Add EnforcePrefix option to Rails/Delegate

[kstein413]

Hi! I'm proposing a change to the Rails/Delegate cop that adds an option (EnforcePrefix) to give users the ability to choose whether or not to enforce the prefix: true case when delegating.

At Betterment, we prefer to use

def foo_bar
  foo.bar
end

over

delegate :bar, to: :foo, prefix: true

because the second way makes it difficult to find where a method is defined (a search of the codebase would come up empty). I've defaulted the EnforcePrefix option to true, leaving current functionality as is, but this way the option is there to turn it off for projects that prefer to.

---

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).
• Used the same coding conventions as the rest of the project.
• 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.
• All tests are passing.
• The new code doesn't generate RuboCop offenses.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Updated cop documentation with rake generate_cops_documentation (required only when you've added a new cop or changed the configuration/documentation of an existing cop).

[kstein413]

@bbatsov I'm sure you're busy, but if you have a chance to take a look it’d be greatly appreciated!

[Drenmi]

This is a great addition to the cop, and the code looks good. My only concern is that the option name might be a bit ambiguous. At first it sounds like it forces you to use prefix: true for all #delegate declarations. 🙂

Maybe EnforceForPrefixed or flip it and name it AllowPrefixed? What do you think @klesse413?

[bbatsov]

The name of the cop should be in backticks here.

[bbatsov]

I wouldn't nest this additionally, as it doesn't look well in the generated documentation.

[bbatsov]

I'd put in backticks the name of the option and true.

[bbatsov]

Same here.

[bbatsov]

because the second way makes it difficult to find where a method is defined (a search of the codebase would come up empty). I've defaulted the EnforcePrefix option to true, leaving current functionality as is, but this way the option is there to turn it off for projects that prefer to.

But what's the value of having this cop for you then? Prefixing unprefixed delegations?

[kstein413]

@Drenmi I like the EnforceForPrefixed name, thanks!

@bbatsov The idea is that we would still like to use the cop to get a violation when using

def bar
  foo.bar
end

since we would prefer to use

delegate :bar, to: :foo

but we don't want to get a violation when using

def foo_bar
  foo.bar
end

so we'd like to be able to turn off enforcing that case

[bbatsov]

I thought as much. 👍