<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/63401>63401</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [clang][c++20] Differing behaviour vs msvc and gcc when mixing CRTP and concepts
        </td>
    </tr>

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

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

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

<pre>
    I was implementing an idea from [the following blog post](https://www.reachablecode.com/2019/06/09/concept-based-interfaces/) and [the followup discussion on Reddit](https://www.reddit.com/r/cpp/comments/c39asd/interfaces_with_c20_concepts/) so as to enforce that any CRTP derived class would implement the interfaces the CRTP base class relies on.

The code is as follows: [testcase.txt](https://github.com/llvm/llvm-project/files/11798407/testcase.txt)

However, `clang` seems to reject this specific piece of code (https://godbolt.org/z/9KGhTPncW).

What is more surprising is that it appears that both:
- `gcc` (https://godbolt.org/z/aWqre6rf5)
- and `msvc` (https://godbolt.org/z/fjbKPqr6j)

Accept this piece of code.

This means that at least one compiler is incorrect or (highly unlikely, but you never know) the C++ standard is ambiguous in that specific case.
</pre>
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