[PATCH] D106577: [clang] Define __STDC_ISO_10646__

Mon Jul 26 05:58:49 PDT 2021

aaron.ballman added a comment.

In D106577#2902091 <https://reviews.llvm.org/D106577#2902091>, @jyknight wrote:

> In D106577#2901654 <https://reviews.llvm.org/D106577#2901654>, @rsmith wrote:
>
>> I think this patch as it stands would cause problems with libc implementations that put their `#define` somewhere other than than `stdc-predef.h` (eg, older versions of glibc that put it in `features.h` or other standard libraries that put it in `yvals.h`) due to the macro redefinition with a conflicting expansion. Such implementations are non-conforming but certainly exist. Likewise it could break the build for the same reason if we start implicitly including `stdc-predef.h` at some point. So I think that blindly predefining this macro will prove problematic in at least some circumstances.
>
> I don't understand what problem you expect to see here. We already suppress -Wmacro-redefined [which this falls under] for system headers -- doesn't that suffice?

I'd like to hear more about this as well, FWIW. I think we get all the benefits you describe by defining the macro in the frontend and letting the macro suppression work if there's a conflicting definition from a system header.

Btw @cor3ntin, it looks like you've got some failing test cases that need to be looked at:

https://reviews.llvm.org/harbormaster/unit/view/898745/
https://reviews.llvm.org/harbormaster/unit/view/898763/

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