Thanks for opening a PR!

I think we should expand the $context argument (which is passed to various describers) based on whatever is set in the #[Context].

Then the DateTimePropertyDescriber can for example set a different format based on the passed context.

Thanks for your feedback, that does seem like a much better solution than what I originally went with!

As far as I could tell, there's no cases yet where the $context value passed to the describers has property/method-level context, and the current behaviour seemed to pass $model->getSerializationContext(). So, I've done some slight refactoring so that ObjectModelDescriber instantiates an array of property context data, which gets passed by reference to AnnotationsReader, so that annotation readers can update the context here. This then gets passed to describeProperty in ObjectModelDescriber, where it's merged with the $model->getSerializationContext() (I originally tried instantiating it to this in describe, but some of the JMS tests fail as I think the context is updated).

I've kept the processing for checking if the Context attribute exists in the SymfonyAnnotationReader class which I renamed from SymfonyConstraintAnnotationReader in my previous commit as this feels like the best place for this to live, but if you'd like this to go somewhere else, please let me know!

The alternative I considered which would have required less refactoring was to store to the _context property of the OA\Schema passed to the describers & annotation readers - although, this felt a lot messier (I'd rather use the intended parameter getting passed around).

I've pushed a new commit with these changes to help keep track of my changes, but can squash everything down into a single commit once you're happy with everything before merging!