[Bug c++/106893] New: auto deduces wrong type for function pointer

[Bug c++/106893] New: auto deduces wrong type for function pointer

[dan at stahlke dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106893

            Bug ID: 106893
           Summary: auto deduces wrong type for function pointer
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dan at stahlke dot org
  Target Milestone: ---

This works in 11.3.0 but not in 12.2.0.

struct IntegerCoordinate {
    int x() const;
    int y() const;
};

template <typename T>
struct CoordTraits
{
    static auto GetX(T const &p) { return p.x(); }
    static auto GetY(T const &p) { return p.y(); }
    using Ordinate = decltype(GetX(T{}));
};

template <typename Traits>
struct Node {
    static constexpr auto GetX = Traits::GetX; // works because of the `using
Ordinate = ...`
    static constexpr auto GetY = Traits::GetY; // compilation error
    // This compiles
    //static constexpr auto GetX = &Traits::GetX;
    //static constexpr auto GetY = &Traits::GetY;
    // This compiles
    //using fptr = int(*)(IntegerCoordinate const &);
    //static constexpr fptr GetX = Traits::GetX;
    //static constexpr fptr GetY = Traits::GetY;

    // Not needed for minimal test case
    auto x(auto const &p) const { return GetX(p); }
    auto y(auto const &p) const { return GetY(p); }
};

int main() {
    Node<CoordTraits<IntegerCoordinate>> node;
    // Not needed for minimal test case
    node.x(IntegerCoordinate{});
    node.y(IntegerCoordinate{});
}


$ g++ -std=c++20 gcc-function-ptr-bug.cpp -c -o gcc-function-ptr-bug.o

gcc-function-ptr-bug.cpp: In instantiation of ‘constexpr auto (* const
Node<CoordTraits<IntegerCoordinate> >::GetY)(const IntegerCoordinate&)’:
gcc-function-ptr-bug.cpp:17:27:   required from ‘struct
Node<CoordTraits<IntegerCoordinate> >’
gcc-function-ptr-bug.cpp:32:42:   required from here
gcc-function-ptr-bug.cpp:17:27: error: invalid conversion from ‘int (*)(const
IntegerCoordinate&)’ to ‘auto (*)(const IntegerCoordinate&)’ [-fpermissive]
   17 |     static constexpr auto GetY = Traits::GetY; // compilation error
      |                           ^~~~
      |                           |
      |                           int (*)(const IntegerCoordinate&)
gcc-function-ptr-bug.cpp: In instantiation of ‘auto Node<Traits>::y(const
auto:2&) const [with auto:2 = IntegerCoordinate; Traits =
CoordTraits<IntegerCoordinate>]’:
gcc-function-ptr-bug.cpp:35:11:   required from here
gcc-function-ptr-bug.cpp:28:46: error: use of
‘Node<CoordTraits<IntegerCoordinate> >::GetY’ before deduction of ‘auto’
   28 |     auto y(auto const &p) const { return GetY(p); }
      |                                          ~~~~^~~

[Bug c++/106893] [12/13 Regression] auto deduces wrong type for function pointer

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106893

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Target Milestone|---                         |12.3
            Summary|auto deduces wrong type for |[12/13 Regression] auto
                   |function pointer            |deduces wrong type for
                   |                            |function pointer
   Last reconfirmed|                            |2022-09-08

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase:
template <typename T>
struct CoordTraits
{
    static auto GetX(T const &p) { return 1; }
};
typedef CoordTraits<int> Traits;
static constexpr auto GetX = Traits::GetX;

[Bug c++/106893] [12/13 Regression] auto deduces wrong type for function pointer

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106893

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Started with r12-1270:

    c++: alias member template [PR100102]

    Patrick already fixed the primary cause of this bug.  But while I was
    looking at this testcase I noticed that with the qualified name k::o we
    ended up with a plain FUNCTION_DECL, whereas without the k:: we got a
    BASELINK.  There seems to be no good reason not to return the BASELINK
    in this case as well.

[Bug c++/106893] [12/13 Regression] auto deduces wrong type for function pointer

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106893

Jason Merrill <jason at gcc dot gnu.org> changed:

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

[Bug c++/106893] [12/13 Regression] auto deduces wrong type for function pointer

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106893

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:03381beccb52c0e2c15da3b8b8dfa3bb6eb71df9

commit r13-2632-g03381beccb52c0e2c15da3b8b8dfa3bb6eb71df9
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Sep 12 13:47:34 2022 -0400

    c++: auto member function and auto variable [PR106893]

    As with PR105623, we need to call mark_single_function sooner to
    resolve the type of a BASELINK.

            PR c++/106893
            PR c++/90451

    gcc/cp/ChangeLog:

            * decl.cc (cp_finish_decl): Call mark_single_function.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1y/auto-fn65.C: New test.

[Bug c++/106893] [12 Regression] auto deduces wrong type for function pointer

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106893

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:999638cb7b126d33d1ea6548c69ba387b7d7a270

commit r12-8758-g999638cb7b126d33d1ea6548c69ba387b7d7a270
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Sep 12 13:47:34 2022 -0400

    c++: auto member function and auto variable [PR106893]

    As with PR105623, we need to call mark_single_function sooner to
    resolve the type of a BASELINK.

            PR c++/106893
            PR c++/90451

    gcc/cp/ChangeLog:

            * decl.cc (cp_finish_decl): Call mark_single_function.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1y/auto-fn65.C: New test.

[Bug c++/106893] [12 Regression] auto deduces wrong type for function pointer

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106893

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |12.3.0, 13.0
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed for 12.3/13.