Add Rails/EnvLocal cop to enforce upcoming Rails.env.local?

[sambostock]

rails/rails#46786 introduces Rails.env.local? as a helper for Rails.env.development? || Rails.env.test?, which should be released as part of the next Rails release (presumably 7.1, although possible 8).

This PR includes the following to support this:

• Add :rails71 shared context so specs can be written against Rails 7.1
• Change Rails/UnknownEnv default config to add local
  Removed in favour of Support local as an environment for Rails/UnknownEnv from Rails 7.1 onward. #894
• Add new Rails/EnvLocal cop to enforce use of Rails.env.local? when applicable
  • Also supports EnforcedStyle: no_local to disallow Rails.env.local?

---

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.
  Good idea!

[sambostock]

Oh, I see #894 uses an alternative approach to add support for .local? to Rails/UnknownEnv, albeit differently. Both approaches have tradeoffs:

PR	Approach	Tradeoff
#906 (this PR)	Add local to config	Blindly allows local in Rails versions that don't support it
#894	Injects local into config if Rails version >= 7.1	Impossible to disallow local, if desired

As I type this, I realize maybe the tradeoff in #894 is actually just best addressed by me making this cop have a configurable enforced style (local? vs development? || test?)... 🤔

[sambostock]

I've updated the PR as follows:

• Removed the addition of local to Rails/UnknownEnv, as I think Support local as an environment for Rails/UnknownEnv from Rails 7.1 onward. #894 does it better
• Added an EnforcedStyle config, which can be set to no_local to disallow Rails.env.local?, instead of enforcing it.

[koic]

The EnforcedStyle: no_local option looks unnecessary. So, it would be sufficient to provide only the default.

[sambostock]

My justification was that authors may prefer to be explicit (or perhaps they need to support an old Rails version, in the case of a gem author) and not want to use local?. Normally this would be covered by updating the UnknownEnv config, except that #894's implementation always injects it in if the target Rails version is >= 7.1.

However, if you think that's too obscure, I can certainly remove the EnforcedStyle option.

[koic]

I think it's not generally downgraded supported version of Rails. If user don't want to replace with this Rails.env.local?, just can disable this cop. So I think it would be better to remove this EnforcedStyle: no_local and keep it simple.

[sambostock]

Done 👍

[koic]

This looks good. However, Rails 7.1 is a development version yet. So, the new cop merge is pending until at least a beta, preferably a release candidate is shipped.

[koic]

Add :rails71 shared context so specs can be written against Rails 7.1

Please open a PR only for c856fa1 if you like. Rails 7.1 development has started, so it can be merged independently.

[sambostock]

@koic I've opened #1134 now Rails 7.1 release candidate 1 has been released.

[koic]

@sambostock #1134 was merged. Can you rebase with the latest master branch?

[koic]

Can you resolve the following offense?
https://app.circleci.com/pipelines/github/rubocop/rubocop-rails/2710/workflows/7b3e5571-a8f9-460f-8fef-eecf228283e3/jobs/18160

[sambostock]

Done! You're too fast for me! 😅

[koic]

Thanks!