[libcxx-commits] [libcxx] [libc++][tuple] Applied `[[nodiscard]]` (PR #172008)

[A. Jiang via libcxx-commits]

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@@ -0,0 +1,64 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++11
+
+// Check that functions are marked [[nodiscard]]
+
+#include <tuple>
+
+#include "test_macros.h"
+
+void test() {
+  struct First {};
+  struct Second {};
+  struct Third {};
+
+  std::tuple<First, Second, Third> t;
+  const std::tuple<First, Second, Third> ct;
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::get<0>(t);
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::get<0>(ct);
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::get<0>(std::move(t));
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::get<0>(std::move(t));
+#if TEST_STD_VER >= 14
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::get<Third>(t);
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::get<Third>(ct);
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::get<Third>(std::move(t));
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::get<Third>(std::move(t));
+#endif
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::tie(ct);
+
+  First e1;
+  Second e2;
+  Third e3;
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::make_tuple(e1, e2, e3);
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::forward_as_tuple(First{}, Second{}, Third{});
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  std::tuple_cat(std::tuple<First>{}, std::tuple<Second, Third>{});
----------------
frederick-vs-ja wrote:

Let's verify `std::tuple_cat()` (nullary call) together.

https://github.com/llvm/llvm-project/pull/172008