error: implicit instantiation of undefined template #131511
Description
This is a regression in Clang 20. It didn't happen in Clang 19 and it does not happen with other compilers.
#include <utility>
namespace mcl::mp {
template <class... E> struct list {};
} // namespace mcl::mp
#include <type_traits>
namespace mcl::mp {
namespace detail {
template <class VL> struct lift_sequence_impl;
template <class T, template <class, T...> class VLT, T... values>
struct lift_sequence_impl<VLT<T, values...>> {
using type = list<std::integral_constant<T, values>...>;
};
} // namespace detail
template <class VL>
using lift_sequence = typename detail::lift_sequence_impl<VL>::type;
} // namespace mcl::mp
int wmain(int argc, wchar_t** argv)
{
using fbits_list = mcl::mp::lift_sequence<std::make_index_sequence<1>>;
return 0;
}<source>:25:1: error: implicit instantiation of undefined template 'mcl::mp::detail::lift_sequence_impl<std::integer_sequence<unsigned long, 0>>'
25 | using lift_sequence = typename detail::lift_sequence_impl<VL>::type;
| ^
<source>:31:33: note: in instantiation of template type alias 'lift_sequence' requested here
31 | using fbits_list = mcl::mp::lift_sequence<std::make_index_sequence<1>>;
| ^
<source>:15:28: note: template is declared here
15 | template <class VL> struct lift_sequence_impl;
| ^
1 error generated.
Compiler returned: 1