[Bug c++/101789] New: Fails to match (re-)declaration of member function of class template when using an alias template for the (dependent) return type

[Bug c++/101789] New: Fails to match (re-)declaration of member function of class template when using an alias template for the (dependent) return type

[davveston at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101789

            Bug ID: 101789
           Summary: Fails to match (re-)declaration of member function of
                    class template when using an alias template for the
                    (dependent) return type
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: davveston at gmail dot com
  Target Milestone: ---

(Broken out into a separate report, from my comment to Bug 69348, after prompt
by Andrew Pinski)

---

The following program 

template<typename T>
struct S {
    using type = int;
    type f() const;  // #1
};

template<typename T>
using type_t = typename S<T>::type;

template <typename T>
type_t<T> S<T>::f() const { }  // #2a
// error: no declaration matches 'type_t<T> S<T>::f() const'

int main() {}


is rejected e.g. for GCC 11.1.0 for all C++ versions (-std=c++X with X in {11,
17, 2a/2b}), failing to match the (re-)declaration and definition at #2a of the
member function of the class template at #1, when using an alias template for
the dependent return type of the member function. Clang accepts this program.

The program is accepted if we remove the alias template

template <typename T>
typename S<T>::type S<T>::f() const { }  // #2b: OK

[Bug c++/101789] Fails to match (re-)declaration of member function of class template when using an alias template for the (dependent) return type

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101789

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-12-26
     Ever confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed (I forgot to confirm it when it was split off).
Both MSVC and clang accept the code.

[Bug c++/101789] Fails to match (re-)declaration of member function of class template when using an alias template for the (dependent) return type

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101789

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fchelnokov at gmail dot com

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
*** Bug 110191 has been marked as a duplicate of this bug. ***