[PATCH] D124351: [Clang] Implement Change scope of lambda trailing-return-type

Fri Mar 10 08:26:04 PST 2023

aaron.ballman added a comment.

Please keep in mind that I don't have a lot of expertise in modules, but this sure seems like a module merging bug from what I can tell, and it might even relate to work happening in D145737 <https://reviews.llvm.org/D145737> (CC @rsmith). That patch does not seem to address this issue, but what I'm seeing when I try to debug this is a bit confusing to me:

In the reproducer from Sam, there are three lambdas: 
`create::Create<R>([] {});` in `main.cpp`, but this does not participate in AST merging because it's within the main source file
`BuildWidget<T>([dummy](Widget<T>*) {});` in `create.h`
`create::Create<float>([] {});` in `instantiate_create.h`
(While `wrap_create.h` includes `create.h`, it never instantiates the template and so should not produce an additional lambda)

So I would expect `ASTDeclReader::ReadCXXDefinitionData()` to find three lambdas, but it finds *four*. The first lambda it reads has no captures, so this is presumably the one in `instantiate_create.h`. The next three all have captures. So where's that fourth lambda coming from?

The reason I think this relates is because `LocalInstantiationScope::findInstantiationOf()` seems to think there's one declaration in the local scope, but the argument passed to the function is not the one found, which suggest to me there's a module merging issue and we wind up hitting our favorite assert.

Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D124351/new/

https://reviews.llvm.org/D124351