get_defined_vars() return type contains know variables

conf/config.neon

@@ -1427,6 +1427,11 @@ services:
 		tags:
 			- phpstan.broker.dynamicFunctionReturnTypeExtension
 
+	-
+		class: PHPStan\Type\Php\GetDefinedVarsFunctionReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicFunctionReturnTypeExtension
+
 	-
 		class: PHPStan\Type\Php\GetParentClassDynamicFunctionReturnTypeExtension
 		tags:

src/Type/Php/GetDefinedVarsFunctionReturnTypeExtension.php

@@ -0,0 +1,55 @@
+<?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\ArrayType;
+use PHPStan\Type\Constant\ConstantArrayType;
+use PHPStan\Type\Constant\ConstantStringType;
+use PHPStan\Type\DynamicFunctionReturnTypeExtension;
+use PHPStan\Type\MixedType;
+use PHPStan\Type\StringType;
+use PHPStan\Type\Type;
+use function array_filter;
+use function array_map;
+use function array_values;
+
+// based on code by @ruudk
+final class GetDefinedVarsFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
+{
+
+	public function isFunctionSupported(FunctionReflection $functionReflection): bool
+	{
+		return $functionReflection->getName() === 'get_defined_vars';
+	}
+
+	public function getTypeFromFunctionCall(FunctionReflection $functionReflection, FuncCall $functionCall, Scope $scope): Type
+	{
+		if ($scope->canAnyVariableExist()) {
+			return new ArrayType(
+				new StringType(),
+				new MixedType(),
+			);
+		}
+
+		$variables = array_values(array_filter(
+			$scope->getDefinedVariables(),
+			static fn ($variable) => $variable !== 'this',
+		));
+
+		$keys = array_map(
+			static fn ($variable) => new ConstantStringType($variable),
+			$variables,
+		);
+
+		$values = array_map(
+			static fn ($variable) => $scope->getVariableType($variable),
+			$variables,
+		);
+
+		return new ConstantArrayType($keys, $values);
+	}
+
+}

tests/PHPStan/Analyser/nsrt/get-defined-vars.php

@@ -0,0 +1,11 @@
+<?php
+
+namespace GetDefinedVars;
+
+use function PHPStan\Testing\assertType;
+
+function doFoo(int $param) {
+	$local = "foo";
+	assertType('array{param: int, local: \'foo\'}', get_defined_vars());
+	assertType('array{\'param\', \'local\'}', array_keys(get_defined_vars()));
+}