<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/136607>136607</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            std::generator usage with Clang causes warning/error when compiling HPX with C++23 and coroutines enabled
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            clang
      </td>
    </tr>

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

    <tr>
      <th>Reporter</th>
      <td>
          Prachethan7
      </td>
    </tr>
</table>

<pre>
    I'm encountering a compiler warning (treated as error) when compiling [HPX](https://github.com/STEllAR-GROUP/hpx) with -std=c++23 and coroutine support using Clang 17.0.6.

The error is related to the usage of std::generator and seems to stem from header processing logic.

```
cmake .. \
  -DHPX_DIR=/home/neo/packages/hpx/install/lib/cmake/HPX \
 -DHPX_WITH_CXX_STANDARD=23 \
  -DHPX_HAVE_CXX23_STD_GENERATOR=ON \
 -DHPX_WITH_CXX20_COROUTINES=ON

cmake --build . --target tests

```

Clang version:
```
Debian clang version 19.1.7 (3)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm-19/bin

```

The error disappears when adding a missing ;, but this raises a concern: the warning may indicate a deeper issue in how std::generator is parsed or supported.

Would it be possible to:

 Confirm whether this is an expected behavior?

    Clarify support status for std::generator with Clang 17?

    Possibly improve diagnostic feedback or preprocessor logic?

[compiler_crash.log](https://github.com/user-attachments/files/19840012/compiler_crash.log)
</pre>
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