Mac SDK: using latest SDK but ensuring backwards compatibility with earlier deployment target

Question

As always when Apple updates OS X, the latest XCode 4.4 dumps the older (10.6) SDK and I find myself needing to use the 10.7 SDK (or 10.8 I suppose) and setting my deploymen

Answer 1

I'm generally copy SDK from older versions to the newer one so that compiler will blain me if i use something not supported.

Also you can simply look at Quick Help when calling some methods that you are not sure about, like in screenshot you can see that launchApplicationAtURL method is only available from 10.6

Answer 2

Since Xcode 9 there is a build setting doing exactly this, turning on the warning -Wunguarded-availability and/or -Wunguarded-availability-new.

The former warns when an API newer than the deployment target is used. The latter only warns when an API introduced newer than macOS 10.13 or iOS 11 is used in a similar manner.

For an existing project, the former is off by default, and the latter is on by default.

This setting is called “unguarded availability” within Xcode’s build settings pane, and you can choose one of Yes, Yes for all versions, or No from the GUI.

For more details, see the WWDC17 session 411, “What's New in LLVM”, https://developer.apple.com/videos/play/wwdc2017/411/ .

Answer 3

i also assumed that the compiler will warn me about "too new" API usage for the deployment target OS version. but it turned out that the compiler doesn't warn you about it by default. one of the reasons might be you could still use the new API by checking the availability during runtime with "respondsToSelector:", for example, on a newer OS version even when the deployment target version was older. you would need to add the compiler option -Wpartial-availability which is available on Xcode 7.3+ (to be confirmed) in order to get the "warning: 'something' is partial: introduced in macOS 10.x" warning message.

on macOS 10.12.3 with Xcode 8.2.1:

$ cat foo.m
#include <Foundation/Foundation.h>

BOOL foo()
{
    return [@"foo" containsString:@"bar"];
}

$ cc -mmacosx-version-min=10.9 -Wpartial-availability foo.m -c -o foo.o
foo.m:5:20: warning: 'containsString:' is partial: introduced in macOS 10.10 [-Wpartial-availability]
    return [@"foo" containsString:@"bar"];
                   ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk/System/Library/Frameworks/Foundation.framework/Headers/NSString.h:132:1: note: 
      'containsString:' has been explicitly marked partial here
- (BOOL)containsString:(NSString *)str NS_AVAILABLE(10_10, 8_0);
^
foo.m:5:20: note: explicitly redeclare 'containsString:' to silence this warning
    return [@"foo" containsString:@"bar"];
                   ^
1 warning generated.

see also: Is there a way for XCode to warn about new API calls?

Answer 4

Surely, by now there's a way to either:

• making sure you don't introduce API calls that are not yet available in your deployment target even if though they are defined in the SDK

• detecting such calls during build or static analysis time

No there is not. Yes, you should open a radar (bugreport.apple.com) against it. If you like, you can dupe mine: rdar://11985733

Yes, the only viable solution, despite Apple's recommendation, is to copy the old SDKs and link against them.

I spent quite some time talking with the Xcode team about exactly this issue at WWDC 2012. They agreed that it's broken. There is not currently a plan to fix it. Escalating radar's is how we influence Apple on these things.

Answer 5

I check my code by hacking around Availability.h to get the compiler to flag weak-linked symbols as warnings/errors. In my current (Xcode 5/llvm) incarnation, I'm using the code below. It warns whenever I use a symbol introduced in iOS 6.0 or later. I think it's fairly self-explanatory. The macros seem to need updating at each and every SDK update, so tread carefully. Oh, and you loose deprecation warnings too, so I only use this once in a while to double-check my conditional code.

#undef __NSi_6_0
#define __NSi_6_0 deprecated=1.0
#undef __NSi_6_1
#define __NSi_6_1 deprecated=1.0
#undef __NSi_7_0
#define __NSi_7_0 deprecated=1.0

#undef __NSd_6_0
#define __NSd_6_0
#undef __NSd_6_1
#define __NSd_6_1
#undef __NSd_7_0
#define  __NSd_7_0

See also http://iphone.m20.nl/wp/2013/10/xcode-5-and-flagging-weak-linked-unavailable-symbols-from-a-newer-sdk/

Answer 6

I've had this annoying problem on iOS too. It's actually even more annoying on iOS as the user has to sync their device with iTunes and enable crash report sending before the crash report gets sent unlike Mac OS X where you don't need to do all that. Recently, I managed to add a compile-time check for checking APIs against older versions of the SDK. I'll first explain how I did it for iOS first and then try and help you to adapt this technique for Mac OS X. I don't code much for Mac atm so I can only really guide you in the right direction from my experience with iOS but I'll test my suggestions later today once I get back from work and give a definite answer.

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So here's what I did for iOS:

I first had to get the older Simulator SDK I wanted to get. I could easily get this by downloading older Xcode 3 (not 4) versions which included the SDK needed.

I next had to install the SDK. This wasn't too hard, so I won't explain much here. But the SDKs are stored in the Packages folder. This folder is clearly visible in earlier Xcode 3 versions but is hidden in later versions. You can easily open it anyway through Terminal. Also, after the change in Xcode 4.3 where the Developer folder moved to within Xcode.app, so I had to install the SDK into a tmp folder and move the SDK into Xcode.app yourself. I would then need to restart Xcode if I had it open.

After that, I duplicated my debug configuration in your project and named it, in my case, something like iOS 4.3 API Check or something like that - doesn't really matter. Then I changed the Base SDK of this new configuration to the old SDK which I installed. The SDK I installed was not listed though so I had to select other and enter, again in my case, iphonesimulator4.3.

Finally, when I needed to check against older versions of the SDK, I changed the configuration for the Run <appname>.app in my project scheme to my iOS 4.3 API Check configuration. And there we go, a compile-time check against iOS 4.3.

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As for Mac OS X, I'm sure you can achieve the same goal with this same method. There isn't Simulators for the Mac SDK so I think the regular SDK will work for this. As for getting the older SDK, if you have Xcode 4.2 still installed (after Xcode 4.3 changed it so the Developer folder is within Xcode.app) then you should find the 10.6 SDK there. If you don't, I'd imagine that Apple has a similar thing to iOS where the SDK downloads are available in the Dev Center or somewhere on the internet...

As for setting the Base SDK, if it's not listed then I think the name is MacOSX10.6 or whatever version you are after.

Everything else should be the same, but as mentioned earlier, I'll test this method later today and edit my answer to give a more definite answer but I would imagine this method would work for the Mac SDK.