[Bug c++/105716] New: CTAD failure with member function returning auto as template argument

[Bug c++/105716] New: CTAD failure with member function returning auto as template argument

[j-l.wynen at hotmail dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105716

            Bug ID: 105716
           Summary: CTAD failure with member function returning auto as
                    template argument
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: j-l.wynen at hotmail dot de
  Target Milestone: ---

gcc 12 fails to compile the following code (tested 12.1 and trunk). Tried with
c++17 and c++20.

template <class T> struct Func {
  static auto apply() {}
};

template <class T>
struct A {
    T x;
};

template <class T>
A(T) -> A<T>;

int main() {
    A a{Func<double>::apply};
}

with an error of

error: 'A<auto (*)()> a' has incomplete type

The code compiles fine with gcc 11, 10, and 9 as well as clang and MSCV.

Changing static auto apply() {} to static void apply() {} or any other concrete
return type (and proper return statement) makes the code compiles.

Also, specifying the template argument of A in main makes it compile.

https://godbolt.org/z/c9cGnGEPq

[Bug c++/105716] [12/13 Regression] CTAD failure with member function returning auto as template argument

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105716

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|CTAD failure with member    |[12/13 Regression] CTAD
                   |function returning auto as  |failure with member
                   |template argument           |function returning auto as
                   |                            |template argument
   Target Milestone|---                         |12.2
           Keywords|                            |rejects-valid
      Known to work|                            |11.3.1

[Bug c++/105716] [12/13 Regression] CTAD failure with member function returning auto as template argument

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105716

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2022-05-24
             Status|UNCONFIRMED                 |NEW
      Known to fail|                            |12.1.0, 13.0
     Ever confirmed|0                           |1
                 CC|                            |jason at gcc dot gnu.org,
                   |                            |ppalka at gcc dot gnu.org

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Confirmed, started with r12-1270-ga1b3484a8e6c53.

[Bug c++/105716] [12/13 Regression] CTAD failure with member function returning auto as template argument

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105716

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|NEW                         |RESOLVED

--- Comment #2 from Jason Merrill <jason at gcc dot gnu.org> ---
Same issue.

*** This bug has been marked as a duplicate of bug 105623 ***