[all-commits] [llvm/llvm-project] 52126d: [Clang] Fix Handling of Init Capture with Paramete...

[Yupei Liu via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 52126dc72c3f6f4d27e3835b0ad53e162af25e53
      https://github.com/llvm/llvm-project/commit/52126dc72c3f6f4d27e3835b0ad53e162af25e53
  Author: Yupei Liu <liuyupei951018 at hotmail.com>
  Date:   2024-08-09 (Fri, 09 Aug 2024)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/Sema/Sema.h
    M clang/lib/Sema/SemaConcept.cpp
    M clang/lib/Sema/SemaLambda.cpp
    M clang/lib/Sema/SemaTemplateVariadic.cpp
    M clang/test/SemaTemplate/concepts-lambda.cpp

  Log Message:
  -----------
  [Clang] Fix Handling of Init Capture with Parameter Packs in LambdaScopeForCallOperatorInstantiationRAII (#100766)

This PR addresses issues related to the handling of `init capture` with
parameter packs in Clang's
`LambdaScopeForCallOperatorInstantiationRAII`.

Previously, `addInstantiatedCapturesToScope` would add `init capture`
containing packs to the scope using the type of the `init capture` to
determine the expanded pack size. However, this approach resulted in a
pack size of 0 because `getType()->containsUnexpandedParameterPack()`
returns `false`. After extensive testing, it appears that the correct
pack size can only be inferred from `getInit`.

But `getInit` may reference parameters and `init capture` from an outer
lambda, as shown in the following example:

```cpp
auto L = [](auto... z) {
    return [... w = z](auto... y) {
        // ...
    };
};
```

To address this, `addInstantiatedCapturesToScope` in
`LambdaScopeForCallOperatorInstantiationRAII` should be called last.
Additionally, `addInstantiatedCapturesToScope` has been modified to only
add `init capture` to the scope. The previous implementation incorrectly
called `MakeInstantiatedLocalArgPack` for other non-init captures
containing packs, resulting in a pack size of 0.

### Impact

This patch affects scenarios where
`LambdaScopeForCallOperatorInstantiationRAII` is passed with
`ShouldAddDeclsFromParentScope = false`, preventing the correct addition
of the current lambda's `init capture` to the scope. There are two main
scenarios for `ShouldAddDeclsFromParentScope = false`:

1. **Constraints**: Sometimes constraints are instantiated in place
rather than delayed. In this case,
`LambdaScopeForCallOperatorInstantiationRAII` does not need to add `init
capture` to the scope.
2. **`noexcept` Expressions**: The expressions inside `noexcept` have
already been transformed, and the packs referenced within have been
expanded. Only `RebuildLambdaInfo` needs to add the expanded captures to
the scope, without requiring `addInstantiatedCapturesToScope` from
`LambdaScopeForCallOperatorInstantiationRAII`.

### Considerations

An alternative approach could involve adding a data structure within the
lambda to record the expanded size of the `init capture` pack. However,
this would increase the lambda's size and require extensive
modifications.

This PR is a prerequisite for implmenting
https://github.com/llvm/llvm-project/issues/61426



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