<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=http://email.email.llvm.org/c/eJylUsuO2zAM_Br5QqzhSH4edEicLtBbge4PyBLXVitbgSV7N_36yqrTBGgXPRQgIA7IGQ5IdVZd-cuA8GqNsW966mEVRiuQViFIsTh0IEDOwg2gJxDGwIqz03ZyYF9BGhEon2EQK4JH51EBofWT84qwsyT0FOJQEdqkJDuT7EjKbI8IPY4XIzwCYW3Qco7QNszxhH0C5-dFehCEnXbux5SYpGn6wOt-8_5gwPsjB64bum7Zj8D_xbmLtLE5uGhj39ayDyLViVTnf9nbdN8ffEnCjrtuVIK_64S2dl-Eupdu20sUZ6phjUjE4gc7c2mNWLUXY7LMhg_eX1yYQ-hziF77YelSaccAjFlvz9Nltt9Q-gC1cwuGTT4XrMyaZOCFEFleqbJkdU4ZVoqp8lA2Zd4pUdVdmRjRoXGcFOHCdMI3iBIhJ8U5-X8HmtOMhsiKQ01pXqRFzrpaMFpkFWtYWZA8w1Fok246qZ37ZOZRslt6F4pGO-_uxXAI3U-I0XBw6LU3yNvbv-7RfxHy-9elc6GyhG_8st_xOPfLiJNPokEe3f0EaVH4tQ>53609</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Crash in getPackSubstitutedTemplateArgument
        </td>
    </tr>

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

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

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

<pre>
    The following valid code causes a crash in all versions of clang I have tested (-std=c++17).
```
template <class, int> struct a;

template <class, class...> struct b;
template <class x, class... y, y... z>
struct b<x, a<y, z>...> {};

template <class... x> struct c: b<x>...  {};

c<int> d;
```
</pre>
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