[all-commits] [llvm/llvm-project] 47747d: [clang] Handle templated operators with reversed a...

[Utkarsh Saxena via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 47747da6340b00e301d3656f95ecf9b04a6ec2bb
      https://github.com/llvm/llvm-project/commit/47747da6340b00e301d3656f95ecf9b04a6ec2bb
  Author: Utkarsh Saxena <usaxena95 at gmail.com>
  Date:   2023-10-20 (Fri, 20 Oct 2023)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/lib/Sema/SemaOverload.cpp
    M clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp

  Log Message:
  -----------
  [clang] Handle templated operators with reversed arguments (#69595)

https://github.com/llvm/llvm-project/pull/68999 correctly computed
conversion sequence for reversed args to a template operators. This was
a breaking change as code, previously accepted in C++17, starts to break
in C++20.

Example:
```cpp
struct P {};
template<class S> bool operator==(const P&, const S &);

struct A : public P {};
struct B : public P {};
bool check(A a, B b) { return a == b; }  // This is now ambiguous in C++20.
```

In order to minimise widespread breakages, as a clang extension, we had
previously accepted such ambiguities with a warning
(`-Wambiguous-reversed-operator`) for non-template operators. Due to the
same reasons, we extend this relaxation for template operators.

Fixes https://github.com/llvm/llvm-project/issues/53954