Info level offenses for likely wrong RBS

[sambostock]

Context

Most RBS annotations are not of the form @key: value, so it is easy¹: to forget the colon in annotations like

-# @requires_ancestor ::Whatever
+# @requires_ancestor: ::Whatever

This can be particularly frustrating when attempting to require a complex ancestor (such as a module including metaprogramming), where one might assume things aren't working because they are requiring the wrong ancestor, or because Sorbet is not statically aware of the method, when in fact it turns out they were simply silently not requiring any ancestor at all.

Proposal

It would be nice if there was a cop that looked for such comments that are probably a mistake and attached an info level warning, saving the developer time debugging.

# @requires_ancestor ::Whatever
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ INFO: This looks like a malformed RBS annotation. Did you mean `@requires_ancestor: ::Whatever`?

Footnotes

1. ↩

[sambostock]

Real world motication: I did something like

# @abstract
# @requires_ancestor ::ActionDispatch::IntegrationTest
#                  ^^^ Note the missing `:`
module WebhookTestHelper
  # Like `post`, but signs the request with the webhook secret, so verification passes.
  def signed_post(...)
    # ...

and spent a bunch of time digging into where the post method actually comes from¹ and why things weren't working without any feedback that I'd simply missed a :.

Footnotes

1. It comes from https://github.com/rails/rails/blob/main/actionpack/lib/action_dispatch/testing/integration.rb, but involves several intermediate modules/concerns. ↩