[clang] [Sema] Reject unqualified lookup of local nested class name (PR #192678)

[Yanzuo Liu via cfe-commits]

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zwuis wrote:

> I guess inside the function scope, the lookup process goes through more contexts which accidentally allowed A::B to be seen as B (the reason for passing).

We can dig deeper. Why it accidently allowed A::B to be seen as B? It is important to know the root cause!

https://github.com/llvm/llvm-project/pull/192678