phpstan · VincentLanglet · May 5, 2026 · May 2, 2026 · May 2, 2026 · May 2, 2026
diff --git a/conf/bleedingEdge.neon b/conf/bleedingEdge.neon
@@ -17,3 +17,4 @@ parameters:
 		assignToByRefForeachExpr: true
 		curlSetOptArrayTypes: true
 		checkDateIntervalConstructor: true
+		reportMethodPurityOverride: true
diff --git a/conf/config.neon b/conf/config.neon
@@ -44,6 +44,7 @@ parameters:
 		assignToByRefForeachExpr: false
 		curlSetOptArrayTypes: false
 		checkDateIntervalConstructor: false
+		reportMethodPurityOverride: false
 	fileExtensions:
 		- php
 	checkAdvancedIsset: false

diff --git a/conf/parametersSchema.neon b/conf/parametersSchema.neon
@@ -46,6 +46,7 @@ parametersSchema:
 		assignToByRefForeachExpr: bool()
 		curlSetOptArrayTypes: bool()
 		checkDateIntervalConstructor: bool()
+		reportMethodPurityOverride: bool()
 	])
 	fileExtensions: listOf(string())
 	checkAdvancedIsset: bool()

diff --git a/conf/services.neon b/conf/services.neon
@@ -98,6 +98,7 @@ services:
 		arguments:
 			reportMaybes: %reportMaybesInMethodSignatures%
 			reportStatic: %reportStaticMethodSignatures%
+			reportMethodPurityOverride: %featureToggles.reportMethodPurityOverride%
 
 	phpstanDiagnoseExtension:
 		class: PHPStan\Diagnose\PHPStanDiagnoseExtension

diff --git a/src/Rules/Methods/MethodSignatureRule.php b/src/Rules/Methods/MethodSignatureRule.php
@@ -41,6 +41,7 @@ public function __construct(
 		private ParentMethodHelper $parentMethodHelper,
 		private bool $reportMaybes,
 		private bool $reportStatic,
+		private bool $reportMethodPurityOverride,
 	)
 	{
 	}
@@ -66,6 +67,16 @@ public function processNode(Node $node, Scope $scope): array
 		$errors = [];
 		$declaringClass = $method->getDeclaringClass();
 		foreach ($this->parentMethodHelper->collectParentMethods($methodName, $method->getDeclaringClass()) as [$parentMethod, $parentMethodDeclaringClass]) {
+			if ($this->reportMethodPurityOverride && $method->isPure()->no() && $parentMethod->isPure()->yes()) {
+				$errors[] = RuleErrorBuilder::message(sprintf(
+					'Impure method %s::%s() overrides pure method %s::%s().',
+					$method->getDeclaringClass()->getDisplayName(),
+					$method->getName(),
+					$parentMethodDeclaringClass->getDisplayName(),
+					$parentMethod->getName(),
+				))->identifier('method.impure')->build();
+			}
+
 			$parentVariants = $parentMethod->getVariants();
 			if (count($parentVariants) !== 1) {
 				continue;

diff --git a/tests/PHPStan/Rules/Methods/MethodSignatureRuleTest.php b/tests/PHPStan/Rules/Methods/MethodSignatureRuleTest.php
@@ -19,6 +19,8 @@ class MethodSignatureRuleTest extends RuleTestCase
 
 	private bool $reportStatic;
 
+	private bool $reportMethodPurityOverride = false;
+
 	protected function getRule(): Rule
 	{
 		$phpVersion = new PhpVersion(PHP_VERSION_ID);
@@ -27,7 +29,7 @@ protected function getRule(): Rule
 
 		return new OverridingMethodRule(
 			$phpVersion,
-			new MethodSignatureRule(new ParentMethodHelper($phpClassReflectionExtension), $this->reportMaybes, $this->reportStatic),
+			new MethodSignatureRule(new ParentMethodHelper($phpClassReflectionExtension), $this->reportMaybes, $this->reportStatic, $this->reportMethodPurityOverride),
 			true,
 			new MethodParameterComparisonHelper($phpVersion),
 			new MethodVisibilityComparisonHelper(),
@@ -565,4 +567,63 @@ public function testBug14320(): void
 		$this->analyse([__DIR__ . '/data/bug-14320.php'], []);
 	}
 
+	public function testBug14563(): void
+	{
+		$this->reportMaybes = true;
+		$this->reportStatic = true;
+		$this->reportMethodPurityOverride = true;
+		$this->analyse([__DIR__ . '/data/bug-14563.php'], [
+			[
+				'Impure method Bug14563\ChildImpureOverridesPure::pure() overrides pure method Bug14563\Foo::pure().',
+				31,
+			],
+			[
+				'Impure method Bug14563\ImpureImplementation::pureMethod() overrides pure method Bug14563\PureInterface::pureMethod().',
+				93,
+			],
+			[
+				'Impure method Bug14563\ImpureChildOfAllMethodsPure::method() overrides pure method Bug14563\AllMethodsPureParent::method().',
+				126,
+			],
+			[
+				'Impure method Bug14563\ChildImpureOverridesPureExtended::pure() overrides pure method Bug14563\Foo::pure().',
+				137,
+			],
+			[
+				'Impure method Bug14563\GrandchildImpureOverridesPure::pure() overrides pure method Bug14563\ChildPureOverridesPure::pure().',
+				148,
+			],
+			[
+				'Impure method Bug14563\ImpureMultipleInterfaces::sharedMethod() overrides pure method Bug14563\PureInterfaceA::sharedMethod().',
+				186,
+			],
+			[
+				'Impure method Bug14563\ImpureMultipleInterfaces::sharedMethod() overrides pure method Bug14563\PureInterfaceB::sharedMethod().',
+				186,
+			],
+			[
+				'Impure method Bug14563\StaticChildImpureOverridesPure::pure() overrides pure method Bug14563\StaticFoo::pure().',
+				219,
+			],
+			[
+				'Impure method Bug14563\StaticImpureImplementation::pureMethod() overrides pure method Bug14563\StaticPureInterface::pureMethod().',
+				270,
+			],
+		]);
+	}
+
+	#[RequiresPhp('>= 8.0.0')]
+	public function testBug14563Trait(): void
+	{
+		$this->reportMaybes = true;
+		$this->reportStatic = true;
+		$this->reportMethodPurityOverride = true;
+		$this->analyse([__DIR__ . '/data/bug-14563-trait.php'], [
+			[
+				'Impure method Bug14563Trait\ImpureTraitUser::pureTraitMethod() overrides pure method Bug14563Trait\PureTrait::pureTraitMethod().',
+				19,
+			],
+		]);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Methods/OverridingMethodRuleTest.php b/tests/PHPStan/Rules/Methods/OverridingMethodRuleTest.php
@@ -30,7 +30,7 @@ protected function getRule(): Rule
 
 		return new OverridingMethodRule(
 			$phpVersion,
-			new MethodSignatureRule(new ParentMethodHelper($phpClassReflectionExtension), true, true),
+			new MethodSignatureRule(new ParentMethodHelper($phpClassReflectionExtension), true, true, false),
 			false,
 			new MethodParameterComparisonHelper($phpVersion),
 			new MethodVisibilityComparisonHelper(),

diff --git a/tests/PHPStan/Rules/Methods/data/bug-14563-trait.php b/tests/PHPStan/Rules/Methods/data/bug-14563-trait.php
@@ -0,0 +1,24 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14563Trait;
+
+trait PureTrait
+{
+
+	/** @phpstan-pure */
+	abstract public function pureTraitMethod(): int;
+
+}
+
+class ImpureTraitUser
+{
+
+	use PureTrait;
+
+	/** @phpstan-impure */
+	public function pureTraitMethod(): int
+	{
+		return random_int(0, 1);
+	}
+
+}