[PATCH] D144654: [Lex] Warn when defining or undefining any builtin macro

[John Brawn via Phabricator via cfe-commits]

john.brawn planned changes to this revision.
john.brawn added a comment.

The clang-tidy failures in pre-merge are because

- clang-tidy tests use the compile database from building llvm (though you have to manually copy it otherwise the tests silently pass without actually running the test, which is why I wasn't seeing this locally)
- this has -D_GNU_SOURCE because llvm/cmake/config-ix.cmake adds it to the defines
- clang predefines _GNU_SOURCE when compiling C++ (for certain targets)
- therefore we get the warning for a redefined builtin

I'm not sure yet what the best fix is here. gcc has the same behaviour of defining _GNU_SOURCE for C++, but does it by adding -D_GNU_SOURCE to the cc1 command line so it doesn't give a warning on redefine, but it doesn't look like copying this behaviour in clang would be easy. I'll think about this some more.


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https://reviews.llvm.org/D144654