Enable existing interfaces to add return type hints with a deprecation message for implementors

There's parent meta to track adding type-hints is this issue actionable?

Yes I think it's actionable but we don't have a clear path forwards for it either.

I think PHP 8.3 feature https://stitcher.io/blog/new-in-php-83##[override]-attribute-rfc is exactly about it

I previously requested PHPStan functionality for this because it's not just problematic for implementers but also for consumers of the code that's changing. Unfortunately the request was rejected.

Since 📌 Make DebugClassLoader ignored deprecations more accurate Fixed we should start getting the Symfony deprecation messages from the classloader. This is not perfect - it's catch-all and doesn't allow for custom messages etc., but it should start to warn modules that have deprecation testing enabled that we might add a type hint later.

Opened an issue to Symfony to see if we can get some tweaks to DebugClassloader to facilitate this task: [ErrorHandler] DebugClassloader: introduce an annotation to signal definite intent to add/change the return typehint of a method

Opened 📌 Introduce a @return-type-will-be-added annotation to indicate return type addition in next major; enforce with a PHPStan rule Active to approach this with a PHPStan custom rule.