[libcxx-commits] [libcxx] [libc++] Make sure that __desugars_to isn't tripped up by reference_wrapper and cv-refs (PR #132092)

[Peng Liu via libcxx-commits]

================
@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <functional>
+
+// reference_wrapper
+
+// Ensure that std::reference_wrapper does not inhibit optimizations based on the
+// std::__desugars_to internal helper.
+
+#include <functional>
+
+static_assert(std::__desugars_to_v<std::__equal_tag, std::equal_to<void>, int, int>,
+              "something is wrong with the test");
+
+// make sure we pass through reference_wrapper
+static_assert(std::__desugars_to_v<std::__equal_tag, std::reference_wrapper<std::equal_to<void> >, int, int>, "");
+static_assert(std::__desugars_to_v<std::__equal_tag, std::reference_wrapper<std::equal_to<void> const>, int, int>, "");
----------------
winner245 wrote:

Thank you for the clarification! This makes more sense to me now. If it works for an arbitrary tag and operation (`Tag/Operation`), it should work for more specific tags and operations such as `__equal_tag/std::__equal`.

https://github.com/llvm/llvm-project/pull/132092