Rule Request: check for method existence in #selector

[sammy-SC]

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

Rule Request

If this is a new rule request, please ignore all sections below this one, format
this issue's title as Rule Request: [Rule Name] and describe:

Describe:
#selector() doesn't warn you if you reference method from different class. In class A you could be adding target to button button.addTarget(self, action: #selector(B.didTap), for: .touchUpInside) and as long as B.didTap is accessible this code compiles but on tap of the button crashes the app. I would keep this rule simple and it would only check for existence of method in case target is being added to self.

1. Why should this rule be added? Share links to existing discussion about what
   the community thinks about this.

I don't have link to an existing discussion.

2. Provide several examples of what would and wouldn't trigger violations.

What would trigger:

final class A: UIViewController {
  override func viewDidLoad() {
    super.viewDidLoad()
    let button = UIButton()
    button.addTarget(self,
                                   action: #selector(B.didTap),
                                   for: .touchUpInside)
  }
}

what wouldn't trigger:

final class A: UIViewController {
  override func viewDidLoad() {
    super.viewDidLoad()
    let button = UIButton()
    button.addTarget(self,
                                   action: #selector(A.didTap),
                                   for: .touchUpInside)
  }
}

3. Should the rule be configurable, if so what parameters should be configurable?

This rule should not be configurable.

4. Should the rule be opt-in or enabled by default? Why?
   See README.md for guidelines on when to mark a
   rule as opt-in.

I believe this rule should be enabled by default.

[marcelofabri]

Should this only work with UIControl APIs? What about other classes that use target-action (e.g. gesture recognizers)?

[sammy-SC]

@marcelofabri you are right, it should work with any class that uses target-action.

However I realised one problem with implementation, what if the method in action is in subclass? That way the method is invisible to SwiftLint but won't crash the application. Is there a way to work around this?

[marcelofabri]

@sammy-SC I don’t think that’s a major use case. The rule should be opt-in anyways, so I’m fine with some false positives.