[libc++][spaceship] P1614R2: Removed `operator!=` from `functional`

[H-G-Hristov]

Summary

Implements parts of P1614R2:

• Removed operator!= from functional

[H-G-Hristov]

The CI error seems unrelated. I'll rebase and try again later.

[Mordante]

In D152704#4414204, @H-G-Hristov wrote:

The CI error seems unrelated. I'll rebase and try again later.

The CI is indeed unrelated, not need to rerun the CI.

LGTM!

libcxx/docs/Status/SpaceshipProjects.csv

 | `[mem.poly.allocator.eq] <https://wg21.link/mem.poly.allocator.eq>`_","|
 | remove ops `memory_resource <https://reviews.llvm.org/D152629>`_
 | remove ops `polymorphic_allocator <https://reviews.llvm.org/D152629>`_",None,Hristo Hristov,|Complete|
 "| `[allocator.adaptor.syn] <https://wg21.link/allocator.adaptor.syn>`_
 | `[scoped.adaptor.operators] <https://wg21.link/scoped.adaptor.operators>`_",| remove ops `scoped_allocator_adaptor`,None,Unassigned,|Not Started|
 "| `[functional.syn] <https://wg21.link/functional.syn>`_
 | `[range.cmp] <https://wg21.link/range.cmp>`_
 | `[func.wrap.func] <https://wg21.link/func.wrap.func>`_
-| `[func.wrap.func.nullptr] <https://wg21.link/func.wrap.func.nullptr>`_",| remove ops `function`,None,Unassigned,|Not Started|
+| `[func.wrap.func.nullptr] <https://wg21.link/func.wrap.func.nullptr>`_",| remove ops `function`,None,Hristo Hristov,|Complete|
 | `[meta.unary.prop] <https://wg21.link/meta.unary.prop>`_,| replaced by `issue LWG3354 <https://wg21.link/LWG3354>`_,None,Unassigned,|Nothing To Do|
 | `[meta.trans.other] <https://wg21.link/meta.trans.other>`_,|,None,Unassigned,|Not Started|
 "| `[type.index.overview] <https://wg21.link/type.index.overview>`_
 | `[type.index.members] <https://wg21.link/type.index.members>`_",| `type_index <https://reviews.llvm.org/D131357>`_,None,Adrian Vogelsgesang,|Complete|
 | `[charconv.syn] <https://wg21.link/charconv.syn>`_,| `to_chars_result <https://reviews.llvm.org/D112366>`_,None,Mark de Wever,|Complete|
 | `[charconv.syn] <https://wg21.link/charconv.syn>`_,| `from_chars_result <https://reviews.llvm.org/D112366>`_,None,Mark de Wever,|Complete|
 - `5.6 Clause 21: Strings library <https://wg21.link/p1614r2#clause-21-strings-library>`_,,,,
 "| `[char.traits.specializations.char] <https://wg21.link/char.traits.specializations.char>`_

libcxx/include/__functional/function.h

#endif
     _LIBCPP_INLINE_VISIBILITY
     explicit operator bool() const _NOEXCEPT {
       return static_cast<bool>(__f_);
     }
 
     // deleted overloads close possible hole in the type system
     template<class _R2, class... _ArgTypes2>
       bool operator==(const function<_R2(_ArgTypes2...)>&) const = delete;
+#if _LIBCPP_STD_VER <= 17
     template<class _R2, class... _ArgTypes2>
       bool operator!=(const function<_R2(_ArgTypes2...)>&) const = delete;
+#endif
 public:
     // function invocation:
     _LIBCPP_HIDE_FROM_ABI _Rp operator()(_ArgTypes...) const;
 
 #ifndef _LIBCPP_HAS_NO_RTTI
     // function target access:
     _LIBCPP_HIDE_FROM_ABI const std::type_info& target_type() const _NOEXCEPT;
     template <typename _Tp>

 
 #endif // _LIBCPP_HAS_NO_RTTI
 
 template <class _Rp, class... _ArgTypes>
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator==(const function<_Rp(_ArgTypes...)>& __f, nullptr_t) _NOEXCEPT {return !__f;}
 
+#if _LIBCPP_STD_VER <= 17
+
 template <class _Rp, class... _ArgTypes>
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator==(nullptr_t, const function<_Rp(_ArgTypes...)>& __f) _NOEXCEPT {return !__f;}
 
 template <class _Rp, class... _ArgTypes>
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator!=(const function<_Rp(_ArgTypes...)>& __f, nullptr_t) _NOEXCEPT {return (bool)__f;}
 
 template <class _Rp, class... _ArgTypes>
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator!=(nullptr_t, const function<_Rp(_ArgTypes...)>& __f) _NOEXCEPT {return (bool)__f;}
 
+#endif // _LIBCPP_STD_VER <= 17
+
 template <class _Rp, class... _ArgTypes>
 inline _LIBCPP_INLINE_VISIBILITY
 void
 swap(function<_Rp(_ArgTypes...)>& __x, function<_Rp(_ArgTypes...)>& __y) _NOEXCEPT
 {return __x.swap(__y);}
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP_CXX03_LANG
 
 #endif // _LIBCPP___FUNCTIONAL_FUNCTION_H

libcxx/include/functional

 template<class F>
 function(F) -> function<see-below>; // since C++17
 
 // Null pointer comparisons:
 template <class R, class ... ArgTypes>
   bool operator==(const function<R(ArgTypes...)>&, nullptr_t) noexcept;
 
 template <class R, class ... ArgTypes>
-  bool operator==(nullptr_t, const function<R(ArgTypes...)>&) noexcept;
+  bool operator==(nullptr_t, const function<R(ArgTypes...)>&) noexcept; // removed in C++20
 
 template <class R, class ... ArgTypes>
-  bool operator!=(const function<R(ArgTypes...)>&, nullptr_t) noexcept;
+  bool operator!=(const function<R(ArgTypes...)>&, nullptr_t) noexcept; // removed in C++20
 
 template <class  R, class ... ArgTypes>
-  bool operator!=(nullptr_t, const function<R(ArgTypes...)>&) noexcept;
+  bool operator!=(nullptr_t, const function<R(ArgTypes...)>&) noexcept; // removed in C++20
 
 // specialized algorithms:
 template <class  R, class ... ArgTypes>
   void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&) noexcept;
 
 template <class T> struct hash;
 
 template <> struct hash<bool>;