[clang-tidy-17] bugprone-non-zero-enum-to-bool-conversion flags false positive

[craffael]

Steps to reproduce:

1. Create the file main.cc:

#include <iostream>

enum class TikzOutputCtrl : unsigned int {
  RenderCells = 1,
  CellNumbering = 2
};

TikzOutputCtrl operator&(const TikzOutputCtrl &lhs, const TikzOutputCtrl &rhs) {
    return static_cast<TikzOutputCtrl>(static_cast<unsigned int>(lhs) &
                                   static_cast<unsigned int>(rhs));
}

int main() {
    auto output_ctrl = TikzOutputCtrl::RenderCells;
    const bool q = static_cast<bool>(output_ctrl & TikzOutputCtrl::CellNumbering);

    std::cout << q << '\n';

}

2. Create a .clang-tidy file:

---
Checks:          'bugprone-non-zero-enum-to-bool-conversion'

3. Run clang-tidy-17 with std=c++20. E.g. use the following CMakeLists.txt and set CMAKE_EXPORT_COMPILE_COMMANDS=On:

add_executable(main main.cc)
target_compile_features(main PUBLIC cxx_std_20)

Output of clang-tidy-17:

main.cc:15:20: warning: conversion of 'TikzOutputCtrl' into 'bool' will always return 'true', enum doesn't have a zero-value enumerator [bugprone-non-zero-enum-to-bool-conversion]
   15 |     const bool q = static_cast<bool>(output_ctrl & TikzOutputCtrl::CellNumbering);
      |                    ^
main.cc:3:12: note: enum is defined here
    3 | enum class TikzOutputCtrl : unsigned int {
      |            ^

[chrchr-github]

Related: 503e315

[PiotrZSL]

Fixed in Clang-tidy 18.
Use // NOLINT(bugprone-non-zero-enum-to-bool-conversion) or disable check under Clang-tidy 17.

Duplicate of #65315

[craffael]

@PiotrZSL Great, thank you!