[libcxx-commits] [libcxx] [libc++] Workaround clang bug in __has_unique_object_representations (PR #95314)

[Louis Dionne via libcxx-commits]

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@@ -22,7 +23,12 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS has_unique_object_representations
-    : public integral_constant<bool, __has_unique_object_representations(_Tp)> {};
+    // TODO: We work around a Clang bug in __has_unique_object_representations by instantiating the
+    //       builtin on the non-array type first and discarding that. This is issue #95311.
+    //       This workaround can be removed once the bug has been fixed in all supported Clangs.
+    : public integral_constant<bool,
+                               ((void)__has_unique_object_representations(remove_all_extents_t<_Tp>),
+                                __has_unique_object_representations(_Tp))> {};
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ldionne wrote:

> Can't we just do __has_unique_object_representations(remove_all_extents_t<_Tp>) instead of the operator, weirdness?

We could, but my idea here was to add the workaround in a way that it could be removed by a mere deletion of code in the future. I can reword the comment and change that.

https://github.com/llvm/llvm-project/pull/95314