[Bug c++/124173] [16 Regression] template argument deduction/substitution failed: candidate 1: ‘template > void f()` since r16-7582

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124173

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1
            Summary|[16 Regression] template    |[16 Regression] template
                   |argument                    |argument
                   |deduction/substitution      |deduction/substitution
                   |failed: candidate 1:        |failed: candidate 1:
                   |‘template<std::nullptr_t    |‘template<std::nullptr_t
                   |<anonymous> > void f()`     |<anonymous> > void f()`
                   |                            |since r16-7582
   Last reconfirmed|                            |2026-02-20
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Target Milestone|---                         |16.0
           Keywords|                            |rejects-valid

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fails with `-std=c++14` and `-std=c++11` works for `-std=c++17` and later.

Even though this was almost definitely caused by r16-7582, it does feel so much
related to PR 123790 too. Though the problem is unrelated to a typedef; that is
this fails too:
```
template <decltype(nullptr)> void f();
int main() {
  static constexpr decltype(nullptr) t = nullptr;
  f<t>();
}
```