Это не трейс

В реальности проблема, кажется, из-за того, что где-то версия библиотеки без нужной фичи

Ну я не думаю, что компилятор мог бы это понять (

Как это не трейс, если трейс.

У раста проблемы с документацией того, что зависит от каких фичурфлагов

Ну да

Покажешь сравнение?

docs.rs вообще отображает неведомую фигню, надо всегда в локальный cargo doc смотреть

file.cpp: In function ‘int main()’:
file.cpp:7:13: error: no matching function for call to ‘std::set<std::pair<int, int> >::find(int)’
   7 |     s.find(5);
     |             ^
In file included from /usr/include/c++/9/set:61,
                from file.cpp:1:
/usr/include/c++/9/bits/stl_set.h:794:7: note: candidate: ‘std::set<_Key, _Compare, _Alloc>::iterator std::set<_Key, _Compare, _Alloc>::find(const key_type&) [with _Key = std::pair<int, int>; _Compare = std::less<std::pair<int, int> >; _Alloc = std::allocator<std::pair<int, int> >; std::set<_Key, _Compare, _Alloc>::iterator = std::_Rb_tree_const_iterator<std::pair<int, int> >; std::set<_Key, _Compare, _Alloc>::key_type = std::pair<int, int>]’
 794 |       find(const key_type& __x)
     |       ^~~~
/usr/include/c++/9/bits/stl_set.h:794:28: note:   no known conversion for argument 1 from ‘int’ to ‘const key_type&’ {aka ‘const std::pair<int, int>&’}
 794 |       find(const key_type& __x)
     |            ~~~~~~~~~~~~~~^
/usr/include/c++/9/bits/stl_set.h:798:7: note: candidate: ‘std::set<_Key, _Compare, _Alloc>::const_iterator std::set<_Key, _Compare, _Alloc>::find(const key_type&) const [with _Key = std::pair<int, int>; _Compare = std::less<std::pair<int, int> >; _Alloc = std::allocator<std::pair<int, int> >; std::set<_Key, _Compare, _Alloc>::const_iterator = std::_Rb_tree_const_iterator<std::pair<int, int> >; std::set<_Key, _Compare, _Alloc>::key_type = std::pair<int, int>]’
 798 |       find(const key_type& __x) const
     |       ^~~~
/usr/include/c++/9/bits/stl_set.h:798:28: note:   no known conversion for argument 1 from ‘int’ to ‘const key_type&’ {aka ‘const std::pair<int, int>&’}
 798 |       find(const key_type& __x) const
     |            ~~~~~~~~~~~~~~^
/usr/include/c++/9/bits/stl_set.h:804:2: note: candidate: ‘template<class _Kt> decltype (std::set<_Key, _Compare, _Alloc>::iterator{((std::set<_Key, _Compare, _Alloc>*)this)->std::set<_Key, _Compare, _Alloc>::_M_t._M_find_tr(__x)}) std::set<_Key, _Compare, _Alloc>::find(const _Kt&) [with _Kt = _Kt; _Key = std::pair<int, int>; _Compare = std::less<std::pair<int, int> >; _Alloc = std::allocator<std::pair<int, int> >]’
 804 |  find(const _Kt& __x)
     |  ^~~~
/usr/include/c++/9/bits/stl_set.h:804:2: note:   template argument deduction/substitution failed:
/usr/include/c++/9/bits/stl_set.h: In substitution of ‘template<class _Kt> decltype (std::set<std::pair<int, int> >::iterator{((std::set<std::pair<int, int> >*)this)->std::set<std::pair<int, int> >::_M_t.std::_Rb_tree<std::pair<int, int>, std::pair<int, int>, std::_Identity<std::pair<int, int> >, std::less<std::pair<int, int> >, std::allocator<std::pair<int, int> > >::_M_find_tr(__x)}) std::set<std::pair<int, int> >::find<_Kt>(const _Kt&) [with _Kt = int]’:
file.cpp:7:13:   required from here
/usr/include/c++/9/bits/stl_set.h:804:2: error: no matching function for call to ‘std::_Rb_tree<std::pair<int, int>, std::pair<int, int>, std::_Identity<std::pair<int, int> >, std::less<std::pair<int, int> >, std::allocator<std::pair<int, int> > >::_M_find_tr(const int&)’
In file included from /usr/include/c++/9/set:60,
                from file.cpp:1:
/usr/include/c++/9/bits/stl_tree.h:1306:2: note: candidate: ‘template<class _Kt, class _Req> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_find_tr(const _Kt&) [with _Kt = _Kt; _Req = _Req; _Key = std::pair<int, int>; _Val = std::pair<int, int>; _KeyOfValue = std::_Identity<std::pair<int, int> >; _Compare = std::less<std::pair<int, int> >; _Alloc = std::allocator<std::pair<int, int> >]’
1306 |  _M_find_tr(const _Kt& __k)
     |  ^~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:1306:2: note:   template argument deduction/substitution failed:
/usr/include/c++/9/bits/stl_tree.h: In substitution of ‘template<class _Cmp, class _SfinaeType> using __has_is_transparent_t = typename std::__has_is_transparent<_Cmp, _SfinaeType>::type [with _Cmp = std::less<std::pair<int, int> >; _SfinaeType = int]’:

/usr/include/c++/9/bits/stl_tree.h:1304:9:   required by substitution of ‘template<class _Kt> decltype (std::set<std::pair<int, int> >::iterator{((std::set<std::pair<int, int> >*)this)->std::set<std::pair<int, int> >::_M_t.std::_Rb_tree<std::pair<int, int>, std::pair<int, int>, std::_Identity<std::pair<int, int> >, std::less<std::pair<int, int> >, std::allocator<std::pair<int, int> > >::_M_find_tr(__x)}) std::set<std::pair<int, int> >::find<_Kt>(const _Kt&) [with _Kt = int]’
file.cpp:7:13:   required from here
/usr/include/c++/9/bits/stl_tree.h:425:11: error: no type named ‘type’ in ‘struct std::__has_is_transparent<std::less<std::pair<int, int> >, int, void>’
 425 |     using __has_is_transparent_t
     |           ^~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/9/bits/stl_set.h: In substitution of ‘template<class _Kt> decltype (std::set<std::pair<int, int> >::iterator{((std::set<std::pair<int, int> >*)this)->std::set<std::pair<int, int> >::_M_t.std::_Rb_tree<std::pair<int, int>, std::pair<int, int>, std::_Identity<std::pair<int, int> >, std::less<std::pair<int, int> >, std::allocator<std::pair<int, int> > >::_M_find_tr(__x)}) std::set<std::pair<int, int> >::find<_Kt>(const _Kt&) [with _Kt = int]’:
file.cpp:7:13:   required from here
/usr/include/c++/9/bits/stl_tree.h:1315:2: note: candidate: ‘template<class _Kt, class _Req> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::const_iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_find_tr(const _Kt&) const [with _Kt = _Kt; _Req = _Req; _Key = std::pair<int, int>; _Val = std::pair<int, int>; _KeyOfValue = std::_Identity<std::pair<int, int> >; _Compare = std::less<std::pair<int, int> >; _Alloc = std::allocator<std::pair<int, int> >]’
1315 |  _M_find_tr(const _Kt& __k) const
     |  ^~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:1315:2: note:   template argument deduction/substitution failed:
In file included from /usr/include/c++/9/set:61,
                from file.cpp:1:
/usr/include/c++/9/bits/stl_set.h:804:2: error: no matching function for call to ‘std::_Rb_tree_const_iterator<std::pair<int, int> >::_Rb_tree_const_iterator(<brace-enclosed initializer list>)’
 804 |  find(const _Kt& __x)
     |  ^~~~
In file included from /usr/include/c++/9/set:60,
                from file.cpp:1:
/usr/include/c++/9/bits/stl_tree.h:348:7: note: candidate: ‘std::_Rb_tree_const_iterator<_Tp>::_Rb_tree_const_iterator(const iterator&) [with _Tp = std::pair<int, int>; std::_Rb_tree_const_iterator<_Tp>::iterator = std::_Rb_tree_iterator<std::pair<int, int> >]’
 348 |       _Rb_tree_const_iterator(const iterator& __it) _GLIBCXX_NOEXCEPT
     |       ^~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:348:7: note:   conversion of argument 1 would be ill-formed:
/usr/include/c++/9/bits/stl_tree.h:345:7: note: candidate: ‘std::_Rb_tree_const_iterator<_Tp>::_Rb_tree_const_iterator(std::_Rb_tree_const_iterator<_Tp>::_Base_ptr) [with _Tp = std::pair<int, int>; std::_Rb_tree_const_iterator<_Tp>::_Base_ptr = const std::_Rb_tree_node_base*]’
 345 |       _Rb_tree_const_iterator(_Base_ptr __x) _GLIBCXX_NOEXCEPT
     |       ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:345:7: note:   conversion of argument 1 would be ill-formed:
/usr/include/c++/9/bits/stl_tree.h:341:7: note: candidate: ‘std::_Rb_tree_const_iterator<_Tp>::_Rb_tree_const_iterator() [with _Tp = std::pair<int, int>]’
 341 |       _Rb_tree_const_iterator() _GLIBCXX_NOEXCEPT
     |       ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:341:7: note:   candidate expects 0 arguments, 1 provided
/usr/include/c++/9/bits/stl_tree.h:326:12: note: candidate: ‘constexpr std::_Rb_tree_const_iterator<std::pair<int, int> >::_Rb_tree_const_iterator(const std::_Rb_tree_const_iterator<std::pair<int, int> >&)’
 326 |     struct _Rb_tree_const_iterator
     |            ^~~~~~~~~~~~~~~~~~~

Всё, что содержит because и прочее - это именно трейс, т.е. дополнительная информация об окружение, почему оно дошло до такой ошибки.

/usr/include/c++/9/bits/stl_tree.h:326:12: note:   conversion of argument 1 would be ill-formed:
/usr/include/c++/9/bits/stl_tree.h:326:12: note: candidate: ‘constexpr std::_Rb_tree_const_iterator<std::pair<int, int> >::_Rb_tree_const_iterator(std::_Rb_tree_const_iterator<std::pair<int, int> >&&)’
/usr/include/c++/9/bits/stl_tree.h:326:12: note:   conversion of argument 1 would be ill-formed:
In file included from /usr/include/c++/9/set:61,
                from file.cpp:1:
/usr/include/c++/9/bits/stl_set.h:810:2: note: candidate: ‘template<class _Kt> decltype (std::set<_Key, _Compare, _Alloc>::const_iterator{((const std::set<_Key, _Compare, _Alloc>*)this)->std::set<_Key, _Compare, _Alloc>::_M_t._M_find_tr(__x)}) std::set<_Key, _Compare, _Alloc>::find(const _Kt&) const [with _Kt = _Kt; _Key = std::pair<int, int>; _Compare = std::less<std::pair<int, int> >; _Alloc = std::allocator<std::pair<int, int> >]’
 810 |  find(const _Kt& __x) const
     |  ^~
/usr/include/c++/9/bits/stl_set.h:810:2: note:   template argument deduction/substitution failed:
/usr/include/c++/9/bits/stl_set.h: In substitution of ‘template<class _Kt> decltype (std::set<std::pair<int, int> >::const_iterator{((const std::set<std::pair<int, int> >*)this)->std::set<std::pair<int, int> >::_M_t.std::_Rb_tree<std::pair<int, int>, std::pair<int, int>, std::_Identity<std::pair<int, int> >, std::less<std::pair<int, int> >, std::allocator<std::pair<int, int> > >::_M_find_tr(__x)}) std::set<std::pair<int, int> >::find<_Kt>(const _Kt&) const [with _Kt = int]’:
file.cpp:7:13:   required from here
/usr/include/c++/9/bits/stl_set.h:810:2: error: no matching function for call to ‘std::_Rb_tree<std::pair<int, int>, std::pair<int, int>, std::_Identity<std::pair<int, int> >, std::less<std::pair<int, int> >, std::allocator<std::pair<int, int> > >::_M_find_tr(const int&) const’
In file included from /usr/include/c++/9/set:60,
                from file.cpp:1:
/usr/include/c++/9/bits/stl_tree.h:1306:2: note: candidate: ‘template<class _Kt, class _Req> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_find_tr(const _Kt&) [with _Kt = _Kt; _Req = _Req; _Key = std::pair<int, int>; _Val = std::pair<int, int>; _KeyOfValue = std::_Identity<std::pair<int, int> >; _Compare = std::less<std::pair<int, int> >; _Alloc = std::allocator<std::pair<int, int> >]’
1306 |  _M_find_tr(const _Kt& __k)
     |  ^~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:1306:2: note:   template argument deduction/substitution failed:
/usr/include/c++/9/bits/stl_tree.h:1315:2: note: candidate: ‘template<class _Kt, class _Req> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::const_iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_find_tr(const _Kt&) const [with _Kt = _Kt; _Req = _Req; _Key = std::pair<int, int>; _Val = std::pair<int, int>; _KeyOfValue = std::_Identity<std::pair<int, int> >; _Compare = std::less<std::pair<int, int> >; _Alloc = std::allocator<std::pair<int, int> >]’
1315 |  _M_find_tr(const _Kt& __k) const
     |  ^~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:1315:2: note:   template argument deduction/substitution failed:
In file included from /usr/include/c++/9/set:61,
                from file.cpp:1:
/usr/include/c++/9/bits/stl_set.h:810:2: error: no matching function for call to ‘std::_Rb_tree_const_iterator<std::pair<int, int> >::_Rb_tree_const_iterator(<brace-enclosed initializer list>)’
 810 |  find(const _Kt& __x) const
     |  ^~~~
In file included from /usr/include/c++/9/set:60,
                from file.cpp:1:
/usr/include/c++/9/bits/stl_tree.h:348:7: note: candidate: ‘std::_Rb_tree_const_iterator<_Tp>::_Rb_tree_const_iterator(const iterator&) [with _Tp = std::pair<int, int>; std::_Rb_tree_const_iterator<_Tp>::iterator = std::_Rb_tree_iterator<std::pair<int, int> >]’
 348 |       _Rb_tree_const_iterator(const iterator& __it) _GLIBCXX_NOEXCEPT
     |       ^~~~~~~~~~~~~~~~~~~~~

/usr/include/c++/9/bits/stl_tree.h:348:7: note:   conversion of argument 1 would be ill-formed:
/usr/include/c++/9/bits/stl_tree.h:345:7: note: candidate: ‘std::_Rb_tree_const_iterator<_Tp>::_Rb_tree_const_iterator(std::_Rb_tree_const_iterator<_Tp>::_Base_ptr) [with _Tp = std::pair<int, int>; std::_Rb_tree_const_iterator<_Tp>::_Base_ptr = const std::_Rb_tree_node_base*]’
 345 |       _Rb_tree_const_iterator(_Base_ptr __x) _GLIBCXX_NOEXCEPT
     |       ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:345:7: note:   conversion of argument 1 would be ill-formed:
/usr/include/c++/9/bits/stl_tree.h:341:7: note: candidate: ‘std::_Rb_tree_const_iterator<_Tp>::_Rb_tree_const_iterator() [with _Tp = std::pair<int, int>]’
 341 |       _Rb_tree_const_iterator() _GLIBCXX_NOEXCEPT
     |       ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:341:7: note:   candidate expects 0 arguments, 1 provided
/usr/include/c++/9/bits/stl_tree.h:326:12: note: candidate: ‘constexpr std::_Rb_tree_const_iterator<std::pair<int, int> >::_Rb_tree_const_iterator(const std::_Rb_tree_const_iterator<std::pair<int, int> >&)’
 326 |     struct _Rb_tree_const_iterator
     |            ^~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/9/bits/stl_tree.h:326:12: note:   conversion of argument 1 would be ill-formed:
/usr/include/c++/9/bits/stl_tree.h:326:12: note: candidate: ‘constexpr std::_Rb_tree_const_iterator<std::pair<int, int> >::_Rb_tree_const_iterator(std::_Rb_tree_const_iterator<std::pair<int, int> >&&)’
/usr/include/c++/9/bits/stl_tree.h:326:12: note:   conversion of argument 1 would be ill-formed:

Ой, кажется немного побилось форматирование, сорян

Причем ошибка-то банальнейшая

А, нет, мне нужно завернуть один тип в арк, потому что он не Sync

И что это за говно ещё и с++/9. Это не С++ и не гцц - это протухшая херня и твоя проблема, что ты её используешь. Там выше у адепта явно самое найтли. Ну и прочитать это не представляется возможным - выкати в нормальном виде. И сообщи почему оно "по с равнению", в чём это выражается

Это не найтли.

Это стейбл, причём не последний, кажется.

Двухлетней давности версия7