[Rule Request]: Private @IBAction opt-in rule

[ornithocoder]

This is a request to introduce a new opt-in rule which warns against public IBActions.

Triggering example:

@IBAction func ↓fooButtonTapped(_ sender: UIButton) {
    // ...
}

Non-triggering example:

@IBAction private func fooSegmentedControlChanged(_ sender: UISegmentedControl) {
    // ...
}

private extension Toto {
    @IBAction func fooSegmentedControlChanged(_ sender: UISegmentedControl) {
        // ...
    }
}

Workaround via custom rule (snippet from .swiftlint.yml) while the rule isn't implemented/merged into master:

custom_rules:
  private_ibaction:
    name: "Private @IBAction"
    regex: "@IBAction\\s+func"
    message: "@IBAction should be private"
    severity: warning

[ornithocoder]

@marcelofabri @jpsim let me know if this makes sense to you. In case it does, I'll work on it.

In my project we keep all our @IBActions private, and we test the code by sending actions (.sendActions(_:)) to the controllers (touch up inside, value changed, etc...).

[marcelofabri]

I think this would be a nice rule 👍

[jpsim]

Sounds reasonable as opt-in.

[ornithocoder]

Super. I'll work on it tomorrow morning :-) Thanks guys!

[marcelofabri]

Implemented in #1935.