[clang] [C++20][Modules] Fix merging of anonymous members of class templates. (PR #155948)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

I am confused that when we try to merge the field from "b.h", the primary DC should be the definition instead of the declaration: https://github.com/llvm/llvm-project/blob/899fb7f663a973d6cef57533c85884631f08f26b/clang/lib/Serialization/ASTReaderDecl.cpp#L3385C1-L3389C42 

I think the definition in your case should be fully instantiated in main.cpp and its value of `isFromASTFile` should be false. What's going on here?

https://github.com/llvm/llvm-project/pull/155948