Do not check the body of an impure method against an inherited @pure-unless-* tag

Author: zonuexe

src/Rules/Pure/FunctionPurityCheck.php

@@ -154,13 +154,14 @@ public function check(
 			}
 
 			$errors = array_merge($errors, $this->reportImpurePoints($impurePoints, $pureUnlessCallableParamNames, $functionDescription));
-		} elseif ($pureUnlessCallableParamNames !== [] || $pureUnlessParameterPassedParamNames !== []) {
+		} elseif (!$isPure->no() && ($pureUnlessCallableParamNames !== [] || $pureUnlessParameterPassedParamNames !== [])) {
 			// A function declared @pure-unless-callable-is-impure is pure except
 			// for the flagged callables, so its body is checked for purity while
 			// the flagged callables' own invocations are exempt. The same holds for
 			// @pure-unless-parameter-passed: writing through the flagged by-ref
 			// parameter is not an impure point, so the rest of the body still has
-			// to be pure for the conditional verdict to hold.
+			// to be pure for the conditional verdict to hold. A method marked
+			// @phpstan-impure that inherits either tag makes no such promise.
 			$errors = array_merge($errors, $this->reportImpurePoints($impurePoints, $pureUnlessCallableParamNames, $functionDescription));
 		} elseif ($isPure->no()) {
 			if (

tests/PHPStan/Rules/Pure/PureMethodRuleTest.php

@@ -438,4 +438,27 @@ public function testPureUnlessParameterPassed(): void
 		]);
 	}
 
+	public function testPureUnlessImpureOverride(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/pure-unless-impure-override.php'], [
+			[
+				'Method PureUnlessImpureOverride\ImpureReplacerWithoutSideEffects::replace() is marked as impure but does not have any side effects.',
+				57,
+			],
+			[
+				'Method PureUnlessImpureOverride\ImpureReplacerWithoutSideEffects::map() is marked as impure but does not have any side effects.',
+				65,
+			],
+			[
+				'Impure echo in pure method PureUnlessImpureOverride\InheritingReplacer::replace().',
+				77,
+			],
+			[
+				'Impure echo in pure method PureUnlessImpureOverride\InheritingReplacer::map().',
+				85,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Pure/data/pure-unless-impure-override.php

@@ -0,0 +1,90 @@
+<?php declare(strict_types = 1);
+
+namespace PureUnlessImpureOverride;
+
+interface Replacer
+{
+
+	/**
+	 * @param-out int $count
+	 * @pure-unless-parameter-passed $count
+	 */
+	public function replace(string $subject, int &$count = 0): string;
+
+	/**
+	 * @param callable(string): string $cb
+	 * @pure-unless-callable-is-impure $cb
+	 */
+	public function map(callable $cb, string $subject): string;
+
+}
+
+final class ImpureReplacer implements Replacer
+{
+
+	/**
+	 * The method is marked impure, so its body is not checked for purity
+	 * although it inherits @pure-unless-parameter-passed.
+	 *
+	 * @phpstan-impure
+	 */
+	public function replace(string $subject, int &$count = 0): string
+	{
+		echo $subject;
+		$count = 1;
+
+		return $subject;
+	}
+
+	/**
+	 * @phpstan-impure
+	 */
+	public function map(callable $cb, string $subject): string
+	{
+		echo $subject;
+
+		return $cb($subject);
+	}
+
+}
+
+final class ImpureReplacerWithoutSideEffects implements Replacer
+{
+
+	/**
+	 * @phpstan-impure
+	 */
+	public function replace(string $subject, int &$count = 0): string
+	{
+		return $subject;
+	}
+
+	/**
+	 * @phpstan-impure
+	 */
+	public function map(callable $cb, string $subject): string
+	{
+		return $subject;
+	}
+
+}
+
+final class InheritingReplacer implements Replacer
+{
+
+	public function replace(string $subject, int &$count = 0): string
+	{
+		echo $subject;
+		$count = 1;
+
+		return $subject;
+	}
+
+	public function map(callable $cb, string $subject): string
+	{
+		echo $subject;
+
+		return $cb($subject);
+	}
+
+}