[Fix #7602] Handle Ruby 2.7 forward arguments properly

[Drenmi]

Note!

Not ready until we fix this.

Background

In Ruby 2.7, a new argument forwarding syntax was introduced. It looks like this:

def foo(...)
  bar(...)
end

This resulted in some unexpected breakage of some of our cops.

What is this fix?

All 2.7 node types have been added to the node traversal class, courtesy of @buehmann.

The biggest change is the introduction of a ForwardArgsNode extension. This allows forward arguments to be handled polymorphically with other argument types. This fixes the majority of the errors.

Additionally, the Naming/MethodParameterName cop has been made aware of forward arguments, so that it does not complain that ... is not a good name.

---

Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[koic]

Not ready until we fix this.

Parser 2.7.0.1 has been released and #7597 workaround has been fixed by #7606. Could you rebase with the latest master branch?

[buehmann]

I just noticed that the traversal methods generated via MANY_CHILD_NODES assume that every child node exists (i.e. is not nil). That is not true for in_pattern nodes, for example. So we need to review those types more carefully.

[Drenmi]

@koic Rebased. 🙏

[bbatsov]

I'll likely cut a new release tomorrow or on Monday. There are a few more PRs I'd like to include it in.