<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/88142>88142</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Clang frontend crash with deduction guide inside class template
        </td>
    </tr>

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

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

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

<pre>
    This seems to be a regression from 17 to 18/trunk. 

```cpp
template <typename, typename...>
struct X {
  template <typename>
  struct Y {
    template <typename T>
    Y(T) {}
  };

  template <typename T, typename... Vs>
  Y(T, Vs...) -> Y<T>;
};

using T = X<int>::Y<int>;
```
https://godbolt.org/z/K5d3sWGjP

</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJx0kk1zmzwQxz_NctkJI1Zg4MAhtsNzeC49eNL4CGgDSgV4WNFO-uk7sp3UTdMZBr39f_si_RsR20_MFWRbyPZRs_phXip2LU9z1M7mtToMVlCYR0E_Y8vY4ML9wiJ2nvB5mUdM8nCUFEC1X9bpW4yg9qDur_-Nunzd6XTZ8TyeXOMZQe_864mnZmSgHb7N4zgG_XDRil_WzuMTQr697CB-yr8BiFfkeIt8DuHhBkM8AhUHoPIM5vu3gzDV29uW_hntzybwUW7iX6Pv8FFCg1TiHegHPILenct4T_FXulXs1OMBQe_xCfTOTv4M3IO-P96stx8u_LIcvD9JEFMNVPezaWfn43npgeqfQPX_mdHy9b-XLxd5ZCptSl02EVdJntAmL5KSoqHitCBKW6U6Trr8uWg3G85y3ZVtniXPpCJbkaJUpapMsmyjKTZJ2ZAyBXVZzkZpSBWPjXWxc9_HUEFkRVauiiJJKXJNy07OTiTqXDP1QBRMuVRBf9euvUCqnBUvvyN46x1XuyAPZpw8Twa7pZEBf1g_oGGzdj5YtV-tYbSThKFzjcj7K0br4qoP92T9sLZxN49Adch2He5Oy_zCnQeqz8ULUH2u_1cAAAD__3039x8">