iana added inline comments.
================
Comment at: clang/lib/Headers/stddef.h:118-122
+#ifdef __cplusplus
+namespace std {
+typedef decltype(nullptr) nullptr_t;
+}
+using ::std::nullptr_t;
----------------
aaron.ballman wrote:
> iana wrote:
> > aaron.ballman wrote:
> > > iana wrote:
> > > > ldionne wrote:
> > > > > iana wrote:
> > > > > > aaron.ballman wrote:
> > > > > > > Related:
> > > > > > >
> > > > > > > https://github.com/llvm/llvm-project/issues/37564
> > > > > > > https://cplusplus.github.io/LWG/issue3484
> > > > > > >
> > > > > > > CC @ldionne
> > > > > > I don't _think_ this change actually changes the way nullptr_t gets
> > > > > > defined in C++, does it?
> > > > > I think we absolutely don't want to touch `std::nullptr_t` from this
> > > > > header. It's libc++'s responsibility to define that, and in fact we
> > > > > define it in `std::__1`, so this is even an ABI break (or I guess it
> > > > > would be a compiler error, not sure).
> > > > I'm really not touching it though. All I did is move it from
> > > > `__need_NULL` to `__need_nullptr_t`.
> > > >
> > > > The old behavior is that `std::nullptr_t` would only be touched if (no
> > > > `__need_` macros were set or if `__need_NULL` was set), and
> > > > (_MSC_EXTENSIONS and _NATIVE_NULLPTR_SUPPORTED are defined).
> > > >
> > > > The new behavior is that `std::nullptr_t` will only be touched if ((no
> > > > `__need_` macros are set) and (_MSC_EXTENSIONS and
> > > > _NATIVE_NULLPTR_SUPPORTED are defined)) or (the new `__need_nullptr_t`
> > > > macro is set)
> > > >
> > > > So the only change is that C++ code that previously set `__need_NULL`
> > > > will no longer get `std::nullptr_t`. @efriedma felt like that was a
> > > > fine change.
> > > Does libc++ provide the symbols for a freestanding compilation?
> > >
> > > I was pointing out those links specifically because the C++ standard
> > > currently says that stddef.h (the C standard library header) needs to
> > > provide a definition of `std::nullptr_t`, but that LWG thinks that's
> > > perhaps not the right way to do that and may be removing that requirement.
> > It is weird the standard puts that in stddef.h and not cstddef. I think
> > libc++ could provide that in their stddef.h anyway, but the intent in this
> > review is to not rock the boat and only do the minimal change discussed
> > above.
> Yeah, this discussion is to figure out whether we have an existing bug we
> need to address and if so, where to address it (libc++, clang, or the C++
> standard). I don't think your changes are exacerbating anything, more just
> that they've potentially pointed out something related.
👍
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D157757/new/
https://reviews.llvm.org/D157757
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