Readonly classes cannot be combined with #[AllowDynamicProperties]

src/Rules/Classes/ClassAttributesRule.php

@@ -8,6 +8,9 @@
 use PHPStan\Node\InClassNode;
 use PHPStan\Rules\AttributesCheck;
 use PHPStan\Rules\Rule;
+use PHPStan\Rules\RuleErrorBuilder;
+use function count;
+use function sprintf;
 
 /**
  * @implements Rule<InClassNode>
@@ -28,12 +31,23 @@ public function processNode(Node $node, Scope $scope): array
 	{
 		$classLikeNode = $node->getOriginalNode();
 
-		return $this->attributesCheck->check(
+		$errors = $this->attributesCheck->check(
 			$scope,
 			$classLikeNode->attrGroups,
 			Attribute::TARGET_CLASS,
 			'class',
 		);
+
+		$classReflection = $scope->getClassReflection();
+		if ($classReflection !== null && $classReflection->isReadOnly()) {
+			if (count($classReflection->getNativeReflection()->getAttributes('AllowDynamicProperties')) > 0) {
+				$errors[] = RuleErrorBuilder::message(sprintf('Cannot apply #[AllowDynamicProperties] to readonly class %s.', $classReflection->getName()))
+					->identifier('class.allowDynamicPropertiesReadonly')
+					->build();
+			}
+		}
+
+		return $errors;
 	}
 
 }

tests/PHPStan/Rules/Classes/ClassAttributesRuleTest.php

@@ -168,4 +168,20 @@ public function testBug12011(): void
 		]);
 	}
 
+	public function testBug12281(): void
+	{
+		if (PHP_VERSION_ID < 80200) {
+			$this->markTestSkipped('Test requires PHP 8.2.');
+		}
+
+		$this->checkExplicitMixed = true;
+		$this->checkImplicitMixed = true;
+		$this->analyse([__DIR__ . '/data/bug-12281.php'], [
+			[
+				'Cannot apply #[AllowDynamicProperties] to readonly class Bug12281\BlogData.',
+				05,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Classes/data/bug-12281.php

@@ -0,0 +1,6 @@
+<?php // lint >= 8.2
+
+namespace Bug12281;
+
+#[\AllowDynamicProperties]
+readonly class BlogData { /* … */ }