DynamicFunctionReturnTypeExtension for the get_debug_type function.

conf/config.neon

@@ -1360,6 +1360,11 @@ services:
 		tags:
 			- phpstan.broker.dynamicFunctionReturnTypeExtension
 
+	-
+		class: PHPStan\Type\Php\GetDebugTypeFunctionReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicFunctionReturnTypeExtension
+
 	-
 		class: PHPStan\Type\Php\GetParentClassDynamicFunctionReturnTypeExtension
 		tags:

src/Type/Php/GetDebugTypeFunctionReturnTypeExtension.php

@@ -0,0 +1,89 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use Closure;
+use PhpParser\Node\Expr\FuncCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\Constant\ConstantStringType;
+use PHPStan\Type\DynamicFunctionReturnTypeExtension;
+use PHPStan\Type\StringType;
+use PHPStan\Type\Type;
+use PHPStan\Type\UnionType;
+use function array_map;
+use function count;
+
+class GetDebugTypeFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
+{
+
+	public function isFunctionSupported(FunctionReflection $functionReflection): bool
+	{
+		return $functionReflection->getName() === 'get_debug_type';
+	}
+
+	public function getTypeFromFunctionCall(FunctionReflection $functionReflection, FuncCall $functionCall, Scope $scope): ?Type
+	{
+		$argType = $scope->getType($functionCall->getArgs()[0]->value);
+		if ($argType instanceof UnionType) {
+			return new UnionType(array_map(Closure::fromCallable([self::class, 'resolveOneType']), $argType->getTypes()));
+		}
+		return self::resolveOneType($argType);
+	}
+
+	/**
+	 * @see https://www.php.net/manual/en/function.get-debug-type.php#refsect1-function.get-debug-type-returnvalues
+	 */
+	private static function resolveOneType(Type $type): Type
+	{
+		if ($type->isNull()->yes()) {
+			return new ConstantStringType('null');
+		}
+		if ($type->isBoolean()->yes()) {
+			return new ConstantStringType('bool');
+		}
+		if ($type->isInteger()->yes()) {
+			return new ConstantStringType('int');
+		}
+		if ($type->isFloat()->yes()) {
+			return new ConstantStringType('float');
+		}
+		if ($type->isString()->yes()) {
+			return new ConstantStringType('string');
+		}
+		if ($type->isArray()->yes()) {
+			return new ConstantStringType('array');
+		}
+
+		// "resources" type+state is skipped since we cannot infer the state
+
+		if ($type->isObject()->yes()) {
+			$classNames = $type->getObjectClassNames();
+			$reflections = $type->getObjectClassReflections();
+
+			$types = [];
+			foreach ($classNames as $index => $className) {
+				// if the class is not final, the actual returned string might be of a child class
+				if ($reflections[$index]->isFinal() && !$reflections[$index]->isAnonymous()) {
+					$types[] = new ConstantStringType($className);
+				}
+
+				if ($reflections[$index]->isAnonymous()) { // phpcs:ignore
+					$types[] = new ConstantStringType('class@anonymous');
+				}
+			}
+
+			switch (count($types)) {
+				case 0:
+					return new StringType();
+				case 1:
+					return $types[0];
+				default:
+					return new UnionType($types);
+			}
+		}
+
+		return new StringType();
+	}
+
+}

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -1385,6 +1385,10 @@ public function dataFileAsserts(): iterable
 			yield from $this->gatherAssertTypes(__DIR__ . '/data/call-user-func-php7.php');
 		}
 
+		if (PHP_VERSION_ID >= 80000) {
+			yield from $this->gatherAssertTypes(__DIR__ . '/data/get-debug-type.php');
+		}
+
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/gettype.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/array_splice.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/../Rules/Methods/data/bug-9542.php');

tests/PHPStan/Analyser/data/get-debug-type.php

@@ -0,0 +1,51 @@
+<?php
+
+namespace GetDebugType;
+
+use function PHPStan\Testing\assertType;
+
+final class A {}
+
+/**
+ * @param double $d
+ * @param resource $r
+ * @param int|string $intOrString
+ * @param array|A $arrayOrObject
+ */
+function doFoo(bool $b, int $i, float $f, $d, $r, string $s, array $a, $intOrString, $arrayOrObject) {
+	$null = null;
+	$resource = fopen('php://memory', 'r');
+	$o = new \stdClass();
+	$A = new A();
+	$anonymous = new class {};
+
+	assertType("'bool'", get_debug_type($b));
+	assertType("'bool'", get_debug_type(true));
+	assertType("'bool'", get_debug_type(false));
+	assertType("'int'", get_debug_type($i));
+	assertType("'float'", get_debug_type($f));
+	assertType("'float'", get_debug_type($d));
+	assertType("'string'", get_debug_type($s));
+	assertType("'array'", get_debug_type($a));
+	assertType("string", get_debug_type($o));
+	assertType("'GetDebugType\\\\A'", get_debug_type($A));
+	assertType("string", get_debug_type($r));
+	assertType("'bool'|string", get_debug_type($resource));
+	assertType("'null'", get_debug_type($null));
+	assertType("'int'|'string'", get_debug_type($intOrString));
+	assertType("'array'|'GetDebugType\\\\A'", get_debug_type($arrayOrObject));
+	assertType("'class@anonymous'", get_debug_type($anonymous));
+}
+
+/**
+ * @param non-empty-string $nonEmptyString
+ * @param non-falsy-string $falsyString
+ * @param numeric-string $numericString
+ * @param class-string $classString
+ */
+function strings($nonEmptyString, $falsyString, $numericString, $classString) {
+	assertType("'string'", get_debug_type($nonEmptyString));
+	assertType("'string'", get_debug_type($falsyString));
+	assertType("'string'", get_debug_type($numericString));
+	assertType("'string'", get_debug_type($classString));
+}