Use new-style _Nullable keywords in obj-c header

[lilyball]

Use the keywords _Nullable, _Nonnull, and _Null_unspecified
instead of the older compatibility forms __nullable, __nonnull, and
__null_unspecified.

Part of rdar://problem/23614638

[jeremyhu]

This would reduce compatibility with older toolchains.

[lattner]

Which ones are relevant to working with swift 2.2?

-Chris

On Dec 6, 2015, at 8:27 AM, Jeremy Huddleston Sequoia [email protected] wrote:

This would reduce compatibility with older toolchains.

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[jeremyhu]

I'm just wondering if we'd have bootstrapping problems by doing that.

[lattner]

I don't think that is a concern. No released public clang supported the __nullable forms, and Swift includes its own drop of clang with it, that does support the new forms. If there was a compatibility issue, a few -D_Nullable=__nullable flags seem like they could be used to work around it.

That said, I'd like @jrose-apple to review this when it isn't the weekend :-)

[jeremyhu]

Ok, then that sounds good to me. I haven't looked at the build system yet, but as long as it uses the built clang instead of the bootstrap compiler, that should be fine. (see https://llvm.org/bugs/show_bug.cgi?id=25753 for why I bring this up).

[DougGregor]

Xcode 6.3 used the double-underscored forms, and we changed the syntax in Xcode 7. That's why I'd been holding off on making this change.

[DougGregor]

That said, this only affects code using the generated (Objective-)C headers, and the double-underscored keywords will cause problems on Linux. Merging.