[libc++] LWG3738 Validates a missing precondition.

[Mordante]

Summary

No real changes were needed, but add an assert for the pre-condition.

This implements:

• 3738 Missing preconditions for take_view constructor

[philnik]

LGTM with comments addressed and green CI.

libcxx/include/__ranges/take_view.h

18

This should be <__assert>, right?

69

Maybe something like "count has to be greater or equal to zero", to be a bit more descriptive?

[Mordante]

Thanks for the review!

libcxx/include/__ranges/take_view.h

69

I think the condition tells the same, but no strong objection against the change.

libcxx/docs/Status/Cxx2bIssues.csv

 "`3629 <https://wg21.link/LWG3629>`__","``make_error_code`` and ``make_error_condition`` are customization points","November 2022","|Complete|","16.0",""
 "`3636 <https://wg21.link/LWG3636>`__","``formatter<T>::format`` should be ``const``-qualified","November 2022","|Complete|","16.0","|format|"
 "`3646 <https://wg21.link/LWG3646>`__","``std::ranges::view_interface::size`` returns a signed type","November 2022","|Complete|","16.0","|ranges|"
 "`3677 <https://wg21.link/LWG3677>`__","Is a cv-qualified ``pair`` specially handled in uses-allocator construction?", "November 2022","","",""
 "`3717 <https://wg21.link/LWG3717>`__","``common_view::end`` should improve ``random_access_range`` case", "November 2022","","","|ranges|"
 "`3732 <https://wg21.link/LWG3732>`__","``prepend_range`` and ``append_range`` can't be amortized constant time", "November 2022","|Nothing to do|","","|ranges|"
 "`3736 <https://wg21.link/LWG3736>`__","``move_iterator`` missing ``disable_sized_sentinel_for`` specialization", "November 2022","","","|ranges|"
 "`3737 <https://wg21.link/LWG3737>`__","``take_view::sentinel`` should provide ``operator-``", "November 2022","","","|ranges|"
-"`3738 <https://wg21.link/LWG3738>`__","Missing preconditions for ``take_view`` constructor", "November 2022","","","|ranges|"
+"`3738 <https://wg21.link/LWG3738>`__","Missing preconditions for ``take_view`` constructor", "November 2022","|Complete|","16.0","|ranges|"
 "`3743 <https://wg21.link/LWG3743>`__","``ranges::to``'s reserve may be ill-formed", "November 2022","","","|ranges|"
 "`3745 <https://wg21.link/LWG3745>`__","``std::atomic_wait`` and its friends lack ``noexcept``", "November 2022","","",""
 "`3746 <https://wg21.link/LWG3746>`__","``optional``'s spaceship with ``U`` with a type derived from optional causes infinite constraint meta-recursion", "November 2022","","","|spaceship|"
 "`3747 <https://wg21.link/LWG3747>`__","``ranges::uninitialized_copy_n``, ``ranges::uninitialized_move_n``, and ``ranges::destroy_n`` should use ``std::move``", "November 2022","","","|ranges|"
 "`3750 <https://wg21.link/LWG3750>`__","Too many papers bump ``__cpp_lib_format``", "November 2022","","","|format|"
 "`3751 <https://wg21.link/LWG3751>`__","Missing feature macro for ``flat_set``", "November 2022","","","|flat_containers|"
 "`3753 <https://wg21.link/LWG3753>`__","Clarify entity vs. freestanding entity", "November 2022","","",""
 "`3754 <https://wg21.link/LWG3754>`__","Class template expected synopsis contains declarations that do not match the detailed description", "November 2022","","",""

libcxx/include/__ranges/take_view.h

 #ifndef _LIBCPP___RANGES_TAKE_VIEW_H
 #define _LIBCPP___RANGES_TAKE_VIEW_H
 
 #include <__algorithm/min.h>
 #include <__algorithm/ranges_min.h>
 #include <__concepts/constructible.h>
 #include <__concepts/convertible_to.h>
 #include <__config>
+#include <__debug>
 #include <__functional/bind_back.h>
 #include <__fwd/span.h>
 #include <__fwd/string_view.h>
 #include <__iterator/concepts.h>
 #include <__iterator/counted_iterator.h>
 #include <__iterator/default_sentinel.h>
 #include <__iterator/distance.h>
 #include <__iterator/iterator_traits.h>
class take_view : public view_interface<take_view<_View>> {
   range_difference_t<_View> __count_ = 0;
 
   template<bool> class __sentinel;
 
 public:
   _LIBCPP_HIDE_FROM_ABI
   take_view() requires default_initializable<_View> = default;
 
-  _LIBCPP_HIDE_FROM_ABI
-  constexpr take_view(_View __base, range_difference_t<_View> __count)
-    : __base_(std::move(__base)), __count_(__count) {}
+  _LIBCPP_HIDE_FROM_ABI constexpr take_view(_View __base, range_difference_t<_View> __count)
+      : __base_(std::move(__base)), __count_(__count) {
+    _LIBCPP_ASSERT(__count >= 0, "precondition failure");
+  }
 
   _LIBCPP_HIDE_FROM_ABI
   constexpr _View base() const& requires copy_constructible<_View> { return __base_; }
 
   _LIBCPP_HIDE_FROM_ABI
   constexpr _View base() && { return std::move(__base_); }
 
   _LIBCPP_HIDE_FROM_ABI