llvm-project/clang-tools-extra/test/clang-tidy/checkers/objc-missing-hash.m

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[clang-tidy] Add check for classes missing -hash ⚠️ Summary: Apple documentation states that: "If two objects are equal, they must have the same hash value. This last point is particularly important if you define isEqual: in a subclass and intend to put instances of that subclass into a collection. Make sure you also define hash in your subclass." https://developer.apple.com/documentation/objectivec/1418956-nsobject/1418795-isequal?language=objc In many or all versions of libobjc, -[NSObject isEqual:] is a pointer equality check and -[NSObject hash] returns the messaged object's pointer. A relatively common form of developer error is for a developer to override -isEqual: in a subclass without overriding -hash to ensure that hashes are equal for objects that are equal. It is assumed that an override of -isEqual: is a strong signal for changing the object's equality operator to something other than pointer equality which implies that a missing override of -hash could result in distinct objects being equal but having distinct hashes because they are independent instances. This added check flags classes that override -isEqual: but inherit NSObject's implementation of -hash to warn of the potential for unexpected behavior. The proper implementation of -hash is the responsibility of the developer and the check will only verify that the developer made an effort to properly implement -hash. Developers can set up unit tests to verify that their implementation of -hash is appropriate. Test Notes: Ran check-clang-tools. Reviewers: aaron.ballman, benhamilton Reviewed By: aaron.ballman Subscribers: Eugene.Zelenko, mgorny, xazax.hun, cfe-commits Tags: #clang Differential Revision: https://reviews.llvm.org/D67737 llvm-svn: 372445
2019-09-21 09:22:22 +08:00
// RUN: %check_clang_tidy %s objc-missing-hash %t
typedef _Bool BOOL;
#define YES 1
#define NO 0
typedef unsigned int NSUInteger;
typedef void *id;
@interface NSObject
- (NSUInteger)hash;
- (BOOL)isEqual:(id)object;
@end
@interface MissingHash : NSObject
@end
@implementation MissingHash
// CHECK-MESSAGES: :[[@LINE-1]]:17: warning: 'MissingHash' implements -isEqual: without implementing -hash [objc-missing-hash]
- (BOOL)isEqual:(id)object {
return YES;
}
@end
@interface HasHash : NSObject
@end
@implementation HasHash
- (NSUInteger)hash {
return 0;
}
- (BOOL)isEqual:(id)object {
return YES;
}
@end
@interface NSArray : NSObject
@end
@interface MayHaveInheritedHash : NSArray
@end
@implementation MayHaveInheritedHash
- (BOOL)isEqual:(id)object {
return YES;
}
@end
@interface AnotherRootClass
@end
@interface NotDerivedFromNSObject : AnotherRootClass
@end
@implementation NotDerivedFromNSObject
- (BOOL)isEqual:(id)object {
return NO;
}
@end