[libc++][spaceship] P1612R2: Removed `operator!=` from `bitset`

[H-G-Hristov]

Summary

Implements parts of P1612R2:

• Removed operator!= from bitset

[Mordante]

In general LGTM, but I would like to land D152297 first and directly update the status page.

[H-G-Hristov]

Addressed comments

[H-G-Hristov]

In D152611#4411167, @Mordante wrote:

In general LGTM, but I would like to land D152297 first and directly update the status page.

Thank you for the review!

libcxx/include/bitset

764–765

constexpr since C++23 but removed in C++20 - Should I remove the macro?

[Mordante]

LGTM modulo some nits.

libcxx/include/bitset

82

It's a bit weird to become constexpr when it's removed. Please remove the constexpr here.

764–765

Yes please.

[H-G-Hristov]

Removed macro

libcxx/docs/Status/SpaceshipProjects.csv

 | `[optional.nullops] <https://wg21.link/optional.nullops>`_
 | `[optional.comp.with.t] <https://wg21.link/optional.comp.with.t>`_","| `optional <https://reviews.llvm.org/D146392>`_
 | `nullopt <https://reviews.llvm.org/D146392>`_",None,Hristo Hristov,|Complete|
 "| `[variant.syn] <https://wg21.link/variant.syn>`_
 | `[variant.relops] <https://wg21.link/variant.relops>`_
 | `[variant.monostate.relops] <https://wg21.link/variant.monostate.relops>`_","| `monostate <https://reviews.llvm.org/D131372>`_
 | `variant <https://reviews.llvm.org/D131372>`_",None,Kent Ross,|Complete|
 "| `[template.bitset] <https://wg21.link/template.bitset>`_
-| `[bitset.members] <https://wg21.link/bitset.members>`_","| remove ops `bitset <https://reviews.llvm.org/D152611>`_",None,Hristo Hristov,|In Progress|
+| `[bitset.members] <https://wg21.link/bitset.members>`_","| remove ops `bitset <https://reviews.llvm.org/D152611>`_",None,Hristo Hristov,|Complete|
 | `[memory.syn] <https://wg21.link/memory.syn>`_,|,None,Unassigned,|Not Started|
 | `[allocator.globals] <https://wg21.link/allocator.globals>`_,| remove ops `allocator <https://reviews.llvm.org/D152612>`_,None,Hristo Hristov,|In Progress|
 | `[unique.ptr.special] <https://wg21.link/unique.ptr.special>`_,| `unique_ptr <https://reviews.llvm.org/D130838>`_,[comparisons.three.way],Adrian Vogelsgesang,|Complete|
 | `[util.smartptr.shared.cmp] <https://wg21.link/util.smartptr.shared.cmp>`_,| `shared_ptr <https://reviews.llvm.org/D130852>`_,[comparisons.three.way],Adrian Vogelsgesang,|Complete|
 "| `[mem.res.syn] <https://wg21.link/mem.res.syn>`_
 | `[mem.res.eq] <https://wg21.link/mem.res.eq>`_
 | `[mem.poly.allocator.eq] <https://wg21.link/mem.poly.allocator.eq>`_","|
 | remove ops `memory_resource <https://reviews.llvm.org/D152629>`_

libcxx/include/bitset

public:
     template <class charT, class traits> // constexpr since C++23
         basic_string<charT, traits, allocator<charT> > to_string(charT zero = charT('0'), charT one = charT('1')) const;
     template <class charT> // constexpr since C++23
         basic_string<charT, char_traits<charT>, allocator<charT> > to_string(charT zero = charT('0'), charT one = charT('1')) const;
     basic_string<char, char_traits<char>, allocator<char> > to_string(char zero = '0', char one = '1') const; // constexpr since C++23
     size_t count() const noexcept;                     // constexpr since C++23
     constexpr size_t size() const noexcept;            // constexpr since C++23
     bool operator==(const bitset& rhs) const noexcept; // constexpr since C++23
-    bool operator!=(const bitset& rhs) const noexcept; // constexpr since C++23
+    bool operator!=(const bitset& rhs) const noexcept; // removed in C++20
     bool test(size_t pos) const;                       // constexpr since C++23
     bool all() const noexcept;                         // constexpr since C++23
     bool any() const noexcept;                         // constexpr since C++23
     bool none() const noexcept;                        // constexpr since C++23
     bitset<N> operator<<(size_t pos) const noexcept;   // constexpr since C++23
     bitset<N> operator>>(size_t pos) const noexcept;   // constexpr since C++23
 };
 
#endif
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23
     basic_string<char, char_traits<char>, allocator<char> > to_string(char __zero = '0',
                                                                       char __one = '1') const;
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23
     size_t count() const _NOEXCEPT;
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR size_t size() const _NOEXCEPT {return _Size;}
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23
     bool operator==(const bitset& __rhs) const _NOEXCEPT;
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23
+#if _LIBCPP_STD_VER <= 17
+    _LIBCPP_INLINE_VISIBILITY
     bool operator!=(const bitset& __rhs) const _NOEXCEPT;
+#endif
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23
     bool test(size_t __pos) const;
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23
     bool all() const _NOEXCEPT;
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23
     bool any() const _NOEXCEPT;
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23 bool none() const _NOEXCEPT {return !any();}
     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23

 inline
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23
 bool
 bitset<_Size>::operator==(const bitset& __rhs) const _NOEXCEPT
 {
     return _VSTD::equal(base::__make_iter(0), base::__make_iter(_Size), __rhs.__make_iter(0));
 }
 
+#if _LIBCPP_STD_VER <= 17
+
 template <size_t _Size>
 inline
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23
+_LIBCPP_HIDE_FROM_ABI
 bool
 bitset<_Size>::operator!=(const bitset& __rhs) const _NOEXCEPT
 {
     return !(*this == __rhs);
 }
 
+#endif
+
 template <size_t _Size>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23
 bool
 bitset<_Size>::test(size_t __pos) const
 {
     if (__pos >= _Size)
         __throw_out_of_range("bitset test argument out of range");