error-concepts-diagnostics.log

prog.cc: In function 'int main()':
prog.cc:6:19: error: no match for 'operator|' (operand types are 'std::forward_list<int, std::allocator<int> >' and 'const std::ranges::views::_Reverse')
    6 |   for (int _: lst | std::views::reverse) {}
      |               ~~~ ^ ~~~~~~~~~~~~~~~~~~~
      |               |                 |
      |               |                 const std::ranges::views::_Reverse
      |               std::forward_list<int, std::allocator<int> >
In file included from prog.cc:2:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:818:7: note: candidate: 'template<class _Lhs, class _Rhs>  requires (derived_from<_Lhs, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (derived_from<_Rhs, std::ranges::views::__adaptor::_RangeAdaptorClosure>) constexpr auto std::ranges::views::__adaptor::operator|(_Lhs, _Rhs)'
  818 |       operator|(_Lhs __lhs, _Rhs __rhs)
      |       ^~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:818:7: note:   template argument deduction/substitution failed:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:818:7: note: constraints not satisfied
In file included from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/iterator_concepts.h:35,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/stl_iterator_base_types.h:71,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/forward_list.h:36,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/forward_list:38,
                 from prog.cc:1:
/opt/wandbox/gcc-head/include/c++/12.0.0/concepts: In substitution of 'template<class _Lhs, class _Rhs>  requires (derived_from<_Lhs, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (derived_from<_Rhs, std::ranges::views::__adaptor::_RangeAdaptorClosure>) constexpr auto std::ranges::views::__adaptor::operator|(_Lhs, _Rhs) [with _Lhs = std::forward_list<int, std::allocator<int> >; _Rhs = std::ranges::views::_Reverse]':
prog.cc:6:33:   required from here
/opt/wandbox/gcc-head/include/c++/12.0.0/concepts:67:13:   required for the satisfaction of 'derived_from<_Lhs, std::ranges::views::__adaptor::_RangeAdaptorClosure>' [with _Lhs = std::forward_list<int, std::allocator<int> >]
/opt/wandbox/gcc-head/include/c++/12.0.0/concepts:67:28: note:   'std::ranges::views::__adaptor::_RangeAdaptorClosure' is not a base of 'std::forward_list<int, std::allocator<int> >'
   67 |     concept derived_from = __is_base_of(_Base, _Derived)
      |                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from prog.cc:2:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:809:7: note: candidate: 'template<class _Self, class _Range>  requires (derived_from<typename std::remove_cvref<_Tp>::type, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (__adaptor_invocable<_Self, _Range>) constexpr auto std::ranges::views::__adaptor::operator|(_Range&&, _Self&&)'
  809 |       operator|(_Range&& __r, _Self&& __self)
      |       ^~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:809:7: note:   template argument deduction/substitution failed:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:809:7: note: constraints not satisfied
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges: In substitution of 'template<class _Self, class _Range>  requires (derived_from<typename std::remove_cvref<_Tp>::type, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (__adaptor_invocable<_Self, _Range>) constexpr auto std::ranges::views::__adaptor::operator|(_Range&&, _Self&&) [with _Self = const std::ranges::views::_Reverse&; _Range = std::forward_list<int, std::allocator<int> >&]':
prog.cc:6:33:   required from here
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:781:13:   required for the satisfaction of '__adaptor_invocable<_Self, _Range>' [with _Self = const std::ranges::views::_Reverse&; _Range = std::forward_list<int, std::allocator<int> >&]
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:782:9:   in requirements  [with _Args = {std::forward_list<int, std::allocator<int> >&}; _Adaptor = const std::ranges::views::_Reverse&]
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:782:44: note: the required expression 'declval<_Adaptor>()((declval<_Args>)()...)' is invalid, because
  782 |       = requires { std::declval<_Adaptor>()(declval<_Args>()...); };
      |                    ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:782:44: error: no match for call to '(const std::ranges::views::_Reverse) (std::forward_list<int, std::allocator<int> >&)'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3729:9: note: candidate: 'template<class _Range>  requires (viewable_range<_Range>) && ((__is_reverse_view<typename std::remove_cvref<_Tp>::type>) || (__is_reversible_subrange<typename std::remove_cvref<_Tp>::type>) || (__can_reverse_view<_Range>)) constexpr auto std::ranges::views::_Reverse::operator()(_Range&&) const'
 3729 |         operator()(_Range&& __r) const
      |         ^~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3729:9: note:   template argument deduction/substitution failed:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3729:9: note: constraints not satisfied
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges: In substitution of 'template<class _Range>  requires (viewable_range<_Range>) && ((__is_reverse_view<typename std::remove_cvref<_Tp>::type>) || (__is_reversible_subrange<typename std::remove_cvref<_Tp>::type>) || (__can_reverse_view<_Range>)) constexpr auto std::ranges::views::_Reverse::operator()(_Range&&) const [with _Range = std::forward_list<int, std::allocator<int> >&]':
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:782:44:   required by substitution of 'template<class _Self, class _Range>  requires (derived_from<typename std::remove_cvref<_Tp>::type, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (__adaptor_invocable<_Self, _Range>) constexpr auto std::ranges::views::__adaptor::operator|(_Range&&, _Self&&) [with _Self = const std::ranges::views::_Reverse&; _Range = std::forward_list<int, std::allocator<int> >&]'
prog.cc:6:33:   required from here
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3729:2:   required by the constraints of 'template<class _Range>  requires (viewable_range<_Range>) && ((__is_reverse_view<typename std::remove_cvref<_Tp>::type>) || (__is_reversible_subrange<typename std::remove_cvref<_Tp>::type>) || (__can_reverse_view<_Range>)) constexpr auto std::ranges::views::_Reverse::operator()(_Range&&) const'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3727:11: note: no operand of the disjunction is satisfied
 3725 |         requires __detail::__is_reverse_view<remove_cvref_t<_Range>>
      |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 3726 |           || __detail::__is_reversible_subrange<remove_cvref_t<_Range>>
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 3727 |           || __detail::__can_reverse_view<_Range>
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3725:28: note: the operand '__is_reverse_view<std::remove_cvref_t<_Tp1> >' is unsatisfied because
 3725 |         requires __detail::__is_reverse_view<remove_cvref_t<_Range>>
      |                  ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 3726 |           || __detail::__is_reversible_subrange<remove_cvref_t<_Range>>
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 3727 |           || __detail::__can_reverse_view<_Range>
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3729:2:   required by the constraints of 'template<class _Range>  requires (viewable_range<_Range>) && ((__is_reverse_view<typename std::remove_cvref<_Tp>::type>) || (__is_reversible_subrange<typename std::remove_cvref<_Tp>::type>) || (__can_reverse_view<_Range>)) constexpr auto std::ranges::views::_Reverse::operator()(_Range&&) const'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3725:28: note: the expression '__is_reverse_view<typename std::remove_cvref<_Tp>::type> [with _Range = std::forward_list<int, std::allocator<int> >&]' evaluated to 'false'
 3725 |         requires __detail::__is_reverse_view<remove_cvref_t<_Range>>
      |                  ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3726:24: note: the operand '__is_reversible_subrange<std::remove_cvref_t<_Tp1> >' is unsatisfied because
 3725 |         requires __detail::__is_reverse_view<remove_cvref_t<_Range>>
      |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 3726 |           || __detail::__is_reversible_subrange<remove_cvref_t<_Range>>
      |           ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 3727 |           || __detail::__can_reverse_view<_Range>
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3729:2:   required by the constraints of 'template<class _Range>  requires (viewable_range<_Range>) && ((__is_reverse_view<typename std::remove_cvref<_Tp>::type>) || (__is_reversible_subrange<typename std::remove_cvref<_Tp>::type>) || (__can_reverse_view<_Range>)) constexpr auto std::ranges::views::_Reverse::operator()(_Range&&) const'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3726:24: note: the expression '__is_reversible_subrange<typename std::remove_cvref<_Tp>::type> [with _Range = std::forward_list<int, std::allocator<int> >&]' evaluated to 'false'
 3726 |           || __detail::__is_reversible_subrange<remove_cvref_t<_Range>>
      |              ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3727:24: note: the operand '__can_reverse_view<_Range>' is unsatisfied because
 3725 |         requires __detail::__is_reverse_view<remove_cvref_t<_Range>>
      |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 3726 |           || __detail::__is_reversible_subrange<remove_cvref_t<_Range>>
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 3727 |           || __detail::__can_reverse_view<_Range>
      |           ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3718:10:   required for the satisfaction of '__can_reverse_view<_Range>' [with _Range = std::forward_list<int, std::allocator<int> >&]
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3719:6:   in requirements  [with _Range = std::forward_list<int, std::allocator<int> >&]
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3719:24: note: the required expression 'reverse_view<...auto...>{declval<_Range>()}' is invalid, because
 3719 |           = requires { reverse_view{std::declval<_Range>()}; };
      |                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3719:24: error: class template argument deduction failed:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3719:24: error: no matching function for call to 'reverse_view(std::forward_list<int, std::allocator<int> >&)'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3641:7: note: candidate: 'template<class _Vp> reverse_view(_Vp)-> std::ranges::reverse_view<_Vp>'
 3641 |       reverse_view(_Vp __r)
      |       ^~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3641:7: note:   template argument deduction/substitution failed:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges: In substitution of 'template<class _Vp> reverse_view(_Vp)-> std::ranges::reverse_view<_Vp> [with _Vp = std::forward_list<int, std::allocator<int> >]':
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3719:17:   required by substitution of 'template<class _Range>  requires (viewable_range<_Range>) && ((__is_reverse_view<typename std::remove_cvref<_Tp>::type>) || (__is_reversible_subrange<typename std::remove_cvref<_Tp>::type>) || (__can_reverse_view<_Range>)) constexpr auto std::ranges::views::_Reverse::operator()(_Range&&) const [with _Range = std::forward_list<int, std::allocator<int> >&]'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:782:44:   required by substitution of 'template<class _Self, class _Range>  requires (derived_from<typename std::remove_cvref<_Tp>::type, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (__adaptor_invocable<_Self, _Range>) constexpr auto std::ranges::views::__adaptor::operator|(_Range&&, _Self&&) [with _Self = const std::ranges::views::_Reverse&; _Range = std::forward_list<int, std::allocator<int> >&]'
prog.cc:6:33:   required from here
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3641:7: error: template constraint failure for 'template<class _Vp>  requires (view<_Vp>) && (bidirectional_range<_Vp>) class std::ranges::reverse_view'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3641:7: note: constraints not satisfied
In file included from /opt/wandbox/gcc-head/include/c++/12.0.0/string_view:44,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/basic_string.h:48,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/string:55,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/locale_classes.h:40,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:41,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/streambuf:41,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/streambuf_iterator.h:35,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/iterator:66,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/ranges:43,
                 from prog.cc:2:
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ranges_base.h: In substitution of 'template<class _Vp>  requires (view<_Vp>) && (bidirectional_range<_Vp>) class std::ranges::reverse_view [with _Vp = std::forward_list<int, std::allocator<int> >]':
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3641:7:   required by substitution of 'template<class _Vp> reverse_view(_Vp)-> std::ranges::reverse_view<_Vp> [with _Vp = std::forward_list<int, std::allocator<int> >]'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3719:17:   required by substitution of 'template<class _Range>  requires (viewable_range<_Range>) && ((__is_reverse_view<typename std::remove_cvref<_Tp>::type>) || (__is_reversible_subrange<typename std::remove_cvref<_Tp>::type>) || (__can_reverse_view<_Range>)) constexpr auto std::ranges::views::_Reverse::operator()(_Range&&) const [with _Range = std::forward_list<int, std::allocator<int> >&]'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:782:44:   required by substitution of 'template<class _Self, class _Range>  requires (derived_from<typename std::remove_cvref<_Tp>::type, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (__adaptor_invocable<_Self, _Range>) constexpr auto std::ranges::views::__adaptor::operator|(_Range&&, _Self&&) [with _Self = const std::ranges::views::_Reverse&; _Range = std::forward_list<int, std::allocator<int> >&]'
prog.cc:6:33:   required from here
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ranges_base.h:621:13:   required for the satisfaction of 'view<_Vp>' [with _Vp = std::forward_list<int, std::allocator<int> >]
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ranges_base.h:622:39: note: the expression 'enable_view<_Tp> [with _Tp = std::forward_list<int, std::allocator<int> >]' evaluated to 'false'
  622 |       = range<_Tp> && movable<_Tp> && enable_view<_Tp>;
      |                                       ^~~~~~~~~~~~~~~~
In file included from prog.cc:2:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges: In substitution of 'template<class _Range>  requires (viewable_range<_Range>) && ((__is_reverse_view<typename std::remove_cvref<_Tp>::type>) || (__is_reversible_subrange<typename std::remove_cvref<_Tp>::type>) || (__can_reverse_view<_Range>)) constexpr auto std::ranges::views::_Reverse::operator()(_Range&&) const [with _Range = std::forward_list<int, std::allocator<int> >&]':
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:782:44:   required by substitution of 'template<class _Self, class _Range>  requires (derived_from<typename std::remove_cvref<_Tp>::type, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (__adaptor_invocable<_Self, _Range>) constexpr auto std::ranges::views::__adaptor::operator|(_Range&&, _Self&&) [with _Self = const std::ranges::views::_Reverse&; _Range = std::forward_list<int, std::allocator<int> >&]'
prog.cc:6:33:   required from here
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3638:7: note: candidate: 'template<class _Vp> reverse_view()-> std::ranges::reverse_view<_Vp> requires  default_initializable<_Vp>'
 3638 |       reverse_view() requires default_initializable<_Vp> = default;
      |       ^~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3638:7: note:   template argument deduction/substitution failed:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3719:24: note:   candidate expects 0 arguments, 1 provided
 3719 |           = requires { reverse_view{std::declval<_Range>()}; };
      |                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3623:11: note: candidate: 'template<class _Vp> reverse_view(std::ranges::reverse_view<_Vp>)-> std::ranges::reverse_view<_Vp>'
 3623 |     class reverse_view : public view_interface<reverse_view<_Vp>>
      |           ^~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3623:11: note:   template argument deduction/substitution failed:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3719:24: note:   'std::forward_list<int, std::allocator<int> >' is not derived from 'std::ranges::reverse_view<_Vp>'
 3719 |           = requires { reverse_view{std::declval<_Range>()}; };
      |                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3692:5: note: candidate: 'template<class _Range> std::ranges::reverse_view(_Range&&)-> std::ranges::reverse_view<std::ranges::views::all_t<_Range> >'
 3692 |     reverse_view(_Range&&) -> reverse_view<views::all_t<_Range>>;
      |     ^~~~~~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3692:5: note:   template argument deduction/substitution failed:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges: In substitution of 'template<class _Range> std::ranges::reverse_view(_Range&&)-> std::ranges::reverse_view<std::ranges::views::all_t<_Range> > [with _Range = std::forward_list<int, std::allocator<int> >&]':
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3719:17:   required by substitution of 'template<class _Range>  requires (viewable_range<_Range>) && ((__is_reverse_view<typename std::remove_cvref<_Tp>::type>) || (__is_reversible_subrange<typename std::remove_cvref<_Tp>::type>) || (__can_reverse_view<_Range>)) constexpr auto std::ranges::views::_Reverse::operator()(_Range&&) const [with _Range = std::forward_list<int, std::allocator<int> >&]'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:782:44:   required by substitution of 'template<class _Self, class _Range>  requires (derived_from<typename std::remove_cvref<_Tp>::type, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (__adaptor_invocable<_Self, _Range>) constexpr auto std::ranges::views::__adaptor::operator|(_Range&&, _Self&&) [with _Self = const std::ranges::views::_Reverse&; _Range = std::forward_list<int, std::allocator<int> >&]'
prog.cc:6:33:   required from here
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3692:5: error: template constraint failure for 'template<class _Vp>  requires (view<_Vp>) && (bidirectional_range<_Vp>) class std::ranges::reverse_view'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3692:5: note: constraints not satisfied
In file included from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/iterator_concepts.h:35,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/stl_iterator_base_types.h:71,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/forward_list.h:36,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/forward_list:38,
                 from prog.cc:1:
/opt/wandbox/gcc-head/include/c++/12.0.0/concepts: In substitution of 'template<class _Vp>  requires (view<_Vp>) && (bidirectional_range<_Vp>) class std::ranges::reverse_view [with _Vp = std::ranges::ref_view<std::forward_list<int, std::allocator<int> > >]':
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3692:5:   required by substitution of 'template<class _Range> std::ranges::reverse_view(_Range&&)-> std::ranges::reverse_view<std::ranges::views::all_t<_Range> > [with _Range = std::forward_list<int, std::allocator<int> >&]'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:3719:17:   required by substitution of 'template<class _Range>  requires (viewable_range<_Range>) && ((__is_reverse_view<typename std::remove_cvref<_Tp>::type>) || (__is_reversible_subrange<typename std::remove_cvref<_Tp>::type>) || (__can_reverse_view<_Range>)) constexpr auto std::ranges::views::_Reverse::operator()(_Range&&) const [with _Range = std::forward_list<int, std::allocator<int> >&]'
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:782:44:   required by substitution of 'template<class _Self, class _Range>  requires (derived_from<typename std::remove_cvref<_Tp>::type, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (__adaptor_invocable<_Self, _Range>) constexpr auto std::ranges::views::__adaptor::operator|(_Range&&, _Self&&) [with _Self = const std::ranges::views::_Reverse&; _Range = std::forward_list<int, std::allocator<int> >&]'
prog.cc:6:33:   required from here
/opt/wandbox/gcc-head/include/c++/12.0.0/concepts:67:13:   required for the satisfaction of 'derived_from<typename std::__detail::__iter_concept_impl<_Iter>::type, std::bidirectional_iterator_tag>' [with _Iter = std::_Fwd_list_iterator<int>]
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/iterator_concepts.h:649:13:   required for the satisfaction of 'bidirectional_iterator<decltype (std::ranges::__cust_access::__begin(declval<_Container&>()))>' [with _Tp = std::ranges::ref_view<std::forward_list<int, std::allocator<int> > >]
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ranges_base.h:642:13:   required for the satisfaction of 'bidirectional_range<_Vp>' [with _Vp = std::ranges::ref_view<std::forward_list<int, std::allocator<int> > >]
/opt/wandbox/gcc-head/include/c++/12.0.0/concepts:67:28: note:   'std::bidirectional_iterator_tag' is not a base of 'std::forward_iterator_tag'
   67 |     concept derived_from = __is_base_of(_Base, _Derived)
      |                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /opt/wandbox/gcc-head/include/c++/12.0.0/streambuf:41,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/streambuf_iterator.h:35,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/iterator:66,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/ranges:43,
                 from prog.cc:2:
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:87:3: note: candidate: 'constexpr std::_Ios_Fmtflags std::operator|(std::_Ios_Fmtflags, std::_Ios_Fmtflags)'
   87 |   operator|(_Ios_Fmtflags __a, _Ios_Fmtflags __b)
      |   ^~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:87:27: note:   no known conversion for argument 1 from 'std::forward_list<int, std::allocator<int> >' to 'std::_Ios_Fmtflags'
   87 |   operator|(_Ios_Fmtflags __a, _Ios_Fmtflags __b)
      |             ~~~~~~~~~~~~~~^~~
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:129:3: note: candidate: 'constexpr std::_Ios_Openmode std::operator|(std::_Ios_Openmode, std::_Ios_Openmode)'
  129 |   operator|(_Ios_Openmode __a, _Ios_Openmode __b)
      |   ^~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:129:27: note:   no known conversion for argument 1 from 'std::forward_list<int, std::allocator<int> >' to 'std::_Ios_Openmode'
  129 |   operator|(_Ios_Openmode __a, _Ios_Openmode __b)
      |             ~~~~~~~~~~~~~~^~~
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:169:3: note: candidate: 'constexpr std::_Ios_Iostate std::operator|(std::_Ios_Iostate, std::_Ios_Iostate)'
  169 |   operator|(_Ios_Iostate __a, _Ios_Iostate __b)
      |   ^~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:169:26: note:   no known conversion for argument 1 from 'std::forward_list<int, std::allocator<int> >' to 'std::_Ios_Iostate'
  169 |   operator|(_Ios_Iostate __a, _Ios_Iostate __b)
      |             ~~~~~~~~~~~~~^~~

error.log

prog.cc: In function 'int main()':
prog.cc:6:19: error: no match for 'operator|' (operand types are 'std::forward_list<int, std::allocator<int> >' and 'const std::ranges::views::_Reverse')
    6 |   for (int _: lst | std::views::reverse) {}
      |               ~~~ ^ ~~~~~~~~~~~~~~~~~~~
      |               |                 |
      |               |                 const std::ranges::views::_Reverse
      |               std::forward_list<int, std::allocator<int> >
In file included from prog.cc:2:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:818:7: note: candidate: 'template<class _Lhs, class _Rhs>  requires (derived_from<_Lhs, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (derived_from<_Rhs, std::ranges::views::__adaptor::_RangeAdaptorClosure>) constexpr auto std::ranges::views::__adaptor::operator|(_Lhs, _Rhs)'
  818 |       operator|(_Lhs __lhs, _Rhs __rhs)
      |       ^~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:818:7: note:   template argument deduction/substitution failed:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:818:7: note: constraints not satisfied
In file included from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/iterator_concepts.h:35,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/stl_iterator_base_types.h:71,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/forward_list.h:36,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/forward_list:38,
                 from prog.cc:1:
/opt/wandbox/gcc-head/include/c++/12.0.0/concepts: In substitution of 'template<class _Lhs, class _Rhs>  requires (derived_from<_Lhs, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (derived_from<_Rhs, std::ranges::views::__adaptor::_RangeAdaptorClosure>) constexpr auto std::ranges::views::__adaptor::operator|(_Lhs, _Rhs) [with _Lhs = std::forward_list<int, std::allocator<int> >; _Rhs = std::ranges::views::_Reverse]':
prog.cc:6:33:   required from here
/opt/wandbox/gcc-head/include/c++/12.0.0/concepts:67:13:   required for the satisfaction of 'derived_from<_Lhs, std::ranges::views::__adaptor::_RangeAdaptorClosure>' [with _Lhs = std::forward_list<int, std::allocator<int> >]
/opt/wandbox/gcc-head/include/c++/12.0.0/concepts:67:28: note:   'std::ranges::views::__adaptor::_RangeAdaptorClosure' is not a base of 'std::forward_list<int, std::allocator<int> >'
   67 |     concept derived_from = __is_base_of(_Base, _Derived)
      |                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from prog.cc:2:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:809:7: note: candidate: 'template<class _Self, class _Range>  requires (derived_from<typename std::remove_cvref<_Tp>::type, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (__adaptor_invocable<_Self, _Range>) constexpr auto std::ranges::views::__adaptor::operator|(_Range&&, _Self&&)'
  809 |       operator|(_Range&& __r, _Self&& __self)
      |       ^~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:809:7: note:   template argument deduction/substitution failed:
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:809:7: note: constraints not satisfied
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges: In substitution of 'template<class _Self, class _Range>  requires (derived_from<typename std::remove_cvref<_Tp>::type, std::ranges::views::__adaptor::_RangeAdaptorClosure>) && (__adaptor_invocable<_Self, _Range>) constexpr auto std::ranges::views::__adaptor::operator|(_Range&&, _Self&&) [with _Self = const std::ranges::views::_Reverse&; _Range = std::forward_list<int, std::allocator<int> >&]':
prog.cc:6:33:   required from here
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:781:13:   required for the satisfaction of '__adaptor_invocable<_Self, _Range>' [with _Self = const std::ranges::views::_Reverse&; _Range = std::forward_list<int, std::allocator<int> >&]
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:782:9:   in requirements  [with _Args = {std::forward_list<int, std::allocator<int> >&}; _Adaptor = const std::ranges::views::_Reverse&]
/opt/wandbox/gcc-head/include/c++/12.0.0/ranges:782:44: note: the required expression 'declval<_Adaptor>()((declval<_Args>)()...)' is invalid
  782 |       = requires { std::declval<_Adaptor>()(declval<_Args>()...); };
      |                    ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~
cc1plus: note: set '-fconcepts-diagnostics-depth=' to at least 2 for more detail
In file included from /opt/wandbox/gcc-head/include/c++/12.0.0/streambuf:41,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/bits/streambuf_iterator.h:35,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/iterator:66,
                 from /opt/wandbox/gcc-head/include/c++/12.0.0/ranges:43,
                 from prog.cc:2:
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:87:3: note: candidate: 'constexpr std::_Ios_Fmtflags std::operator|(std::_Ios_Fmtflags, std::_Ios_Fmtflags)'
   87 |   operator|(_Ios_Fmtflags __a, _Ios_Fmtflags __b)
      |   ^~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:87:27: note:   no known conversion for argument 1 from 'std::forward_list<int, std::allocator<int> >' to 'std::_Ios_Fmtflags'
   87 |   operator|(_Ios_Fmtflags __a, _Ios_Fmtflags __b)
      |             ~~~~~~~~~~~~~~^~~
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:129:3: note: candidate: 'constexpr std::_Ios_Openmode std::operator|(std::_Ios_Openmode, std::_Ios_Openmode)'
  129 |   operator|(_Ios_Openmode __a, _Ios_Openmode __b)
      |   ^~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:129:27: note:   no known conversion for argument 1 from 'std::forward_list<int, std::allocator<int> >' to 'std::_Ios_Openmode'
  129 |   operator|(_Ios_Openmode __a, _Ios_Openmode __b)
      |             ~~~~~~~~~~~~~~^~~
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:169:3: note: candidate: 'constexpr std::_Ios_Iostate std::operator|(std::_Ios_Iostate, std::_Ios_Iostate)'
  169 |   operator|(_Ios_Iostate __a, _Ios_Iostate __b)
      |   ^~~~~~~~
/opt/wandbox/gcc-head/include/c++/12.0.0/bits/ios_base.h:169:26: note:   no known conversion for argument 1 from 'std::forward_list<int, std::allocator<int> >' to 'std::_Ios_Iostate'
  169 |   operator|(_Ios_Iostate __a, _Ios_Iostate __b)
      |             ~~~~~~~~~~~~~^~~

source.cpp

#include <forward_list>
#include <ranges>

int main() {
  std::forward_list lst = {1, 2, 3, 4, 5};
  for (int _: lst | std::views::reverse) {}
}