[libcxx-commits] [libcxx] [libc++] Allow a disengaged `optional` to be `constexpr` since C++20 (PR #192888)

[A. Jiang via libcxx-commits]

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@@ -402,6 +402,12 @@ struct __optional_destruct_base<_Tp, false> {
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void reset() noexcept {
     if (__engaged_) {
       __val_.~value_type();
+      // TODO: Remove the workaround when supported compilers have CWG2424 implemented.
+#    if _LIBCPP_STD_VER >= 20
+      if consteval {
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frederick-vs-ja wrote:

I think we should just use the extension as it's available in C++20 mode. See https://libcxx.llvm.org/CodingGuidelines.html#use-extensions-if-they-simplify-the-code.

I personally don't want to expose the workaround to C++17 mode or non-constant evaluation. If less code branches is desired, we may switch to use assignment unconditionally.

https://github.com/llvm/llvm-project/pull/192888