Dynamic return type extension for pow()

Author: ondrejmirtes

conf/config.neon

@@ -976,6 +976,11 @@ services:
 		tags:
 			- phpstan.broker.dynamicFunctionReturnTypeExtension
 
+	-
+		class: PHPStan\Type\Php\PowFunctionReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicFunctionReturnTypeExtension
+
 	-
 		class: PHPStan\Type\Php\StrtotimeFunctionReturnTypeExtension
 		tags:

src/Reflection/SignatureMap/NativeFunctionReflectionProvider.php

@@ -12,7 +12,6 @@
 use PHPStan\Type\IntegerType;
 use PHPStan\Type\NullType;
 use PHPStan\Type\StringAlwaysAcceptingObjectWithToStringType;
-use PHPStan\Type\TypeUtils;
 use PHPStan\Type\UnionType;
 
 class NativeFunctionReflectionProvider
@@ -44,9 +43,6 @@ public function findFunctionReflection(string $functionName): ?NativeFunctionRef
 		while ($this->signatureMapProvider->hasFunctionSignature($lowerCasedFunctionName, $i)) {
 			$functionSignature = $this->signatureMapProvider->getFunctionSignature($lowerCasedFunctionName, null, $i);
 			$returnType = $functionSignature->getReturnType();
-			if ($lowerCasedFunctionName === 'pow') {
-				$returnType = TypeUtils::toBenevolentUnion($returnType);
-			}
 			$variants[] = new FunctionVariant(
 				TemplateTypeMap::createEmpty(),
 				null,

src/Type/Php/PowFunctionReturnTypeExtension.php

@@ -0,0 +1,52 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use PhpParser\Node\Expr\FuncCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\BenevolentUnionType;
+use PHPStan\Type\DynamicFunctionReturnTypeExtension;
+use PHPStan\Type\FloatType;
+use PHPStan\Type\IntegerType;
+use PHPStan\Type\MixedType;
+use PHPStan\Type\ObjectWithoutClassType;
+use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
+
+class PowFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
+{
+
+	public function isFunctionSupported(FunctionReflection $functionReflection): bool
+	{
+		return $functionReflection->getName() === 'pow';
+	}
+
+	public function getTypeFromFunctionCall(FunctionReflection $functionReflection, FuncCall $functionCall, Scope $scope): Type
+	{
+		$defaultReturnType = new BenevolentUnionType([
+			new FloatType(),
+			new IntegerType(),
+		]);
+		if (count($functionCall->args) < 2) {
+			return $defaultReturnType;
+		}
+
+		$firstArgType = $scope->getType($functionCall->args[0]->value);
+		$secondArgType = $scope->getType($functionCall->args[1]->value);
+		if ($firstArgType instanceof MixedType || $secondArgType instanceof MixedType) {
+			return $defaultReturnType;
+		}
+
+		$object = new ObjectWithoutClassType();
+		if (
+			!$object->isSuperTypeOf($firstArgType)->no()
+			|| !$object->isSuperTypeOf($secondArgType)->no()
+		) {
+			return TypeCombinator::union($firstArgType, $secondArgType);
+		}
+
+		return $defaultReturnType;
+	}
+
+}

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -10141,6 +10141,11 @@ public function dataBugFromPr339(): array
 		return $this->gatherAssertTypes(__DIR__ . '/data/bug-pr-339.php');
 	}
 
+	public function dataPow(): array
+	{
+		return $this->gatherAssertTypes(__DIR__ . '/data/pow.php');
+	}
+
 	/**
 	 * @dataProvider dataBug2574
 	 * @dataProvider dataBug2577
@@ -10217,6 +10222,7 @@ public function dataBugFromPr339(): array
 	 * @dataProvider dataBug3866
 	 * @dataProvider dataBug1014
 	 * @dataProvider dataBugFromPr339
+	 * @dataProvider dataPow
 	 * @param string $assertType
 	 * @param string $file
 	 * @param mixed ...$args

tests/PHPStan/Analyser/data/pow.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace PowFunction;
+
+use function PHPStan\Analyser\assertType;
+
+function ($a, $b): void {
+	assertType('(float|int)', pow($a, $b));
+};
+
+function (int $a, int $b): void {
+	assertType('(float|int)', pow($a, $b));
+};
+
+function (\GMP $a, \GMP $b): void {
+	assertType('GMP', pow($a, $b));
+};
+
+function (\stdClass $a, \GMP $b): void {
+	assertType('GMP|stdClass', pow($a, $b));
+};