[Bug c++/103783] New: Ambiguous overload between constrained static member and unconstrained non-static member

[Bug c++/103783] New: Ambiguous overload between constrained static member and unconstrained non-static member

[barry.revzin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103783

            Bug ID: 103783
           Summary: Ambiguous overload between constrained static member
                    and unconstrained non-static member
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: barry.revzin at gmail dot com
  Target Milestone: ---

>From StackOverflow (https://stackoverflow.com/q/70429541/2069064):

template<bool b>
struct s {
    void f() const;
    static void f() requires b;
};

void g() {
    s<true>().f();
}

gcc rejects with:

<source>: In function 'void g()':
<source>:8:20: error: call of overloaded 'f()' is ambiguous
    8 |         s<true>().f();
      |         ~~~~~~~~~~~^~
<source>:3:14: note: candidate: 'void s<b>::f() const [with bool b = true]'
    3 |         void f() const;
      |              ^
<source>:4:21: note: candidate: 'static void s<b>::f() requires  b [with bool b
= true]'
    4 |         static void f() requires b;
      |                     ^

I don't think this is an instance of P2113 with non-equivalent templates, seems
like this case should compile. clang and msvc accept.

[Bug c++/103783] Ambiguous overload between constrained static member and unconstrained non-static member

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103783

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-12-21
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed, the constraint on f does not even need to be depdent to the
incorrect behavior from GCC:
int sc();
int mc();
template<int>
struct s {
    void f() const {mc();}
    static void f() requires true {sc();}
};

void g() {
    s<0>().f();
}

[Bug c++/103783] Ambiguous overload between constrained static member and unconstrained non-static member

[fchelnokov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103783

Fedor Chelnokov <fchelnokov at gmail dot com> changed:

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

--- Comment #2 from Fedor Chelnokov <fchelnokov at gmail dot com> ---
I think this code is invalid per
https://timsong-cpp.github.io/cppwp/n4861/class.static.mfct#2:
> There shall not be a static and a non-static member function with the same name and the same parameter types ([over.load]).

So GCC just prints confusing diagnostics here, while it shall reject the
definition of `struct` with static and not-static `f`.

[Bug c++/103783] Ambiguous overload between constrained static member and unconstrained non-static member

[davidfromonline at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103783

--- Comment #3 from David Stone <davidfromonline at gmail dot com> ---
Fedor, it looks like that wording was changed to a non-normative note and
expanded in N4868 to say: "There cannot be a static and a non-static member
function with the same name, parameter-type-list, and trailing requires-clause
([over.load]).". https://timsong-cpp.github.io/cppwp/n4868/class.static.mfct#2.
Later versions of the standard (for C++23) removed the sentence entirely.

[Bug c++/103783] Ambiguous overload between constrained static member and unconstrained non-static member

[davidfromonline at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103783

--- Comment #4 from David Stone <davidfromonline at gmail dot com> ---
A correction to my previous comment: n4868 is technically a C++23 working draft
(but claims to have only editorial fixes to the C++20 paper). However, I
believe the wording fixes to this section are intended to be a bug fix for
wording that was not updated when we added concepts and thus is the intended
C++20 behavior.

[Bug c++/103783] Ambiguous overload between constrained static member and unconstrained non-static member

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103783

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org

[Bug c++/103783] Ambiguous overload between constrained static member and unconstrained non-static member

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103783

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:3e95a974c39e922d19bf7ac1246730c516ae01f2

commit r12-6424-g3e95a974c39e922d19bf7ac1246730c516ae01f2
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Jan 10 14:57:51 2022 -0500

    c++: "more constrained" vs staticness of memfn [PR103783]

    Here we're rejecting the calls to g1 and g2 as ambiguous even though one
    overload is more constrained than the other (and they're otherwise tied),
    because the implicit 'this' parameter of the non-static overload causes
    cand_parms_match to think the function parameter lists aren't equivalent.

    This patch fixes this by making cand_parms_match skip over 'this'
    appropriately.  Note that this bug only affects partial ordering of
    non-template member functions because for member function templates
    more_specialized_fn seems to already skip over 'this' appropriately.

            PR c++/103783

    gcc/cp/ChangeLog:

            * call.c (cand_parms_match): Skip over 'this' when given one
            static and one non-static member function.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-memfun2.C: New test.

[Bug c++/103783] Ambiguous overload between constrained static member and unconstrained non-static member

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103783

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:1e4a9f22ac21da012fc93198a22e30b70e8fdf84

commit r11-9450-g1e4a9f22ac21da012fc93198a22e30b70e8fdf84
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Jan 10 14:57:51 2022 -0500

    c++: "more constrained" vs staticness of memfn [PR103783]

    Here we're rejecting the calls to g1 and g2 as ambiguous even though one
    overload is more constrained than the other (and they're otherwise tied),
    because the implicit 'this' parameter of the non-static overload causes
    cand_parms_match to think the function parameter lists aren't equivalent.

    This patch fixes this by making cand_parms_match skip over 'this'
    appropriately.  Note that this bug only affects partial ordering of
    non-template member functions because for member function templates
    more_specialized_fn seems to already skip over 'this' appropriately.

            PR c++/103783

    gcc/cp/ChangeLog:

            * call.c (cand_parms_match): Skip over 'this' when given one
            static and one non-static member function.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/concepts-memfun2.C: New test.

    (cherry picked from commit 3e95a974c39e922d19bf7ac1246730c516ae01f2)

[Bug c++/103783] Ambiguous overload between constrained static member and unconstrained non-static member

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103783

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
   Target Milestone|---                         |11.3
             Status|ASSIGNED                    |RESOLVED

--- Comment #7 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 11.3/12