Fix wrong usage of Array#reject!: this might return nil

[r7kamura]

About

I found a behavior that seems to be a bug and would like to correct it.

In some condition, the #all_rules might raise NoMethodError.

Details

Why?

reject! は要素が 1 つ以上削除されれば self を、 1 つも削除されなければ nil を返します。

• https://docs.ruby-lang.org/ja/latest/method/Array/i/delete_if.html
• https://docs.ruby-lang.org/ja/latest/method/Enumerable/i/reject.html

How to reproduce

I coudn't write test about this behavior, but let me share how to reproduce this:

Modify the example .rubocop_todo.yml:

diff --git a/spec/fixtures/.rubocop_todo.yml b/spec/fixtures/.rubocop_todo.yml
index 7977dc7..4b73d25 100644
--- a/spec/fixtures/.rubocop_todo.yml
+++ b/spec/fixtures/.rubocop_todo.yml
@@ -1,11 +1,3 @@
-# This configuration was generated by
-# `rubocop --auto-gen-config`
-# on 2018-10-14 13:25:00 +0900 using RuboCop version 0.59.2.
-# The point is for the user to remove these configuration records
-# one by one as the offenses are removed from the code base.
-# Note that changes in the inspected code, or installation of new
-# versions of RuboCop, may require this file to be generated again.
-
 # Offense count: 1
 # This cop supports safe auto-correction (--auto-correct).
 # Configuration parameters: EnforcedStyle.

Then run rspec:

$ bundle exec rspec spec/lib/rubocop_challenger/rubocop/todo_reader_spec.rb:149
Run options: include {:locations=>{"./spec/lib/rubocop_challenger/rubocop/todo_reader_spec.rb"=>[149]}}

RubocopChallenger::Rubocop::TodoReader
  #any_rule
    returns a auto correctable rule at random (FAILED - 1)

Failures:

  1) RubocopChallenger::Rubocop::TodoReader#any_rule returns a auto correctable rule at random
     Failure/Error:
       file_contents
       .split(/\n{2,}/)
       .map! { |content| Rule.new(content) }
       .reject! { |rule| invalid?(rule) }
       .sort!
     
     NoMethodError:
       undefined method `sort!' for nil:NilClass
     # ./lib/rubocop_challenger/rubocop/todo_reader.rb:27:in `all_rules'
     # ./lib/rubocop_challenger/rubocop/todo_reader.rb:32:in `auto_correctable_rules'
     # ./lib/rubocop_challenger/rubocop/todo_reader.rb:47:in `any_rule'
     # ./spec/lib/rubocop_challenger/rubocop/todo_reader_spec.rb:150:in `block (3 levels) in <top (required)>'

Finished in 0.00117 seconds (files took 0.28482 seconds to load)
1 example, 1 failure

Failed examples:

rspec ./spec/lib/rubocop_challenger/rubocop/todo_reader_spec.rb:149 # RubocopChallenger::Rubocop::TodoReader#any_rule returns a auto correctable rule at random

Coverage report generated for RSpec to /home/r7kamura/ghq/github.com/r7kamura/rubocop_challenger/coverage. 229 / 386 LOC (59.33%) covered.
Stopped processing SimpleCov as a previous error not related to SimpleCov has been detected

Other concerns

I found this while investigating another problem. The recent rubocop has --no-offense-counts option and it's enabled in my project, so rubocop_challenger doesn't work well there...

[r7kamura]

This is the error log where I found this bug:

Switched to a new branch 'rubocop-challenge/20220513042015'
Bundler attempted to update rubocop but its version stayed the same
Bundler attempted to update rubocop-performance but its version stayed the same
Bundler attempted to update rubocop-rails but its version stayed the same
Bundler attempted to update rubocop-rake but its version stayed the same
Bundler attempted to update rubocop-rspec but its version stayed the same
Bundler attempted to update rubocop-thread_safety but its version stayed the same
cannot load such file -- rubocop-rails_deprecation
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/config_loader_resolver.rb:17:in `require'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/config_loader_resolver.rb:17:in `block (2 levels) in resolve_requires'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/config_loader_resolver.rb:13:in `each'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/config_loader_resolver.rb:13:in `block in resolve_requires'
<internal:kernel>:90:in `tap'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/config_loader_resolver.rb:12:in `resolve_requires'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/config_loader.rb:44:in `load_file'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/config_loader.rb:103:in `configuration_from_file'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/config_store.rb:68:in `for_dir'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/config_store.rb:47:in `for_pwd'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/cli/command/auto_genenerate_config.rb:30:in `maybe_run_line_length_cop'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/cli/command/auto_genenerate_config.rb:23:in `run'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/cli/command.rb:11:in `run'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/cli/environment.rb:18:in `run'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/cli.rb:71:in `run_command'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/cli.rb:76:in `execute_runners'
/usr/local/bundle/gems/rubocop-1.29.1/lib/rubocop/cli.rb:47:in `run'
/usr/local/bundle/gems/rubocop-1.29.1/exe/rubocop:12:in `block in <top (required)>'
/usr/local/lib/ruby/3.1.0/benchmark.rb:311:in `realtime'
/usr/local/bundle/gems/rubocop-1.29.1/exe/rubocop:12:in `<top (required)>'
/usr/local/bundle/bin/rubocop:25:in `load'
/usr/local/bundle/bin/rubocop:25:in `<top (required)>'
/usr/local/lib/ruby/3.1.0/bundler/cli/exec.rb:58:in `load'
/usr/local/lib/ruby/3.1.0/bundler/cli/exec.rb:58:in `kernel_load'
/usr/local/lib/ruby/3.1.0/bundler/cli/exec.rb:23:in `run'
/usr/local/lib/ruby/3.1.0/bundler/cli.rb:484:in `exec'
/usr/local/lib/ruby/3.1.0/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
/usr/local/lib/ruby/3.1.0/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
/usr/local/lib/ruby/3.1.0/bundler/vendor/thor/lib/thor.rb:392:in `dispatch'
/usr/local/lib/ruby/3.1.0/bundler/cli.rb:31:in `dispatch'
/usr/local/lib/ruby/3.1.0/bundler/vendor/thor/lib/thor/base.rb:485:in `start'
/usr/local/lib/ruby/3.1.0/bundler/cli.rb:25:in `start'
/usr/local/lib/ruby/gems/3.1.0/gems/bundler-2.3.7/libexec/bundle:48:in `block in <top (required)>'
/usr/local/lib/ruby/3.1.0/bundler/friendly_errors.rb:103:in `with_friendly_errors'
/usr/local/lib/ruby/gems/3.1.0/gems/bundler-2.3.7/libexec/bundle:36:in `<top (required)>'
/usr/local/bin/bundle:25:in `load'
/usr/local/bin/bundle:25:in `<main>'
/usr/local/bundle/gems/rubocop_challenger-2.7.0/lib/rubocop_challenger/rubocop/todo_reader.rb:27:in `all_rules': undefined method `sort!' for nil:NilClass (NoMethodError)

          .sort!
          ^^^^^^
	from /usr/local/bundle/gems/rubocop_challenger-2.7.0/lib/rubocop_challenger/rubocop/todo_reader.rb:32:in `auto_correctable_rules'
	from /usr/local/bundle/gems/rubocop_challenger-2.7.0/lib/rubocop_challenger/rubocop/todo_reader.rb:47:in `any_rule'
	from /usr/local/bundle/gems/rubocop_challenger-2.7.0/lib/rubocop_challenger/rubocop/challenge.rb:41:in `target_rule'
	from /usr/local/bundle/gems/rubocop_challenger-2.7.0/lib/rubocop_challenger/rubocop/challenge.rb:32:in `verify_target_rule'
	from /usr/local/bundle/gems/rubocop_challenger-2.7.0/lib/rubocop_challenger/rubocop/challenge.rb:25:in `exec'
	from /usr/local/bundle/gems/rubocop_challenger-2.7.0/lib/rubocop_challenger/rubocop/challenge.rb:8:in `exec'
	from /usr/local/bundle/gems/rubocop_challenger-2.7.0/lib/rubocop_challenger/go.rb:97:in `rubocop_challenge!'
	from /usr/local/bundle/gems/rubocop_challenger-2.7.0/lib/rubocop_challenger/go.rb:42:in `exec'
	from /usr/local/bundle/gems/rubocop_challenger-2.7.0/lib/rubocop_challenger/cli.rb:74:in `go'
	from /usr/local/bundle/gems/thor-1.2.1/lib/thor/command.rb:27:in `run'
	from /usr/local/bundle/gems/thor-1.2.1/lib/thor/invocation.rb:127:in `invoke_command'
	from /usr/local/bundle/gems/thor-1.2.1/lib/thor.rb:392:in `dispatch'
	from /usr/local/bundle/gems/thor-1.2.1/lib/thor/base.rb:485:in `start'
	from /usr/local/bundle/gems/rubocop_challenger-2.7.0/exe/rubocop_challenger:6:in `<top (required)>'
	from /usr/local/bundle/bin/rubocop_challenger:25:in `load'
	from /usr/local/bundle/bin/rubocop_challenger:25:in `<top (required)>'
	from /usr/local/lib/ruby/3.1.0/bundler/cli/exec.rb:58:in `load'
	from /usr/local/lib/ruby/3.1.0/bundler/cli/exec.rb:58:in `kernel_load'
	from /usr/local/lib/ruby/3.1.0/bundler/cli/exec.rb:23:in `run'
	from /usr/local/lib/ruby/3.1.0/bundler/cli.rb:484:in `exec'
	from /usr/local/lib/ruby/3.1.0/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
	from /usr/local/lib/ruby/3.1.0/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
	from /usr/local/lib/ruby/3.1.0/bundler/vendor/thor/lib/thor.rb:392:in `dispatch'
	from /usr/local/lib/ruby/3.1.0/bundler/cli.rb:31:in `dispatch'
	from /usr/local/lib/ruby/3.1.0/bundler/vendor/thor/lib/thor/base.rb:485:in `start'
	from /usr/local/lib/ruby/3.1.0/bundler/cli.rb:25:in `start'
	from /usr/local/lib/ruby/gems/3.1.0/gems/bundler-2.3.7/libexec/bundle:48:in `block in <top (required)>'
	from /usr/local/lib/ruby/3.1.0/bundler/friendly_errors.rb:103:in `with_friendly_errors'
	from /usr/local/lib/ruby/gems/3.1.0/gems/bundler-2.3.7/libexec/bundle:36:in `<top (required)>'
	from /usr/local/bin/bundle:25:in `load'
	from /usr/local/bin/bundle:25:in `<main>'
undefined method `sort!' for nil:NilClass

          .sort!
          ^^^^^^

[ryz310]

LGTM! Thank you so much!

[ryz310]

@r7kamura

Other concerns

I found this while investigating another problem. The recent rubocop has --no-offense-counts option and it's enabled in my project, so rubocop_challenger doesn't work well there...

I see. I understand why you use the "random mode" as default on your custom action.
I'll consider about #613. Thanks.