No way to weakly reference string constants introduced after OS X major release

Number:rdar://12772011 Date Originated:
Status:Open Resolved:
Product:OS X SDK Product Version:
Classification: Reproducible:Always
The Illustrious Greg Parker asked that I file the following bug:

AppKit introduced a few string constants in 10.7.3 that we need to weakly reference. Unfortunately, our minimum deployment target is also 10.7, so we don't get these automatically weak-linked for us automatically by Xcode:

APPKIT_EXTERN NSString * const NSWindowDidChangeBackingPropertiesNotification NS_AVAILABLE_MAC(10_7); // added in 10.7.3; userInfo keys: NSBackingPropertyOldScaleFactorKey, NSBackingPropertyOldColorSpaceKey

APPKIT_EXTERN NSString * const NSBackingPropertyOldScaleFactorKey NS_AVAILABLE_MAC(10_7); // added in 10.7.3; an NSNumber
APPKIT_EXTERN NSString * const NSBackingPropertyOldColorSpaceKey NS_AVAILABLE_MAC(10_7);  // added in 10.7.3; an NSColorSpace

when running on 10.7.2 and below we hit the following crash:

OS Version:      Mac OS X 10.7.2 (11C74)

Exception Codes: 0x0000000000000002, 0x0000000000000000

Application Specific Information:
dyld: launch, loading dependent libraries

There is apparently no way to work around this problem other than modifying the system headers, which is a mega bummer.

It would be great if these headers were corrected to not require this.



One suggested workaround:

You can manually force weak-import of those symbols by re-declaring them:

#import <AppKit/AppKit.h> __attribute__((weak_import)) extern NSString * const NSBackingPropertyOldScaleFactorKey;

Don't forget to remove the redeclaration when your deployment target improves in the future.

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