[libcxx-commits] [libcxx] [libc++] Enable _LIBCPP_HAS_TRIVIAL_MUTEX_DESTRUCTION for Bionic (PR #218055)

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enh-google wrote:

> Looks good to me. I asked Gemini what unit tests for this might look like; consider adding them:
> 
> AI comment below:
> 
> Purpose: standard C++ does not require mutex to have a trivial destructor (and platforms like Darwin intentionally do not support it due to D64298):
> 
> ```c++
>     //===----------------------------------------------------------------------===//
>     //
>     // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
>     // See https://llvm.org/LICENSE.txt for license information.
>     // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
>     //
>     //===----------------------------------------------------------------------===//
>     
>     // UNSUPPORTED: no-threads
>     
>     // <mutex>
>     
>     // class mutex;
>     
>     // Test that std::mutex has trivial destruction when and only when
>     // _LIBCPP_HAS_TRIVIAL_MUTEX_DESTRUCTION is enabled.
>     
>     #include <mutex>
>     #include <type_traits>
>     
>     #include "test_macros.h"
> 
>     #if _LIBCPP_HAS_TRIVIAL_MUTEX_DESTRUCTION
>     static_assert(std::is_trivially_destructible<std::mutex>::value, "");
>     #else
>     static_assert(!std::is_trivially_destructible<std::mutex>::value, "");
>     #endif
> ```

i don't think this makes sense because the [possibly] problematic code is opaque to c++.

> Purpose: Verifies that static/global instances do not trigger exit-time destructor diagnostics on platforms with _LIBCPP_HAS_TRIVIAL_MUTEX_DESTRUCTION:
> 
> ```c++
>     //===----------------------------------------------------------------------===//
>     //
>     // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
>     // See https://llvm.org/LICENSE.txt for license information.
>     // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
>     //
>     //===----------------------------------------------------------------------===//
> 
>     // UNSUPPORTED: no-threads
>     // ADDITIONAL_COMPILE_FLAGS: -Wexit-time-destructors -Werror
> 
>     // <mutex>
> 
>     #include <mutex>
> 
>     #if _LIBCPP_HAS_TRIVIAL_MUTEX_DESTRUCTION
>     static std::mutex global_mutex;
>     #endif
> 
>     int main(int, char**) {
>     #if _LIBCPP_HAS_TRIVIAL_MUTEX_DESTRUCTION
>       static std::mutex local_mutex;
>       (void)local_mutex;
>     #endif
>       return 0;
>     }
> ```

this seems pointless?

https://github.com/llvm/llvm-project/pull/218055