Fix Rails/Presence cop when #present? or #blank? is used in if or unless modifier

[eitoball]

This PR should fix Rails/Presence cop when #present? on #blank? is used in if or unless modifier.

Below is a sample output that represents bug.

$ cat sample.rb
# frozen_string_literal: true

v if v.present?
$ rubocop -c .rubocop_empty.yml -d --rails sample.rb
bundle exec rubocop -c .rubocop_empty.yml -d --rails sample.rb
configuration from /.../.rubocop_empty.yml
Default configuration from /.../gems/rubocop-0.52.0/config/default.yml                                             Inheriting configuration from /.../gems/rubocop-0.52.0/config/enabled.yml
Inheriting configuration from /.../gems/rubocop-0.52.0/config/disabled.yml
Inspecting 1 file
Scanning /.../sample.rb
An error occurred while Rails/Presence cop was inspecting /.../sample.rb:3:0.
undefined method `nil_type?' for nil:NilClass
/.../gems/rubocop-0.52.0/lib/rubocop/cop/rails/presence.rb:99:in `replacement'
/.../gems/rubocop-0.52.0/lib/rubocop/cop/rails/presence.rb:80:in `on_if'
<snip>
.

1 file inspected, no offenses detected

1 error occurred:
An error occurred while Rails/Presence cop was inspecting /.../sample.rb:3:0.
Errors are usually caused by RuboCop bugs.
Please, report your problems to RuboCop's issue tracker.
Mention the following information in the issue report:
0.52.0 (using Parser 2.4.0.2, running on ruby 2.4.2 x86_64-darwin16)
Finished in 0.22184800007380545 seconds

---

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• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
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[wata727]

In this case, I think it should register an offense for this code...

[eitoball]

I tried to register this pattern as offense, but I could not get it right. Could somebody help me?

[pocke]

Probably we should rewrite the redundant_receiver_and_other and/or redundant_negative_receiver_and_other patterns. Let's try to rewrite the patterns with a documentation of Node Pattern, or replace the expect_no_offenses with expect_offense and make pending the test case.

[eitoball]

Thank you for your advice. I didn't have to rewrite neither redundant_receiver_and_other or redundant_negative_receiver_and_other. What I did was that adding a unless a.blank? to offense.

[wata727]

Thank you for fixing. I think this is a serious bug 🙇‍♂️

[pocke]

Maybe it should use blocks.
For example:

redundant_receiver_and_other(node)  do |receiver, other|
  # ...
end

redundant_negative_receiver_and_other(node) do |receiver, other|
  # ...
end

[bbatsov]

Good idea!

[bbatsov]

👍