RSpec/LeadingSubject is crashing if subject[] is used inside let

[ojab]

subject { {foo: 1} }
let(:bar) { subject[:foo] }

leads to

$ rubocop -rrubocop-rspec -V
1.14.0 (using Parser 3.0.1.1, rubocop-ast 1.5.0, running on ruby 3.0.0 x86_64-linux)
  - rubocop-rspec 2.2.0
$ rubocop -rrubocop-rspec --only RSpec/LeadingSubject /tmp/email_spec.rb
Inspecting 1 file
An error occurred while RSpec/LeadingSubject cop was inspecting /tmp/email_spec.rb:1:0.
To see the complete backtrace run rubocop -d.
.

1 file inspected, no offenses detected

1 error occurred:
An error occurred while RSpec/LeadingSubject cop was inspecting /tmp/email_spec.rb:1:0.
Errors are usually caused by RuboCop bugs.
Please, report your problems to RuboCop's issue tracker.
https://github.com/rubocop/rubocop/issues

Mention the following information in the issue report:
1.14.0 (using Parser 3.0.1.1, rubocop-ast 1.5.0, running on ruby 3.0.0 x86_64-linux)

[pirj]

I can't reproduce this with an example group:

RSpec.describe 'A' do
  subject { { foo: 1 } }

  let(:bar) { subject[:foo] }

  it { foo }
end

Do you use subject/let outside an example group?

[ojab]

The code above is the whole reproducer, found the crash when playing with subject in #1149.
Probably it can't be reproduced in the real example group, but should be fixed anyway.

[pirj]

Sorry, RuboCop RSpec is not supposed to work on source files that are not valid RSpec files.

[ojab]

I can provide valid spec then :)

def example_setup
  subject { { foo: 1 } }
  let(:bar) { subject[:foo] }
end

RSpec.describe Mail do
  instance_exec(&method(:example_setup))

  specify do
    p subject
    p bar
  end
end

Anyway, while IMHO all the crashes should be handled, I understand if this one will be WONTIX though.

[pirj]

We make assumptions that RSpec DSL elements are properly structured, and LeadingSubject expects that subject is wrapped in a block. Please take into consideration that it is very flexible, and doesn't care if it's a describe do block.

Do you suggest we made explicit checks to all the cops that the RSpec DSL is in order, and skip checking those files?

RSpec DSL configuration feature (#956) has been released not long ago, to tell RuboCop RSpec about project-specific custom example group aliases. I believe if we start skipping those blocks that are actually example groups, but just are not configured as such in .rubocop.yml, and only in spec/spec_helper.rb, we risk skipping the inspection of those files that we detect as non-RSpec, and risk false negatives.

In any case, a pull request is welcome if you have an idea how to elegantly fix such a case with no side effects.