[clang] [Clang] raise extension warning for unknown namespaced attributes (PR #120925)

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cor3ntin wrote:

Thanks for this patch.

Sorry I did not see this sooner.

I am not convinced this the best way to resolve #120875 - and I suspect in practice it would be a bit difficult to use/be under used.
I think the general desire is for users to have a way (maybe a file) where they can list all the attributes they want the implementation to ignore when unknown (with their namespaces).
Additionally this should be used to typo correct.
I am not convinced that the current subset that just allows a list of namespace hidden in a warning flag is sufficient / worth it.

-- 
I think we should definitely display the namespace name in the current diagnostic, but for the opt-out mechanism, i think we should have a better sense of a solution that covers all the use cases and then implement that.

Note that I haven't chatted to @AaronBallman and @erichkeane yet, but I think that's worth discussing before proceeding.


-- 

P.S: Please offer a description in your non-trivial changes, explaining your design choices and so forth. thanks a lot


https://github.com/llvm/llvm-project/pull/120925