Clang fails to warn -Wunused-private-field

[VitorRamos]

clang version: 19.1
os: ubuntu 22.04

class A
{
public:
   A() : m_x(0)
   {
   }
private:
   const int m_x;
};

#ifdef BUG
class C
{
    friend auto operator==(C, C) -> bool = default;
};
#endif

int main()
{
   [[maybe_unused]] auto c = A();
}

clang++ -std=c++20 -Wall main.cpp

main.cpp:8:14: warning: private field 'm_x' is not used [-Wunused-private-field]
    8 |    const int m_x;
      |              ^
1 warning generated.

clang++ -DBUG -std=c++20 -Wall main.cpp

no warnings

[AaronBallman]

The behavior seems to have changed between Clang 12 and Clang 13: https://godbolt.org/z/Wbn1drhxs

[VitorRamos]

Bisected to 78d404a seems like that fix should be limited to the class that has the default comparison operator.

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. Check that no other contributor has already been assigned to this issue. If you believe that no one is actually working on it despite an assignment, ping the person. After one week without a response, the assignee may be changed.
2. In the comments of this issue, request for it to be assigned to you, or just create a pull request after following the steps below. Mention this issue in the description of the pull request.
3. Fix the issue locally.
4. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
5. Create a Git commit.
6. Run git clang-format HEAD~1 to format your changes.
7. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation. Mention this issue in the description of the pull request.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Vitor Ramos (VitorRamos)

clang version: 19.1 os: ubuntu 22.04

class A
{
public:
   A() : m_x(0)
   {
   }
private:
   const int m_x;
};

#ifdef BUG
class C
{
    friend auto operator==(C, C) -> bool = default;
};
#endif

int main()
{
   [[maybe_unused]] auto c = A();
}

clang++ -std=c++20 -Wall main.cpp

main.cpp:8:14: warning: private field 'm_x' is not used [-Wunused-private-field]
    8 |    const int m_x;
      |              ^
1 warning generated.

clang++ -DBUG -std=c++20 -Wall main.cpp

no warnings

[whiteio]

Hey! Could I be assigned to this please?