Open Radar

 
Summary:

In particular cases, selector validity checking isn't working as expected – warning about unimplemented methods.

Specifically, when defining some protocol with required and optional methods:

– required methods which are not implemented by the class are handled by a non-conforming warning
– non-existing methods are handled by `undeclared selector` warning
– an implemented optional method is okay

BUT

– unimplemented optional methods throw no warning at all – they are hypothetically declared (by the protocol), but not actually implemented (as these don't need to be because of optionality), but once one attempts to reference using a @selector(), no warning (f.e. `unimplemented` warning) is given. Calling such selector via `-canPerformSelector:`/`-performSelector` may prevent the issue (but only silently), calling the `-selector` directly throws an error, but using it when binding f.e. via `-addTarget:action:` using a @selector() remains silent, eventually leading to `unrecognized selector sent to instance` runtime error.

See the attached files for details.

Strict selector checking is set ON.

Expected Results:
Better selector checking in optional case.

Actual Results:
Uncaught cases which may result in `unrecognized selector sent to instance` crashes.

Version/Build:
Xcode 10.2

Configuration:
macOS Mojave 10.14.5 beta @ MacBook Air 2012
macOS Mojave 10.14.4 @ Mac mini 2012