:kind_of? vs :is_a? automation?

[jdickey]

This is a continuation of Ruby Style Guide issue 307. Let me start out by saying that I understand and tend to agree with what @anthonyryan1 had to say when he closed the issue, before @bbatsov recommended I open a new automation issue on the topic.

I'd suggest that

1. a :refactor or :convention notice (which?) be emitted when the source being examined includes calls to both :is_a? and :kind_of?, suggesting to the developer that s/he might want to standardise on one or the other.
2. that be raised to an :error-level offence when the configuration contains a Preferred: is_a? or Preferred: kind_of? setting for this cop.
3. that the scope of comparison for (1) and (2) be optionally limited by a LimitedTo: configuration setting with the allowable settings of File, Class or Method. Specifying Default, or omitting the LimitedTo: configuration entirely, defaults the scope to all files being examined.

You could well argue, and I'd agree, that this would be a pretty arbitrarily limited form of what was being grappled with in the earlier issue. On the other hand, it "shouldn't" be incredibly hard to implement.

Thoughts?

[bbatsov]

All cops have file scope, so the only viable option would be to have a mandatory enforced style. Implementing this would be fairly easy, indeed.