[Bug c++/94102] New: Variadic template deduction guide issue - error: 'In instantiation of'

[Bug c++/94102] New: Variadic template deduction guide issue - error: 'In instantiation of'

[rosemberg at ymail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94102

            Bug ID: 94102
           Summary: Variadic template deduction guide issue - error: 'In
                    instantiation of'
           Product: gcc
           Version: 9.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rosemberg at ymail dot com
  Target Milestone: ---

The gcc9.2 (I tested with gcc7) return the follow error due the deduction guide
declaration:

In instantiation of 'Merged::Merged(T&& ...) (with T = {const main()::&, const
main()::&, main()::}; B = {}]':

#include <utility>

template<typename ... B>
struct Merged : B ... {
       template<typename ... T>
       Merged(T&& ... t) : B(std::forward<T>(t))... {}

    using B::operator()...;
};

template<typename ... T>
Merged(T...) -> Merged<std::decay_t<T>...>;

int main() {
    const auto l1 = []() { return 4; };
    const auto l2 = [](const int i) { return i * 10; };

    Merged merged(l1,
                  l2,
                  [](const double d) { return d * 3.2; });

    return 0;
}

[Bug c++/94102] Variadic template deduction guide issue - error: 'In instantiation of'

[rosemberg at ymail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94102

--- Comment #1 from rosemberg at ymail dot com ---
The work around to solve it was to add the follow deduction guide:

template <typename T0, typename ... T>
Merged (T0, T ...) 
   -> Merged<std::decay_t<T0>, std::decay_t<T>...>;

[Bug c++/94102] Variadic template deduction guide issue - error: 'In instantiation of'

[rosemberg at ymail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94102

--- Comment #2 from rosemberg at ymail dot com ---
*** Bug 94101 has been marked as a duplicate of this bug. ***

[Bug c++/94102] Variadic template deduction guide issue - error: 'In instantiation of'

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94102

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2020-09-16
           Assignee|unassigned at gcc dot gnu.org      |mpolacek at gcc dot gnu.org
     Ever confirmed|0                           |1
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed by r11-1571.

[Bug c++/94102] Variadic template deduction guide issue - error: 'In instantiation of'

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94102

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

https://gcc.gnu.org/g:f24702258fc78ac37b3e8154d76239cccd30c422

commit r12-294-gf24702258fc78ac37b3e8154d76239cccd30c422
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Apr 29 13:30:39 2021 -0400

    c++: Add testcase for already fixed PR [PR94102]

    We correctly accept this testcase since r11-1571.

    gcc/testsuite/ChangeLog:

            PR c++/94102
            * g++.dg/cpp1z/class-deduction87.C: New test.

[Bug c++/94102] Variadic template deduction guide issue - error: 'In instantiation of'

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94102

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Reduced test added.