Mark preg_filter() as @pure-unless-parameter-passed

preg_filter() has the same signature as the already-covered preg_replace()
(a pure regex substitution with an optional by-ref $count out-parameter), so
it stays pure unless $count is passed.

Author: zonuexe

bin/functionMetadata_original.php

@@ -268,6 +268,7 @@
 	'output_reset_rewrite_vars' => ['hasSideEffects' => true],
 	'pclose' => ['hasSideEffects' => true],
 	'popen' => ['hasSideEffects' => true],
+	'preg_filter' => ['pureUnlessParameterPassedParameters' => ['count' => true]],
 	// 'matches'/'subpatterns': PHP 8+ uses the php-8-stubs parameter name, PHP <8 falls
 	// back to the legacy functionMap.php name.
 	'preg_match' => ['pureUnlessParameterPassedParameters' => ['matches' => true, 'subpatterns' => true]],

resources/functionMetadata.php

@@ -1634,6 +1634,7 @@
 	'posix_ttyname' => ['hasSideEffects' => false],
 	'posix_uname' => ['hasSideEffects' => false],
 	'pow' => ['hasSideEffects' => false],
+	'preg_filter' => ['pureUnlessParameterPassedParameters' => ['count' => true]],
 	'preg_grep' => ['hasSideEffects' => false],
 	'preg_last_error' => ['hasSideEffects' => true],
 	'preg_last_error_msg' => ['hasSideEffects' => true],

tests/PHPStan/Rules/Pure/PureFunctionRuleTest.php

@@ -456,6 +456,10 @@ public function testPureUnlessParameterPassedBuiltin(): void
 				'Impure call to function preg_match() in pure function PureUnlessParameterPassedBuiltin\purePregMatchWithMatches().',
 				40,
 			],
+			[
+				'Impure call to function preg_filter() in pure function PureUnlessParameterPassedBuiltin\purePregFilterWithCount().',
+				60,
+			],
 		]);
 	}
 

tests/PHPStan/Rules/Pure/data/pure-unless-parameter-passed-builtin.php

@@ -39,3 +39,23 @@ function purePregMatchWithMatches(string $s): int
 	// The by-ref $matches is passed, so preg_match() is impure (the flag is certain).
 	return (int) preg_match('/a/', $s, $matches);
 }
+
+/**
+ * @phpstan-pure
+ */
+function purePregFilterWithoutCount(string $s): ?string
+{
+	// The by-ref $count is omitted, so preg_filter() is pure.
+	return preg_filter('/a/', 'b', $s);
+}
+
+/**
+ * @phpstan-pure
+ */
+function purePregFilterWithCount(string $s): ?string
+{
+	// The by-ref $count is passed, so preg_filter() is impure (the flag is certain).
+	$count = 0;
+
+	return preg_filter('/a/', 'b', $s, -1, $count);
+}