[Rails/Blank & Rails/Present cops] new cop configs allowing return unless present?|blank? for multiple unless guard clauses

[RDeckard]

Proposition

TL;DR

Both Rails/Blank cop and Rails/Present cop are really useful, but their UnlessPresent and UnlessBlank rules can be frustrating when dealing with multiple return unless guard clauses, so we should have some cop configs allowing those return unless foo.present?/return unless foo.blank? ONLY in this very specific case (i.e. in multiple unless guard clauses).

Context

Here the current targeted rules in a guard clause context:

# bad
return unless foo.present?

# good
return if foo.blank?

(This is related to the Rails/Blank cop here, but that's the same inverted logic for Rails/Present.)

Specific case this PR aims to address

Those rules are simple and legit in most cases 👌, but we should be able to disable them specifically on multiple return unless guard clauses like in this example:

return unless foo.active?
return unless bar.present? # <= here the case that we want be able to allow through a new cop config
return unless baz.enable?

New cop configs

In order to address the case described just above ☝️, this PR propose those two new optional cop configs: (which of course should stay false by default to avoid any changed behaviors)

Rails/Blank:
  AllowMultipleUnlessPresentGuardClauses: true

Rails/Present:
  AllowMultipleUnlessBlankGuardClauses: true

Reasoning

Arguments in favor of these two new cop configs:

• return unless a_condition is a very common idiom in guard clauses, as it simply means that a_condition is required in order to go further.
• In the example above ⬆️⬆️, the second line (return unless bar.present?) triggers the UnlessPresent rule, which suggests changing the code to return if bar.blank?. But IMO:
  • This change would disrupt the reading flow in this very common list of guard clauses.
  • As a get around, we could actually just omit .present? in some cases, which is not good for explicitness, and therefore a counterproductive incentive.

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• 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.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.

[koic]

Enabling the Style/InvertibleUnlessCondition cop, which is disabled by default, should resolve this. In RuboCop Rails, it can detect present? and blank? by default.
#1097

Additionally, adding similar configuration options would compromise simplicity, so this proposal will be closed. Thank you.