C++20 reversed operator== not properly suppressed by operator!= in namespace

[jyknight]

namespace N {
  struct A {};
  bool operator==(A, int);
  bool operator!=(A, int);
}
bool a = 0 == N::A();

This should fail to compile, because the existence of operator!= should suppress the reversed operator==(int, A). However, on Clang it does not.

Moving bool a within the namespace does make it correctly fail to compile, which suggests that name lookup for the operator!= is not being done in the correct scope.

@usx95

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: James Y Knight (jyknight)

``` namespace N { struct A {}; bool operator==(A, int); bool operator!=(A, int); } bool a = 0 == N::A(); ```

This should fail to compile, because the existence of operator!= should suppress the reversed operator==(int, A). However, on Clang it does not.

Moving bool a within the namespace does make it correctly fail to compile, which suggests that name lookup for the operator!= is not being done in the correct scope.

@usx95

[llvmbot]

@llvm/issue-subscribers-c-20

Author: James Y Knight (jyknight)

``` namespace N { struct A {}; bool operator==(A, int); bool operator!=(A, int); } bool a = 0 == N::A(); ```

This should fail to compile, because the existence of operator!= should suppress the reversed operator==(int, A). However, on Clang it does not.

Moving bool a within the namespace does make it correctly fail to compile, which suggests that name lookup for the operator!= is not being done in the correct scope.

@usx95

[usx95]

Same issue but this errors instead:

namespace A {
struct Derived {};
struct Base : Derived {};

bool operator==(Derived& a, Base& b);
bool operator!=(Derived& a, Base& b);
}  // namespace A

void foo() {
    A::Base a, b;
    (void)(a == b);
}

https://godbolt.org/z/xvEjrEYre

[usx95]

/cherry-pick 9330261

[llvmbot]

Failed to cherry-pick: 9330261

https://github.com/llvm/llvm-project/actions/runs/6876823292

Please manually backport the fix and push it to your github fork. Once this is done, please add a comment like this:

/branch <user>/<repo>/<branch>

[usx95]

/branch usx95/llvm-project/release/17.x

[llvmbot]

/pull-request llvm/llvm-project-release-prs#778

[usx95]

/branch usx95/llvm-project/release/17.x