cartesian_product doesn't work with filter_view

[brevzin]

Reduced from StackOverflow:

#include <range/v3/view/cartesian_product.hpp>
#include <range/v3/view/filter.hpp>

int main() {
    int data[] = {1};
    ranges::view::cartesian_product(
        data | ranges::view::filter([](int){ return true; }),
        data);
}

fails with a huge error, the top of which is:

In file included from /opt/compiler-explorer/libs/rangesv3/trunk/include/range/v3/view/cartesian_product.hpp:21,
                 from <source>:1:
/opt/compiler-explorer/libs/rangesv3/trunk/include/range/v3/range_concepts.hpp: In instantiation of 'class ranges::v3::cartesian_product_view<ranges::v3::remove_if_view<ranges::v3::iterator_range<int*, int*>, ranges::v3::logical_negate_<main()::<lambda(int)> > >, ranges::v3::iterator_range<int*, int*> >':
<source>:8:17:   required from here
/opt/compiler-explorer/libs/rangesv3/trunk/include/range/v3/range_concepts.hpp:78:50: error: no match for call to '(const ranges::v3::_begin_::fn) (const ranges::v3::remove_if_view<ranges::v3::iterator_range<int*, int*>, ranges::v3::logical_negate_<main()::<lambda(int)> > >&)'
   78 |                 using iterator_t = decltype(begin(std::declval<T &>()));
      |                                             ~~~~~^~~~~~~~~~~~~~~~~~~~~
In file included from /opt/compiler-explorer/libs/rangesv3/trunk/include/range/v3/view/cartesian_product.hpp:19,
                 from <source>:1:
/opt/compiler-explorer/libs/rangesv3/trunk/include/range/v3/begin_end.hpp:88:32: note: candidate: 'template<class R> constexpr decltype (ranges::v3::_begin_::fn::impl_(r, 42)) ranges::v3::_begin_::fn::operator()(R&) const'
   88 |                 constexpr auto operator()(R &r) const
      |                                ^~~~~~~~

[brevzin]

I don't know enough about the metaprogramming library range-v3 uses, but I think the problem is that:

 82             template<bool IsConst>                                      
 83             using CanDistance = meta::strict_and<                            
 84                 CanSize<IsConst>,                                            
 85                 SizedSentinel<                                               
 86                     iterator_t<meta::if_c<IsConst, Views const, Views>>,     
 87                     iterator_t<meta::if_c<IsConst, Views const, Views>>>...>;
 88             template<bool IsConst>                                
 89             using CanRandom = meta::strict_and<                   
 90                 CanDistance<IsConst>,                             
 91                 RandomAccessIterator<iterator_t<                  
 92                     meta::if_c<IsConst, Views const, Views>>>...>;
 93             template<bool IsConst>                                           
 94             using CanBidi = meta::strict_or<                                 
 95                 CanRandom<IsConst>,                                          
 96                 meta::strict_and<                                            
 97                     BoundedRange<meta::if_c<IsConst, Views const, Views>>...,
 98                     BidirectionalIterator<iterator_t<                  
 99                         meta::if_c<IsConst, Views const, Views>>>...>>;

We can't just Concept<iterator_t<X>> cause that might be ill-formed. We want to like do a deferred_validate<Concept, iterator_t, X> or some such.

[ericniebler]

For the record, this works on the deep-integration branch, where I have substantially reworked these constraints.