[libc++][ranges] Implement ranges::min

Reviewed By: var-const, Mordante, #libc

Spies: jwakely, ldionne, libcxx-commits, mgorny

Differential Revision: https://reviews.llvm.org/D119589

Author: philnik777

libcxx/docs/Status/RangesAlgorithms.csv

@@ -15,11 +15,11 @@ Search,lower_bound,Christopher Di Bella,`D105795 <https://llvm.org/D105795>`_,Un
 Search,upper_bound,Christopher Di Bella,`D105795 <https://llvm.org/D105795>`_,Under review
 Search,equal_range,Christopher Di Bella,n/a,Not started
 Search,binary_search,Christopher Di Bella,n/a,Not started
-Search,min,Not assigned,n/a,Not started
+Search,min,Nikolas Klauser,`D119589 <https://llvm.org/D119589>`_,✅
 Search,max,Not assigned,n/a,Not started
 Search,minmax,Not assigned,n/a,Not started
-Search,min_element,Nikolas Klauser,n/a,✅
-Search,max_element,Not assigned,n/a,Not started
+Search,min_element,Nikolas Klauser,`D117025 <https://llvm.org/D117025>`_,✅
+Search,max_element,Nikolas Klauser,`D117523 <https://llvm.org/D117523>`_,✅
 Search,minmax_element,Not assigned,n/a,Not started
 Search,count,Not assigned,n/a,Not started
 Search,count_if,Not assigned,n/a,Not started

libcxx/include/CMakeLists.txt

@@ -70,6 +70,7 @@ set(files
   __algorithm/ranges_find_if.h
   __algorithm/ranges_find_if_not.h
   __algorithm/ranges_max_element.h
+  __algorithm/ranges_min.h
   __algorithm/ranges_min_element.h
   __algorithm/ranges_mismatch.h
   __algorithm/ranges_swap_ranges.h

libcxx/include/__algorithm/ranges_min.h

@@ -0,0 +1,89 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_MIN_H
+#define _LIBCPP___ALGORITHM_RANGES_MIN_H
+
+#include <__algorithm/ranges_min_element.h>
+#include <__assert>
+#include <__concepts/copyable.h>
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
+#include <__functional/ranges_operations.h>
+#include <__iterator/concepts.h>
+#include <__iterator/projected.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <initializer_list>
+
+#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_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+namespace __min {
+struct __fn {
+  template <class _Tp, class _Proj = identity,
+            indirect_strict_weak_order<projected<const _Tp*, _Proj>> _Comp = ranges::less>
+  _LIBCPP_HIDE_FROM_ABI constexpr
+  const _Tp& operator()(const _Tp& __a, const _Tp& __b, _Comp __comp = {}, _Proj __proj = {}) const {
+    return std::invoke(__comp, std::invoke(__proj, __b), std::invoke(__proj, __a)) ? __b : __a;
+  }
+
+  template <copyable _Tp, class _Proj = identity,
+            indirect_strict_weak_order<projected<const _Tp*, _Proj>> _Comp = ranges::less>
+  _LIBCPP_HIDE_FROM_ABI constexpr
+  _Tp operator()(initializer_list<_Tp> __il, _Comp __comp = {}, _Proj __proj = {}) const {
+    _LIBCPP_ASSERT(__il.begin() != __il.end(), "initializer_list must contain at least one element");
+    return *ranges::__min_element_impl(__il.begin(), __il.end(), __comp, __proj);
+  }
+
+  template <input_range _Rp, class _Proj = identity,
+            indirect_strict_weak_order<projected<iterator_t<_Rp>, _Proj>> _Comp = ranges::less>
+    requires indirectly_copyable_storable<iterator_t<_Rp>, range_value_t<_Rp>*>
+  _LIBCPP_HIDE_FROM_ABI constexpr
+  range_value_t<_Rp> operator()(_Rp&& __r, _Comp __comp = {}, _Proj __proj = {}) const {
+    auto __first = ranges::begin(__r);
+    auto __last = ranges::end(__r);
+
+    _LIBCPP_ASSERT(__first != __last, "range must contain at least one element");
+
+    if constexpr (forward_range<_Rp>) {
+      return *ranges::__min_element_impl(__first, __last, __comp, __proj);
+    } else {
+      range_value_t<_Rp> __result = *__first;
+      while (++__first != __last) {
+        if (std::invoke(__comp, std::invoke(__proj, *__first), std::invoke(__proj, __result)))
+          __result = *__first;
+      }
+      return __result;
+    }
+  }
+};
+} // namespace __min
+
+inline namespace __cpo {
+  inline constexpr auto min = __min::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP_STD_VER > 17 && && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+#endif // _LIBCPP___ALGORITHM_RANGES_MIN_H

libcxx/include/__algorithm/ranges_min_element.h

@@ -29,33 +29,34 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
-namespace __min_element {
-struct __fn {
-  template <class _Ip, class _Sp, class _Proj, class _Comp>
-  _LIBCPP_HIDE_FROM_ABI static constexpr
-  _Ip __go(_Ip __first, _Sp __last, _Comp& __comp, _Proj& __proj) {
-    if (__first == __last)
-      return __first;
 
-    _Ip __i = __first;
-    while (++__i != __last)
-      if (std::invoke(__comp, std::invoke(__proj, *__i), std::invoke(__proj, *__first)))
-        __first = __i;
+template <class _Ip, class _Sp, class _Proj, class _Comp>
+_LIBCPP_HIDE_FROM_ABI static constexpr
+_Ip __min_element_impl(_Ip __first, _Sp __last, _Comp& __comp, _Proj& __proj) {
+  if (__first == __last)
     return __first;
-  }
 
+  _Ip __i = __first;
+  while (++__i != __last)
+    if (std::invoke(__comp, std::invoke(__proj, *__i), std::invoke(__proj, *__first)))
+      __first = __i;
+  return __first;
+}
+
+namespace __min_element {
+struct __fn {
   template <forward_iterator _Ip, sentinel_for<_Ip> _Sp, class _Proj = identity,
             indirect_strict_weak_order<projected<_Ip, _Proj>> _Comp = ranges::less>
   _LIBCPP_HIDE_FROM_ABI constexpr
   _Ip operator()(_Ip __first, _Sp __last, _Comp __comp = {}, _Proj __proj = {}) const {
-    return __go(__first, __last, __comp, __proj);
+    return ranges::__min_element_impl(__first, __last, __comp, __proj);
   }
 
   template <forward_range _Rp, class _Proj = identity,
             indirect_strict_weak_order<projected<iterator_t<_Rp>, _Proj>> _Comp = ranges::less>
   _LIBCPP_HIDE_FROM_ABI constexpr
   borrowed_iterator_t<_Rp> operator()(_Rp&& __r, _Comp __comp = {}, _Proj __proj = {}) const {
-    return __go(ranges::begin(__r), ranges::end(__r), __comp, __proj);
+    return ranges::__min_element_impl(ranges::begin(__r), ranges::end(__r), __comp, __proj);
   }
 };
 } // namespace __min_element

libcxx/include/__ranges/take_view.h

@@ -9,7 +9,7 @@
 #ifndef _LIBCPP___RANGES_TAKE_VIEW_H
 #define _LIBCPP___RANGES_TAKE_VIEW_H
 
-#include <__algorithm/min.h>
+#include <__algorithm/ranges_min.h>
 #include <__config>
 #include <__iterator/concepts.h>
 #include <__iterator/counted_iterator.h>
@@ -118,15 +118,13 @@ namespace ranges {
     _LIBCPP_HIDE_FROM_ABI
     constexpr auto size() requires sized_range<_View> {
       auto __n = ranges::size(__base_);
-      // TODO: use ranges::min here.
-      return std::min(__n, static_cast<decltype(__n)>(__count_));
+      return ranges::min(__n, static_cast<decltype(__n)>(__count_));
     }
 
     _LIBCPP_HIDE_FROM_ABI
     constexpr auto size() const requires sized_range<const _View> {
       auto __n = ranges::size(__base_);
-      // TODO: use ranges::min here.
-      return std::min(__n, static_cast<decltype(__n)>(__count_));
+      return ranges::min(__n, static_cast<decltype(__n)>(__count_));
     }
   };
 

libcxx/include/algorithm

@@ -57,7 +57,6 @@ namespace ranges {
   constexpr mismatch_result<borrowed_iterator_t<R1>, borrowed_iterator_t<R2>>
   mismatch(R1&& r1, R2&& r2, Pred pred = {}, Proj1 proj1 = {}, Proj2 proj2 = {})                           // since C++20
 
-  template<input_iterator I, sentinel_for<I> S, class T, class Proj = identity>
     requires indirect_binary_predicate<ranges::equal_to, projected<I, Proj>, const T*>
     constexpr I find(I first, S last, const T& value, Proj proj = {});              // since C++20
 
@@ -83,9 +82,22 @@ namespace ranges {
            indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred>
     constexpr borrowed_iterator_t<R>
       find_if_not(R&& r, Pred pred, Proj proj = {});                                // since C++20
+
+ template<class T, class Proj = identity,
+          indirect_strict_weak_order<projected<const T*, Proj>> Comp = ranges::less>
+   constexpr const T& min(const T& a, const T& b, Comp comp = {}, Proj proj = {});  // since C++20
+
+ template<copyable T, class Proj = identity,
+          indirect_strict_weak_order<projected<const T*, Proj>> Comp = ranges::less>
+   constexpr T min(initializer_list<T> r, Comp comp = {}, Proj proj = {});          // since C++20
+
+ template<input_range R, class Proj = identity,
+          indirect_strict_weak_order<projected<iterator_t<R>, Proj>> Comp = ranges::less>
+   requires indirectly_copyable_storable<iterator_t<R>, range_value_t<R>*>
+   constexpr range_value_t<R>
+     min(R&& r, Comp comp = {}, Proj proj = {});                                    // since C++20
 }
 
-template <class InputIterator, class Predicate>
     constexpr bool     // constexpr in C++20
     all_of(InputIterator first, InputIterator last, Predicate pred);
 
@@ -804,6 +816,7 @@ template <class BidirectionalIterator, class Compare>
 #include <__algorithm/ranges_find_if.h>
 #include <__algorithm/ranges_find_if_not.h>
 #include <__algorithm/ranges_max_element.h>
+#include <__algorithm/ranges_min.h>
 #include <__algorithm/ranges_min_element.h>
 #include <__algorithm/ranges_mismatch.h>
 #include <__algorithm/ranges_swap_ranges.h>

libcxx/include/module.modulemap

@@ -298,6 +298,7 @@ module std [system] {
       module ranges_find_if           { private header "__algorithm/ranges_find_if.h" }
       module ranges_find_if_not       { private header "__algorithm/ranges_find_if_not.h" }
       module ranges_max_element       { private header "__algorithm/ranges_max_element.h" }
+      module ranges_min               { private header "__algorithm/ranges_min.h" }
       module ranges_min_element       { private header "__algorithm/ranges_min_element.h" }
       module ranges_mismatch          { private header "__algorithm/ranges_mismatch.h" }
       module ranges_swap_ranges       { private header "__algorithm/ranges_swap_ranges.h" }

libcxx/test/libcxx/diagnostics/detail.headers/algorithm/ranges_min.module.verify.cpp

@@ -0,0 +1,15 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: modules-build
+
+// WARNING: This test was generated by 'generate_private_header_tests.py'
+// and should not be edited manually.
+
+// expected-error@*:* {{use of private header from outside its module: '__algorithm/ranges_min.h'}}
+#include <__algorithm/ranges_min.h>