[libcxx] adds __cpp_lib_concepts feature-test macro

[cjdb]

Summary

Also adjusts C++20 status paper to indicate full concepts support.

Depends on D96477, D99817.

[zoecarver]

I think it would be best to make this a NFC, so please add the change in libcxx/include/concepts to a different patch with a regression test.

It's also too bad that this relies on D96477. Ideally, we'd land this quickly and then update D96477 to reflect that, but I'm unsure of the timeline, so I'm OK if you want to land D96477 first.

[curdeius]

Why do you mark it as complete in version 14? Next release is going to be 13.
And, I agree with Zoe that it should be a NFC commit and the change in <concepts> should be regression tested.

[cjdb]

applies @zoecarver and @curdeius' feedback

[Mordante]

I would like to see this patch rebased on main once all it's dependencies have landed. Just to give it a another CI run.
Doesn't finishing P0898R3 mean we should set __cpp_lib_concepts ?
(Note I haven't looked whether all parts of the papers have been implemented.)

[cjdb]

enables feature-test macro, revises commit message

[Mordante]

In D99805#2668334, @cjdb wrote:

enables feature-test macro, revises commit message

Please update utils/generate_feature_test_macro_components.py and run this script. This will properly update the feature-test macros.
Just remove the line "unimplemented": True, for __cpp_lib_concepts.

[cjdb]

properly updates feature-test macro per @Mordante's request

[cjdb]

@zoecarver @curdeius this patch now changes a feature-test macro, so I don't think it can be NFC. Are you okay with that?

[cjdb]

rebases to fix CI

[curdeius]

In D99805#2670041, @cjdb wrote:

@zoecarver @curdeius this patch now changes a feature-test macro, so I don't think it can be NFC. Are you okay with that?

If there's doubt, don't mark it as NFC.
Adding NFC when it's not NFC would make more harm than not adding NFC when it really is.

[curdeius]

LGTM. Please rebase to run the CI once the dependencies have landed.

[cjdb]

rebases to activate CI, applies @curdeius' comment suggestions from D96477 (putting them in this patch makes more sense due to this patch's detachment from anything specific)

[Mordante]

LGTM!

libcxx/docs/Cxx2aStatusIssuesStatus.csv

 "`3276 <https://wg21.link/LWG3276>`__","Class ``split_view::outer_iterator::value_type``\  should inherit from ``view_interface``\ ","Belfast","",""
 "`3277 <https://wg21.link/LWG3277>`__","Pre-increment on prvalues is not a requirement of ``weakly_incrementable``\ ","Belfast","",""
 "`3149 <https://wg21.link/LWG3149>`__","``DefaultConstructible``\  should require default initialization","Belfast","|Complete|","13.0"
 "","","","",""
 "`1203 <https://wg21.link/LWG1203>`__","More useful rvalue stream insertion","Prague","|Complete|","12.0"
 "`2859 <https://wg21.link/LWG2859>`__","Definition of *reachable* in [ptr.launder] misses pointer arithmetic from pointer-interconvertible object","Prague","",""
 "`3018 <https://wg21.link/LWG3018>`__","``shared_ptr``\  of function type","Prague","",""
 "`3050 <https://wg21.link/LWG3050>`__","Conversion specification problem in ``chrono::duration``\  constructor","Prague","",""
-"`3141 <https://wg21.link/LWG3141>`__","``CopyConstructible``\  doesn't preserve source values","Prague","",""
-"`3150 <https://wg21.link/LWG3150>`__","``UniformRandomBitGenerator``\  should validate ``min``\  and ``max``\ ","Prague","",""
-"`3175 <https://wg21.link/LWG3175>`__","The ``CommonReference``\  requirement of concept ``SwappableWith``\  is not satisfied in the example","Prague","",""
-"`3194 <https://wg21.link/LWG3194>`__","``ConvertibleTo``\  prose does not match code","Prague","",""
+"`3141 <https://wg21.link/LWG3141>`__","``CopyConstructible``\  doesn't preserve source values","Prague","|Nothing to do|",""
+"`3150 <https://wg21.link/LWG3150>`__","``UniformRandomBitGenerator``\  should validate ``min``\  and ``max``\ ","Prague","|Complete|","14.0"
+"`3175 <https://wg21.link/LWG3175>`__","The ``CommonReference``\  requirement of concept ``SwappableWith``\  is not satisfied in the example","Prague","|Complete|","14.0"
+"`3194 <https://wg21.link/LWG3194>`__","``ConvertibleTo``\  prose does not match code","Prague","|Complete|","14.0"
 "`3200 <https://wg21.link/LWG3200>`__","``midpoint``\  should not constrain ``T``\  is complete","Prague","|Nothing To Do|",""
 "`3201 <https://wg21.link/LWG3201>`__","``lerp``\  should be marked as ``noexcept``\ ","Prague","|Complete|",""
 "`3226 <https://wg21.link/LWG3226>`__","``zoned_time``\  constructor from ``string_view``\  should accept ``zoned_time<Duration2, TimeZonePtr2>``\ ","Prague","",""
 "`3233 <https://wg21.link/LWG3233>`__","Broken requirements for ``shared_ptr``\  converting constructors","Prague","",""
 "`3237 <https://wg21.link/LWG3237>`__","LWG 3038 and 3190 have inconsistent PRs","Prague","",""
 "`3238 <https://wg21.link/LWG3238>`__","Insufficiently-defined behavior of ``std::function``\  deduction guides","Prague","",""
 "`3242 <https://wg21.link/LWG3242>`__","``std::format``\ : missing rules for ``arg-id``\  in ``width``\  and ``precision``\ ","Prague","",""
 "`3243 <https://wg21.link/LWG3243>`__","``std::format``\  and negative zeroes","Prague","",""

 "`3320 <https://wg21.link/LWG3320>`__","``span::cbegin/cend``\  methods produce different results than ``std::[ranges::]cbegin/cend``\ ","Prague","|Complete|",""
 "`3321 <https://wg21.link/LWG3321>`__","``uninitialized_construct_using_allocator``\  should use ``construct_at``\ ","Prague","",""
 "`3323 <https://wg21.link/LWG3323>`__","``*has-tuple-element*``\  helper concept needs ``convertible_to``\ ","Prague","",""
 "`3324 <https://wg21.link/LWG3324>`__","Special-case ``std::strong/weak/partial_order``\  for pointers","Prague","",""
 "`3325 <https://wg21.link/LWG3325>`__","Constrain return type of transformation function for ``transform_view``\ ","Prague","",""
 "`3326 <https://wg21.link/LWG3326>`__","``enable_view``\  has false positives","Prague","",""
 "`3327 <https://wg21.link/LWG3327>`__","Format alignment specifiers vs. text direction","Prague","",""
 "`3328 <https://wg21.link/LWG3328>`__","Clarify that ``std::string``\  is not good for UTF-8","Prague","",""
-"`3329 <https://wg21.link/LWG3329>`__","``totally_ordered_with``\  both directly and indirectly requires ``common_reference_with``\ ","Prague","",""
+"`3329 <https://wg21.link/LWG3329>`__","``totally_ordered_with``\  both directly and indirectly requires ``common_reference_with``\ ","Prague","|Complete|","14.0"
 "`3330 <https://wg21.link/LWG3330>`__","Include ``<compare>``\  from most library headers","Prague","",""
-"`3331 <https://wg21.link/LWG3331>`__","Define ``totally_ordered/_with``\  in terms of ``*partially-ordered-with*``\ ","Prague","",""
+"`3331 <https://wg21.link/LWG3331>`__","Define ``totally_ordered/_with``\  in terms of ``*partially-ordered-with*``\ ","Prague","|Complete|","14.0"
 "`3332 <https://wg21.link/LWG3332>`__","Issue in |sect|\ [time.format]","Prague","",""
 "`3334 <https://wg21.link/LWG3334>`__","``basic_osyncstream``\  move assignment and destruction calls ``basic_syncbuf::emit()``\  twice","Prague","",""
 "`3335 <https://wg21.link/LWG3335>`__","Resolve C++20 NB comments US 273 and GB 274","Prague","",""
-"`3338 <https://wg21.link/LWG3338>`__","Rename ``default_constructible``\  to ``default_initializable``\ ","Prague","",""
+"`3338 <https://wg21.link/LWG3338>`__","Rename ``default_constructible``\  to ``default_initializable``\ ","Prague","|Complete|","14.0"
 "`3340 <https://wg21.link/LWG3340>`__","Formatting functions should throw on argument/format string mismatch in |sect|\ [format.functions]","Prague","",""
 "`3346 <https://wg21.link/LWG3346>`__","``pair``\  and ``tuple``\  copy and move constructor have backwards specification","Prague","",""
 "`3347 <https://wg21.link/LWG3347>`__","``std::pair<T, U>``\  now requires ``T``\  and ``U``\  to be less-than-comparable","Prague","",""
 "`3348 <https://wg21.link/LWG3348>`__","``__cpp_lib_unwrap_ref``\  in wrong header","Prague","",""
 "`3349 <https://wg21.link/LWG3349>`__","Missing ``__cpp_lib_constexpr_complex``\  for P0415R1","Prague","",""
 "`3350 <https://wg21.link/LWG3350>`__","Simplify return type of ``lexicographical_compare_three_way``\ ","Prague","",""
 "`3351 <https://wg21.link/LWG3351>`__","``ranges::enable_safe_range``\  should not be constrained","Prague","",""
 "`3352 <https://wg21.link/LWG3352>`__","``strong_equality``\  isn't a thing","Prague","",""

libcxx/docs/Cxx2aStatusPaperStatus.csv

 "`P0722R3 <https://wg21.link/P0722R3>`__","CWG","Efficient sized delete for variable sized classes","Rapperswil","|Complete|","9.0"
 "`P0758R1 <https://wg21.link/P0758R1>`__","LWG","Implicit conversion traits and utility functions","Rapperswil","|Complete|",""
 "`P0759R1 <https://wg21.link/P0759R1>`__","LWG","fpos Requirements","Rapperswil","|Complete|","11.0"
 "`P0769R2 <https://wg21.link/P0769R2>`__","LWG","Add shift to <algorithm>","Rapperswil","|Complete|","12.0"
 "`P0788R3 <https://wg21.link/P0788R3>`__","LWG","Standard Library Specification in a Concepts and Contracts World","Rapperswil","*Removed in Cologne*","n/a"
 "`P0879R0 <https://wg21.link/P0879R0>`__","LWG","Constexpr for swap and swap related functions Also resolves LWG issue 2800.","Rapperswil","|Complete|","13.0"
 "`P0887R1 <https://wg21.link/P0887R1>`__","LWG","The identity metafunction","Rapperswil","|Complete|","8.0"
 "`P0892R2 <https://wg21.link/P0892R2>`__","CWG","explicit(bool)","Rapperswil","",""
-"`P0898R3 <https://wg21.link/P0898R3>`__","LWG","Standard Library Concepts","Rapperswil","|In Progress|",""
+"`P0898R3 <https://wg21.link/P0898R3>`__","LWG","Standard Library Concepts","Rapperswil","|Complete|","14.0"
 "`P0935R0 <https://wg21.link/P0935R0>`__","LWG","Eradicating unnecessarily explicit default constructors from the standard library","Rapperswil","|Complete|","12.0"
 "`P0941R2 <https://wg21.link/P0941R2>`__","CWG","Integrating feature-test macros into the C++ WD","Rapperswil","|In Progress|",""
 "`P1023R0 <https://wg21.link/P1023R0>`__","LWG","constexpr comparison operators for std::array","Rapperswil","|Complete|","8.0"
 "`P1025R1 <https://wg21.link/P1025R1>`__","CWG","Update The Reference To The Unicode Standard","Rapperswil","",""
 "`P1120R0 <https://wg21.link/P1120R0>`__","CWG","Consistency improvements for <=> and other comparison operators","Rapperswil","",""
 "","","","","",""
 "`P0318R1 <https://wg21.link/P0318R1>`__","LWG","unwrap_ref_decay and unwrap_reference","San Diego","|Complete|","8.0"
 "`P0356R5 <https://wg21.link/P0356R5>`__","LWG","Simplified partial function application","San Diego","|Complete|","13.0"

 "`P1739 <https://wg21.link/P1739>`__","LWG","Avoid template bloat for safe_ranges in combination with ""subrange-y"" view adaptors","Prague","* *",""
 "`P1831 <https://wg21.link/P1831>`__","LWG","Deprecating volatile: library","Prague","* *",""
 "`P1868 <https://wg21.link/P1868>`__","LWG","width: clarifying units of width and precision in std::format","Prague","* *",""
 "`P1908 <https://wg21.link/P1908>`__","CWG","Reserving Attribute Namespaces for Future Use","Prague","* *",""
 "`P1937 <https://wg21.link/P1937>`__","CWG","Fixing inconsistencies between constexpr and consteval functions","Prague","* *",""
 "`P1956 <https://wg21.link/P1956>`__","LWG","On the names of low-level bit manipulation functions","Prague","|Complete|","12.0"
 "`P1957 <https://wg21.link/P1957>`__","CWG","Converting from ``T*``\  to bool should be considered narrowing (re: US 212)","Prague","* *",""
 "`P1963 <https://wg21.link/P1963>`__","LWG","Fixing US 313","Prague","* *",""
-"`P1964 <https://wg21.link/P1964>`__","LWG","Wording for boolean-testable","Prague","* *",""
+"`P1964 <https://wg21.link/P1964>`__","LWG","Wording for boolean-testable","Prague","|Complete|","14.0"
 "`P1970 <https://wg21.link/P1970>`__","LWG","Consistency for size() functions: Add ranges::ssize","Prague","* *",""
 "`P1973 <https://wg21.link/P1973>`__","LWG","Rename ""_default_init"" Functions, Rev1","Prague","* *",""
 "`P1976 <https://wg21.link/P1976>`__","LWG","Fixed-size span construction from dynamic range","Prague","|Complete|","11.0"
 "`P1981 <https://wg21.link/P1981>`__","LWG","Rename leap to leap_second","Prague","* *",""
 "`P1982 <https://wg21.link/P1982>`__","LWG","Rename link to time_zone_link","Prague","* *",""
 "`P1983 <https://wg21.link/P1983>`__","LWG","Wording for GB301, US296, US292, US291, and US283","Prague","* *",""
 "`P1994 <https://wg21.link/P1994>`__","LWG","elements_view needs its own sentinel","Prague","* *",""
 "`P2002 <https://wg21.link/P2002>`__","CWG","Defaulted comparison specification cleanups","Prague","* *",""
 "`P2045 <https://wg21.link/P2045>`__","LWG","Missing Mandates for the standard library","Prague","* *",""
 "`P2085 <https://wg21.link/P2085>`__","CWG","Consistent defaulted comparisons","Prague","* *",""
 "`P2091 <https://wg21.link/P2091>`__","LWG","Issues with range access CPOs","Prague","* *",""
 "`P2101 <https://wg21.link/P2101>`__","LWG","'Models' subsumes 'satisfies' (Wording for US298 and US300)","Prague","* *",""
 "`P2102 <https://wg21.link/P2102>`__","LWG","Make 'implicit expression variations' more explicit (Wording for US185)","Prague","* *",""
 "`P2106 <https://wg21.link/P2106>`__","LWG","Alternative wording for GB315 and GB316","Prague","* *",""
 "`P2116 <https://wg21.link/P2116>`__","LWG","Remove tuple-like protocol support from fixed-extent span","Prague","|Complete|","11.0"

libcxx/include/concepts

namespace ranges::inline __cpo {
   inline constexpr auto swap = __swap::__fn{};
 } // namespace ranges::__cpo
 
 template<class _Tp>
 concept swappable = requires(_Tp& __a, _Tp& __b) { ranges::swap(__a, __b); };
 
 template<class _Tp, class _Up>
 concept swappable_with =
-  common_reference_with<_Tp&, _Up&> &&
+  common_reference_with<_Tp, _Up> &&
   requires(_Tp&& __t, _Up&& __u) {
     ranges::swap(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Tp>(__t));
     ranges::swap(_VSTD::forward<_Up>(__u), _VSTD::forward<_Up>(__u));
     ranges::swap(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u));
     ranges::swap(_VSTD::forward<_Up>(__u), _VSTD::forward<_Tp>(__t));
   };
 
 // [concept.booleantestable]