std::vector incompatible? about any_invocable

I have a fork that demonstrates the problem with GitHub Actions: https://github.com/alexhultman-2fa/any_invocable

g++ -std=c++17 -Wall -Wextra -Wpedantic main.cpp
  shell: /bin/bash -e {0}
In file included from main.cpp:1:
In file included from ./include/ofats/invocable.h:4:
In file included from /Applications/Xcode_12.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/functional:501:
/Applications/Xcode_12.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/type_traits:2814:40: error: no member named 'value' in 'std::__1::is_constructible<ofats::any_invocable<void ()>, const ofats::any_invocable<void ()> &>'
    = is_constructible<_Tp, _Args...>::value;
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
./include/ofats/invocable.h:321:1: note: in instantiation of variable template specialization 'std::__1::is_constructible_v<ofats::any_invocable<void ()>, const ofats::any_invocable<void ()> &>' requested here
__OFATS_ANY_INVOCABLE(, , false, &);               // 000
^
./include/ofats/invocable.h:265:24: note: expanded from macro '__OFATS_ANY_INVOCABLE'
                  std::is_constructible_v<FDec, F> &&                          \
                       ^
./include/ofats/invocable.h:321:1: note: in instantiation of default argument for 'any_invocable<const ofats::any_invocable<void ()> &, ofats::any_invocable<void ()> >' required here
__OFATS_ANY_INVOCABLE(, , false, &);               // 000
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
./include/ofats/invocable.h:270:5: note: expanded from macro '__OFATS_ANY_INVOCABLE'
    any_invocable(F&& f) {                                                     \
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Applications/Xcode_12.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/type_traits:2803:38: note: while substituting deduced template arguments into function template 'any_invocable' [with F = const ofats::any_invocable<void ()> &, FDec = (no value), $2 = (no value)]
    : public integral_constant<bool, __is_constructible(_Tp, _Args...)>
                                     ^
/Applications/Xcode_12.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/type_traits:2858:14: note: in instantiation of template class 'std::__1::is_constructible<ofats::any_invocable<void ()>, const ofats::any_invocable<void ()> &>' requested here
    : public is_constructible<_Tp,
             ^
/Applications/Xcode_12.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/utility:262:51: note: in instantiation of template class 'std::__1::is_copy_constructible<ofats::any_invocable<void ()> >' requested here
    !is_nothrow_move_constructible<_Tp>::value && is_copy_constructible<_Tp>::value,
                                                  ^
/Applications/Xcode_12.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/memory:1733:25: note: while substituting deduced template arguments into function template 'move_if_noexcept' [with _Tp = ofats::any_invocable<void ()>]
                        _VSTD::move_if_noexcept(*--__end1)
                        ^
/Applications/Xcode_12.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/__config:840:15: note: expanded from macro '_VSTD'
#define _VSTD std::_LIBCPP_ABI_NAMESPACE
              ^
/Applications/Xcode_12.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/vector:952:21: note: in instantiation of function template specialization 'std::__1::allocator_traits<std::__1::allocator<ofats::any_invocable<void ()> > >::__construct_backward_with_exception_guarantees<ofats::any_invocable<void ()> *>' requested here
    __alloc_traits::__construct_backward_with_exception_guarantees(
                    ^
/Applications/Xcode_12.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/vector:1668:5: note: in instantiation of member function 'std::__1::vector<ofats::any_invocable<void ()>, std::__1::allocator<ofats::any_invocable<void ()> > >::__swap_out_circular_buffer' requested here
    __swap_out_circular_buffer(__v);
    ^
/Applications/Xcode_12.2.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/vector:1686:9: note: in instantiation of function template specialization 'std::__1::vector<ofats::any_invocable<void ()>, std::__1::allocator<ofats::any_invocable<void ()> > >::__emplace_back_slow_path<(lambda at main.cpp:10:20)>' requested here
        __emplace_back_slow_path(_VSTD::forward<_Args>(__args)...);
        ^
main.cpp:10:7: note: in instantiation of function template specialization 'std::__1::vector<ofats::any_invocable<void ()>, std::__1::allocator<ofats::any_invocable<void ()> > >::emplace_back<(lambda at main.cpp:10:20)>' requested here
    v.emplace_back([]() {
      ^
1 error generated.
Error: Process completed with exit code 1.

[ofats]

Looks like it should compile to me, will take a look shortly.
Sorry for a delay in response.

[ofats]

According to last wg21.link/p0288r7 paper, there is additional compile time checks for constructors that should fix the problem.

Meaning that this is a bug in the design docs and not in your implementation of said design?

[ofats]

@alexhultman yes, looks so. What happens is: macOS clang calls is_constructible for any_invocable somewhere in the guts of vector's emplace_back, which then tries to call the most generic constructor of any_invocable. Since compile-time checks that were proposed in 5th revision aren't strict enough, it calls is_constructible for the same type again while still being in the evaluation chain of previous value, so it's recursive evaluation of unknown value.

I don't want to share more details here, it's pretty common problem that appears when having generic constructors. I will work on the code to be up to date with 7th revision once getting back from vacation.

Great! Looking forward to swap over to this implementation once done 👍