<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/55642>55642</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            template template reportedly undefined
        </td>
    </tr>

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

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

    <tr>
      <th>Reporter</th>
      <td>
          uohmak4fvpqe
      </td>
    </tr>
</table>

<pre>
    clang trunk (```-std=c++20```) fails on the following code :

```
#include<tuple>
#include<type_traits>

template<class>struct type_unpack;
    template<template<class/*...*/>class Pack,class T>struct type_unpack<Pack<T>>:std::type_identity<T>{};

static type_unpack<std::tuple<int>> t[[maybe_unused]];
int main(){
    return 0;
}

```
the fix I found is to add the ```...```. GCC trunk compiles with or without the ellipsis.
Tested on godbolt
</pre>
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