[clang] [Clang][Sema] Fix crash when MS dependent base class lookup occurs in an incomplete context (PR #83024)

[Krystian Stasiowski via cfe-commits]

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@@ -283,6 +283,7 @@ Bug Fixes to C++ Support
   (`#78524 <https://github.com/llvm/llvm-project/issues/78524>`_)
 - Clang no longer instantiates the exception specification of discarded candidate function
   templates when determining the primary template of an explicit specialization.
+- Fixed a crash when MS unqualified dependent base class lookup occurs in an incomplete class.
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sdkrystian wrote:

I think "incomplete class context" is a bit too close to the standardese term "[complete class context](http://eel.is/c++draft/class.mem#general-7)", and wouldn't make sense here (since the completeness of the class isn't context dependent here). How about:

> Fixed a crash in Microsoft compatibility mode where unqualified dependent base class lookup searches an incomplete class.

or

> Fixed a crash in Microsoft compatibility mode where unqualified dependent base class lookup searches the bases of an incomplete class.

I prefer the latter.

https://github.com/llvm/llvm-project/pull/83024