<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/131391>131391</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            clang: regression - template partial specialization with integer_sequence
        </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>
    Partial specialization of a template with an integer sequence or similar seems to be failing.

```cpp
#include <utility>

template <typename L> struct S;

template <template <typename, auto...> typename L, typename T, T... Vs>
struct S<L<T, Vs...>> {
    constexpr static auto value = 0;
};

auto main() -> int {
    using T = std::make_index_sequence<3>;
 return S<T>::value;
}
```
https://godbolt.org/z/GY9M44nzM

Produces:
```console
<source>:12:12: error: implicit instantiation of undefined template 'S<std::integer_sequence<unsigned long, 0, 1, 2>>'
   12 |     return S<T>::value;
      |            ^
```

This seems to be a regression after clang-19.

</pre>
<img width="1" height="1" alt="" src="http://email.email.llvm.org/o/eJyEVFGPozYQ_jXmZRQENgnhgYccu-nLnXRSo5P6dDIwIW6NTe3x9nZ_fWWTTdLVSkWWwdY3M9_MN4z0Xk0GsWXbL2z7lMlAF-ta1D0am_V2fG2_S0dKavALDkpq9SZJWQP2DBII50VLQvhH0QWkAWUIJ3Tg8e-AZkCwDryalZbxDmcPZKFHOEullZlyVhzi2hXrGpYlHrlQZtBhRGCiC6S0olcmnlfwLSYTHb0uaOSM8JWJZ_DkwkDwOxNfPoF-YsZ4BzKQzfM82j944939dIqnU57n8MOvLO6Buq9MdAnww69eoiNWRwIAAIM1nvDX4sCTJDWkcPAidYhEnqC4cq2fbqQTYpbKML5nvIFN9KgMPXgNXpkJTsmDp5GJAxOHWf6FP5UZ8dfP9-oz0YlEKRk6pOBMYn1Kt9EqUbmTeNCCFYcL0eIjjh8ZP0527K2m3LqJ8eMb48ff_mi-VZV5-7Yy_-7sGAZMFo-iWuOtxnglOm-Di8Ri-JK_b4DOWRc_1LxoNSgCZTxJQ-rWbcGMeFYGx3vXMV7HbG4luHbfY_7BpAYfQVszRZ2KuJVx46tajNdrWUsOrO5iff-3VAl0Q18ftn3-UD9WHE4X5f_T-RIcTg69j2nJM6GDQUszbcom_g3Z2IqxEY3MsC3rqmz2u11RZpdWiJKPQ8_5fjv0exzrar8_4ziKHTa47ZtMtbzg20KUFS_Loijz8VwNcmj6uq75tioaVhU4S6VzrV_mqGKmvA_YlqIUTZlp2aP2aRBwnigxzuNMcG002PRh8qwqtPLk7y5IkcZ2hYvDY26bu07L5yMkDY2PmmXB6fZD4ym6hD4f7Mz4MUa-vjaLs3_iQIwfUyae8eM1mZeW_xsAAP__-Op8kA">