Anonymous classes are final

src/Reflection/ClassReflection.php

@@ -1079,6 +1079,10 @@ public function hasConsistentConstructor(): bool
 
 	public function isFinalByKeyword(): bool
 	{
+		if ($this->isAnonymous()) {
+			return true;
+		}
+
 		return $this->reflection->isFinal();
 	}
 

tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php

@@ -6,6 +6,7 @@
 use PHPStan\Rules\Rule;
 use PHPStan\Rules\RuleLevelHelper;
 use PHPStan\Testing\RuleTestCase;
+use const PHP_VERSION_ID;
 
 /**
  * @extends RuleTestCase<ReturnTypeRule>
@@ -735,4 +736,14 @@ public function testTaggedUnions(): void
 		]);
 	}
 
+	public function testBug7904(): void
+	{
+		if (PHP_VERSION_ID < 80000) {
+			$this->markTestSkipped('Test requires PHP 8.0.');
+		}
+
+		$this->checkExplicitMixed = true;
+		$this->analyse([__DIR__ . '/data/bug-7904.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Methods/data/bug-7904.php

@@ -0,0 +1,13 @@
+<?php // lint >= 8.0
+
+namespace Bug7904;
+
+interface Test {
+	public static function create(): static;
+}
+
+$impl = new class implements Test {
+	public static function create(): static {
+		return new self();
+	}
+};