<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/85385>85385</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            CTAD: clang crashes on an invalid case
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            c++20,
            clang:frontend
      </td>
    </tr>

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

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

<pre>
    The following code crashes clang (and gcc as well), https://godbolt.org/z/x8E95sfTo

```
template <template <typename> typename Iterator>
struct K {};

template <typename C, typename IteratorPolicy>
class Foo {};

template <typename C, template<typename> typename TTP>
using Bar = Foo<C, K<TTP>>;

void s() {
   Bar(1);
}
```

The crash doesn't exist in clang18, I think it is introduced by the recent change of CTAD for alias templates.
</pre>
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