Add new Lint/RedundantWithObject cop

[koic]

Follow up for #4708 (review).

This PR adds a cop @rrosenblum kindly suggested to me.

Feature

This cop checks for unneeded with_object.

% cat /tmp/example.rb
# frozen_string_literal: true

ary.each_with_object([]) do |v|
  v
end

ary.each.with_object([]) do |v|
  v
end

% bundle exec rubocop /tmp/example.rb
Inspecting 1 file
W

Offenses:

/tmp/example.rb:3:5: W: Use each instead of each_with_object.
ary.each_with_object([]) do |v|
    ^^^^^^^^^^^^^^^^^^^^
/tmp/example.rb:7:10: W: Remove redundant with_object.
ary.each.with_object([]) do |v|
         ^^^^^^^^^^^^^^^

1 file inspected, 2 offenses detected

---

Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Used the same coding conventions as the rest of the project.
• 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. See changelog entry format.
• All tests(rake spec) are passing.
• The new code doesn't generate RuboCop offenses that are checked by rake internal_investigation.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Updated cop documentation with rake generate_cops_documentation (required only when you've added a new cop or changed the configuration/documentation of an existing cop).

[pocke]

Could you add tests for without parens and/or do-end keyword block.

For example:

a.each_with_object([]) do |v|
end
a.each_with_object [] do |v|
end
a.each_with_object([]) {|v| v}
a.each_with_object [] {|v| v}

And the auto-correction for the first case generates a broken code.

[koic]

Oh, I didn't realize that. I'm going to look in detail later. Thanks for your advise!

[koic]

I added some test cases and fixed it with 95b0c46.

[rrosenblum]

Aside from the questions about consistency with the with_index cop, this looks good to me.

The commits will need to be squashed.

[rrosenblum]

I was expecting this pattern to be the same as the one of with_index with index swapped for object, but this pattern is slightly different. The pattern for with_object has an extra (_) after with_object and before args. Is it needed for this pattern? Should it be added to the with_index pattern?

def_node_matcher :redundant_with_index?, <<-PATTERN
  (block
    $(send
      _ {:each_with_index :with_index})
    (args
      (arg _))
    ...)
PATTERN

[koic]

Yes. As you pointed out, the with_index pattern of Lint/RedundantWithObject cop can be improved.

[rrosenblum]

The end range is different than the with_index cop. I saw that this was changed from send.loc.selector.end_pos + 1 when tests were added for the method call without parentheses. Does this need to be changed in the with_index cop?

[koic]

Current Lint/RedundantWithObject cop does not check the argument with_index. This is an oversight of me, in fact it would be better to handle the case with the with_index argument. It can be improved as an implementation of Lint/RedundantWithObject cop.

[bbatsov]

@koic Can you do the improvements suggested by @rrosenblum?

[koic]

@bbatsov Thanks for the mention. I'm considering improving Lint/RedundantWithIndex cop. On the other hand, I don't consider changing this Lint/RedundantWithObject cop.

[bbatsov]

Got it.

[bbatsov]

Any idea why the build is currently failing on JRuby?

[koic]

I was not aware of the failing on JRuby. Since failure in master branch has been fixed, rebasing in the latest master branch may fix the failing on JRuby.

If not, investigation is necessary. In that case, I'd like to investigate.

[koic]

@bbatsov May I git reset the merge commit 0f2d5f1 and try rebasing on the latest master branch?

[bbatsov]

Of course.

[koic]

Thanks. I'll try.

[koic]

CI has failed, so I will investigate. Please wait for a little while.

[koic]

CI passed. What I did was rebase with the latest master branch, and I autocorrected it. 0d1f22b