Style/ConditionalAssignment triggers RuboCop parsing error in specific circumstances

[SaltwaterC]

It's bit difficult to explain this in the title itself. Found a piece of code in a Chef recipe triggering an issue in RuboCop. A simplified representation of this code is:

default['key-with-dash'] = []

dirs.each do |dir|
  if user == system_user
    default['key-with-dash'] << {
      'owner' => user,
      'group' => 'group',
      'dir' => "/path1/#{dir}"
    }
  else
    default['key-with-dash'] << {
      'owner' => user,
      'group' => 'group',
      'dir' => "/path2/#{dir}"
    }
  end
end

$ rubocop
Inspecting 1 file
An error occurred while Style/ConditionalAssignment cop was inspecting /Users/user/path/code.rb.
To see the complete backtrace run rubocop -d.
.

1 file inspected, no offenses detected

1 error occurred:
An error occurred while Style/ConditionalAssignment cop was inspecting /Users/user/path/code.rb.
Errors are usually caused by RuboCop bugs.
Please, report your problems to RuboCop's issue tracker.
Mention the following information in the issue report:
0.37.2 (using Parser 2.3.0.5, running on ruby 2.1.6 x86_64-darwin12.0)

The reported error in the backtrace is:

empty range in char class: /default['key-with-dash']\s*<<\s*/

To break the parser, the "default" array key needs to have dashes. This code doesn't trigger any issue:

default['key_without_dash'] = []

dirs.each do |dir|
  if user == system_user
    default['key_without_dash'] << {
      'owner' => user,
      'group' => 'group',
      'dir' => "/path1/#{dir}"
    }
  else
    default['key_without_dash'] << {
      'owner' => user,
      'group' => 'group',
      'dir' => "/path2/#{dir}"
    }
  end
end

rubocop
Inspecting 1 file
.

1 file inspected, no offenses detected

The issue appeared after upgrading to ChefDK 0.11.0 which bundles the latest RuboCop. Built a ChefDK 0.10.0 POC in Test Kitchen which doesn't have this issue:

[kitchen@cfaf8d46339e ~]$ rubocop
warning: parser/current is loading parser/ruby21, which recognizes
warning: 2.1.7-compliant syntax, but you are running 2.1.6.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.
Inspecting 1 file
.

1 file inspected, no offenses detected
[kitchen@cfaf8d46339e ~]$ rubocop -V
warning: parser/current is loading parser/ruby21, which recognizes
warning: 2.1.7-compliant syntax, but you are running 2.1.6.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.
0.34.2 (using Parser 2.2.3.0, running on ruby 2.1.6 x86_64-linux)
[kitchen@cfaf8d46339e ~]$ cat code.rb
default['key-with-dash'] = []

dirs.each do |dir|
  if user == system_user
    default['key-with-dash'] << {
      'owner' => user,
      'group' => 'group',
      'dir' => "/path1/#{dir}"
    }
  else
    default['key-with-dash'] << {
      'owner' => user,
      'group' => 'group',
      'dir' => "/path2/#{dir}"
    }
  end
end

[SaltwaterC]

# rubocop:disable Style/ConditionalAssignment does not workaround the issue. Style/ConditionalAssignment needs to be disabled in .rubocop.yml. Tried to wrap the code with disable/enable inline statements. RuboCop correctly reports "Unnecessary disabling of Style/ConditionalAssignment" even though the parsing failure is triggered by this cop.

[alexdowad]

Thanks for the bug report. Just pushed a fix to my open PR.