[Bug c++/66092] [c++-concepts] Concept can't check variadic template arguments

[Bug c++/66092] [c++-concepts] Concept can't check variadic template arguments

[yingpo.liao at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66092

--- Comment #1 from Ying-Po Liao <yingpo.liao at gmail dot com> ---
Here's another implementation, which results in the same consequence.

template <typename T, typename U, typename... Args>
  struct Checker
  {
    constexpr static decltype(auto) check( std::true_type )
    { return std::integral_constant<bool, __is_same_as(T, U)>(); }

    constexpr static decltype(auto) check( std::false_type )
    { return std::integral_constant<bool, __is_same_as(T, U) 
          && Checker<U, Args...>::value>(); }

    constexpr static bool value = decltype( 
      check( std::integral_constant<bool, (sizeof...(Args)==0)>() ) 
    )::value;
  };

template <typename T, typename U, typename... Args>
  concept bool Same()
  {
    return Checker<T, U, Args...>::value;
  }

[Bug c++/66092] [c++-concepts] Concept can't check variadic template arguments

[andrew.n.sutton at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66092

Andrew Sutton <andrew.n.sutton at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |andrew.n.sutton at gmail dot com

--- Comment #2 from Andrew Sutton <andrew.n.sutton at gmail dot com> ---
I think that this should be ill-formed.

template <typename T, typename U, typename... Args>
  concept bool Same()
  {
    return decltype(check<T, U, Args...>())::value;
  }

template <typename... Args>
requires Same<Args...>()
  void foo( Args... args ) {}


Template constraint processing requires that flatten (inline) the check for
Same<Args...>(), but I don't see how we can substitute a dependent argument
pack into three distinct template parameters (T, U, and ...Args). 

The wording prohibiting this is missing in the TS.

[Bug c++/66092] [c++-concepts] Concept can't check variadic template arguments

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66092

--- Comment #4 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Fri Jul 10 07:25:49 2015
New Revision: 225649

URL: https://gcc.gnu.org/viewcvs?rev=225649&root=gcc&view=rev
Log:
        PR c++/66092
        * gcc/cp/cp-tree.h (concept_template_p): New.
        * gcc/cp/pt.c (coerce_template_parms): Concepts are also affected
        by DR 1430.
        * gcc/cp/constraint.cc (lift_template_id): Use location_of.
        * gcc/cp/parser.c (cp_parser_template_id): SET_EXPR_LOCATION.

Added:
    branches/c++-concepts/gcc/testsuite/g++.dg/concepts/dr1430.C
Modified:
    branches/c++-concepts/ChangeLog.concepts
    branches/c++-concepts/gcc/cp/constraint.cc
    branches/c++-concepts/gcc/cp/cp-tree.h
    branches/c++-concepts/gcc/cp/parser.c
    branches/c++-concepts/gcc/cp/pt.c
    branches/c++-concepts/gcc/testsuite/g++.dg/concepts/var-concept3.C

[Bug c++/66092] [c++-concepts] Concept can't check variadic template arguments

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66092

--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Tue Jul 14 04:11:11 2015
New Revision: 225758

URL: https://gcc.gnu.org/viewcvs?rev=225758&root=gcc&view=rev
Log:
        PR c++/66092
        PR c++/66834
        * gcc/cp/pt.c (coerce_template_parms): Revert earlier change.

Removed:
    branches/c++-concepts/gcc/testsuite/g++.dg/concepts/dr1430.C
Modified:
    branches/c++-concepts/ChangeLog.concepts
    branches/c++-concepts/gcc/cp/pt.c

[Bug c++/66092] [c++-concepts] Concept can't check variadic template arguments

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66092

--- Comment #6 from Jason Merrill <jason at gcc dot gnu.org> ---
Author: jason
Date: Fri Jul 17 17:43:09 2015
New Revision: 225959

URL: https://gcc.gnu.org/viewcvs?rev=225959&root=gcc&view=rev
Log:
        PR c++/66092
        PR c++/66834
        * gcc/cp/pt.c (coerce_template_parms): Re-apply earlier change.

Added:
    branches/c++-concepts/gcc/testsuite/g++.dg/concepts/dr1430.C
Modified:
    branches/c++-concepts/ChangeLog.concepts
    branches/c++-concepts/gcc/cp/pt.c

[Bug c++/66092] [c++-concepts] Concept can't check variadic template arguments

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66092

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

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

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> ---
Crash was fixed.