[Bug c++/121351] [15/16 Regression] Ambiguous resolution of constrained overloads imported from base class

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121351

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2025-08-01
                 CC|                            |ppalka at gcc dot gnu.org
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=119859
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Confirmed, started with r15-3740 and indeed very related to PR119859 but not
quite the same.  One would expect Derived::f to hide the using'd Base::f, but
we keep both overloads since we consider them to have different constraints. 
And after r15-3740 we no longer have the inherited-ness tiebreaker to resolve
the ambiguity.

template<class T> concept C = true;

template<class D>
struct Base {
  void f(auto a) requires C<D>;
};

struct Derived : Base<Derived> {
  using Base::f;
  void f(auto a) requires C<Derived>;
};

int main() {
  Derived d;
  d.f(42);
}