check variance of template types in properties

conf/bleedingEdge.neon

@@ -34,3 +34,4 @@ parameters:
 		paramOutVariance: true
 		allInvalidPhpDocs: true
 		strictStaticMethodTemplateTypeVariance: true
+		propertyVariance: true

conf/config.level2.neon

@@ -53,6 +53,8 @@ conditionalTags:
 		phpstan.rules.rule: %featureToggles.illegalConstructorMethodCall%
 	PHPStan\Rules\PhpDoc\VarTagChangedExpressionTypeRule:
 		phpstan.rules.rule: %featureToggles.varTagType%
+	PHPStan\Rules\Generics\PropertyVarianceRule:
+		phpstan.rules.rule: %featureToggles.propertyVariance%
 
 services:
 	-
@@ -102,3 +104,5 @@ services:
 			checkTypeAgainstNativeType: %featureToggles.varTagType%
 		tags:
 			- phpstan.rules.rule
+	-
+		class: PHPStan\Rules\Generics\PropertyVarianceRule

conf/config.neon

@@ -64,6 +64,7 @@ parameters:
 		paramOutVariance: false
 		allInvalidPhpDocs: false
 		strictStaticMethodTemplateTypeVariance: false
+		propertyVariance: false
 	fileExtensions:
 		- php
 	checkAdvancedIsset: false
@@ -298,6 +299,7 @@ parametersSchema:
 		paramOutVariance: bool()
 		allInvalidPhpDocs: bool()
 		strictStaticMethodTemplateTypeVariance: bool()
+		propertyVariance: bool()
 	])
 	fileExtensions: listOf(string())
 	checkAdvancedIsset: bool()

src/Rules/Generics/PropertyVarianceRule.php

@@ -0,0 +1,52 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Generics;
+
+use PhpParser\Node;
+use PHPStan\Analyser\Scope;
+use PHPStan\Internal\SprintfHelper;
+use PHPStan\Node\ClassPropertyNode;
+use PHPStan\Reflection\ClassReflection;
+use PHPStan\Rules\Rule;
+use function sprintf;
+
+/**
+ * @implements Rule<ClassPropertyNode>
+ */
+class PropertyVarianceRule implements Rule
+{
+
+	public function __construct(private VarianceCheck $varianceCheck)
+	{
+	}
+
+	public function getNodeType(): string
+	{
+		return ClassPropertyNode::class;
+	}
+
+	public function processNode(Node $node, Scope $scope): array
+	{
+		$classReflection = $scope->getClassReflection();
+		if (!$classReflection instanceof ClassReflection) {
+			return [];
+		}
+
+		if (!$classReflection->hasNativeProperty($node->getName())) {
+			return [];
+		}
+
+		$propertyReflection = $classReflection->getNativeProperty($node->getName());
+
+		if ($propertyReflection->isPrivate()) {
+			return [];
+		}
+
+		return $this->varianceCheck->checkProperty(
+			$propertyReflection,
+			sprintf('in property %s::$%s', SprintfHelper::escapeFormatString($classReflection->getDisplayName()), SprintfHelper::escapeFormatString($node->getName())),
+			$propertyReflection->isReadOnly(),
+		);
+	}
+
+}

src/Rules/Generics/VarianceCheck.php

@@ -3,6 +3,7 @@
 namespace PHPStan\Rules\Generics;
 
 use PHPStan\Reflection\ParametersAcceptorWithPhpDocs;
+use PHPStan\Reflection\Php\PhpPropertyReflection;
 use PHPStan\Rules\RuleError;
 use PHPStan\Rules\RuleErrorBuilder;
 use PHPStan\Type\Generic\TemplateType;
@@ -87,6 +88,21 @@ public function checkParametersAcceptor(
 		return $errors;
 	}
 
+	/** @return RuleError[] */
+	public function checkProperty(
+		PhpPropertyReflection $propertyReflection,
+		string $message,
+		bool $isReadOnly,
+	): array
+	{
+		$type = $propertyReflection->getReadableType();
+		$variance = $isReadOnly
+			? TemplateTypeVariance::createCovariant()
+			: TemplateTypeVariance::createInvariant();
+
+		return $this->check($variance, $type, $message);
+	}
+
 	/** @return RuleError[] */
 	public function check(TemplateTypeVariance $positionVariance, Type $type, string $messageContext): array
 	{

tests/PHPStan/Rules/Generics/PropertyVarianceRuleTest.php

@@ -0,0 +1,136 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Generics;
+
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+use const PHP_VERSION_ID;
+
+/**
+ * @extends RuleTestCase<PropertyVarianceRule>
+ */
+class PropertyVarianceRuleTest extends RuleTestCase
+{
+
+	protected function getRule(): Rule
+	{
+		return new PropertyVarianceRule(
+			self::getContainer()->getByType(VarianceCheck::class),
+		);
+	}
+
+	public function testRule(): void
+	{
+		$this->analyse([__DIR__ . '/data/property-variance.php'], [
+			[
+				'Template type X is declared as covariant, but occurs in invariant position in property PropertyVariance\B::$a.',
+				51,
+			],
+			[
+				'Template type X is declared as covariant, but occurs in invariant position in property PropertyVariance\B::$b.',
+				54,
+			],
+			[
+				'Template type X is declared as covariant, but occurs in invariant position in property PropertyVariance\B::$c.',
+				57,
+			],
+			[
+				'Template type X is declared as covariant, but occurs in invariant position in property PropertyVariance\B::$d.',
+				60,
+			],
+			[
+				'Template type X is declared as contravariant, but occurs in invariant position in property PropertyVariance\C::$a.',
+				80,
+			],
+			[
+				'Template type X is declared as contravariant, but occurs in invariant position in property PropertyVariance\C::$b.',
+				83,
+			],
+			[
+				'Template type X is declared as contravariant, but occurs in invariant position in property PropertyVariance\C::$c.',
+				86,
+			],
+			[
+				'Template type X is declared as contravariant, but occurs in invariant position in property PropertyVariance\C::$d.',
+				89,
+			],
+		]);
+	}
+
+	public function testPromoted(): void
+	{
+		if (PHP_VERSION_ID < 80000) {
+			$this->markTestSkipped('Test requires PHP 8.0.');
+		}
+
+		$this->analyse([__DIR__ . '/data/property-variance-promoted.php'], [
+			[
+				'Template type X is declared as covariant, but occurs in invariant position in property PropertyVariance\Promoted\B::$a.',
+				58,
+			],
+			[
+				'Template type X is declared as covariant, but occurs in invariant position in property PropertyVariance\Promoted\B::$b.',
+				59,
+			],
+			[
+				'Template type X is declared as covariant, but occurs in invariant position in property PropertyVariance\Promoted\B::$c.',
+				60,
+			],
+			[
+				'Template type X is declared as covariant, but occurs in invariant position in property PropertyVariance\Promoted\B::$d.',
+				61,
+			],
+			[
+				'Template type X is declared as contravariant, but occurs in invariant position in property PropertyVariance\Promoted\C::$a.',
+				84,
+			],
+			[
+				'Template type X is declared as contravariant, but occurs in invariant position in property PropertyVariance\Promoted\C::$b.',
+				85,
+			],
+			[
+				'Template type X is declared as contravariant, but occurs in invariant position in property PropertyVariance\Promoted\C::$c.',
+				86,
+			],
+			[
+				'Template type X is declared as contravariant, but occurs in invariant position in property PropertyVariance\Promoted\C::$d.',
+				87,
+			],
+		]);
+	}
+
+	public function testReadOnly(): void
+	{
+		if (PHP_VERSION_ID < 80100) {
+			$this->markTestSkipped('Test requires PHP 8.1.');
+		}
+
+		$this->analyse([__DIR__ . '/data/property-variance-readonly.php'], [
+			[
+				'Template type X is declared as covariant, but occurs in contravariant position in property PropertyVariance\ReadOnly\B::$b.',
+				45,
+			],
+			[
+				'Template type X is declared as covariant, but occurs in invariant position in property PropertyVariance\ReadOnly\B::$d.',
+				51,
+			],
+			[
+				'Template type X is declared as contravariant, but occurs in covariant position in property PropertyVariance\ReadOnly\C::$a.',
+				62,
+			],
+			[
+				'Template type X is declared as contravariant, but occurs in covariant position in property PropertyVariance\ReadOnly\C::$c.',
+				68,
+			],
+			[
+				'Template type X is declared as contravariant, but occurs in invariant position in property PropertyVariance\ReadOnly\C::$d.',
+				71,
+			],
+			[
+				'Template type X is declared as contravariant, but occurs in covariant position in property PropertyVariance\ReadOnly\D::$a.',
+				86,
+			],
+		]);
+	}
+
+}

tests/PHPStan/Rules/Generics/data/property-variance-promoted.php

@@ -0,0 +1,93 @@
+<?php // lint >= 8.0
+
+namespace PropertyVariance\Promoted;
+
+/** @template-contravariant T */
+interface In {
+}
+
+/** @template-covariant T */
+interface Out {
+}
+
+/** @template T */
+interface Invariant {
+}
+
+/**
+ * @template X
+ */
+class A {
+	/**
+	 * @param X $a
+	 * @param In<X> $b
+	 * @param Out<X> $c
+	 * @param Invariant<X> $d
+	 * @param X $e
+	 * @param In<X> $f
+	 * @param Out<X> $g
+	 * @param Invariant<X> $h
+	 */
+	public function __construct(
+		public $a,
+		public $b,
+		public $c,
+		public $d,
+		private $e,
+		private $f,
+		private $g,
+		private $h,
+	) {}
+}
+
+/**
+ * @template-covariant X
+ */
+class B {
+	/**
+	 * @param X $a
+	 * @param In<X> $b
+	 * @param Out<X> $c
+	 * @param Invariant<X> $d
+	 * @param X $e
+	 * @param In<X> $f
+	 * @param Out<X> $g
+	 * @param Invariant<X> $h
+	 */
+	public function __construct(
+		public $a,
+		public $b,
+		public $c,
+		public $d,
+		private $e,
+		private $f,
+		private $g,
+		private $h,
+	) {}
+}
+
+/**
+ * @template-contravariant X
+ */
+class C {
+	/**
+	 * @param X $a
+	 * @param In<X> $b
+	 * @param Out<X> $c
+	 * @param Invariant<X> $d
+	 * @param X $e
+	 * @param In<X> $f
+	 * @param Out<X> $g
+	 * @param Invariant<X> $h
+	 */
+	public function __construct(
+		public $a,
+		public $b,
+		public $c,
+		public $d,
+		private $e,
+		private $f,
+		private $g,
+		private $h,
+	) {}
+}