[libcxx-commits] [libcxx] WIP [libc++][ranges] Applied [[nodiscard]] to `transform_view` (PR #204014)

[Hristo Hristov via libcxx-commits]

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@@ -0,0 +1,138 @@
+//===----------------------------------------------------------------------===//
+//
+// 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: std-at-least-c++20
+
+// Test the libc++ extension that std::ranges::transform_view and std::views::transform are marked as [[nodiscard]].
+
+#include <ranges>
+#include <functional>
+
+struct TestView : std::ranges::view_interface<TestView> {
+  int* begin();
+  char* begin() const;
+  const int* end();
+  const char* end() const;
+};
+
+void test() {
+  int range[] = {1, 2, 3};
+  auto f      = [](int i) { return i; };
+
+  auto identity_view     = TestView{} | std::views::transform(std::identity{});
+  auto transformed_range = range | std::views::transform(f);
+
+  const auto const_identity_view     = TestView{} | std::views::transform(std::identity{});
+  const auto const_transformed_range = range | std::views::transform(f);
+
+  auto it             = identity_view.begin();
+  const auto const_it = identity_view.begin();
+
+  auto transformed_range_sent             = transformed_range.end();
+  auto identity_view_sent                 = identity_view.end();
+  const auto const_transformed_range_sent = transformed_range.end();
+  const auto const_identity_view_sent     = identity_view.end();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  const_it.base();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  it.base();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::views::transform(identity_view, fn).base();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  transformed_range.begin();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  const_transformed_range.begin();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  transformed_range.end();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  identity_view.end();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  const_transformed_range.end();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  const_identity_view.end();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::views::transform(f);
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::views::transform(range, f);
+
+
+  const_it[0];
+
+  {
+    // ===== Non-const views =====
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    it + 1;
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    1 + it;
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    it - 1;
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    it - it;
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    *it;
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    it[0];
+  }
+
+  {
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    const_it + 1;
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    1 + const_it;
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    const_it - 1;
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    const_it - const_it;
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    *const_it;
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    const_it[0];
+  }
+
+  {
+    // ===== Non-const sentinels =====
----------------
Zingam wrote:

Try not to "resolve" comments if you haven't done so. If you think that you don't want to do something, explain why and then it is best to leave to the author to press the "resolve" button. 
This is to avoid forgetting to address something.

https://github.com/llvm/llvm-project/pull/204014