<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/61811>61811</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang type substitution for concepts is too eager
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            c++20,
            clang:frontend,
            rejects-valid,
            concepts
      </td>
    </tr>

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

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

<pre>
    GCC test `concepts4.C` fails when it should pass. Apparently this part of [temp.constr](http://eel.is/c++draft/temp.constr#normal-1.4) points out that the type substitution happens later than when we're applying it (cc @zygoloid in case I botched the explanation).
```cpp
template <class T> struct A { static const int x = 42; };

template <class Ta> concept A42 = A<Ta>::x == 42;
template <class Tv> concept Void = __is_same_as(Tv, void);
template <class Tb, class Ub> concept A42b = Void<Tb> || A42<Ub>;
template <class Tc> concept R42c = A42b<Tc, Tc&>;

static_assert (R42c<void>);
```
</pre>
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