Fix RSpec/NamedSubject when block has no body

[splattael]

This MR fixes a regression for 👮‍♂️ RSpec/NamedSubject with EnforcedStyle: named_only in case a block has no body. For example:

describe User do
  it "is a User" do
    subject.each do
      # empty body
    end
  end
end

Exception/failure

Failures:

  1) RuboCop::Cop::RSpec::NamedSubject when EnforcedStyle is :named_only ignores subject when block has no body
     Failure/Error: block_node.body.child_nodes.find { |send_node| subject?(send_node) }

     NoMethodError:
       undefined method `child_nodes' for nil:NilClass

                 block_node.body.child_nodes.find { |send_node| subject?(send_node) }
                                ^^^^^^^^^^^^
     # ./lib/rubocop/cop/rspec/named_subject.rb:148:in `find_subject'
     # ./lib/rubocop/cop/rspec/named_subject.rb:143:in `block in nearest_subject'
     # ./lib/rubocop/cop/rspec/named_subject.rb:144:in `each'
     # ./lib/rubocop/cop/rspec/named_subject.rb:144:in `each'
     # ./lib/rubocop/cop/rspec/named_subject.rb:144:in `each'
     # ./lib/rubocop/cop/rspec/named_subject.rb:144:in `each'
     # ./lib/rubocop/cop/rspec/named_subject.rb:144:in `find'
     # ./lib/rubocop/cop/rspec/named_subject.rb:144:in `nearest_subject'
     # ./lib/rubocop/cop/rspec/named_subject.rb:134:in `subject_definition_is_named?'
     # ./lib/rubocop/cop/rspec/named_subject.rb:130:in `named_only?'
     # ./lib/rubocop/cop/rspec/named_subject.rb:121:in `allow_explicit_subject?'
     # ./lib/rubocop/cop/rspec/named_subject.rb:115:in `check_explicit_subject'
     # ./lib/rubocop/cop/rspec/named_subject.rb:103:in `block in on_block'
     # ./lib/rubocop/cop/rspec/named_subject.rb:104:in `block in subject_usage'
     # ./lib/rubocop/cop/rspec/named_subject.rb:99:in `subject_usage'
     # ./lib/rubocop/cop/rspec/named_subject.rb:102:in `on_block'
     # ./spec/support/expect_offense.rb:21:in `expect_no_offenses'
     # ./spec/rubocop/cop/rspec/named_subject_spec.rb:158:in `block (3 levels) in <top (required)>'

Finished in 0.09781 seconds (files took 0.70907 seconds to load)
20 examples, 1 failure

Failed examples:

rspec ./spec/rubocop/cop/rspec/named_subject_spec.rb:157 # RuboCop::Cop::RSpec::NamedSubject when EnforcedStyle is :named_only ignores subject when block has no body

Randomized with seed 26613

Coverage report generated for RSpec to /home/peter/devel/rubocop-rspec/coverage. 2012 / 3392 LOC (59.32%) covered.
Stopped processing SimpleCov as a previous error not related to SimpleCov has been detected

Found at GitLab in https://gitlab.com/gitlab-org/gitlab/-/issues/249446#note_1461446904.

---

Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• [-] Updated documentation.
• Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

[splattael]

👋 @kuahyeow

Can you review this PR? 🙏

[pirj]

Is this a real-life example?
How did you find this in the first place?

[splattael]

@pirj Yes, it is in the GitLab code base. See https://gitlab.com/gitlab-org/gitlab/-/issues/249446#note_1461446904

bundle exec rubocop -d --only RSpec/NamedSubject spec/lib/gitlab/github_import/importer/single_endpoint_issue_notes_importer_spec.rb

For example: https://gitlab.com/gitlab-org/gitlab/-/blob/70654c7306d007eb6bdfa970747f682a7f556718/spec/lib/gitlab/github_import/importer/single_endpoint_issue_notes_importer_spec.rb#L40

[splattael]

In total, I found 38 locations where this RSpec/NamedSubject with EnforcedStyle: named_only would fail because of passing an empty block to subject's method.

spec/lib/api/helpers/authentication_spec.rb:16:6.
spec/lib/gitlab/database/with_lock_retries_outside_transaction_spec.rb:118:12.
spec/lib/gitlab/database/with_lock_retries_outside_transaction_spec.rb:130:12.
spec/lib/gitlab/database/with_lock_retries_outside_transaction_spec.rb:154:8.
spec/lib/gitlab/database/with_lock_retries_outside_transaction_spec.rb:219:4.
spec/lib/gitlab/database/with_lock_retries_outside_transaction_spec.rb:223:4.
spec/lib/gitlab/database/with_lock_retries_outside_transaction_spec.rb:231:4.
spec/lib/gitlab/database/with_lock_retries_outside_transaction_spec.rb:238:4.
spec/lib/gitlab/database/with_lock_retries_spec.rb:118:12.
spec/lib/gitlab/database/with_lock_retries_spec.rb:130:12.
spec/lib/gitlab/database/with_lock_retries_spec.rb:155:10.
spec/lib/gitlab/database/with_lock_retries_spec.rb:166:10.
spec/lib/gitlab/database/with_lock_retries_spec.rb:233:4.
spec/lib/gitlab/database/with_lock_retries_spec.rb:237:4.
spec/lib/gitlab/database/with_lock_retries_spec.rb:245:4.
spec/lib/gitlab/database/with_lock_retries_spec.rb:254:4.
spec/lib/gitlab/database/with_lock_retries_spec.rb:265:4.
spec/lib/gitlab/database/with_lock_retries_spec.rb:271:4.
spec/lib/gitlab/github_import/importer/protected_branches_importer_spec.rb:188:6.
spec/lib/gitlab/github_import/importer/single_endpoint_diff_notes_importer_spec.rb:32:4.
spec/lib/gitlab/github_import/importer/single_endpoint_diff_notes_importer_spec.rb:51:4.
spec/lib/gitlab/github_import/importer/single_endpoint_diff_notes_importer_spec.rb:64:4.
spec/lib/gitlab/github_import/importer/single_endpoint_issue_notes_importer_spec.rb:31:4.
spec/lib/gitlab/github_import/importer/single_endpoint_issue_notes_importer_spec.rb:50:4.
spec/lib/gitlab/github_import/importer/single_endpoint_issue_notes_importer_spec.rb:63:4.
spec/lib/gitlab/github_import/importer/single_endpoint_merge_request_notes_importer_spec.rb:32:4.
spec/lib/gitlab/github_import/importer/single_endpoint_merge_request_notes_importer_spec.rb:51:4.
spec/lib/gitlab/github_import/importer/single_endpoint_merge_request_notes_importer_spec.rb:64:4.
spec/lib/gitlab/sidekiq_logging/structured_logger_spec.rb:390:6.
spec/lib/gitlab/sidekiq_middleware/size_limiter/server_spec.rb:28:2.
spec/lib/mattermost/session_spec.rb:39:6.
spec/lib/mattermost/session_spec.rb:97:8.
spec/services/projects/lfs_pointers/lfs_object_download_list_service_spec.rb:113:12.
spec/services/projects/lfs_pointers/lfs_object_download_list_service_spec.rb:127:8.
spec/services/projects/lfs_pointers/lfs_object_download_list_service_spec.rb:135:8.
spec/services/projects/lfs_pointers/lfs_object_download_list_service_spec.rb:55:8.
spec/services/projects/lfs_pointers/lfs_object_download_list_service_spec.rb:86:8.
spec/services/projects/lfs_pointers/lfs_object_download_list_service_spec.rb:98:10.

[pirj]

Thank you!

[ydah]

Thank you 😊