErrorBuilder::message(
+			sprintf('Method %s::%s() for memoization can be simplified.', $classReflection->getDisplayName(), $methodName),
+		)->fixNode($node->getOriginalNode(), static function (Node\Stmt\ClassMethod $method) use ($ifThenNode) {
+			$method->stmts = [
+				new Return_(
+					new Coalesce($ifThenNode->var, $ifThenNode->expr),
+				),
+			];
+
+			return $method;
+		})->identifier('phpstan.memoizationProperty');
+
+		return [
+			$errorBuilder->build(),
+		];
+	}
+
+}

build/phpstan.neon

@@ -123,6 +123,7 @@ rules:
 	- PHPStan\Build\NamedArgumentsRule
 	- PHPStan\Build\OverrideAttributeThirdPartyMethodRule
 	- PHPStan\Build\SkipTestsWithRequiresPhpAttributeRule
+	- PHPStan\Build\MemoizationPropertyRule
 
 services:
 	-

src/Analyser/Ignore/IgnoreLexer.php

@@ -41,9 +41,7 @@ final class IgnoreLexer
 	 */
 	public function tokenize(string $input): array
 	{
-		if ($this->regexp === null) {
-			$this->regexp = $this->generateRegexp();
-		}
+		$this->regexp ??= $this->generateRegexp();
 
 		$matches = Strings::matchAll($input, $this->regexp, PREG_SET_ORDER);
 

src/DependencyInjection/Type/LazyDynamicReturnTypeExtensionRegistryProvider.php

@@ -20,16 +20,12 @@ public function __construct(private Container $container)
 
 	public function getRegistry(): DynamicReturnTypeExtensionRegistry
 	{
-		if ($this->registry === null) {
-			$this->registry = new DynamicReturnTypeExtensionRegistry(
-				$this->container->getByType(ReflectionProvider::class),
-				$this->container->getServicesByTag(BrokerFactory::DYNAMIC_METHOD_RETURN_TYPE_EXTENSION_TAG),
-				$this->container->getServicesByTag(BrokerFactory::DYNAMIC_STATIC_METHOD_RETURN_TYPE_EXTENSION_TAG),
-				$this->container->getServicesByTag(BrokerFactory::DYNAMIC_FUNCTION_RETURN_TYPE_EXTENSION_TAG),
-			);
-		}
-
-		return $this->registry;
+		return $this->registry ??= new DynamicReturnTypeExtensionRegistry(
+			$this->container->getByType(ReflectionProvider::class),
+			$this->container->getServicesByTag(BrokerFactory::DYNAMIC_METHOD_RETURN_TYPE_EXTENSION_TAG),
+			$this->container->getServicesByTag(BrokerFactory::DYNAMIC_STATIC_METHOD_RETURN_TYPE_EXTENSION_TAG),
+			$this->container->getServicesByTag(BrokerFactory::DYNAMIC_FUNCTION_RETURN_TYPE_EXTENSION_TAG),
+		);
 	}
 
 }

src/DependencyInjection/Type/LazyExpressionTypeResolverExtensionRegistryProvider.php

@@ -19,13 +19,9 @@ public function __construct(private Container $container)
 
 	public function getRegistry(): ExpressionTypeResolverExtensionRegistry
 	{
-		if ($this->registry === null) {
-			$this->registry = new ExpressionTypeResolverExtensionRegistry(
-				$this->container->getServicesByTag(BrokerFactory::EXPRESSION_TYPE_RESOLVER_EXTENSION_TAG),
-			);
-		}
-
-		return $this->registry;
+		return $this->registry ??= new ExpressionTypeResolverExtensionRegistry(
+			$this->container->getServicesByTag(BrokerFactory::EXPRESSION_TYPE_RESOLVER_EXTENSION_TAG),
+		);
 	}
 
 }

src/DependencyInjection/Type/LazyOperatorTypeSpecifyingExtensionRegistryProvider.php

@@ -19,13 +19,9 @@ public function __construct(private Container $container)
 
 	public function getRegistry(): OperatorTypeSpecifyingExtensionRegistry
 	{
-		if ($this->registry === null) {
-			$this->registry = new OperatorTypeSpecifyingExtensionRegistry(
-				$this->container->getServicesByTag(BrokerFactory::OPERATOR_TYPE_SPECIFYING_EXTENSION_TAG),
-			);
-		}
-
-		return $this->registry;
+		return $this->registry ??= new OperatorTypeSpecifyingExtensionRegistry(
+			$this->container->getServicesByTag(BrokerFactory::OPERATOR_TYPE_SPECIFYING_EXTENSION_TAG),
+		);
 	}
 
 }

src/PhpDoc/LazyTypeNodeResolverExtensionRegistryProvider.php

@@ -17,14 +17,10 @@ public function __construct(private Container $container)
 
 	public function getRegistry(): TypeNodeResolverExtensionRegistry
 	{
-		if ($this->registry === null) {
-			$this->registry = new TypeNodeResolverExtensionAwareRegistry(
-				$this->container->getByType(TypeNodeResolver::class),
-				$this->container->getServicesByTag(TypeNodeResolverExtension::EXTENSION_TAG),
-			);
-		}
-
-		return $this->registry;
+		return $this->registry ??= new TypeNodeResolverExtensionAwareRegistry(
+			$this->container->getByType(TypeNodeResolver::class),
+			$this->container->getServicesByTag(TypeNodeResolverExtension::EXTENSION_TAG),
+		);
 	}
 
 }

src/PhpDoc/ResolvedPhpDocBlock.php

@@ -733,65 +733,47 @@ public function getDeprecatedTag(): ?DeprecatedTag
 
 	public function isDeprecated(): bool
 	{
-		if ($this->isDeprecated === null) {
-			$this->isDeprecated = $this->phpDocNodeResolver->resolveIsDeprecated(
-				$this->phpDocNode,
-			);
-		}
-		return $this->isDeprecated;
+		return $this->isDeprecated ??= $this->phpDocNodeResolver->resolveIsDeprecated(
+			$this->phpDocNode,
+		);
 	}
 
 	/**
 	 * @internal
 	 */
 	public function isNotDeprecated(): bool
 	{
-		if ($this->isNotDeprecated === null) {
-			$this->isNotDeprecated = $this->phpDocNodeResolver->resolveIsNotDeprecated(
-				$this->phpDocNode,
-			);
-		}
-		return $this->isNotDeprecated;
+		return $this->isNotDeprecated ??= $this->phpDocNodeResolver->resolveIsNotDeprecated(
+			$this->phpDocNode,
+		);
 	}
 
 	public function isInternal(): bool
 	{
-		if ($this->isInternal === null) {
-			$this->isInternal = $this->phpDocNodeResolver->resolveIsInternal(
-				$this->phpDocNode,
-			);
-		}
-		return $this->isInternal;
+		return $this->isInternal ??= $this->phpDocNodeResolver->resolveIsInternal(
+			$this->phpDocNode,
+		);
 	}
 
 	public function isFinal(): bool
 	{
-		if ($this->isFinal === null) {
-			$this->isFinal = $this->phpDocNodeResolver->resolveIsFinal(
-				$this->phpDocNode,
-			);
-		}
-		return $this->isFinal;
+		return $this->isFinal ??= $this->phpDocNodeResolver->resolveIsFinal(
+			$this->phpDocNode,
+		);
 	}
 
 	public function hasConsistentConstructor(): bool
 	{
-		if ($this->hasConsistentConstructor === null) {
-			$this->hasConsistentConstructor = $this->phpDocNodeResolver->resolveHasConsistentConstructor(
-				$this->phpDocNode,
-			);
-		}
-		return $this->hasConsistentConstructor;
+		return $this->hasConsistentConstructor ??= $this->phpDocNodeResolver->resolveHasConsistentConstructor(
+			$this->phpDocNode,
+		);
 	}
 
 	public function acceptsNamedArguments(): bool
 	{
-		if ($this->acceptsNamedArguments === null) {
-			$this->acceptsNamedArguments = $this->phpDocNodeResolver->resolveAcceptsNamedArguments(
-				$this->phpDocNode,
-			);
-		}
-		return $this->acceptsNamedArguments;
+		return $this->acceptsNamedArguments ??= $this->phpDocNodeResolver->resolveAcceptsNamedArguments(
+			$this->phpDocNode,
+		);
 	}
 
 	public function getTemplateTypeMap(): TemplateTypeMap
@@ -826,33 +808,23 @@ public function isPure(): ?bool
 
 	public function isReadOnly(): bool
 	{
-		if ($this->isReadOnly === null) {
-			$this->isReadOnly = $this->phpDocNodeResolver->resolveIsReadOnly(
-				$this->phpDocNode,
-			);
-		}
-		return $this->isReadOnly;
+		return $this->isReadOnly ??= $this->phpDocNodeResolver->resolveIsReadOnly(
+			$this->phpDocNode,
+		);
 	}
 
 	public function isImmutable(): bool
 	{
-		if ($this->isImmutable === null) {
-			$this->isImmutable = $this->phpDocNodeResolver->resolveIsImmutable(
-				$this->phpDocNode,
-			);
-		}
-		return $this->isImmutable;
+		return $this->isImmutable ??= $this->phpDocNodeResolver->resolveIsImmutable(
+			$this->phpDocNode,
+		);
 	}
 
 	public function isAllowedPrivateMutation(): bool
 	{
-		if ($this->isAllowedPrivateMutation === null) {
-			$this->isAllowedPrivateMutation = $this->phpDocNodeResolver->resolveAllowPrivateMutation(
-				$this->phpDocNode,
-			);
-		}
-
-		return $this->isAllowedPrivateMutation;
+		return $this->isAllowedPrivateMutation ??= $this->phpDocNodeResolver->resolveAllowPrivateMutation(
+			$this->phpDocNode,
+		);
 	}
 
 	/**

src/Reflection/Annotations/AnnotationMethodReflection.php

@@ -68,20 +68,17 @@ public function getName(): string
 
 	public function getVariants(): array
 	{
-		if ($this->variants === null) {
-			$this->variants = [
-				new ExtendedFunctionVariant(
-					$this->templateTypeMap,
-					null,
-					$this->parameters,
-					$this->isVariadic,
-					$this->returnType,
-					$this->returnType,
-					new MixedType(),
-				),
-			];
-		}
-		return $this->variants;
+		return $this->variants ??= [
+			new ExtendedFunctionVariant(
+				$this->templateTypeMap,
+				null,
+				$this->parameters,
+				$this->isVariadic,
+				$this->returnType,
+				$this->returnType,
+				new MixedType(),
+			),
+		];
 	}
 
 	public function getOnlyVariant(): ExtendedParametersAcceptor

src/Reflection/Php/PhpFunctionFromParserNodeReflection.php

@@ -105,21 +105,17 @@ public function getName(): string
 
 	public function getVariants(): array
 	{
-		if ($this->variants === null) {
-			$this->variants = [
-				new ExtendedFunctionVariant(
-					$this->getTemplateTypeMap(),
-					$this->getResolvedTemplateTypeMap(),
-					$this->getParameters(),
-					$this->isVariadic(),
-					$this->getReturnType(),
-					$this->getPhpDocReturnType(),
-					$this->getNativeReturnType(),
-				),
-			];
-		}
-
-		return $this->variants;
+		return $this->variants ??= [
+			new ExtendedFunctionVariant(
+				$this->getTemplateTypeMap(),
+				$this->getResolvedTemplateTypeMap(),
+				$this->getParameters(),
+				$this->isVariadic(),
+				$this->getReturnType(),
+				$this->getPhpDocReturnType(),
+				$this->getNativeReturnType(),
+			),
+		];
 	}
 
 	public function getOnlyVariant(): ExtendedParametersAcceptor