Add OptionalBooleanParameter AllowedMethods configuration

[bkuhlmann]

Describe the solution you'd like

When using Style/OptionalBooleanParameter, it would be nice to define a set of allowed methods as used via Style/NestedParenthesizedCalls, for example. For instance, when metaprograming, it's common to want to use Object#respond_to_missing?:

def respond_to_missing? name, include_private = false
  # Implementation details...
end

The use of include_private = false, in this case, is what causes this cop to flag the code as a violation. I agree, it is. ...but this is a standard library method which is out of my control as an implementer.

Describe alternatives you've considered

I've been able temporarily work around this issue by using an exclude:

Style/OptionalBooleanParameter:
  Exclude:
    - "path/to/implementation"

This is not ideal as I'd rather not exclude the entire file but ignore a bad practice within the standard library that is out of my control instead.

[marcandre]

Good point.
We should definitely exclude respond_to_missing? by default. Can you think of any other builtin callback like that?
Adding the ability to exclude more methods would be a bonus (could be a separate PR)

[bkuhlmann]

@marcandre Can you think of any other builtin callback like that?

Hmm, I don't know. Object#respond_to_missing? is what I see most often. I know there are others but when searching through my various code bases I came up empty for additional use cases. If I can find more, I'll post back here.

[natematykiewicz]

Can we start by fixing this for respond_to_missing?, and then fix it for more if more come up?

[bkuhlmann]

🙇 @natematykiewicz Yeah, I'd like that too. I've still not found another more pressing example other than #respond_to_missing? for the time being. This would be a good start, though!