<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/99825>99825</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Unexpected internal linkage of const/constexpr variable within extern "C++"
        </td>
    </tr>

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

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

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

<pre>
    clang rejects the following with `error: declaration of 'x' with internal linkage cannot be exported`:
```
export module mod;

extern "C++"
{
 export constexpr auto x = 10;
}

```
Compiler explorer: https://godbolt.org/z/a6nhazoKr

According to [[basic.link] 3.2](https://eel.is/c++draft/basic.link#3.2), `const` (or `constexpr` ) implies internal linkage for a namespace scope variable, with some exceptions, and 3.2.1 states that one such exception is if the declaration is in the purview of a module interface. clang appears to respect this generally, but in the case of `extern "C++"` it seems to not apply this exception, as if it considers the contents of such a block to not be part of the module's purview. This feels like a corner case, since obviously the symbols are not attached to the module; but the purview is nonetheless defined as all tokens following the module declaration and I can't see anywhere that states a linkage block is exempt.

Note that MSVC accepts the code.
</pre>
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