[PATCH] D27827: [ObjC] CodeGen support for @available on macOS

[Erik Pilkington via Phabricator via cfe-commits]

erik.pilkington added a comment.

I seem to remember that mapping from kernel versions to marketing versions was tossed around as a potential alternative to Gestalt. I think that the problem was Apple sometimes introduces (or reserves the right to introduce) new SDKs in a patch release (ie, Z in X.Y.Z), which wouldn't necessary imply a new kernel version, and would still need to be queried by @available. This makes it impossible to use kernel version in the general case (Or at least I think, it would be nice if someone internal to Apple could confirm this?). This rules out using `sysctl()` and the like.

AFAIK this just leaves `Gestalt()` and Objective-C's `NSProcessInfo`, the latter would mean pulling in the Objective-C runtime, which would be unfortunate for C users (using the `__builtin_available` spelling). I don't think `Gestalt()` is in any danger of actually being removed, so we might as well use it. The only alternative I know of to those would be manually parsing the `SystemVersion.plist` XML file, but I think that might cause problems with sandboxed processes (right?). Any thoughts here would be much appreciated, `Gestalt()` is by no means a perfect solution.

Compiler-rt does seem like a good place it put this, should I move the runtime code there instead?

Thanks for taking a look!
Erik


https://reviews.llvm.org/D27827