[Bug c++/103684] New: Ambiguous template template overload resolution

[Bug c++/103684] New: Ambiguous template template overload resolution

[weidmann at acm dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103684

            Bug ID: 103684
           Summary: Ambiguous template template overload resolution
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: weidmann at acm dot org
  Target Milestone: ---

The following code compiles with -std=c++11, but does not with -std=c++17.
Works with clang.

#include <list>
#include <set>

template<template<typename, typename> typename T> constexpr std::size_t hello()
{
    return 2;
}

template<template<typename, typename, typename> typename T> constexpr
std::size_t hello()
{
    return 3;
}

void foo()
{
    auto i = hello<std::list>();
    auto j = hello<std::set>();
}

[Bug c++/103684] Ambiguous template template overload resolution

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103684

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase:
template <class T, class T1 = int, class T2 = int> struct f{};
template <class T, class T1 = int> struct g{};
template<template<typename, typename> class T> constexpr int hello()
{
    return 2;
}
template<template<typename, typename, typename> class T> constexpr int hello()
{
    return 3;
}
void foo()
{
    auto i = hello<g>();
    auto j = hello<f>();
}

----- CUT -----
I think clang here is wrong, MSVC and ICC both reject it for the same reason as
GCC.  Basically it looks like clang is not taking into account the default
template arugments.

[Bug c++/103684] Ambiguous template template overload resolution

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103684

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#150
[Moved to DR at the November, 2016 meeting as paper P0522R0.]

[Picked up by evolution group at October 2002 meeting.]


paper P0522R0:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0522r0.html

Anyways this used to be a GCC extension which was removed and then added back
as part of the C++ standard.  GCC is correct here in C++17 and above.

[Bug c++/103684] Ambiguous template template overload resolution

[weidmann at acm dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103684

--- Comment #3 from Nicolas Weidmann <weidmann at acm dot org> ---
Ok, thanks for the update!