john.brawn added inline comments.
================
Comment at: clang/test/Preprocessor/macro-reserved.cpp:15
-#undef __cplusplus
+#undef __cplusplus // expected-warning {{undefining builtin macro}}
#define __cplusplus
----------------
aaron.ballman wrote:
> Why do we diagnose the undef but not the define?
After the undef the builtin macro definition no longer exists, so when
Preprocessor::HandleDefineDirective checks for an existing definition to see if
it's a builtin it doesn't find one.
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D144654/new/
https://reviews.llvm.org/D144654
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