[clang] [Clang][Sema] Avoid duplicate diagnostics for incomplete types in nested name specifier (C++20+) (PR #147036)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 commented:

Why doesn't C++20 below suffer from the issue?

I think it's a waste to add a Sema scope object just for diagnostic issues. It's more like that there's an underlying issue that would be otherwise hidden by the patch. Can you explore?


https://github.com/llvm/llvm-project/pull/147036