Fix preg_replace() return type

src/Type/Php/ReplaceFunctionsDynamicReturnTypeExtension.php

@@ -8,6 +8,7 @@
 use PHPStan\Reflection\ParametersAcceptorSelector;
 use PHPStan\Type\Accessory\AccessoryNonEmptyStringType;
 use PHPStan\Type\Accessory\AccessoryNonFalsyStringType;
+use PHPStan\Type\Constant\ConstantArrayTypeBuilder;
 use PHPStan\Type\DynamicFunctionReturnTypeExtension;
 use PHPStan\Type\IntersectionType;
 use PHPStan\Type\MixedType;
@@ -17,6 +18,7 @@
 use PHPStan\Type\TypeUtils;
 use function array_key_exists;
 use function count;
+use function in_array;
 
 final class ReplaceFunctionsDynamicReturnTypeExtension implements DynamicFunctionReturnTypeExtension
 {
@@ -101,9 +103,30 @@ private function getPreliminarilyResolvedTypeFromFunctionCall(
 		if ($compareSuperTypes === $isStringSuperType) {
 			return new StringType();
 		} elseif ($compareSuperTypes === $isArraySuperType) {
-			if (count($subjectArgumentType->getArrays()) > 0) {
+			$subjectArrays = $subjectArgumentType->getArrays();
+			if (count($subjectArrays) > 0) {
 				$result = [];
-				foreach ($subjectArgumentType->getArrays() as $arrayType) {
+				foreach ($subjectArrays as $arrayType) {
+					$constantArrays = $arrayType->getConstantArrays();
+
+					if (
+						$constantArrays !== []
+						&& in_array($functionReflection->getName(), ['preg_replace', 'preg_replace_callback', 'preg_replace_callback_array'], true)
+					) {
+						foreach ($constantArrays as $constantArray) {
+							$generalizedArray = $constantArray->generalizeValues();
+
+							$builder = ConstantArrayTypeBuilder::createEmpty();
+							// turn all keys optional
+							foreach ($constantArray->getKeyTypes() as $keyType) {
+								$builder->setOffsetValueType($keyType, $generalizedArray->getOffsetValueType($keyType), true);
+							}
+							$result[] = $builder->getArray();
+						}
+
+						continue;
+					}
+
 					$result[] = $arrayType->generalizeValues();
 				}
 
@@ -134,6 +157,20 @@ private function canReturnNull(
 		Scope $scope,
 	): bool
 	{
+		if (
+			in_array($functionReflection->getName(), ['preg_replace', 'preg_replace_callback', 'preg_replace_callback_array'], true)
+			&& count($functionCall->getArgs()) > 0
+		) {
+			$subjectArgumentType = $this->getSubjectType($functionReflection, $functionCall, $scope);
+
+			if (
+				$subjectArgumentType !== null
+				&& $subjectArgumentType->isArray()->yes()
+			) {
+				return false;
+			}
+		}
+
 		$possibleTypes = ParametersAcceptorSelector::selectFromArgs(
 			$scope,
 			$functionCall->getArgs(),

tests/PHPStan/Analyser/LegacyNodeScopeResolverTest.php

@@ -7426,11 +7426,11 @@ public function dataReplaceFunctions(): array
 				'$expectedArray',
 			],
 			[
-				'array{a: string, b: string}|null',
+				'array{a?: string, b?: string}',
 				'$expectedArray2',
 			],
 			[
-				'array{a: string, b: string}|null',
+				'array{a?: string, b?: string}',
 				'$anotherExpectedArray',
 			],
 			[
@@ -7450,7 +7450,7 @@ public function dataReplaceFunctions(): array
 				'$anotherExpectedArrayOrString',
 			],
 			[
-				'array{a: string, b: string}|null',
+				'array{a?: string, b?: string}',
 				'preg_replace_callback_array($callbacks, $array)',
 			],
 			[

tests/PHPStan/Analyser/nsrt/bug-11547.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace Bug11547;
+
+use function PHPStan\Testing\assertType;
+
+function foo(string $s)
+{
+	$r = preg_replace('/^a/', 'b', $s);
+	assertType('string|null', $r);
+	return $r;
+}
+
+function foobar(string $s, string $pattern)
+{
+	$r = preg_replace($pattern, 'b', $s);
+	assertType('string|null', $r);
+	return $r;
+}
+
+/**
+ * @param array{a: string, b:string} $arr
+ */
+function bar(array $arr): array
+{
+	$r = preg_replace('/^a/', 'x', $arr);
+	assertType('array{a?: string, b?: string}', $r);
+	return $r;
+}
+
+/**
+ * @param array{a: string, b:string} $arr
+ */
+function barbar($arr, string $pattern)
+{
+	$r = preg_replace($pattern, 'b', $arr);
+	assertType('array{a?: string, b?: string}', $r);
+	return $r;
+}
+
+// see https://github.com/phpstan/phpstan/issues/11547#issuecomment-2307156443
+// see https://3v4l.org/c70bG
+function validPatternWithEmptyResult(string $s, array $arr) {
+	$r = preg_replace('/(\D+)*[12]/', 'x', $s);
+	assertType('string|null', $r);
+
+	$r = preg_replace('/(\D+)*[12]/', 'x', $arr);
+	assertType('array', $r);
+}
+
+
+/**
+ * @return string
+ */
+function fooCallback(string $s)
+{
+	$r = preg_replace_callback('/^a/', function ($matches) {
+		return strtolower($matches[0]);
+	}, $s);
+	assertType('string|null', $r);
+	return $r;
+}