As we all know, Apple decided in its wisdom to remove the OS X 10.10 SDK from Xcode as of version 7 (this happened in one of the betas). At the time, I filed a bug (rdar://22378220), to which I got the response:
Some considerations:
1) setting the deployment target lets you target older OSes
2) for iOS SDK, Xcode only ever supported one SDK
3) Swift offers a great new availability checking syntax
On observing that the deployment target setting is all well and good, but that I was getting errors about libkmod, the bug was closed with the comment:
We're not pulling back the 10.10 SDK into Xcode 7. Yes, there will be some adjustment for developers, but we think this is the right path forward.
We're addressing the libkmod issue with our internal Bug ID 22720041.
We are now closing this bug report.
Well, we’re now up to Xcode 7.2 and there’s still no fix for the libkmod problem. Moreover, when I filed another bug report about the fact that KEXTs built against the 10.11 SDK don’t load on older systems, even if you set the deployment target setting appropriately (rdar://23690193), I was told:
We don't expect code compiled with new SDK run on older system. Please contact the Apple Developer Program Support Team for help with downloading the older SDK. You can contact them directly via web form (http://developer.apple.com/contact/submit.php) or via phone (http://developer.apple.com/contact/phone.php).
We are now closing this bug report.
Which begs the question… how is one supposed to build KEXTs that work on 10.10 using a machine running 10.11 and Xcode 7? And if the answer genuinely is to use the 10.10 SDK, shoehorned into Xcode 7 somehow, then why not just ship Xcode 7 with the 10.10 SDK in the first place? Apple may be able to decide to drop support for all but the most recent version of OS X on every release, but most of us third-party developers simply don’t have that option.