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

[via libcxx-commits]

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@@ -0,0 +1,242 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// Test the libc++ extension that std::views::transform is 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);
+
+  {
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    identity_view.begin();
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    const_identity_view.begin();
+
+    // 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}}
+    identity_view.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}}
+    transformed_range.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}}
+    std::views::transform(f);
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::views::transform(range, f);
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    range | std::views::transform(f);
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::views::all | std::views::transform(f);
----------------
lknknm wrote:

These were old tests present in `range.transform/adaptor.nodiscard.verify.cpp` which I just ported to the new renamed file. Should I delete them/port them back?

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