<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/64810>64810</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            |libc++] Compilation errors when compiling libc++ std module on windows
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            new issue
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          Arthapz
      </td>
    </tr>
</table>

<pre>
    Hello, i'm getting a weird error with clang and libc++ std module on windows (using ucrt)

```
C:\Dev\llvm\include\c++\v1\__expected\expected.h:84:29: error: missing '#include <__expected/expected.h>'; '_Err' must be declared before it is used
   84 |   throw bad_expected_access<_Err>(std::forward<_Arg>(__arg));
      | ^
C:\Dev\llvm\include\c++\v1\__expected\expected.h:81:17: note: declaration here is not visible
   81 | template <class _Err, class _Arg>
      | ^
C:\Dev\llvm\include\c++\v1\__expected\expected.h:84:48: error: missing '#include <__expected/expected.h>'; '_Arg' must be declared before it is used
   84 |   throw bad_expected_access<_Err>(std::forward<_Arg>(__arg));
      | ^
C:\Dev\llvm\include\c++\v1\__expected\expected.h:81:29: note: declaration here is not visible
   81 | template <class _Err, class _Arg>
      | ^
C:\Dev\llvm\include\c++\v1\__expected\expected.h:84:54: error: missing '#include <__expected/expected.h>'; '__arg' must be declared before it is used
   84 |   throw bad_expected_access<_Err>(std::forward<_Arg>(__arg));
      | ^
C:\Dev\llvm\include\c++\v1\__expected\expected.h:82:63: note: declaration here is not visible
   82 | _LIBCPP_HIDE_FROM_ABI void __throw_bad_expected_access(_Arg&& __arg) {
   ```

here a self contained reproducer with full logs: https://github.com/Arthapz/libc--error-expected

```
> clang --version 18:58:30  
clang version 18.0.0 (https://github.com/llvm/llvm-project.git ef82a53bbb89e831bb524d1b8a60458abb86ce99)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Dev\llvm\bin
``` 
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzkVlGPozYQ_jWTl1EisDGQBx4Iu9Gt1Kqnqu_I4Am4cnBkm-TaX18ZuN3T6dqq1falJ0XGZIaZ-T6P_Vl6r4eJqAJxAvG0k3MYratqF0Z5-33XWfVb9YGMscAa1MCKKw4Ugp4GlPgg7RSSc9bhQ4cReyOjYVJodNcDOwE7oQ8Kr1bNhtBO-NCTsg-PwMrZxzBz7wKwIyRPkNTbmCfbb3ltgNcgmie6g2iMuV9BNHrqzawIRLOlAdHcUxBN29KnG_WBFIjm8_QwAq_LDHjNjsDrteQ4uWq_FAGsAMa3oAj8yzDs_GWY5-jKT_GL9tk5YAVeZx-wI1TUG-lIYUcX6wh1QO1x9qRWHIhYZghFg4hhdPaBnVSveVrZ9-R9zB3jxkSlDypi5_XFuod0KhprN6zGtpVuiMxFTKfXFIhLChDP78teCrxOi0jaZAPF54pXBm0nHCkC9tGGd-11Z-gNdLpUFOh6MzIs9PZGeo8rgQ1ubxuy_xpIbIOsfMc2iHV_V22wbqL_QRuI7B3bYF2H76UPGPA65_-qD9hSUfvDy6n5-LH98PL03J5__unHtj694N1qhW278NF-iw9WrvstB5bjZ8wIxRvir9RjHZeCJHoyF-ztFKSeSKGjm7Nq7mnTr8tsDBo7-IhnDOEWJ8DOwM6DDuPcHXp7BXbe5BHYOercfr900P6Vqz-XMuDPm0ju93dyPnKVxrNIxIEniKvf6vPmcUgOSZTMv6hpWcv1sb85-yv14TDogHQpmRS867rySCVPu06wTKVdKfMkE6XsujLv6Xh81eBfpBsoRAY-lXmbZ_tbv99Ue3_1937zGh3JRdjJRN-b9frTanqZfJDGkHrSy7b6Vst1evqKINypiqsjP8odVWl-ZLwojoXYjRWptCguSZKR6vOMC56XmRQqvYhUKcbUTlcsYTwp0zLNxZGLg0i6XCUFiS7JyrIvIEvoKrU5xOwH64ad9n6mKs_KNNkZ2ZHxyw2IsYkeuBiBsXghctXCaDcPHrLEaB_8W5Sgg6EKiubtugPiCRt7vWmz7oSlNTw-RpqwX_6PJ8zfXY92szPVP1tsYOelbg_svOD6IwAA___WMvj1">