[Bug c++/80962] New: No more access violation control after certain declarations using concepts

["okannen at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80962

            Bug ID: 80962
           Summary: No more access violation control after certain
                    declarations using concepts
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: okannen at gmail dot com
  Target Milestone: ---

Created attachment 41462
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41462&action=edit
The buggy code as described in the comment.

GCC VERSION: (gcc -v)
    Utilisation des specs internes.
    COLLECT_GCC=3Dgcc
   
COLLECT_LTO_WRAPPER=3D/usr/local/gcc7/libexec/gcc/x86_64-pc-linux-gnu/7.1.1/lto-wrapper
    Cible : x86_64-pc-linux-gnu
    Configur=C3=A9 avec: ../configure --prefix=3D/usr/local/gcc7
--disable-=multilib
    Mod=C3=A8le de thread: posix
    gcc version 7.1.1 20170503 (GCC)

BUG DESCRIPTION:
gcc stops to perform member access violation rule checking:
If in a compound requirement using a partialy specialized concept as
placeholder, then gcc stop any access schecking test (one can have access
to private member of classes).

COMMAND LINE:
c++ -fconcepts file.cpp

BUGGY CODE:
This code should not compile, but it does (no access violation performed).

    class a_class
       {
       int f(int){return 33;} //private member
       };

    template<class T,class Y>
    concept bool AnyConcept =true;

    template<class T>
    concept bool OtherConcept = 
      requires(const T& a)
      {
      //Gcc do not bug without the the following line.
      //{a && a} -> AnyConcept<bool>;
      {a && a} -> bool;
      };

    int main()
      {
      a_class obj;
      obj.f(10);  //Error not reported by gcc.
      }


BUGGY CODE:
This code shows normal gcc behavior, an error is reported:
"int a_class::f(int) is private in this context"

    class a_class
       {
       int f(int){return 33;} //private member
       };

    template<class T,class Y>
    concept bool AnyConcept =true;

    template<class T>
    concept bool OtherConcept = 
      requires(const T& a)
      {
      //Gcc do not bug without the the following line.
      //{a && a} -> AnyConcept<bool>;
      {a && a} -> bool;
      };


    int main()
      {
      a_class obj;
      obj.f(10);  //Error not reported by gcc.
      }


OTHER PROBABLY RELATED ISSUES:
   with larger code I have observed that the same issue
   could happen if any of the following code line occurs:
     1. partialy specialized concept used as placeholder inside function
argument list
          template<class T,class U>
          concept bool Same = std::is_same<T,U>::value;
          int afunc(Same<int>&& x);
     2. partialy specialized concept used as placeholder inside template
argument list
          template<Same<int> T>
          void afunc(T&&);
     3. concept inside if constexpr (not sure it is inside the concept TS, but
it causes the exact same trouble, + command line option -std=c++17)
          template<class...Args>
          concept bool Constructible = std::is_constructible<Args...>::value;
          ...
          if constexpr(Constructible<int,int>)