[Bug c++/66686] New: Instantiation of dependent template template parameter with non-dependent template rejected

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66686

            Bug ID: 66686
           Summary: Instantiation of dependent template template parameter
                    with non-dependent template rejected
           Product: gcc
           Version: 5.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ppalka at gcc dot gnu.org
  Target Milestone: ---

The following code should probably compile:

template <template <int> class>
struct A { };

template <int>
struct Y { };

template <class A, class B, template <template <B> class Z> class C>
struct X
{
    C<Y> a;
};

X<int, int, A> a;


With GCC 5.1 it does not:

foo.cc:10:8: error: type/value mismatch at argument 1 in template parameter
list for ‘template<template<B <anonymous> > class Z> class C’
     C<Y> a;
        ^
foo.cc:10:8: error:   expected a template of type ‘template<B <anonymous> >
class Z’, got ‘template<int <anonymous> > struct Y’

Is this valid code in the first place?