[PATCH] D140002: [C++20] [Modules] Merging of lambda types in deserialization

[Chuanqi Xu via Phabricator via cfe-commits]

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Close https://github.com/llvm/llvm-project/issues/57222

The previous deserialization code wouldn't try to merge lambdas since every lambda has a unique type before C++20. In C++20 and later, lambdas can have the same type under certain condition. See the issue link or the comment for example.

Due to we don't care about merging unnamed entities before, now it is pretty problematic to fix it in a well formed.

This is a workaround for the problem but the cost is the inefficiency.  And if we want to fix the problem properly, it looks like we need to touch something very fundamentally and it may affect a lot of things beyond the C++20 modules or even modules.

See my inline comments for details.

The bug/defect has a strong impact. I feel like fixing bug is more important so I prefer to land this one first and file an issue for this to record it.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D140002

Files:
  clang/lib/Serialization/ASTReaderDecl.cpp
  clang/test/Modules/MergeLambdas.cppm
  clang/test/Modules/MergeLambdas2.cppm
  clang/test/Modules/MergeLambdas3.cppm

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