[all-commits] [llvm/llvm-project] 0370be: [Clang] Perform derived-to-base conversion on expl...

[Sirraide via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0370beb230a35f00b7d07c50ab95f8777662a0c6
      https://github.com/llvm/llvm-project/commit/0370beb230a35f00b7d07c50ab95f8777662a0c6
  Author: Sirraide <aeternalmail at gmail.com>
  Date:   2024-05-22 (Wed, 22 May 2024)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/AST/ASTContext.h
    M clang/include/clang/Basic/DiagnosticSemaKinds.td
    M clang/include/clang/Sema/Sema.h
    M clang/lib/CodeGen/CGExpr.cpp
    M clang/lib/Sema/SemaLambda.cpp
    M clang/lib/Sema/SemaOverload.cpp
    M clang/test/CXX/drs/cwg28xx.cpp
    M clang/test/CodeGenCXX/cxx2b-deducing-this.cpp
    M clang/www/cxx_dr_status.html

  Log Message:
  -----------
  [Clang] Perform derived-to-base conversion on explicit object parameter in lambda (#89828)

Consider this code:
```c++
template <typename... Ts>
struct Overloaded : Ts... { using Ts::operator()...; };

template <typename... Ts>
Overloaded(Ts...) -> Overloaded<Ts...>;

void f() {
  int x;
  Overloaded o {
    [&](this auto& self) {
      return &x;
    }
  };
  o();
}
```

To access `x` in the lambda, we need to perform derived-to-base
conversion on `self` (since the type of `self` is not the lambda type,
but rather `Overloaded<(lambda type)>`). We were previously missing this
step, causing us to attempt to load the entire lambda (as the base
class, it would end up being the ‘field’ with index `0` here), which
would then assert later on in codegen.

Moreover, this is only valid in the first place if there is a unique and
publicly accessible cast path from the derived class to the lambda’s
type, so this also adds a check in Sema to diagnose problematic
cases.

This fixes #87210 and fixes #89541.



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