ian-twilightcoder wrote: > > > FWIW, I did verify that it's very unlikely the changes in this PR will > > > break existing code: > > > https://sourcegraph.com/search?q=context:global+__need_unreachable+-file:.*clang.*&patternType=keyword&sm=0, > > > so that's a good thing. > > > > I do wonder if we could have the broader builtin headers discussion > > > > independent of this patch? Is everyone happy with this patch? We can > > > > keep talking about the builtin headers in here independent of merging > > > > right? > > > > > > > > > I guess I don't see these as independent topics; if we decide that C++ > > > mode should not have observable differences in C headers, then the > > > changes here are incorrect. I think we should have this discussion in a > > > broader context (like Discourse) before moving forward with these changes. > > > Also, I'd still like an explanation for [this > > > question](https://github.com/llvm/llvm-project/pull/86748#issuecomment-2023145043): > > > > I don't understand why this is making into C++ builds at all: > > > > > > > > > because it may turn out we don't need these changes in the first place > > > because the issue is elsewhere. > > > > > > Right now I just noticed that in a C++ test I was writing that stddef.h > > alone doesn't give me unreachable, but __needs_unreachable does. And that's > > probably wrong because unreachable belongs to in C++ and _not_ stddef.h. > > The C++ standard has some frustrating divergence with the C standard as to > > what the c stdlib headers declare... > > I don't yet agree that it's wrong -- you define the macro saying you want > `unreachable` from `stddef.h`, so you get `unreachable` from `stddef.h`. > Morally, it's very similar to: > > ``` > #define unreachable "I am doing something which causes myself pain" > #include <utility> > ```
I was thinking that a lot of the low level Apple SDK C headers use the `__need_` macros to add things they use, and that shouldn't mess up C++ clients. Although I guess if they actually use `unreachable` then they need to have a `__cplusplus` in there to include \<utility> instead of just not getting `unreachable` at all. So, I guess there's a problem either way. However, I still don't really like the idea that someone can make a mistake in the SDK and break the C++ declaration of `unreachable`. I also don't like that `unreachable` is currently inconsistent with `nullptr_t`, which we almost never declare in C++ mode either, for similar reasons. https://github.com/llvm/llvm-project/pull/86748 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
