Do not complain about impure(Function|Method).pure if it has @phpstan-assert tags

Author: ondrejmirtes

src/Rules/Pure/FunctionPurityCheck.php

@@ -89,7 +89,11 @@ public function check(
 					->build();
 			}
 		} elseif ($isPure->no()) {
-			if (count($impurePoints) === 0) {
+			if (
+				count($throwPoints) === 0
+				&& count($impurePoints) === 0
+				&& count($functionReflection->getAsserts()->getAll()) === 0
+			) {
 				$errors[] = RuleErrorBuilder::message(sprintf(
 					'%s is marked as impure but does not have any side effects.',
 					$functionDescription,

tests/PHPStan/Rules/Pure/data/pure-method.php

@@ -360,3 +360,18 @@ private function doBaz(): void
 	}
 
 }
+
+class AssertingImpureVoidMethod
+{
+
+	/**
+	 * @param mixed $value
+	 * @phpstan-assert array $value
+	 * @phpstan-impure
+	 */
+	public function assertSth($value): void
+	{
+
+	}
+
+}