[LLVMbugs] [Bug 20581] New: Declaring '+(instancetype) alloc __attribute__((unavailable(""))); ' forbids calling alloc on variables of Class type

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20581

            Bug ID: 20581
           Summary: Declaring '+(instancetype) alloc
                    __attribute__((unavailable("")));' forbids calling
                    alloc on variables of Class type
           Product: new-bugs
           Version: unspecified
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: rsanchez.saez at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

I have an Objective-C singleton class for which I declare these:

@interface MySingleton : NSObject

+ (instancetype) sharedInstance;
+ (instancetype) alloc __attribute__((unavailable("call sharedInstance
instead")));
- (instancetype) init __attribute__((unavailable("call sharedInstance
instead")));
+ (instancetype) new __attribute__((unavailable("call sharedInstance
instead")));

@end

My implementation is as follows:

@implementation MySingleton

+ (instancetype)sharedInstance
{                                                               
    static dispatch_once_t s_dispatchOnceToken;                 
    static id s_sharedInstance = nil;                           
    dispatch_once(&s_dispatchOnceToken, ^                       
    {                                                           
        s_sharedInstance = [[super alloc] initSharedInstance];  
    });                                                         
    return s_sharedInstance;                                    
}                                                               

- (instancetype)initSharedInstance                              
{                                                               
    return [super init];                                        
}                                                               

@end

All this works as expected.

However, I have a MySingleton instance method like this:

- (void)instanceMethod
{
         Class unrelatedClass = [self getClassWithType:classType]; //classType
is a NSString. This method never returns the MySingleton class
            id activity = [[unrelatedClass alloc] init];
}

which should compile fine, but the compiler wrongly says:

      'alloc' is unavailable: call sharedInstance instead

This issue is present in both CLANG versions included on Xcode 6 Beta 5 and on
5.1.1.

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