Symfony version(s) affected

6.0

Description

Having a #[AsMessageHandler] on a method (except __invoke) taking a union will prevent compilation.

How to reproduce

#[AsMessageHandler]
public function method(A|B $message): void {}

Possible Solution

In the MessengerPass::guessHandledClasses() method, every path except the one dealing with union types return if method is known array<class-string, method> else array<int, class-string>. Code path dealing with unions does not.