dexonsmith added inline comments.
================ Comment at: clang/lib/Headers/__stddef_null.h:14 + * __need_NULL and rely on stddef.h to redefine NULL to the correct value again. + * Modules don't support redefining macros like that, but support that pattern + * in the non-modules case. ---------------- iana wrote: > I couldn't come up with anything clever to support this in modules. If I get > rid of the guard, `NULL` still doesn't get redefined in modules. If I move > the `undef` to stddef.h then `NULL` gets undefined, but not redefined. So I > think precompiled modules must inherently have `#pragma once` semantics. If > we really had to, we could move this back into stddef.h and let it be > textual, but it's distasteful that `NULL` gets defined in every single module > that includes stddef.h and has to be merged later. Modules are, in a way, stronger than `#pragma once`. Each module is a separate translation unit. If there's a module around `__stddef_null.h`, then it will only be compiled once, and any definitions imported from there. Other importing TUs get those definitions per the context the module was compiled in (they don't re-compile the code in their own context...). It seems like a regression for `NULL` to degrade from `((void *)0)` to `0` since it loses type safety, which is rather rare and precious in C code. Maybe this header should remain textual when deployed to platforms that rely on this dance. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D159064/new/ https://reviews.llvm.org/D159064 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
