[clang] [libc++] Implement ranges::contains (PR #65148)

[Konstantin Varlamov via cfe-commits]

================
@@ -0,0 +1,190 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <algorithm>
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, 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 bool ranges::contains(I first, S last, const T& value, Proj proj = {});       // since C++23
+
+// template<input_range R, class T, class Proj = identity>
+//     requires indirect_binary_predicate<ranges::equal_to, projected<iterator_t<R>, Proj>, const T*>
+//     constexpr bool ranges::contains(R&& r, const T& value, Proj proj = {});                 // since C++23
+
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <ranges>
+#include <vector>
+
+#include "almost_satisfies_types.h"
+#include "boolean_testable.h"
+#include "test_iterators.h"
+
+struct NotEqualityComparable {};
+
+template <class Iter, class Sent = Iter>
+concept HasContainsIt = requires(Iter iter, Sent sent) { std::ranges::contains(iter, sent, *iter); };
+
+static_assert(HasContainsIt<int*>);
+static_assert(!HasContainsIt<NotEqualityComparable*>);
+static_assert(!HasContainsIt<InputIteratorNotDerivedFrom>);
+static_assert(!HasContainsIt<InputIteratorNotIndirectlyReadable>);
+static_assert(!HasContainsIt<InputIteratorNotInputOrOutputIterator>);
+static_assert(!HasContainsIt<cpp20_input_iterator<int*>, SentinelForNotSemiregular>);
+static_assert(!HasContainsIt<cpp20_input_iterator<int*>, InputRangeNotSentinelEqualityComparableWith>);
+
+static_assert(!HasContainsIt<int*, int>);
+static_assert(!HasContainsIt<int, int*>);
+
+template <class Range, class ValT>
+concept HasContainsR = requires(Range range) { std::ranges::contains(range, ValT{}); };
+
+static_assert(HasContainsR<std::array<int, 1>, int>);
+static_assert(!HasContainsR<int, int>);
+static_assert(!HasContainsR<std::array<NotEqualityComparable, 1>, NotEqualityComparable>);
+static_assert(!HasContainsR<InputRangeNotDerivedFrom, int>);
+static_assert(!HasContainsR<InputRangeNotIndirectlyReadable, int>);
+static_assert(!HasContainsR<InputRangeNotInputOrOutputIterator, int>);
+static_assert(!HasContainsR<InputRangeNotSentinelSemiregular, int>);
+static_assert(!HasContainsR<InputRangeNotSentinelEqualityComparableWith, int>);
+
+static std::vector<int> comparable_data;
+
+// clang-format off
+template <class Iter, class Sent = Iter>
+constexpr void test_iterators() {
+  using ValueT = std::iter_value_t<Iter>;
+  {  // simple tests
+    {
+      ValueT a[] = {1, 2, 3, 4, 5, 6};
+      std::same_as<bool> auto ret =
+        std::ranges::contains(Iter(a), Sent(Iter(a + 6)), 3);
+      assert(ret);
+    }
+    {
+      ValueT a[] = {1, 2, 3, 4, 5, 6};
+      auto range = std::ranges::subrange(Iter(a), Sent(Iter(a + 6)));
+      std::same_as<bool> decltype(auto) ret =
+        std::ranges::contains(range, 3);
+      assert(ret);
+    }
+  }
+
+  { // check that an empty range works
+    {
+      ValueT a[] = {};
+      auto ret = std::ranges::contains(Iter(a), Sent(Iter(a)), 1);
+      assert(!ret);
+    }
+    {
+      ValueT a[] = {};
+      auto range = std::ranges::subrange(Iter(a), Sent(Iter(a)));
+      auto ret = std::ranges::contains(range, 1);
+      assert(!ret);
+    }
+  }
+
+  { // check that no match
+    {
+      ValueT a[] = {13, 1, 21, 4, 5};
+      auto ret = std::ranges::contains(Iter(a), Sent(Iter(a + 5)), 10);
+      assert(!ret);
+    }
+    {
+      ValueT a[] = {13, 1, 21, 4, 5};
+      auto range = std::ranges::subrange(Iter(a), Sent(Iter(a + 5)));
+      auto ret = std::ranges::contains(range, 10);
+      assert(!ret);
+    }
+  }
----------------
var-const wrote:

I think we also need a test to check that the projection is used (for example, the data is an array of positive numbers, the projection returns the negative counterpart of the number, and we're searching for a negative number).

https://github.com/llvm/llvm-project/pull/65148