NSError** without a nullability type shows as a warning which can't be suppressed

Originator:stephen.groom
Number:rdar://21766176 Date Originated:10-Jul-2015 04:05 PM
Status:Behaves correctly Resolved:15-Jul-2015 03:42 PM
Product:Developer Tools Product Version:Xcode 7.0 beta (7A121l)
Classification:Other Bug Reproducible:Always
 
When defining a method with nullability specifiers which takes a NSError** as a parameter, it shows a compiler warning stating that “Pointer is missing a nullability type specifier (__nonnull or __nullable)”.  As far as I can tell there is no way to annotate it with such a declaration.

It is my understanding based on https://developer.apple.com/swift/blog/?id=25 - “The particular type NSError ** is so often used to return errors via method parameters that it is always assumed to be a nullable pointer to a nullable NSError reference.” that this should both pointers should be assumed to be nullable.

Example:

- (void)exampleMethod:(nonnull id)aParameter error:(NSError **)error;
//Pointer is missing a nullability type specifier (__nonnull or __nullable)

Change this to:

- (void)exampleMethod:(nonnull id)aParameter error:(nullable NSError **)error
//Pointer is missing a nullability type specifier (__nonnull or __nullable)
//Nullability keyword 'nullable' cannot be applied to multi-level pointer type 'NSError *__autoreleasing *' (fix it?)

Tapping fix it generates

- (void)exampleMethod:(nonnull id)aParameter error:(__nullable NSError **)error; 
//Pointer is missing a nullability type specifier (__nonnull or __nullable)

It should be possible to annotate both pointers in a double pointer.
The NSError** type specifically could be made to be assumed nullable

Comments

Apple Developer Relations

Engineering has determined that this issue behaves as intended based on the following information:

The compiler is behaving correctly. The correct spelling for this case is

NSError * __nullable * __nullable

Both “__nullable”s will be inferred when the code is wrapped in an audit region with NS_ASSUME_NONNULL_BEGIN/NS_ASSUME_NONNULL_END.

By stephen.groom at July 16, 2015, 4:17 p.m. (reply...)

Breaks NSError transformation from Swift?

I can't get a 2 arity Objective-C method with an annotated last argument (NSError * __nullable * __nullable) to be callable from Swift as try Foo.bar("first arg").

I get the error:

Cannot convert value of type 'String' to expected argument type '(String, error: NSErrorPointer)' (aka '(String, error: AutoreleasingUnsafeMutablePointer<Optional<NSError>>)')

Do nullability annotations turn off the automatic do..try..catch conversion?

EDIT: My problem turned out to be the setting of the return type of my class method to nonnull instead of nullable

By abruce at Jan. 8, 2016, 11:10 a.m. (reply...)

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