[clang] [compiler-rt] [libunwind] [flang] [llvm] [libcxx] [libc] [lldb] [clang-tools-extra] [libc++] Implement ranges::iota (PR #68494)

[Nikolas Klauser via cfe-commits]

================
@@ -0,0 +1,123 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// Testing std::ranges::iota
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+#include <cassert>
+#include <numeric>
+#include <algorithm>
+#include <array>
+
+#include "test_macros.h"
+#include "test_iterators.h"
+#include "almost_satisfies_types.h"
+
+// Concepts to check different overloads of std::ranges::iota
+template <class Iter = int*, class Sent = int*, class Value = int>
+concept HasIotaIter = requires(Iter&& iter, Sent&& sent, Value&& val) {
+  std::ranges::iota(std::forward<Iter>(iter), std::forward<Sent>(sent), std::forward<Value>(val));
+};
+
+template <class Range, class Value = int>
+concept HasIotaRange =
+    requires(Range&& range, Value&& val) { std::ranges::iota(std::forward<Range>(range), std::forward<Value>(val)); };
+
+constexpr void test_constraints() {
+  // Test constraints of the iterator/sentinel overload
+  // ==================================================
+  static_assert(HasIotaIter<int*, int*, int>);
+
+  // !input_or_output_iterator<O>
+  static_assert(!HasIotaIter<InputIteratorNotInputOrOutputIterator>);
+
+  // !sentinel_for<S, O>
+  static_assert(!HasIotaIter<int*, SentinelForNotSemiregular>);
+  static_assert(!HasIotaIter<int*, SentinelForNotWeaklyEqualityComparableWith>);
+
+  // !weakly_incrementable<T>
+  static_assert(!HasIotaIter<int*, int*, WeaklyIncrementableNotMovable>);
+
+  // !indirectly writable <O, T>
+  static_assert(!HasIotaIter<OutputIteratorNotIndirectlyWritable, int*, int>);
+
+  // Test constraints for the range overload
+  // =======================================
+  static_assert(HasIotaRange<UncheckedRange<int*>, int>);
+
+  // !weakly_incrementable<T>
+  static_assert(!HasIotaRange<UncheckedRange<int*>, WeaklyIncrementableNotMovable>);
+
+  // !ranges::output_range<const _Tp&>
+  static_assert(!HasIotaRange<UncheckedRange<int*>, OutputIteratorNotIndirectlyWritable>);
+}
+
+template <class Iter, class Sent, std::size_t N>
+constexpr void test_result(std::array<int, N> input, int starting_value, std::array<int, N> const expected) {
+  { // (iterator, sentinel) overload
+    auto in_begin = Iter(input.data());
+    auto in_end   = Sent(Iter(input.data() + input.size()));
+    std::same_as<std::ranges::out_value_result<Iter, int>> decltype(auto) result =
+        std::ranges::iota(std::move(in_begin), std::move(in_end), starting_value);
+    assert(result.out == in_end);
+    if constexpr (expected.size() > 0) {
+      assert(result.value == expected.back() + 1);
+    } else {
+      assert(result.value == starting_value);
+    }
+    assert(std::ranges::equal(input, expected));
+  }
+
+  // The range overload adds the additional constraint that it must be an outputrange
+  // so skip this for the input iterators we test
+  if constexpr (!std::is_same_v<Iter, cpp17_input_iterator<int*>> &&
+                !std::is_same_v<Iter, cpp20_input_iterator<int*>>) { // (range) overload
+    auto in_begin = Iter(input.data());
+    auto in_end   = Sent(Iter(input.data() + input.size()));
+    auto range    = std::ranges::subrange(std::move(in_begin), std::move(in_end));
+
+    std::same_as<std::ranges::out_value_result<Iter, int>> decltype(auto) result =
+        std::ranges::iota(range, starting_value);
+    assert(result.out == in_end);
+    if constexpr (expected.size() > 0) {
+      assert(result.value == expected.back() + 1);
+    } else {
+      assert(result.value == starting_value);
+    }
+    assert(std::ranges::equal(input, expected));
+  }
+}
+
+template <class Iter, class Sent = sentinel_wrapper<Iter>>
+constexpr void test_results() {
+  // Empty
+  test_result<Iter, Sent, 0>({}, 0, {});
+  // 1-element sequence
+  test_result<Iter, Sent, 1>({1}, 0, {0});
+  // Longer sequence
+  test_result<Iter, Sent, 5>({1, 2, 3, 4, 5}, 0, {0, 1, 2, 3, 4});
+}
+
+void test_results() {
+  test_results<cpp17_input_iterator<int*>>();
+  test_results<cpp20_input_iterator<int*>>();
+  test_results<cpp17_output_iterator<int*>>();
+  test_results<cpp20_output_iterator<int*>>();
+  test_results<forward_iterator<int*>>();
+  test_results<bidirectional_iterator<int*>>();
+  test_results<random_access_iterator<int*>>();
+  test_results<contiguous_iterator<int*>>();
+  test_results<int*>();
----------------
philnik777 wrote:

```suggestion
  types::for_each(types::cpp20_input_iterator_list{}, []<class Iter> { test_results<Iter>(); });
  test_results<cpp17_output_iterator<int*>>();
  test_results<cpp20_output_iterator<int*>>();
```
You should also test with different sentinel types.

https://github.com/llvm/llvm-project/pull/68494