[libcxx][ranges] implement std::ranges::set_difference

implement `std::ranges::set_difference`
reused classic std::set_difference
added unit tests

Differential Revision: https://reviews.llvm.org/D128983

libcxx/docs/Status/RangesAlgorithms.csv

@@ -61,7 +61,7 @@ Write,unique_copy,Not assigned,n/a,Not started
 Write,partition_copy,Not assigned,n/a,Not started
 Write,partial_sort_copy,Not assigned,n/a,Not started
 Merge,merge,Hui Xie,`D128611 <https://llvm.org/D128611>`_,✅
-Merge,set_difference,Hui Xie,n/a,Not started
+Merge,set_difference,Hui Xie,`D128983 <https://llvm.org/D128983>`,✅
 Merge,set_intersection,Hui Xie,n/a,Not started
 Merge,set_symmetric_difference,Hui Xie,n/a,Not started
 Merge,set_union,Hui Xie,n/a,Not started

libcxx/include/CMakeLists.txt

@@ -108,6 +108,7 @@ set(files
   __algorithm/ranges_replace.h
   __algorithm/ranges_replace_if.h
   __algorithm/ranges_reverse.h
+  __algorithm/ranges_set_difference.h
   __algorithm/ranges_sort.h
   __algorithm/ranges_stable_sort.h
   __algorithm/ranges_swap_ranges.h

libcxx/include/__algorithm/make_projected.h

@@ -13,6 +13,8 @@
 #include <__config>
 #include <__functional/identity.h>
 #include <__functional/invoke.h>
+#include <__type_traits/decay.h>
+#include <__type_traits/is_member_pointer.h>
 #include <__utility/forward.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -28,7 +30,7 @@ namespace ranges {
 template <class _Comp, class _Proj>
 _LIBCPP_HIDE_FROM_ABI constexpr static
 decltype(auto) __make_projected_comp(_Comp& __comp, _Proj& __proj) {
-  if constexpr (same_as<_Proj, identity>) {
+  if constexpr (same_as<decay_t<_Proj>, identity> && !is_member_pointer_v<decay_t<_Comp>>) {
     // Avoid creating the lambda and just use the pristine comparator -- for certain algorithms, this would enable
     // optimizations that rely on the type of the comparator.
     return __comp;
@@ -42,6 +44,24 @@ decltype(auto) __make_projected_comp(_Comp& __comp, _Proj& __proj) {
   }
 }
 
+template <class _Comp, class _Proj1, class _Proj2>
+_LIBCPP_HIDE_FROM_ABI constexpr static
+decltype(auto) __make_projected_comp(_Comp& __comp, _Proj1& __proj1, _Proj2& __proj2) {
+  if constexpr (same_as<decay_t<_Proj1>, identity> && same_as<decay_t<_Proj2>, identity> &&
+                !is_member_pointer_v<decay_t<_Comp>>) {
+    // Avoid creating the lambda and just use the pristine comparator -- for certain algorithms, this would enable
+    // optimizations that rely on the type of the comparator.
+    return __comp;
+
+  } else {
+    return [&](auto&& __lhs, auto&& __rhs) {
+      return std::invoke(__comp,
+                        std::invoke(__proj1, std::forward<decltype(__lhs)>(__lhs)),
+                        std::invoke(__proj2, std::forward<decltype(__rhs)>(__rhs)));
+    };
+  }
+}
+
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD

libcxx/include/__algorithm/ranges_set_difference.h

@@ -0,0 +1,104 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 _LIBCPP___ALGORITHM_RANGES_SET_DIFFERENCE_H
+#define _LIBCPP___ALGORITHM_RANGES_SET_DIFFERENCE_H
+
+#include <__algorithm/in_out_result.h>
+#include <__algorithm/make_projected.h>
+#include <__algorithm/set_difference.h>
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
+#include <__functional/ranges_operations.h>
+#include <__iterator/concepts.h>
+#include <__iterator/mergeable.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/dangling.h>
+#include <__type_traits/decay.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+
+template <class _InIter, class _OutIter>
+using set_difference_result = in_out_result<_InIter, _OutIter>;
+
+namespace __set_difference {
+
+struct __fn {
+  template <
+      input_iterator _InIter1,
+      sentinel_for<_InIter1> _Sent1,
+      input_iterator _InIter2,
+      sentinel_for<_InIter2> _Sent2,
+      weakly_incrementable _OutIter,
+      class _Comp  = less,
+      class _Proj1 = identity,
+      class _Proj2 = identity>
+    requires mergeable<_InIter1, _InIter2, _OutIter, _Comp, _Proj1, _Proj2>
+  _LIBCPP_HIDE_FROM_ABI constexpr set_difference_result<_InIter1, _OutIter> operator()(
+      _InIter1 __first1,
+      _Sent1 __last1,
+      _InIter2 __first2,
+      _Sent2 __last2,
+      _OutIter __result,
+      _Comp __comp   = {},
+      _Proj1 __proj1 = {},
+      _Proj2 __proj2 = {}) const {
+    auto __ret = std::__set_difference(
+        __first1, __last1, __first2, __last2, __result, ranges::__make_projected_comp(__comp, __proj1, __proj2));
+    return {std::move(__ret.first), std::move(__ret.second)};
+  }
+
+  template <
+      input_range _Range1,
+      input_range _Range2,
+      weakly_incrementable _OutIter,
+      class _Comp  = less,
+      class _Proj1 = identity,
+      class _Proj2 = identity>
+    requires mergeable<iterator_t<_Range1>, iterator_t<_Range2>, _OutIter, _Comp, _Proj1, _Proj2> 
+  _LIBCPP_HIDE_FROM_ABI constexpr set_difference_result<borrowed_iterator_t<_Range1>, _OutIter>
+    operator()(
+        _Range1&& __range1,
+        _Range2&& __range2,
+        _OutIter __result,
+        _Comp __comp   = {},
+        _Proj1 __proj1 = {},
+        _Proj2 __proj2 = {}) const {
+    auto __ret = std::__set_difference(
+        ranges::begin(__range1),
+        ranges::end(__range1),
+        ranges::begin(__range2),
+        ranges::end(__range2),
+        __result,
+        ranges::__make_projected_comp(__comp, __proj1, __proj2));
+    return {std::move(__ret.first), std::move(__ret.second)};
+  }
+};
+
+} // namespace __set_difference
+
+inline namespace __cpo {
+  inline constexpr auto set_difference = __set_difference::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+#endif // _LIBCPP___ALGORITHM_RANGES_SET_DIFFERENCE_H

libcxx/include/__algorithm/set_difference.h

@@ -13,58 +13,65 @@
 #include <__algorithm/comp_ref_type.h>
 #include <__algorithm/copy.h>
 #include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
 #include <__iterator/iterator_traits.h>
+#include <__utility/move.h>
+#include <__utility/pair.h>
+#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-template <class _Compare, class _InputIterator1, class _InputIterator2, class _OutputIterator>
-_LIBCPP_CONSTEXPR_AFTER_CXX17 _OutputIterator
-__set_difference(_InputIterator1 __first1, _InputIterator1 __last1,
-                 _InputIterator2 __first2, _InputIterator2 __last2, _OutputIterator __result, _Compare __comp)
-{
-    while (__first1 != __last1)
-    {
-        if (__first2 == __last2)
-            return _VSTD::copy(__first1, __last1, __result);
-        if (__comp(*__first1, *__first2))
-        {
-            *__result = *__first1;
-            ++__result;
-            ++__first1;
-        }
-        else
-        {
-            if (!__comp(*__first2, *__first1))
-                ++__first1;
-            ++__first2;
-        }
+template < class _Comp, class _InIter1, class _Sent1, class _InIter2, class _Sent2, class _OutIter>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17 pair<__uncvref_t<_InIter1>, __uncvref_t<_OutIter> >
+__set_difference(
+    _InIter1&& __first1, _Sent1&& __last1, _InIter2&& __first2, _Sent2&& __last2, _OutIter&& __result, _Comp&& __comp) {
+  while (__first1 != __last1 && __first2 != __last2) {
+    if (__comp(*__first1, *__first2)) {
+      *__result = *__first1;
+      ++__first1;
+      ++__result;
+    } else if (__comp(*__first2, *__first1)) {
+      ++__first2;
+    } else {
+      ++__first1;
+      ++__first2;
     }
-    return __result;
+  }
+  return std::__copy(std::move(__first1), std::move(__last1), std::move(__result));
 }
 
 template <class _InputIterator1, class _InputIterator2, class _OutputIterator, class _Compare>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-_OutputIterator
-set_difference(_InputIterator1 __first1, _InputIterator1 __last1,
-               _InputIterator2 __first2, _InputIterator2 __last2, _OutputIterator __result, _Compare __comp)
-{
-    typedef typename __comp_ref_type<_Compare>::type _Comp_ref;
-    return _VSTD::__set_difference<_Comp_ref>(__first1, __last1, __first2, __last2, __result, __comp);
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17 _OutputIterator set_difference(
+    _InputIterator1 __first1,
+    _InputIterator1 __last1,
+    _InputIterator2 __first2,
+    _InputIterator2 __last2,
+    _OutputIterator __result,
+    _Compare __comp) {
+  typedef typename __comp_ref_type<_Compare>::type _Comp_ref;
+  return std::__set_difference<_Comp_ref>(__first1, __last1, __first2, __last2, __result, __comp).second;
 }
 
 template <class _InputIterator1, class _InputIterator2, class _OutputIterator>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
-_OutputIterator
-set_difference(_InputIterator1 __first1, _InputIterator1 __last1,
-               _InputIterator2 __first2, _InputIterator2 __last2, _OutputIterator __result)
-{
-    return _VSTD::set_difference(__first1, __last1, __first2, __last2, __result,
-                                __less<typename iterator_traits<_InputIterator1>::value_type,
-                                       typename iterator_traits<_InputIterator2>::value_type>());
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17 _OutputIterator set_difference(
+    _InputIterator1 __first1,
+    _InputIterator1 __last1,
+    _InputIterator2 __first2,
+    _InputIterator2 __last2,
+    _OutputIterator __result) {
+  return std::__set_difference(
+      __first1,
+      __last1,
+      __first2,
+      __last2,
+      __result,
+      __less<typename iterator_traits<_InputIterator1>::value_type,
+             typename iterator_traits<_InputIterator2>::value_type>()).second;
 }
 
 _LIBCPP_END_NAMESPACE_STD

libcxx/include/algorithm

@@ -530,6 +530,24 @@ namespace ranges {
     requires permutable<iterator_t<R>>
     constexpr borrowed_subrange_t<R>
       ranges::remove_if(R&& r, Pred pred, Proj proj = {});                                          // since C++20
+  
+  template<class I, class O>
+    using set_difference_result = in_out_result<I, O>;                                              // since C++20                                              
+
+  template<input_iterator I1, sentinel_for<I1> S1, input_iterator I2, sentinel_for<I2> S2,
+           weakly_incrementable O, class Comp = ranges::less,
+           class Proj1 = identity, class Proj2 = identity>
+    requires mergeable<I1, I2, O, Comp, Proj1, Proj2>
+    constexpr set_difference_result<I1, O>
+      set_difference(I1 first1, S1 last1, I2 first2, S2 last2, O result,
+                     Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {});                           // since C++20
+
+  template<input_range R1, input_range R2, weakly_incrementable O,
+           class Comp = ranges::less, class Proj1 = identity, class Proj2 = identity>
+    requires mergeable<iterator_t<R1>, iterator_t<R2>, O, Comp, Proj1, Proj2>
+    constexpr set_difference_result<borrowed_iterator_t<R1>, O>
+      set_difference(R1&& r1, R2&& r2, O result,
+                     Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {});                           // since C++20
 
 }
 
@@ -1300,6 +1318,7 @@ template <class BidirectionalIterator, class Compare>
 #include <__algorithm/ranges_replace.h>
 #include <__algorithm/ranges_replace_if.h>
 #include <__algorithm/ranges_reverse.h>
+#include <__algorithm/ranges_set_difference.h>
 #include <__algorithm/ranges_sort.h>
 #include <__algorithm/ranges_stable_sort.h>
 #include <__algorithm/ranges_swap_ranges.h>

libcxx/include/module.modulemap.in

@@ -347,6 +347,7 @@ module std [system] {
       module ranges_replace                  { private header "__algorithm/ranges_replace.h" }
       module ranges_replace_if               { private header "__algorithm/ranges_replace_if.h" }
       module ranges_reverse                  { private header "__algorithm/ranges_reverse.h" }
+      module ranges_set_difference           { private header "__algorithm/ranges_set_difference.h" }
       module ranges_sort                     { private header "__algorithm/ranges_sort.h" }
       module ranges_stable_sort              { private header "__algorithm/ranges_stable_sort.h" }
       module ranges_swap_ranges              { private header "__algorithm/ranges_swap_ranges.h" }

libcxx/test/libcxx/algorithms/ranges_robust_against_copying_comparators.pass.cpp

@@ -199,8 +199,8 @@ constexpr bool all_the_algorithms()
     //(void)std::ranges::search(a, b, Equal(&copies)); assert(copies == 0);
     //(void)std::ranges::search_n(first, last, count, value, Equal(&copies)); assert(copies == 0);
     //(void)std::ranges::search_n(a, count, value, Equal(&copies)); assert(copies == 0);
-    //(void)std::ranges::set_difference(first, mid, mid, last, first2, Less(&copies)); assert(copies == 0);
-    //(void)std::ranges::set_difference(a, b, first2, Less(&copies)); assert(copies == 0);
+    (void)std::ranges::set_difference(first, mid, mid, last, first2, Less(&copies)); assert(copies == 0);
+    (void)std::ranges::set_difference(a, b, first2, Less(&copies)); assert(copies == 0);
     //(void)std::ranges::set_intersection(first, mid, mid, last, first2, Less(&copies)); assert(copies == 0);
     //(void)std::ranges::set_intersection(a, b, first2, Less(&copies)); assert(copies == 0);
     //(void)std::ranges::set_symmetric_difference(first, mid, mid, last, first2, Less(&copies)); assert(copies == 0);

libcxx/test/libcxx/algorithms/ranges_robust_against_copying_projections.pass.cpp

@@ -190,8 +190,8 @@ constexpr bool all_the_algorithms()
     //(void)std::ranges::search(a, b, Equal(), Proj(&copies), Proj(&copies)); assert(copies == 0);
     //(void)std::ranges::search_n(first, last, count, value, Equal(), Proj(&copies)); assert(copies == 0);
     //(void)std::ranges::search_n(a, count, value, Equal(), Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::set_difference(first, mid, mid, last, first2, Less(), Proj(&copies), Proj(&copies)); assert(copies == 0);
-    //(void)std::ranges::set_difference(a, b, first2, Less(), Proj(&copies), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::set_difference(first, mid, mid, last, first2, Less(), Proj(&copies), Proj(&copies)); assert(copies == 0);
+    (void)std::ranges::set_difference(a, b, first2, Less(), Proj(&copies), Proj(&copies)); assert(copies == 0);
     //(void)std::ranges::set_intersection(first, mid, mid, last, first2, Less(), Proj(&copies), Proj(&copies)); assert(copies == 0);
     //(void)std::ranges::set_intersection(a, b, first2, Less(), Proj(&copies), Proj(&copies)); assert(copies == 0);
     //(void)std::ranges::set_symmetric_difference(first, mid, mid, last, first2, Less(), Proj(&copies), Proj(&copies)); assert(copies == 0);

libcxx/test/libcxx/private_headers.verify.cpp

@@ -145,6 +145,7 @@ END-SCRIPT
 #include <__algorithm/ranges_replace.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_replace.h'}}
 #include <__algorithm/ranges_replace_if.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_replace_if.h'}}
 #include <__algorithm/ranges_reverse.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_reverse.h'}}
+#include <__algorithm/ranges_set_difference.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_set_difference.h'}}
 #include <__algorithm/ranges_sort.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_sort.h'}}
 #include <__algorithm/ranges_stable_sort.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_stable_sort.h'}}
 #include <__algorithm/ranges_swap_ranges.h> // expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_swap_ranges.h'}}