Implement PregGrepDynamicReturnTypeExtension

conf/config.neon

@@ -1411,6 +1411,11 @@ services:
 		tags:
 			- phpstan.broker.dynamicFunctionReturnTypeExtension
 
+	-
+		class: PHPStan\Type\Php\PregGrepDynamicReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicFunctionReturnTypeExtension
+
 	-
 		class: PHPStan\Type\Php\ReflectionClassIsSubclassOfTypeSpecifyingExtension
 		tags:
@@ -1724,6 +1729,9 @@ services:
 	-
 		class: PHPStan\Type\Constant\OversizedArrayBuilder
 
+	-
+		class: PHPStan\Rules\Regexp\PatternValidator
+
 	exceptionTypeResolver:
 		class: PHPStan\Rules\Exceptions\ExceptionTypeResolver
 		factory: @PHPStan\Rules\Exceptions\DefaultExceptionTypeResolver

src/Rules/Regexp/PatternValidator.php

@@ -0,0 +1,22 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\Regexp;
+
+use Nette\Utils\RegexpException;
+use Nette\Utils\Strings;
+
+final class PatternValidator
+{
+
+	public function validatePattern(string $pattern): ?string
+	{
+		try {
+			Strings::match('', $pattern);
+		} catch (RegexpException $e) {
+			return $e->getMessage();
+		}
+
+		return null;
+	}
+
+}

src/Type/Php/PregGrepDynamicReturnTypeExtension.php

@@ -0,0 +1,57 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use PhpParser\Node\Expr\FuncCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Reflection\ParametersAcceptorSelector;
+use PHPStan\Rules\Regexp\PatternValidator;
+use PHPStan\Type\Constant\ConstantBooleanType;
+use PHPStan\Type\DynamicFunctionReturnTypeExtension;
+use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
+use function count;
+
+class PregGrepDynamicReturnTypeExtension implements DynamicFunctionReturnTypeExtension
+{
+
+	public function __construct(private PatternValidator $patternValidator)
+	{
+	}
+
+	public function isFunctionSupported(FunctionReflection $functionReflection): bool
+	{
+		return $functionReflection->getName() === 'preg_grep';
+	}
+
+	public function getTypeFromFunctionCall(
+		FunctionReflection $functionReflection,
+		FuncCall $functionCall,
+		Scope $scope,
+	): ?Type
+	{
+		$args = $functionCall->getArgs();
+		if (count($args) < 2) {
+			return null;
+		}
+
+		$patternType = $scope->getType($args[0]->value);
+		$constantStrings = $patternType->getConstantStrings();
+		if (count($constantStrings) === 0) {
+			return null;
+		}
+
+		foreach ($constantStrings as $constantString) {
+			if ($this->patternValidator->validatePattern($constantString->getValue()) !== null) {
+				return null;
+			}
+		}
+
+		return TypeCombinator::remove(
+			ParametersAcceptorSelector::selectSingle($functionReflection->getVariants())->getReturnType(),
+			new ConstantBooleanType(false),
+		);
+	}
+
+}

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -1340,6 +1340,7 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-9293.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/nullsafe-vs-scalar.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-8517.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/preg_grep.php');
 	}
 
 	/**

tests/PHPStan/Analyser/data/preg_grep.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace PregGrep;
+
+use function PHPStan\Testing\assertType;
+
+function doFoo(array $arr, $mixed, $flags) {
+	assertType('array|false', preg_grep($mixed, $arr));
+	assertType('array|false', preg_grep($mixed, $arr, $flags));
+	assertType('array', preg_grep('/^[0-9]+$/', $arr));
+	assertType('array', preg_grep('/^[0-9]+$/', $arr, $flags));
+
+	// invalid pattern
+	assertType('array|false', preg_grep('/((/', $arr));
+}