[libcxx-commits] [libcxx] [libc++][type_traits] Implements "A type trait to detect reference binding to temporary" (PR #128649)

[Hristo Hristov via libcxx-commits]

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@@ -1215,6 +1215,21 @@ typedef __char32_t char32_t;
 #    define _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER 0
 #  endif
 
+// TODO(LLVM 22): Remove this macro once LLVM19 support ends.
+#  if __has_builtin(__reference_constructs_from_temporary) ||                                                          \
+      (defined(_LIBCPP_CLANG_VER) && (_LIBCPP_CLANG_VER >= 1900))
+#    define _LIBCPP_HAS_REFERENCE_CONSTRUCTS_FROM_TEMPORARY 1
+#  else
+#    define _LIBCPP_HAS_REFERENCE_CONSTRUCTS_FROM_TEMPORARY 0
+#  endif
+
+// TODO(LLVM 22): Remove this macro once LLVM19 support ends.
+#  if __has_builtin(__reference_converts_from_temporary) || (defined(_LIBCPP_CLANG_VER) && (_LIBCPP_CLANG_VER >= 1901))
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Zingam wrote:

Android Clang reports for example as Clang 19.0. It gets branched off `main` in between official LLVM releases with cherry-picked commits, therefore Clang 19.0 could have some features of Clang 19.1, which were committed to `main` before it got branched off. In our case:
- Android Clang 19.0 is missing `__reference_converts_from_temporary`
- Android Clang 20.0 is missing `__has_builtin(__reference_{constructs|converts|_from_temporary)` fixes

I updated the macro to make this clearer. I hope that this is no longer confusing.


https://github.com/llvm/llvm-project/pull/128649