[libcxx-commits] [libcxx] 84a50f5 - [libc++] Add bind_front function (P0356R5).

via libcxx-commits libcxx-commits at lists.llvm.org
Tue Mar 2 16:18:28 PST 2021


Author: zoecarver
Date: 2021-03-02T16:18:06-08:00
New Revision: 84a50f5911bf8300cc4bea1f60673ede2145345b

URL: https://github.com/llvm/llvm-project/commit/84a50f5911bf8300cc4bea1f60673ede2145345b
DIFF: https://github.com/llvm/llvm-project/commit/84a50f5911bf8300cc4bea1f60673ede2145345b.diff

LOG: [libc++] Add bind_front function (P0356R5).

Implementes [[ http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0356r5.html | P0356R5 ]]. Adds `bind_front` to `functional`.

Reviewed By: ldionne, #libc, Quuxplusone

Differential Revision: https://reviews.llvm.org/D60368

Added: 
    libcxx/test/std/utilities/function.objects/func.bind_front/bind_front.pass.cpp
    libcxx/test/std/utilities/function.objects/func.bind_front/bind_front.verify.cpp
    libcxx/test/support/callable_types.h

Modified: 
    libcxx/docs/Cxx2aStatusIssuesStatus.csv
    libcxx/docs/Cxx2aStatusPaperStatus.csv
    libcxx/docs/FeatureTestMacroTable.rst
    libcxx/include/functional
    libcxx/include/version
    libcxx/test/std/language.support/support.limits/support.limits.general/functional.version.pass.cpp
    libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
    libcxx/test/std/utilities/function.objects/func.not_fn/not_fn.pass.cpp
    libcxx/utils/generate_feature_test_macro_components.py

Removed: 
    


################################################################################
diff  --git a/libcxx/docs/Cxx2aStatusIssuesStatus.csv b/libcxx/docs/Cxx2aStatusIssuesStatus.csv
index b411f12d0ce35..064adf29df333 100644
--- a/libcxx/docs/Cxx2aStatusIssuesStatus.csv
+++ b/libcxx/docs/Cxx2aStatusIssuesStatus.csv
@@ -147,7 +147,7 @@
 "`3158 <https://wg21.link/LWG3158>`__","``tuple(allocator_arg_t, const Alloc&)``\  should be conditionally explicit","Cologne","",""
 "`3169 <https://wg21.link/LWG3169>`__","``ranges``\  permutation generators discard useful information","Cologne","",""
 "`3183 <https://wg21.link/LWG3183>`__","Normative permission to specialize Ranges variable templates","Cologne","",""
-"`3184 <https://wg21.link/LWG3184>`__","Inconsistencies in ``bind_front``\  wording","Cologne","",""
+"`3184 <https://wg21.link/LWG3184>`__","Inconsistencies in ``bind_front``\  wording","Cologne","|Complete|","13.0"
 "`3185 <https://wg21.link/LWG3185>`__","Uses-allocator construction functions missing ``constexpr``\  and ``noexcept``\ ","Cologne","",""
 "`3186 <https://wg21.link/LWG3186>`__","``ranges``\  removal, partition, and ``partial_sort_copy``\  algorithms discard useful information","Cologne","",""
 "`3187 <https://wg21.link/LWG3187>`__","`P0591R4 <https://wg21.link/p0591r4>`__ reverted DR 2586 fixes to ``scoped_allocator_adaptor::construct()``\ ","Cologne","",""

diff  --git a/libcxx/docs/Cxx2aStatusPaperStatus.csv b/libcxx/docs/Cxx2aStatusPaperStatus.csv
index d3819a83fa43d..fd73d8978fc11 100644
--- a/libcxx/docs/Cxx2aStatusPaperStatus.csv
+++ b/libcxx/docs/Cxx2aStatusPaperStatus.csv
@@ -51,7 +51,7 @@
 "`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","* *",""
+"`P0356R5 <https://wg21.link/P0356R5>`__","LWG","Simplified partial function application","San Diego","|Complete|","13.0"
 "`P0357R3 <https://wg21.link/P0357R3>`__","LWG","reference_wrapper for incomplete types","San Diego","|Complete|","8.0"
 "`P0482R6 <https://wg21.link/P0482R6>`__","CWG","char8_t: A type for UTF-8 characters and strings","San Diego","|In Progress|",""
 "`P0487R1 <https://wg21.link/P0487R1>`__","LWG","Fixing ``operator>>(basic_istream&, CharT*)``\  (LWG 2499)","San Diego","|Complete|","8.0"
@@ -128,7 +128,7 @@
 "`P1643 <https://wg21.link/P1643>`__","LWG","Add wait/notify to atomic_ref","Cologne","",""
 "`P1644 <https://wg21.link/P1644>`__","LWG","Add wait/notify to atomic<shared_ptr>","Cologne","",""
 "`P1650 <https://wg21.link/P1650>`__","LWG","Output std::chrono::days with 'd' suffix","Cologne","",""
-"`P1651 <https://wg21.link/P1651>`__","LWG","bind_front should not unwrap reference_wrapper","Cologne","",""
+"`P1651 <https://wg21.link/P1651>`__","LWG","bind_front should not unwrap reference_wrapper","Cologne","|Complete|","13.0"
 "`P1652 <https://wg21.link/P1652>`__","LWG","Printf corner cases in std::format","Cologne","",""
 "`P1661 <https://wg21.link/P1661>`__","LWG","Remove dedicated precalculated hash lookup interface","Cologne","|Nothing To Do|",""
 "`P1754 <https://wg21.link/P1754>`__","LWG","Rename concepts to standard_case for C++20, while we still can","Cologne","|In Progress|",""

diff  --git a/libcxx/docs/FeatureTestMacroTable.rst b/libcxx/docs/FeatureTestMacroTable.rst
index 997d2136714de..77010b574eb32 100644
--- a/libcxx/docs/FeatureTestMacroTable.rst
+++ b/libcxx/docs/FeatureTestMacroTable.rst
@@ -188,7 +188,7 @@ Status
     ------------------------------------------------- -----------------
     ``__cpp_lib_barrier``                             ``201907L``
     ------------------------------------------------- -----------------
-    ``__cpp_lib_bind_front``                          *unimplemented*
+    ``__cpp_lib_bind_front``                          ``201907L``
     ------------------------------------------------- -----------------
     ``__cpp_lib_bit_cast``                            *unimplemented*
     ------------------------------------------------- -----------------

diff  --git a/libcxx/include/functional b/libcxx/include/functional
index f8565e7e6e670..c4830e16ad356 100644
--- a/libcxx/include/functional
+++ b/libcxx/include/functional
@@ -2992,61 +2992,107 @@ invoke(_Fn&& __f, _Args&&... __args)
     return _VSTD::__invoke(_VSTD::forward<_Fn>(__f), _VSTD::forward<_Args>(__args)...);
 }
 
-template <class _DecayFunc>
-class _LIBCPP_TEMPLATE_VIS __not_fn_imp {
-  _DecayFunc __fd;
-
-public:
-    __not_fn_imp() = delete;
-
-    template <class ..._Args>
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-    auto operator()(_Args&& ...__args) &
-            noexcept(noexcept(!_VSTD::invoke(__fd, _VSTD::forward<_Args>(__args)...)))
-        -> decltype(          !_VSTD::invoke(__fd, _VSTD::forward<_Args>(__args)...))
-        { return              !_VSTD::invoke(__fd, _VSTD::forward<_Args>(__args)...); }
-
-    template <class ..._Args>
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-    auto operator()(_Args&& ...__args) &&
-            noexcept(noexcept(!_VSTD::invoke(_VSTD::move(__fd), _VSTD::forward<_Args>(__args)...)))
-        -> decltype(          !_VSTD::invoke(_VSTD::move(__fd), _VSTD::forward<_Args>(__args)...))
-        { return              !_VSTD::invoke(_VSTD::move(__fd), _VSTD::forward<_Args>(__args)...); }
-
-    template <class ..._Args>
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-    auto operator()(_Args&& ...__args) const&
-            noexcept(noexcept(!_VSTD::invoke(__fd, _VSTD::forward<_Args>(__args)...)))
-        -> decltype(          !_VSTD::invoke(__fd, _VSTD::forward<_Args>(__args)...))
-        { return              !_VSTD::invoke(__fd, _VSTD::forward<_Args>(__args)...); }
-
+template<class _Op, class _Tuple,
+         class _Idxs = typename __make_tuple_indices<tuple_size<_Tuple>::value>::type>
+struct __perfect_forward_impl;
+
+template<class _Op, class... _Bound, size_t... _Idxs>
+struct __perfect_forward_impl<_Op, __tuple_types<_Bound...>, __tuple_indices<_Idxs...>>
+{
+    tuple<_Bound...> __bound_;
+
+    template<class... _Args>
+    _LIBCPP_INLINE_VISIBILITY constexpr auto operator()(_Args&&... __args) &
+    noexcept(noexcept(_Op::__call(_VSTD::get<_Idxs>(__bound_)..., _VSTD::forward<_Args>(__args)...)))
+    -> decltype(      _Op::__call(_VSTD::get<_Idxs>(__bound_)..., _VSTD::forward<_Args>(__args)...))
+    {return           _Op::__call(_VSTD::get<_Idxs>(__bound_)..., _VSTD::forward<_Args>(__args)...);}
+
+    template<class... _Args>
+    _LIBCPP_INLINE_VISIBILITY constexpr auto operator()(_Args&&... __args) const&
+    noexcept(noexcept(_Op::__call(_VSTD::get<_Idxs>(__bound_)..., _VSTD::forward<_Args>(__args)...)))
+    -> decltype(      _Op::__call(_VSTD::get<_Idxs>(__bound_)..., _VSTD::forward<_Args>(__args)...))
+    {return           _Op::__call(_VSTD::get<_Idxs>(__bound_)..., _VSTD::forward<_Args>(__args)...);}
+
+    template<class... _Args>
+    _LIBCPP_INLINE_VISIBILITY constexpr auto operator()(_Args&&... __args) &&
+    noexcept(noexcept(_Op::__call(_VSTD::get<_Idxs>(_VSTD::move(__bound_))...,
+                                  _VSTD::forward<_Args>(__args)...)))
+    -> decltype(      _Op::__call(_VSTD::get<_Idxs>(_VSTD::move(__bound_))...,
+                                  _VSTD::forward<_Args>(__args)...))
+    {return           _Op::__call(_VSTD::get<_Idxs>(_VSTD::move(__bound_))...,
+                                  _VSTD::forward<_Args>(__args)...);}
+
+    template<class... _Args>
+    _LIBCPP_INLINE_VISIBILITY constexpr auto operator()(_Args&&... __args) const&&
+    noexcept(noexcept(_Op::__call(_VSTD::get<_Idxs>(_VSTD::move(__bound_))...,
+                                  _VSTD::forward<_Args>(__args)...)))
+    -> decltype(      _Op::__call(_VSTD::get<_Idxs>(_VSTD::move(__bound_))...,
+                                  _VSTD::forward<_Args>(__args)...))
+    {return           _Op::__call(_VSTD::get<_Idxs>(_VSTD::move(__bound_))...,
+                                  _VSTD::forward<_Args>(__args)...);}
+
+    template<class _Fn = typename tuple_element<0, tuple<_Bound...>>::type,
+             class = _EnableIf<is_copy_constructible_v<_Fn>>>
+    constexpr __perfect_forward_impl(__perfect_forward_impl const& __other)
+        : __bound_(__other.__bound_) {}
+
+    template<class _Fn = typename tuple_element<0, tuple<_Bound...>>::type,
+             class = _EnableIf<is_move_constructible_v<_Fn>>>
+    constexpr __perfect_forward_impl(__perfect_forward_impl && __other)
+        : __bound_(_VSTD::move(__other.__bound_)) {}
+
+    template<class... _BoundArgs>
+    explicit constexpr __perfect_forward_impl(_BoundArgs&&... __bound) :
+        __bound_(_VSTD::forward<_BoundArgs>(__bound)...) { }
+};
+
+template<class _Op, class... _Args>
+using __perfect_forward =
+    __perfect_forward_impl<_Op, __tuple_types<decay_t<_Args>...>>;
+
+struct __not_fn_op
+{
+    template<class... _Args>
+    static _LIBCPP_CONSTEXPR_AFTER_CXX17 auto __call(_Args&&... __args)
+    noexcept(noexcept(!_VSTD::invoke(_VSTD::forward<_Args>(__args)...)))
+    -> decltype(      !_VSTD::invoke(_VSTD::forward<_Args>(__args)...))
+    { return          !_VSTD::invoke(_VSTD::forward<_Args>(__args)...); }
+};
+
+template<class _Fn,
+         class = _EnableIf<is_constructible_v<decay_t<_Fn>, _Fn> &&
+                           is_move_constructible_v<_Fn>>>
+_LIBCPP_CONSTEXPR_AFTER_CXX17 auto not_fn(_Fn&& __f)
+{
+    return __perfect_forward<__not_fn_op, _Fn>(_VSTD::forward<_Fn>(__f));
+}
 
-    template <class ..._Args>
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-    auto operator()(_Args&& ...__args) const&&
-            noexcept(noexcept(!_VSTD::invoke(_VSTD::move(__fd), _VSTD::forward<_Args>(__args)...)))
-        -> decltype(          !_VSTD::invoke(_VSTD::move(__fd), _VSTD::forward<_Args>(__args)...))
-        { return              !_VSTD::invoke(_VSTD::move(__fd), _VSTD::forward<_Args>(__args)...); }
+#endif // _LIBCPP_STD_VER > 14
 
-private:
-    template <class _RawFunc,
-              class = enable_if_t<!is_same<decay_t<_RawFunc>, __not_fn_imp>::value>>
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-    explicit __not_fn_imp(_RawFunc&& __rf)
-        : __fd(_VSTD::forward<_RawFunc>(__rf)) {}
+#if _LIBCPP_STD_VER > 17
 
-    template <class _RawFunc>
-    friend inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-    __not_fn_imp<decay_t<_RawFunc>> not_fn(_RawFunc&&);
+struct __bind_front_op
+{
+    template<class... _Args>
+    constexpr static auto __call(_Args&&... __args)
+    noexcept(noexcept(_VSTD::invoke(_VSTD::forward<_Args>(__args)...)))
+    -> decltype(      _VSTD::invoke(_VSTD::forward<_Args>(__args)...))
+    { return          _VSTD::invoke(_VSTD::forward<_Args>(__args)...); }
 };
 
-template <class _RawFunc>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-__not_fn_imp<decay_t<_RawFunc>> not_fn(_RawFunc&& __fn) {
-    return __not_fn_imp<decay_t<_RawFunc>>(_VSTD::forward<_RawFunc>(__fn));
+template<class _Fn, class... _Args,
+         class = _EnableIf<conjunction<is_constructible<decay_t<_Fn>, _Fn>,
+                                       is_move_constructible<decay_t<_Fn>>,
+                                       is_constructible<decay_t<_Args>, _Args>...,
+                                       is_move_constructible<decay_t<_Args>>...
+                                       >::value>>
+constexpr auto bind_front(_Fn&& __f, _Args&&... __args)
+{
+    return __perfect_forward<__bind_front_op, _Fn, _Args...>(_VSTD::forward<_Fn>(__f),
+                                                             _VSTD::forward<_Args>(__args)...);
 }
 
-#endif
+#endif // _LIBCPP_STD_VER > 17
 
 // struct hash<T*> in <memory>
 

diff  --git a/libcxx/include/version b/libcxx/include/version
index e8697232bac52..49648a0fa9e91 100644
--- a/libcxx/include/version
+++ b/libcxx/include/version
@@ -290,7 +290,7 @@ __cpp_lib_void_t                                        201411L <type_traits>
 # if !defined(_LIBCPP_HAS_NO_THREADS) && !defined(_LIBCPP_AVAILABILITY_DISABLE_FTM___cpp_lib_barrier)
 #   define __cpp_lib_barrier                            201907L
 # endif
-// # define __cpp_lib_bind_front                           201907L
+# define __cpp_lib_bind_front                           201907L
 // # define __cpp_lib_bit_cast                             201806L
 // # define __cpp_lib_bitops                               201907L
 # define __cpp_lib_bounded_array_traits                 201902L

diff  --git a/libcxx/test/std/language.support/support.limits/support.limits.general/functional.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/functional.version.pass.cpp
index 6e65a8fbd7747..77ceb9f31457b 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/functional.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/functional.version.pass.cpp
@@ -174,17 +174,11 @@
 
 #elif TEST_STD_VER == 20
 
-# if !defined(_LIBCPP_VERSION)
-#   ifndef __cpp_lib_bind_front
-#     error "__cpp_lib_bind_front should be defined in c++20"
-#   endif
-#   if __cpp_lib_bind_front != 201907L
-#     error "__cpp_lib_bind_front should have the value 201907L in c++20"
-#   endif
-# else // _LIBCPP_VERSION
-#   ifdef __cpp_lib_bind_front
-#     error "__cpp_lib_bind_front should not be defined because it is unimplemented in libc++!"
-#   endif
+# ifndef __cpp_lib_bind_front
+#   error "__cpp_lib_bind_front should be defined in c++20"
+# endif
+# if __cpp_lib_bind_front != 201907L
+#   error "__cpp_lib_bind_front should have the value 201907L in c++20"
 # endif
 
 # if !defined(_LIBCPP_VERSION)
@@ -257,17 +251,11 @@
 
 #elif TEST_STD_VER > 20
 
-# if !defined(_LIBCPP_VERSION)
-#   ifndef __cpp_lib_bind_front
-#     error "__cpp_lib_bind_front should be defined in c++2b"
-#   endif
-#   if __cpp_lib_bind_front != 201907L
-#     error "__cpp_lib_bind_front should have the value 201907L in c++2b"
-#   endif
-# else // _LIBCPP_VERSION
-#   ifdef __cpp_lib_bind_front
-#     error "__cpp_lib_bind_front should not be defined because it is unimplemented in libc++!"
-#   endif
+# ifndef __cpp_lib_bind_front
+#   error "__cpp_lib_bind_front should be defined in c++2b"
+# endif
+# if __cpp_lib_bind_front != 201907L
+#   error "__cpp_lib_bind_front should have the value 201907L in c++2b"
 # endif
 
 # if !defined(_LIBCPP_VERSION)

diff  --git a/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
index d7fabec6c1b06..337714f1e385a 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
@@ -2268,17 +2268,11 @@
 #   endif
 # endif
 
-# if !defined(_LIBCPP_VERSION)
-#   ifndef __cpp_lib_bind_front
-#     error "__cpp_lib_bind_front should be defined in c++20"
-#   endif
-#   if __cpp_lib_bind_front != 201907L
-#     error "__cpp_lib_bind_front should have the value 201907L in c++20"
-#   endif
-# else // _LIBCPP_VERSION
-#   ifdef __cpp_lib_bind_front
-#     error "__cpp_lib_bind_front should not be defined because it is unimplemented in libc++!"
-#   endif
+# ifndef __cpp_lib_bind_front
+#   error "__cpp_lib_bind_front should be defined in c++20"
+# endif
+# if __cpp_lib_bind_front != 201907L
+#   error "__cpp_lib_bind_front should have the value 201907L in c++20"
 # endif
 
 # if !defined(_LIBCPP_VERSION)
@@ -3481,17 +3475,11 @@
 #   endif
 # endif
 
-# if !defined(_LIBCPP_VERSION)
-#   ifndef __cpp_lib_bind_front
-#     error "__cpp_lib_bind_front should be defined in c++2b"
-#   endif
-#   if __cpp_lib_bind_front != 201907L
-#     error "__cpp_lib_bind_front should have the value 201907L in c++2b"
-#   endif
-# else // _LIBCPP_VERSION
-#   ifdef __cpp_lib_bind_front
-#     error "__cpp_lib_bind_front should not be defined because it is unimplemented in libc++!"
-#   endif
+# ifndef __cpp_lib_bind_front
+#   error "__cpp_lib_bind_front should be defined in c++2b"
+# endif
+# if __cpp_lib_bind_front != 201907L
+#   error "__cpp_lib_bind_front should have the value 201907L in c++2b"
 # endif
 
 # if !defined(_LIBCPP_VERSION)

diff  --git a/libcxx/test/std/utilities/function.objects/func.bind_front/bind_front.pass.cpp b/libcxx/test/std/utilities/function.objects/func.bind_front/bind_front.pass.cpp
new file mode 100644
index 0000000000000..ecfe69396e1bb
--- /dev/null
+++ b/libcxx/test/std/utilities/function.objects/func.bind_front/bind_front.pass.cpp
@@ -0,0 +1,302 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// functional
+
+// template <class F, class... Args> constexpr unspecified bind_front(F&&, Args&&...);
+
+#include <functional>
+
+#include "callable_types.h"
+#include "test_macros.h"
+
+constexpr int add(int a, int b) { return a + b; }
+
+constexpr int long_test(int a, int b, int c, int d, int e, int f) {
+  return a + b + c + d + e + f;
+}
+
+struct Foo {
+  int a;
+  int b;
+};
+
+struct FooCall {
+  constexpr Foo operator()(int a, int b) { return Foo{a, b}; }
+};
+
+struct S {
+  constexpr bool operator()(int a) { return a == 1; }
+};
+
+struct CopyMoveInfo {
+  enum { none, copy, move } copy_kind;
+
+  constexpr CopyMoveInfo() : copy_kind(none) {}
+  constexpr CopyMoveInfo(CopyMoveInfo const&) : copy_kind(copy) {}
+  constexpr CopyMoveInfo(CopyMoveInfo&&) : copy_kind(move) {}
+};
+
+constexpr bool wasCopied(CopyMoveInfo info) {
+  return info.copy_kind == CopyMoveInfo::copy;
+}
+constexpr bool wasMoved(CopyMoveInfo info) {
+  return info.copy_kind == CopyMoveInfo::move;
+}
+
+constexpr void basic_tests() {
+  int n = 2;
+  int m = 1;
+
+  auto a = std::bind_front(add, m, n);
+  assert(a() == 3);
+
+  auto b = std::bind_front(long_test, m, n, m, m, m, m);
+  assert(b() == 7);
+
+  auto c = std::bind_front(long_test, n, m);
+  assert(c(1, 1, 1, 1) == 7);
+
+  auto d = std::bind_front(S{}, m);
+  assert(d());
+
+  auto f = std::bind_front(add, n);
+  assert(f(3) == 5);
+
+  auto g = std::bind_front(add, n, 1);
+  assert(g() == 3);
+
+  auto h = std::bind_front(long_test, 1, 1, 1);
+  assert(h(2, 2, 2) == 9);
+
+  // Make sure the arg is passed by value.
+  auto i = std::bind_front(add, n, 1);
+  n = 100;
+  assert(i() == 3);
+
+  CopyMoveInfo info;
+  auto copied = std::bind_front(wasCopied, info);
+  assert(copied());
+
+  auto moved = std::bind_front(wasMoved, info);
+  assert(std::move(moved)());
+}
+
+struct variadic_fn {
+  template <class... Args>
+  constexpr int operator()(Args&&... args) {
+    return sizeof...(args);
+  }
+};
+
+constexpr void test_variadic() {
+  variadic_fn value;
+  auto fn = std::bind_front(value, 0, 0, 0);
+  assert(fn(0, 0, 0) == 6);
+}
+
+struct mutable_callable {
+  bool should_call_const;
+
+  constexpr bool operator()(int, int) {
+    assert(!should_call_const);
+    return true;
+  }
+  constexpr bool operator()(int, int) const {
+    assert(should_call_const);
+    return true;
+  }
+};
+
+constexpr void test_mutable() {
+  const mutable_callable v1{true};
+  const auto fn1 = std::bind_front(v1, 0);
+  assert(fn1(0));
+
+  mutable_callable v2{false};
+  auto fn2 = std::bind_front(v2, 0);
+  assert(fn2(0));
+};
+
+struct call_member {
+  constexpr bool member(int, int) { return true; }
+};
+
+constexpr void test_call_member() {
+  call_member value;
+  auto fn = std::bind_front(&call_member::member, value, 0);
+  assert(fn(0));
+}
+
+struct no_const_lvalue {
+  constexpr void operator()(int) && {};
+};
+
+constexpr auto make_no_const_lvalue(int x) {
+  // This is to test that bind_front works when something like the following would not:
+  // return [nc = no_const_lvalue{}, x] { return nc(x); };
+  // Above would not work because it would look for a () const & overload.
+  return std::bind_front(no_const_lvalue{}, x);
+}
+
+constexpr void test_no_const_lvalue() { make_no_const_lvalue(1)(); }
+
+constexpr void constructor_tests() {
+  {
+    MoveOnlyCallable value(true);
+    using RetT = decltype(std::bind_front(std::move(value), 1));
+
+    static_assert(std::is_move_constructible<RetT>::value);
+    static_assert(!std::is_copy_constructible<RetT>::value);
+    static_assert(!std::is_move_assignable<RetT>::value);
+    static_assert(!std::is_copy_assignable<RetT>::value);
+
+    auto ret = std::bind_front(std::move(value), 1);
+    assert(ret());
+    assert(ret(1, 2, 3));
+
+    auto ret1 = std::move(ret);
+    assert(!ret());
+    assert(ret1());
+    assert(ret1(1, 2, 3));
+  }
+  {
+    CopyCallable value(true);
+    using RetT = decltype(std::bind_front(value, 1));
+
+    static_assert(std::is_move_constructible<RetT>::value);
+    static_assert(std::is_copy_constructible<RetT>::value);
+    static_assert(!std::is_move_assignable<RetT>::value);
+    static_assert(!std::is_copy_assignable<RetT>::value);
+
+    auto ret = std::bind_front(value, 1);
+    assert(ret());
+    assert(ret(1, 2, 3));
+
+    auto ret1 = std::move(ret);
+    assert(ret1());
+    assert(ret1(1, 2, 3));
+
+    auto ret2 = std::bind_front(std::move(value), 1);
+    assert(!ret());
+    assert(ret2());
+    assert(ret2(1, 2, 3));
+  }
+  {
+    CopyAssignableWrapper value(true);
+    using RetT = decltype(std::bind_front(value, 1));
+
+    static_assert(std::is_move_constructible<RetT>::value);
+    static_assert(std::is_copy_constructible<RetT>::value);
+    static_assert(std::is_move_assignable<RetT>::value);
+    static_assert(std::is_copy_assignable<RetT>::value);
+  }
+  {
+    MoveAssignableWrapper value(true);
+    using RetT = decltype(std::bind_front(std::move(value), 1));
+
+    static_assert(std::is_move_constructible<RetT>::value);
+    static_assert(!std::is_copy_constructible<RetT>::value);
+    static_assert(std::is_move_assignable<RetT>::value);
+    static_assert(!std::is_copy_assignable<RetT>::value);
+  }
+}
+
+template <class Res, class F, class... Args>
+constexpr void test_return(F&& value, Args&&... args) {
+  auto ret =
+      std::bind_front(std::forward<F>(value), std::forward<Args>(args)...);
+  static_assert(std::is_same<decltype(ret()), Res>::value);
+}
+
+constexpr void test_return_types() {
+  test_return<Foo>(FooCall{}, 1, 2);
+  test_return<bool>(S{}, 1);
+  test_return<int>(add, 2, 2);
+}
+
+constexpr void test_arg_count() {
+  using T = decltype(std::bind_front(add, 1));
+  static_assert(!std::is_invocable<T>::value);
+  static_assert(std::is_invocable<T, int>::value);
+}
+
+template <class... Args>
+struct is_bind_frontable {
+  template <class... LocalArgs>
+  static auto test(int)
+      -> decltype((void)std::bind_front(std::declval<LocalArgs>()...),
+                  std::true_type());
+
+  template <class...>
+  static std::false_type test(...);
+
+  static constexpr bool value = decltype(test<Args...>(0))::value;
+};
+
+struct NotCopyMove {
+  NotCopyMove() = delete;
+  NotCopyMove(const NotCopyMove&) = delete;
+  NotCopyMove(NotCopyMove&&) = delete;
+  void operator()() {}
+};
+
+struct NonConstCopyConstructible {
+  explicit NonConstCopyConstructible() {}
+  NonConstCopyConstructible(NonConstCopyConstructible&) {}
+};
+
+struct MoveConstructible {
+  explicit MoveConstructible() {}
+  MoveConstructible(MoveConstructible&&) {}
+};
+
+constexpr void test_invocability() {
+  static_assert(!std::is_constructible_v<NotCopyMove, NotCopyMove>);
+  static_assert(!std::is_move_constructible_v<NotCopyMove>);
+  static_assert(!is_bind_frontable<NotCopyMove>::value);
+  static_assert(!is_bind_frontable<NotCopyMove&>::value);
+
+  static_assert(
+      !std::is_constructible_v<MoveConstructible, MoveConstructible&>);
+  static_assert(std::is_move_constructible_v<MoveConstructible>);
+  static_assert(is_bind_frontable<variadic_fn, MoveConstructible>::value);
+  static_assert(
+      !is_bind_frontable<variadic_fn, MoveConstructible&>::value);
+
+  static_assert(std::is_constructible_v<NonConstCopyConstructible,
+                                        NonConstCopyConstructible&>);
+  static_assert(!std::is_move_constructible_v<NonConstCopyConstructible>);
+  static_assert(
+      !is_bind_frontable<variadic_fn, NonConstCopyConstructible&>::value);
+  static_assert(
+      !is_bind_frontable<variadic_fn, NonConstCopyConstructible>::value);
+}
+
+constexpr bool test() {
+  basic_tests();
+  constructor_tests();
+  test_return_types();
+  test_arg_count();
+  test_variadic();
+  test_mutable();
+  test_call_member();
+  test_no_const_lvalue();
+  test_invocability();
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
+
+  return 0;
+}

diff  --git a/libcxx/test/std/utilities/function.objects/func.bind_front/bind_front.verify.cpp b/libcxx/test/std/utilities/function.objects/func.bind_front/bind_front.verify.cpp
new file mode 100644
index 0000000000000..adb8236b2547b
--- /dev/null
+++ b/libcxx/test/std/utilities/function.objects/func.bind_front/bind_front.verify.cpp
@@ -0,0 +1,49 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// functional
+
+// template <class F, class... Args> constexpr unspecified bind_front(F&&, Args&&...);
+
+#include <functional>
+
+#include "test_macros.h"
+
+constexpr int pass(const int n) { return n; }
+
+int simple(int n) { return n; }
+
+template<class T>
+T do_nothing(T t) { return t; }
+
+struct NotMoveConst
+{
+    NotMoveConst(NotMoveConst &&) = delete;
+    NotMoveConst(NotMoveConst const&) = delete;
+
+    NotMoveConst(int) { }
+};
+
+void testNotMoveConst(NotMoveConst) { }
+
+int main(int, char**)
+{
+    int n = 1;
+    const int c = 1;
+
+    auto p = std::bind_front(pass, c);
+    static_assert(p() == 1); // expected-error {{static_assert expression is not an integral constant expression}}
+
+    auto d = std::bind_front(do_nothing, n); // expected-error {{no matching function for call to 'bind_front'}}
+
+    auto t = std::bind_front(testNotMoveConst, NotMoveConst(0)); // expected-error {{no matching function for call to 'bind_front'}}
+
+    return 0;
+}

diff  --git a/libcxx/test/std/utilities/function.objects/func.not_fn/not_fn.pass.cpp b/libcxx/test/std/utilities/function.objects/func.not_fn/not_fn.pass.cpp
index bb86dc9a8b6fd..f9b7e439cc3e9 100644
--- a/libcxx/test/std/utilities/function.objects/func.not_fn/not_fn.pass.cpp
+++ b/libcxx/test/std/utilities/function.objects/func.not_fn/not_fn.pass.cpp
@@ -17,178 +17,7 @@
 
 #include "test_macros.h"
 #include "type_id.h"
-
-
-///////////////////////////////////////////////////////////////////////////////
-//                       CALLABLE TEST TYPES
-///////////////////////////////////////////////////////////////////////////////
-
-constexpr bool returns_true() { return true; }
-
-template <class Ret = bool>
-struct MoveOnlyCallable {
-  MoveOnlyCallable(MoveOnlyCallable const&) = delete;
-  constexpr MoveOnlyCallable(MoveOnlyCallable&& other)
-      : value(other.value)
-  { other.value = !other.value; }
-
-  template <class ...Args>
-  constexpr Ret operator()(Args&&...) { return Ret{value}; }
-
-  constexpr explicit MoveOnlyCallable(bool x) : value(x) {}
-  Ret value;
-};
-
-template <class Ret = bool>
-struct CopyCallable {
-  constexpr CopyCallable(CopyCallable const& other)
-      : value(other.value) {}
-
-  constexpr CopyCallable(CopyCallable&& other)
-      : value(other.value) { other.value = !other.value; }
-
-  template <class ...Args>
-  constexpr Ret operator()(Args&&...) { return Ret{value}; }
-
-  constexpr explicit CopyCallable(bool x) : value(x)  {}
-  Ret value;
-};
-
-
-template <class Ret = bool>
-struct ConstCallable {
-  constexpr ConstCallable(ConstCallable const& other)
-      : value(other.value) {}
-
-  constexpr ConstCallable(ConstCallable&& other)
-      : value(other.value) { other.value = !other.value; }
-
-  template <class ...Args>
-  constexpr Ret operator()(Args&&...) const { return Ret{value}; }
-
-  constexpr explicit ConstCallable(bool x) : value(x)  {}
-  Ret value;
-};
-
-
-
-template <class Ret = bool>
-struct NoExceptCallable {
-  constexpr NoExceptCallable(NoExceptCallable const& other)
-      : value(other.value) {}
-
-  template <class ...Args>
-  constexpr Ret operator()(Args&&...) noexcept { return Ret{value}; }
-
-  template <class ...Args>
-  constexpr Ret operator()(Args&&...) const noexcept { return Ret{value}; }
-
-  constexpr explicit NoExceptCallable(bool x) : value(x)  {}
-  Ret value;
-};
-
-struct CopyAssignableWrapper {
-  constexpr CopyAssignableWrapper(CopyAssignableWrapper const&) = default;
-  constexpr CopyAssignableWrapper(CopyAssignableWrapper&&) = default;
-  constexpr CopyAssignableWrapper& operator=(CopyAssignableWrapper const&) = default;
-  constexpr CopyAssignableWrapper& operator=(CopyAssignableWrapper &&) = default;
-
-  template <class ...Args>
-  constexpr bool operator()(Args&&...) { return value; }
-
-  constexpr explicit CopyAssignableWrapper(bool x) : value(x) {}
-  bool value;
-};
-
-
-struct MoveAssignableWrapper {
-  constexpr MoveAssignableWrapper(MoveAssignableWrapper const&) = delete;
-  constexpr MoveAssignableWrapper(MoveAssignableWrapper&&) = default;
-  constexpr MoveAssignableWrapper& operator=(MoveAssignableWrapper const&) = delete;
-  constexpr MoveAssignableWrapper& operator=(MoveAssignableWrapper &&) = default;
-
-  template <class ...Args>
-  constexpr bool operator()(Args&&...) { return value; }
-
-  constexpr explicit MoveAssignableWrapper(bool x) : value(x) {}
-  bool value;
-};
-
-struct MemFunCallable {
-  constexpr explicit MemFunCallable(bool x) : value(x) {}
-
-  constexpr bool return_value() const { return value; }
-  constexpr bool return_value_nc() { return value; }
-  bool value;
-};
-
-enum CallType : unsigned {
-  CT_None,
-  CT_NonConst = 1,
-  CT_Const = 2,
-  CT_LValue = 4,
-  CT_RValue = 8
-};
-
-inline constexpr CallType operator|(CallType LHS, CallType RHS) {
-    return static_cast<CallType>(static_cast<unsigned>(LHS) | static_cast<unsigned>(RHS));
-}
-
-struct ForwardingCallObject {
-  struct State {
-    CallType      last_call_type = CT_None;
-    TypeID const& (*last_call_args)() = nullptr;
-
-    template <class ...Args>
-    constexpr void set_call(CallType type) {
-      assert(last_call_type == CT_None);
-      assert(last_call_args == nullptr);
-      last_call_type = type;
-      last_call_args = &makeArgumentID<Args...>;
-    }
-
-    template <class ...Args>
-    constexpr bool check_call(CallType type) {
-      bool result =
-           last_call_type == type
-        && last_call_args
-        && *last_call_args == &makeArgumentID<Args...>;
-      last_call_type = CT_None;
-      last_call_args = nullptr;
-      return result;
-    }
-  };
-
-  State *st_;
-
-  explicit constexpr ForwardingCallObject(State& st) : st_(&st) {}
-
-  template <class ...Args>
-  constexpr bool operator()(Args&&...) & {
-      st_->set_call<Args&&...>(CT_NonConst | CT_LValue);
-      return true;
-  }
-
-  template <class ...Args>
-  constexpr bool operator()(Args&&...) const & {
-      st_->set_call<Args&&...>(CT_Const | CT_LValue);
-      return true;
-  }
-
-  // Don't allow the call operator to be invoked as an rvalue.
-  template <class ...Args>
-  constexpr bool operator()(Args&&...) && {
-      st_->set_call<Args&&...>(CT_NonConst | CT_RValue);
-      return true;
-  }
-
-  template <class ...Args>
-  constexpr bool operator()(Args&&...) const && {
-      st_->set_call<Args&&...>(CT_Const | CT_RValue);
-      return true;
-  }
-};
-
+#include "callable_types.h"
 
 ///////////////////////////////////////////////////////////////////////////////
 //                        BOOL TEST TYPES
@@ -298,6 +127,10 @@ bool constructor_tests()
         assert(ret() == false);
         assert(ret2() == true);
         assert(ret2("abc") == true);
+        // initialize not_fn with rvalue
+        auto ret3 = std::not_fn(std::move(value));
+        assert(ret(0) == false);
+        assert(ret3(0) == true);
     }
     {
         using T = CopyAssignableWrapper;
@@ -306,17 +139,10 @@ bool constructor_tests()
         using RetT = decltype(std::not_fn(value));
         static_assert(std::is_move_constructible<RetT>::value, "");
         static_assert(std::is_copy_constructible<RetT>::value, "");
-        LIBCPP_STATIC_ASSERT(std::is_move_assignable<RetT>::value, "");
-        LIBCPP_STATIC_ASSERT(std::is_copy_assignable<RetT>::value, "");
         auto ret = std::not_fn(value);
         assert(ret() == false);
         auto ret2 = std::not_fn(value2);
         assert(ret2() == true);
-#if defined(_LIBCPP_VERSION)
-        ret = ret2;
-        assert(ret() == true);
-        assert(ret2() == true);
-#endif // _LIBCPP_VERSION
     }
     {
         using T = MoveAssignableWrapper;
@@ -325,16 +151,11 @@ bool constructor_tests()
         using RetT = decltype(std::not_fn(std::move(value)));
         static_assert(std::is_move_constructible<RetT>::value, "");
         static_assert(!std::is_copy_constructible<RetT>::value, "");
-        LIBCPP_STATIC_ASSERT(std::is_move_assignable<RetT>::value, "");
         static_assert(!std::is_copy_assignable<RetT>::value, "");
         auto ret = std::not_fn(std::move(value));
         assert(ret() == false);
         auto ret2 = std::not_fn(std::move(value2));
         assert(ret2() == true);
-#if defined(_LIBCPP_VERSION)
-        ret = std::move(ret2);
-        assert(ret() == true);
-#endif // _LIBCPP_VERSION
     }
     return true;
 }

diff  --git a/libcxx/test/support/callable_types.h b/libcxx/test/support/callable_types.h
new file mode 100644
index 0000000000000..9bc27249c7a8b
--- /dev/null
+++ b/libcxx/test/support/callable_types.h
@@ -0,0 +1,186 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef TEST_CALLABLE_TYPES_H
+#define TEST_CALLABLE_TYPES_H
+
+#include "test_macros.h"
+#include "type_id.h"
+
+///////////////////////////////////////////////////////////////////////////////
+//                       CALLABLE TEST TYPES
+///////////////////////////////////////////////////////////////////////////////
+
+constexpr bool returns_true() { return true; }
+
+template <class Ret = bool>
+struct MoveOnlyCallable {
+  MoveOnlyCallable(MoveOnlyCallable const&) = delete;
+  constexpr MoveOnlyCallable(MoveOnlyCallable&& other)
+      : value(other.value)
+  { other.value = !other.value; }
+
+  template <class ...Args>
+  constexpr Ret operator()(Args&&...) { return Ret{value}; }
+
+  constexpr explicit MoveOnlyCallable(bool x) : value(x) {}
+  Ret value;
+};
+
+template <class Ret = bool>
+struct CopyCallable {
+  constexpr CopyCallable(CopyCallable const& other)
+      : value(other.value) {}
+
+  constexpr CopyCallable(CopyCallable&& other)
+      : value(other.value) { other.value = !other.value; }
+
+  template <class ...Args>
+  constexpr Ret operator()(Args&&...) { return Ret{value}; }
+
+  constexpr explicit CopyCallable(bool x) : value(x)  {}
+  Ret value;
+};
+
+
+template <class Ret = bool>
+struct ConstCallable {
+  constexpr ConstCallable(ConstCallable const& other)
+      : value(other.value) {}
+
+  constexpr ConstCallable(ConstCallable&& other)
+      : value(other.value) { other.value = !other.value; }
+
+  template <class ...Args>
+  constexpr Ret operator()(Args&&...) const { return Ret{value}; }
+
+  constexpr explicit ConstCallable(bool x) : value(x)  {}
+  Ret value;
+};
+
+
+
+template <class Ret = bool>
+struct NoExceptCallable {
+  constexpr NoExceptCallable(NoExceptCallable const& other)
+      : value(other.value) {}
+
+  template <class ...Args>
+  constexpr Ret operator()(Args&&...) noexcept { return Ret{value}; }
+
+  template <class ...Args>
+  constexpr Ret operator()(Args&&...) const noexcept { return Ret{value}; }
+
+  constexpr explicit NoExceptCallable(bool x) : value(x)  {}
+  Ret value;
+};
+
+struct CopyAssignableWrapper {
+  constexpr CopyAssignableWrapper(CopyAssignableWrapper const&) = default;
+  constexpr CopyAssignableWrapper(CopyAssignableWrapper&&) = default;
+  constexpr CopyAssignableWrapper& operator=(CopyAssignableWrapper const&) = default;
+  constexpr CopyAssignableWrapper& operator=(CopyAssignableWrapper &&) = default;
+
+  template <class ...Args>
+  constexpr bool operator()(Args&&...) { return value; }
+
+  constexpr explicit CopyAssignableWrapper(bool x) : value(x) {}
+  bool value;
+};
+
+
+struct MoveAssignableWrapper {
+  constexpr MoveAssignableWrapper(MoveAssignableWrapper const&) = delete;
+  constexpr MoveAssignableWrapper(MoveAssignableWrapper&&) = default;
+  constexpr MoveAssignableWrapper& operator=(MoveAssignableWrapper const&) = delete;
+  constexpr MoveAssignableWrapper& operator=(MoveAssignableWrapper &&) = default;
+
+  template <class ...Args>
+  constexpr bool operator()(Args&&...) { return value; }
+
+  constexpr explicit MoveAssignableWrapper(bool x) : value(x) {}
+  bool value;
+};
+
+struct MemFunCallable {
+  constexpr explicit MemFunCallable(bool x) : value(x) {}
+
+  constexpr bool return_value() const { return value; }
+  constexpr bool return_value_nc() { return value; }
+  bool value;
+};
+
+enum CallType : unsigned {
+  CT_None,
+  CT_NonConst = 1,
+  CT_Const = 2,
+  CT_LValue = 4,
+  CT_RValue = 8
+};
+
+inline constexpr CallType operator|(CallType LHS, CallType RHS) {
+    return static_cast<CallType>(static_cast<unsigned>(LHS) | static_cast<unsigned>(RHS));
+}
+
+struct ForwardingCallObject {
+  struct State {
+    CallType      last_call_type = CT_None;
+    TypeID const& (*last_call_args)() = nullptr;
+
+    template <class ...Args>
+    constexpr void set_call(CallType type) {
+      assert(last_call_type == CT_None);
+      assert(last_call_args == nullptr);
+      last_call_type = type;
+      last_call_args = &makeArgumentID<Args...>;
+    }
+
+    template <class ...Args>
+    constexpr bool check_call(CallType type) {
+      bool result =
+           last_call_type == type
+        && last_call_args
+        && *last_call_args == &makeArgumentID<Args...>;
+      last_call_type = CT_None;
+      last_call_args = nullptr;
+      return result;
+    }
+  };
+
+  State *st_;
+
+  explicit constexpr ForwardingCallObject(State& st) : st_(&st) {}
+
+  template <class ...Args>
+  constexpr bool operator()(Args&&...) & {
+      st_->set_call<Args&&...>(CT_NonConst | CT_LValue);
+      return true;
+  }
+
+  template <class ...Args>
+  constexpr bool operator()(Args&&...) const & {
+      st_->set_call<Args&&...>(CT_Const | CT_LValue);
+      return true;
+  }
+
+  // Don't allow the call operator to be invoked as an rvalue.
+  template <class ...Args>
+  constexpr bool operator()(Args&&...) && {
+      st_->set_call<Args&&...>(CT_NonConst | CT_RValue);
+      return true;
+  }
+
+  template <class ...Args>
+  constexpr bool operator()(Args&&...) const && {
+      st_->set_call<Args&&...>(CT_Const | CT_RValue);
+      return true;
+  }
+};
+
+
+#endif // TEST_CALLABLE_TYPES_H

diff  --git a/libcxx/utils/generate_feature_test_macro_components.py b/libcxx/utils/generate_feature_test_macro_components.py
index 1544baf737c7f..24780f87a58aa 100755
--- a/libcxx/utils/generate_feature_test_macro_components.py
+++ b/libcxx/utils/generate_feature_test_macro_components.py
@@ -123,7 +123,6 @@ def add_version_header(tc):
     "name": "__cpp_lib_bind_front",
     "values": { "c++20": 201907 },
     "headers": ["functional"],
-    "unimplemented": True,
   }, {
     "name": "__cpp_lib_bit_cast",
     "values": { "c++20": 201806 },


        


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