https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123590
Bug ID: 123590
Summary: [REGRESSION] error: ‘...’ resolves to ‘...’, which is
not a class type
Product: gcc
Version: 15.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: jonathan.poelen at gmail dot com
Target Milestone: ---
```cpp
template<bool>
struct something
{
template<class TC>
using f = TC;
};
template<int... i>
struct iota_c_result
{
template<class C>
using f = typename something<sizeof...(i) < 1000>
::template f<C>
::template f<i...>; // HERE
};
struct numbers
{
template<int... n>
struct f {};
};
using seq = iota_c_result<0,1,2>::f<numbers>;
```
test.cpp: In instantiation of ‘struct iota_c_result<0, 1, 2>’:
test.cpp:23:33: required from here
23 | using seq = iota_c_result<0,1,2>::f<numbers>;
| ^~
test.cpp:12:9: error: ‘class something<(sizeof... (i) < 1000)>::f<C>’ resolves
to ‘something<true>::f<TC>’, which is not a class type
12 | using f = typename something<sizeof...(i) < 1000>
| ^
This code works with 15.2 and trunk (16.0.1 20260114), but gives compilation
error with 15.2.1 20251112 (compiler explorer does not offer 15.2.1)
(https://godbolt.org/z/avM3s4a65)
