[Bug c++/115430] New: Cannot take address of template function

[Bug c++/115430] New: Cannot take address of template function

[thomaspkhealy at yahoo dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115430

            Bug ID: 115430
           Summary: Cannot take address of template function
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: thomaspkhealy at yahoo dot com
  Target Milestone: ---

template<typename... Params>
    constexpr int Func(Params&&...)
    {
        return 0;
    }

    int main(void)
    {
        constexpr auto fp1 = &Func<int,double,float>;              // compiles
        constexpr auto fp2 = (nullptr, &Func<int,double,float>);   // doesn't
compile
    }

The above program compiles without failure on LLVM clang, Microsoft Visual C++
and Intel ICX. But GNU g++ fail to compile it:

    <source>: In function 'int main()':
    <source>:10:36: error: no context to resolve type of '& Func<int, double,
float>'
      10 |    constexpr auto fp2 = (nullptr, &Func<int,double,float>);  //
doesn't compile

[Bug c++/115430] Cannot take address of template function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115430

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2024-06-11
     Ever confirmed|0                           |1
      Known to fail|                            |4.5.3
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced (and modified to be C++98):
```
template<typename T>
int Func(T);
typedef int (*funcptrtype)(int);
funcptrtype fp1 = &Func<int>;
funcptrtype fp2 = (0, &Func<int>);
```

[Bug c++/115430] Cannot take address of template function

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115430

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |3.4.6

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note GCC 4.4.7 and before gave the following error message:
<source>:5: error: argument of type 'void' does not match 'int (*)(int)'

[Bug c++/115430] Cannot take address of template function

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115430

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

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

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Testing a patch.

[Bug c++/115430] Cannot take address of template function

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115430

--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:c847dcf94499da62e5a28921b404e6e561645d99

commit r15-1759-gc847dcf94499da62e5a28921b404e6e561645d99
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Jun 25 17:42:01 2024 -0400

    c++: unresolved overload with comma op [PR115430]

    This works:

      template<typename T>
      int Func(T);
      typedef int (*funcptrtype)(int);
      funcptrtype fp0 = &Func<int>;

    but this doesn't:

      funcptrtype fp2 = (0, &Func<int>);

    because we only call resolve_nondeduced_context on the LHS (via
    convert_to_void) but not on the RHS, so cp_build_compound_expr's
    type_unknown_p check issues an error.

            PR c++/115430

    gcc/cp/ChangeLog:

            * typeck.cc (cp_build_compound_expr): Call
resolve_nondeduced_context
            on RHS.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/noexcept41.C: Remove dg-error.
            * g++.dg/overload/addr3.C: New test.

[Bug c++/115430] Cannot take address of template function

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115430

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed on trunk.  I think I'll backport the fix to 14 as well.