[4.2] [Type checker] Warn about overrides of NSObject.hashValue. #18411
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NSObject.hashValue is provided to satisfy the hashValue constraint of the Hashable protocol. However, it is not the correct customization point for interoperating with Objective-C, because Objective-C code will call through the -hash method. Warn about overrides of NSObject.hashValue; users should override NSObject.hash instead. Fixes rdar://problem/42780635. (cherry picked from commit cc4c992)
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Explanation:
NSObject.hashValueis provided to satisfy thehashValueconstraint ofthe
Hashableprotocol. However, it is not the correct customizationpoint for interoperating with Objective-C, because Objective-C code
will call through the
-hashmethod. Warn about overrides ofNSObject.hashValue; users should overrideNSObject.hashinstead. This is meant asstaging in Swift 4.2, so that a future Swift release can make
NSObject.hashValuepublicrather thanopen.Scope: Warns about code that is overriding an API that is not meant to be overridden. Overriding
this method can cause strange runtime behavior when bridging, so we don't expect that it's too common.
Risk: Very low; it's an isolated new warning.
Testing: Compiler regression tests, including new tests.
Reviewer: @rudkx
SR / Radar: rdar://problem/42780635