https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119859
--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> --- (In reply to Andrew Pinski from comment #2) > GCC trunk seemly only rejects the template member function as being > ambigious though. Yes, because https://eel.is/c++draft/namespace.udecl#11 says "The set of declarations named by a using-declarator that inhabits a class C does not include member functions and member function templates of a base class that correspond to (and thus would conflict with) a declaration of a function or function template in C." And "correspond" is defined in terms of the parameters for non-template functions, while it considers the return type for function templates. So A::g corresponds to B::g (and so is not added), but A::f does not correspond to B::f (and is added). So both declarations of f are candidates. As others have pointed out, there is no difference in the conversion for the object parameter. The return type does not participate in overload resolution. And I don't see anything in [over.match.best] that would apply here. The tiebreaker in https://eel.is/c++draft/over#match.best.general-2.7 was originally proposed to apply to all functions, but was limited to only constructors at the 2017-05-08 CWG teleconference. So I agree with Patrick, this seems ambiguous under the current draft. It is mysterious why Clang would treat this differently from the non-template default argument case.
