[libcxx-commits] [libcxx] [llvm] [libc++] Implement P1885R12: `<text_encoding>` (PR #141312)

[A. Jiang via libcxx-commits]

================
@@ -0,0 +1,67 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++26
+
+// UNSUPPORTED: no-localization
+
+// <text_encoding>
+
+#include <functional>
+#include <text_encoding>
+
+#include "test_macros.h"
+
+int main(int, char**) {
+  std::text_encoding te = std::text_encoding();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  te.mib();
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  te.name();
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  te.aliases();
+
+#ifndef TEST_HAS_NO_LOCALIZATION
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  te.environment();
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  te.environment_is<std::text_encoding::UTF8>();
+#endif
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  te.aliases();
+
+  auto alias = te.aliases();
+
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  alias.begin();
+  // expected-warning at +1 {{ignoring return value of function declared with 'nodiscard' attribute}}
+  alias.end();
+
+  auto it = alias.begin();
+
+  // 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}}
+  it + 1;
+  // 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}}
+  std::hash<std::text_encoding>()(std::text_encoding::id::ASCII);
+
+  // Clang does not emit a nodiscard warning for consteval functions with [[nodiscard]]: See issue #141536
+  // expected-warning at +1 {{expression result unused}}
+  std::text_encoding::literal();
----------------
frederick-vs-ja wrote:

I think we can move this line to a separated `consteval` function and verify the warning message in the usual way. I used such technique in #200760.

https://github.com/llvm/llvm-project/pull/141312