Fix: Return of parent::__set_state() method is only object

src/Reflection/Php/PhpMethodReflection.php

@@ -314,30 +314,33 @@ private function getReturnType(): Type
 	{
 		if ($this->returnType === null) {
 			$name = strtolower($this->getName());
-			if (
-				$name === '__construct'
-				|| $name === '__destruct'
-				|| $name === '__unset'
-				|| $name === '__wakeup'
-				|| $name === '__clone'
-			) {
-				return $this->returnType = TypehintHelper::decideType(new VoidType(), $this->phpDocReturnType);
-			}
-			if ($name === '__tostring') {
-				return $this->returnType = TypehintHelper::decideType(new StringType(), $this->phpDocReturnType);
-			}
-			if ($name === '__isset') {
-				return $this->returnType = TypehintHelper::decideType(new BooleanType(), $this->phpDocReturnType);
-			}
-			if ($name === '__sleep') {
-				return $this->returnType = TypehintHelper::decideType(new ArrayType(new IntegerType(), new StringType()), $this->phpDocReturnType);
-			}
-			if ($name === '__set_state') {
-				return $this->returnType = TypehintHelper::decideType(new ObjectWithoutClassType(), $this->phpDocReturnType);
+			$returnType = $this->reflection->getReturnType();
+			if ($returnType === null) {
+				if (
+					$name === '__construct'
+					|| $name === '__destruct'
+					|| $name === '__unset'
+					|| $name === '__wakeup'
+					|| $name === '__clone'
+				) {
+					return $this->returnType = TypehintHelper::decideType(new VoidType(), $this->phpDocReturnType);
+				}
+				if ($name === '__tostring') {
+					return $this->returnType = TypehintHelper::decideType(new StringType(), $this->phpDocReturnType);
+				}
+				if ($name === '__isset') {
+					return $this->returnType = TypehintHelper::decideType(new BooleanType(), $this->phpDocReturnType);
+				}
+				if ($name === '__sleep') {
+					return $this->returnType = TypehintHelper::decideType(new ArrayType(new IntegerType(), new StringType()), $this->phpDocReturnType);
+				}
+				if ($name === '__set_state') {
+					return $this->returnType = TypehintHelper::decideType(new ObjectWithoutClassType(), $this->phpDocReturnType);
+				}
 			}
 
 			$this->returnType = TypehintHelper::decideTypeFromReflection(
-				$this->reflection->getReturnType(),
+				$returnType,
 				$this->phpDocReturnType,
 				$this->declaringClass->getName(),
 			);

tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php

@@ -815,4 +815,9 @@ public function testBug8146bErrors(): void
 		$this->analyse([__DIR__ . '/data/bug-8146b-errors.php'], []); // there could be a valid error
 	}
 
+	public function testBug8573(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-8573.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Methods/data/bug-8573.php

@@ -0,0 +1,26 @@
+<?php declare(strict_types = 1);
+
+class A
+{
+	final public function __construct() { }
+
+	/**
+	 * @param array<string, mixed> $data
+	 */
+	public static function __set_state(array $data): static
+	{
+		$obj = new static();
+
+		return $obj;
+	}
+}
+
+class B extends A
+{
+	public static function __set_state(array $data): static
+	{
+		$obj = parent::__set_state($data);
+
+		return $obj;
+	}
+}