https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100443
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- C++11 7.3.3 [namespace.udecl] p15: "When a using-declarator brings declarations from a base class into a derived class scope, member functions and member function templates in the derived class override and/or hide member functions and member function templates with the same name, parameter-type-list (11.3.5), cv-qualification, and ref-qualifier (if any) in a base class (rather than conflicting)." C++14 7.3.3 [namespace.udecl] p15: Same text. C++17 10.3.3 [namespace.udecl] p15: Same text minus the word "scope", and addition of "Such hidden or overridden declarations are excluded from the set of declarations introduced by the using-declarator." C++20 9.9 [namespace.udecl] p15: Same text with the addition of "trailing requires-clause (if any)," So I don't see where you're finding anything about signatures in p11. The rule is based on name, parameter-type-list, cv-qualification, and ref-qualifier. It doesn't depend on return type. It is the same for member functions and member function templates.
