[libcxx-commits] [libcxx] [libc++][variant] Applied `[[nodiscard]]` (PR #172058)

[Nico Weber via libcxx-commits]

================
@@ -0,0 +1,74 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++17
+
+// Check that functions are marked [[nodiscard]]
+
+#include <variant>
+
+#include <test_macros.h>
+
+void test() {
+  {
+    std::bad_variant_access ex;
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    ex.what();
+  }
+
+  {
+    struct First {};
+    struct Second {};
+
+    std::variant<First, Second> v;
+    const std::variant<First, Second> cv;
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    cv.valueless_by_exception();
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    cv.index();
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::holds_alternative<First>(v);
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::get<0>(v);
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::get<0>(cv);
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::get<0>(std::move(v));
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::get<0>(std::move(cv));
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::get<First>(v);
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::get<First>(cv);
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::get<First>(std::move(v));
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::get<First>(std::move(cv));
+
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::get_if<0>(&v);
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::get_if<0>(&cv);
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::get_if<First>(&v);
+    // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+    std::get_if<First>(&cv);
+  }
+
+  {
+    std::hash< std::variant<int, float>> hash;
----------------
nico wrote:

nit: stray space

https://github.com/llvm/llvm-project/pull/172058