[clang] [Clang] restrict use of attribute names reserved by the C++ standard (PR #106036)

[Aaron Ballman via cfe-commits]

================
@@ -0,0 +1,33 @@
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,cxx11 -pedantic -std=c++11 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,cxx14 -pedantic -std=c++14 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,cxx17 -pedantic -std=c++17 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,cxx20 -pedantic -std=c++20 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,cxx23 -pedantic -std=c++23 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,cxx26 -pedantic -std=c++26 %s
+
+#define noreturn 1           // cxx11-warning {{keyword is hidden by macro definition}}
----------------
AaronBallman wrote:

Please also add test cases for `#undef` of the name when it's not currently defined as a macro, as that's also undefined behavior. (@ldionne @jwakely any interest in an LWG issue over this? It's harmless to do `#undef noreturn` or whatever because these identifiers aren't macros to begin with; and if they were, the user hit the UB already.)

https://github.com/llvm/llvm-project/pull/106036