Add RuboCop RSpec support

[pirj]

What is the purpose of this pull request?

Previously, RuboCop RSpec failed to detect RSpec aliases. A number of cops were failing false offences, and some cops were unable to lint, as they were skipping locally defined RSpec aliases taking them for arbitrary blocks and method calls.

See:

• Add docs and provide a reference implementation on RSpec DSL aliases configuration in third-party gems rubocop/rubocop-rspec#1077
• RSpec aliases runtime matchers rubocop/rubocop-rspec#956

Sibling pull requests:

• Add RuboCop RSpec support palkan/action_policy#138

Gemfile:

# frozen_string_literal: true

source 'https://rubygems.org'

gem 'rubocop-rspec'
gem 'test-prof', path: '../../test-prof'

.rubocop.yml:

require:
  - rubocop-rspec

inherit_gem:
  test-prof: .rubocop-rspec-aliases.yml

spec/o_spec.rb:

# frozen_string_literal: true

RSpec.describe 'O' do
  let_it_be(:x) { 'the_one_and_only' }

  # I must come above any other memoized helper! (disclaimer: due to an arguable default linter setting)
  subject(:o) { 'everchanging' } # Not really everchanging with a frozen_string_literal

  it { expect(o).not_to eq("#{x}#{x}") }
end

Before (let_it_be is not detected as a memoized helper)

$ rubocop
Inspecting 2 files
..

2 files inspected, no offenses detected

After (let_it_be is properly detected)

$ rubocop
Inspecting 2 files
.C

Offenses:

spec/o_spec.rb:7:3: C: RSpec/LeadingSubject: Declare subject above any other let_it_be declarations.
  subject(:o) { 'everchanging' } # Not really everchanging with a frozen_string_literal
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

2 files inspected, 1 offense detected, 1 offense auto-correctable

What changes did you make? (overview)

• added an RSpec alias config file that RuboCop is able to load and append to the default RuboCop RSpec alias configuration.
• added docs on how to tell RuboCop to use those aliases

Is there anything you'd like reviewers to focus on?

Should I through in some test to make sure the detection works as expected?

I don't have a project that uses let_it_be/before_all handy at the moment.
Do you mind to checking this against a live project?

Checklist

• [-] I've added tests for this change
• I've added a Changelog entry
• I've updated a documentation

[pirj]

Liche fail seems unrelated:

 docs/profilers/factory_prof.md
	ERROR	http://www.brendangregg.com/flamegraphs.html
Error: 		Dial tcp4 <nil>->50.63.8.6:80: i/o timeout
Error: Process completed with exit code 1.

[palkan]

👍

Same here: can we move the config to config/rubocop-rspec.yml?

[pirj]

Moved the config and tested again, works.

[palkan]

Thanks!