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

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

I have a work in progress patch which fixes this issue, and doesn't need to take this approach of storing diagnosed entities.

It's a big patch that doesn't target this issue specifically, but I remember I encountered this problem while refactoring things, and I removed the duplicated paths.

I don't remember specific details anymore, but here is the patch: https://github.com/llvm/llvm-project/commit/6b69e5abda3ee972a122ef581aae79147660b825
And I plan on submitting a PR for it within the next couple of weeks.

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