Add ImplicitBlockExpectation cop #789

pirj · 2019-07-23T23:45:28Z

Based on https://rspec.rubystyle.guide/#implicit-block-expectations

The implicit syntax is discouraged to use by RSpec Core team and the majority of voters.

There were no good arguments for using the syntax except for brevity and avoiding repetition, but there are better options to achieve the same goal, e.g. by extracting the lengthy block to methods (instead of putting it inside the lambda).

It's barely possible to restrict the usage of this syntax on RSpec side. It's possible to detect if a matcher supports block expectations, but it's impossible to detect if it exclusively supports block expectations and not value expectations. A matcher may support both styles at the same time.
An attempt that results in 86 spec failures pirj/rspec-expectations@a7f0d7a

References:
https://blog.rubystyle.guide/rspec/2019/07/17/rspec-implicit-block-syntax.html
https://www.reddit.com/r/ruby/comments/cejl3q/call_for_discussion_rspec_implicit_block/
https://lobste.rs/s/e8yxmd/call_for_discussion_rspec_implicit_block
rubocop/rspec-style-guide#76
rubocop/rspec-style-guide#103

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.
Added an entry to the changelog 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).

If you have created a new cop:

Added the new cop to config/default.yml.
The cop documents examples of good and bad code.
The tests assert both that bad code is reported and that good code is not reported.
Tested on a 10k+ files repo, no false offences raised.

lib/rubocop/cop/rspec/implicit_block_expectation.rb

pirj · 2019-07-24T09:13:57Z

It could be written with the use of def_node_search:

        def_node_matcher :lambda?, <<-PATTERN
          {
            (send (const nil? :Proc) :new)
            (send nil? :proc)
            (send nil? :lambda)
          }
        PATTERN
        def_node_matcher :lambda_block, '$(block #lambda? ...)'
        def_node_search :subject_block, Subject::ALL.block_pattern

        def on_block(node)
          subject_block(node) do |block_node|
            lambda_block(block_node.body) { |lambda| add_offense(lambda) }
          end
        end

I'm wary with def_node_search knowing its recursive nature, but couldn't find a case when it fails.

Which do you prefer, @Darhazer, the current or the one above?

Darhazer · 2019-07-24T09:15:43Z

def_node_search will perform the recursive search on each block. If you go in this direction, you should limit the search only in the top level describe, to avoid wasting CPU cycles.
I'm ok with the previous version though

pirj · 2019-07-24T09:17:20Z

Thanks, pushed the former solution without def_node_search and squashed the commits.

Darhazer

Let fist merge the style guide though

pirj · 2019-07-24T09:22:34Z

Let fist merge the style guide though

Agree. 👍
Looking forward to your approval of the style guide pull request.

Darhazer · 2019-07-24T09:37:20Z

Just noticed that the cop flags subject { -> ... } while the guide only suggests avoiding is_expected with such a subject ;)

pirj · 2019-07-24T09:41:20Z

Fair enough.
I couldn't find any good reason to put a lambda to subject other than to use is_expected, but it's better to be explicit on what is detected, and the offence message might be confusing when attached to subject definition as opposed to is_expected.

I'll take care of that, will add detection of is_expected usages in the scope where subject is defined with a lambda.

pirj

Added notes to facilitate code review.
@bquorning Can you please take a look?

pirj · 2019-07-24T20:50:32Z

spec/rubocop/cop/rspec/implicit_block_expectation_spec.rb

+      describe do
+        subject { -> { boom } }
+        it { should change { something }.to(new_value) }
+             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Avoid implicit block expectations.


The range is not ideal, but I decided to avoid complicating the cop for the sake of highlighting should itself.
The difference is that is_expected is a self-contained send, while for should it's the whole should(change { something }.to(new_value)).

pirj · 2019-07-24T20:52:29Z

lib/rubocop/cop/rspec/implicit_block_expectation.rb

+
+        def on_send(node)
+          implicit_expect(node) do |implicit_expect|
+            subject = nearest_subject(implicit_expect)


We're finding the nearest subject, and only then checking if it's a lambda subject.
Check this example.

pirj · 2019-07-24T20:53:36Z

lib/rubocop/cop/rspec/implicit_block_expectation.rb

+        def nearest_subject(node)
+          node
+            .each_ancestor(:block)
+            .lazy


lazy is here to avoid mapping/selecting through all of the ancestors just to find the nearest subject.

pirj · 2019-07-24T20:55:45Z

lib/rubocop/cop/rspec/implicit_block_expectation.rb

+        end
+
+        def multi_statement_example_group?(node)
+          example_group_with_body?(node) && node.body.begin_type?


Non-begin_type blocks (example groups) are no interest for us, they don't have other blocks than those we came from, and we're searching for subject. If there are at least two statements in the block, it's a begin_type.

pirj · 2019-07-24T20:57:51Z

lib/rubocop/cop/rspec/implicit_block_expectation.rb

+          (block _ _args $(block #lambda? ...))
+        PATTERN
+
+        def_node_matcher :implicit_expect, <<-PATTERN


Shamelessly borrowed from ImplicitSubject. Not sure if it makes sense to extract this with just two usages.

Darhazer

Excellent work. Few minor comments

lib/rubocop/cop/rspec/implicit_block_expectation.rb

Based on https://rspec.rubystyle.guide/#implicit-block-expectations

bquorning · 2019-07-31T11:55:27Z

lib/rubocop/cop/rspec/implicit_block_expectation.rb

+            .lazy
+            .select { |block_node| multi_statement_example_group?(block_node) }
+            .map { |block_node| find_subject(block_node) }
+            .find(&:itself)


This line is equivalent to .reject(&:nil?).first, right? Just trying to understand.

Yes, I think those are equivalent.

pirj · 2019-07-31T12:06:49Z

Thank you!

bquorning · 2019-07-31T12:07:28Z

And thank you for the new cop :-)

Darhazer reviewed Jul 24, 2019

View reviewed changes

lib/rubocop/cop/rspec/implicit_block_expectation.rb Outdated Show resolved Hide resolved

pirj force-pushed the add-implicit-block-expectation-cop branch from d04e9f9 to 571542f Compare July 24, 2019 09:16

Darhazer approved these changes Jul 24, 2019

View reviewed changes

pirj commented Jul 24, 2019

View reviewed changes

pirj force-pushed the add-implicit-block-expectation-cop branch from 0df2736 to a92f085 Compare July 24, 2019 21:02

Darhazer reviewed Jul 25, 2019

View reviewed changes

lib/rubocop/cop/rspec/implicit_block_expectation.rb Outdated Show resolved Hide resolved

lib/rubocop/cop/rspec/implicit_block_expectation.rb Outdated Show resolved Hide resolved

pirj force-pushed the add-implicit-block-expectation-cop branch 3 times, most recently from 0c8450f to 7f135df Compare July 30, 2019 23:17

Add ImplicitBlockExpectation cop

02e41c7

Based on https://rspec.rubystyle.guide/#implicit-block-expectations

pirj force-pushed the add-implicit-block-expectation-cop branch from 7f135df to 02e41c7 Compare July 31, 2019 11:50

bquorning reviewed Jul 31, 2019

View reviewed changes

bquorning approved these changes Jul 31, 2019

View reviewed changes

bquorning merged commit 0d8c1f3 into rubocop:master Jul 31, 2019

pirj deleted the add-implicit-block-expectation-cop branch July 31, 2019 12:06

AlexWayfer mentioned this pull request Oct 13, 2019

Improve Indonesian translation r18n/r18n#219

Merged

pirj mentioned this pull request Oct 13, 2019

Prevent block-only matchers from being used with value expectation target rspec/rspec-expectations#1125

Merged

pirj mentioned this pull request Oct 29, 2019

Print deprecation message when implicit block expectation syntax is used rspec/rspec-expectations#1139

Merged

pirj mentioned this pull request Oct 5, 2020

RSpec/ExpectChange doesn't work well with nested class #1037

Closed

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Add ImplicitBlockExpectation cop #789

Add ImplicitBlockExpectation cop #789

pirj commented Jul 23, 2019 •

edited

Loading

pirj commented Jul 24, 2019

Darhazer commented Jul 24, 2019

pirj commented Jul 24, 2019

Darhazer left a comment

pirj commented Jul 24, 2019 •

edited

Loading

Darhazer commented Jul 24, 2019

pirj commented Jul 24, 2019

pirj left a comment

pirj Jul 24, 2019

pirj Jul 24, 2019

pirj Jul 24, 2019

pirj Jul 24, 2019

pirj Jul 24, 2019

Darhazer left a comment

bquorning Jul 31, 2019

pirj Jul 31, 2019

pirj commented Jul 31, 2019

bquorning commented Jul 31, 2019

Add ImplicitBlockExpectation cop #789

Add ImplicitBlockExpectation cop #789

Conversation

pirj commented Jul 23, 2019 • edited Loading

pirj commented Jul 24, 2019

Darhazer commented Jul 24, 2019

pirj commented Jul 24, 2019

Darhazer left a comment

Choose a reason for hiding this comment

pirj commented Jul 24, 2019 • edited Loading

Darhazer commented Jul 24, 2019

pirj commented Jul 24, 2019

pirj left a comment

Choose a reason for hiding this comment

pirj Jul 24, 2019

Choose a reason for hiding this comment

pirj Jul 24, 2019

Choose a reason for hiding this comment

pirj Jul 24, 2019

Choose a reason for hiding this comment

pirj Jul 24, 2019

Choose a reason for hiding this comment

pirj Jul 24, 2019

Choose a reason for hiding this comment

Darhazer left a comment

Choose a reason for hiding this comment

bquorning Jul 31, 2019

Choose a reason for hiding this comment

pirj Jul 31, 2019

Choose a reason for hiding this comment

pirj commented Jul 31, 2019

bquorning commented Jul 31, 2019

pirj commented Jul 23, 2019 •

edited

Loading

pirj commented Jul 24, 2019 •

edited

Loading