Infinite loop from TrailingWhitespace + EmptyInterpolation

[bpo]

Using autocorrect (rubocop -a) with Layout/TrailingWhitespace and Lint/EmptyInterpolation causes infinite loops when encountering empty lines containing only indentation within heredocs.

---

Expected behavior

No infinite loop.

Actual behavior

 rubocop -a --debug
For ~/Code/linebreak_heredoc: Default configuration from ~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/config/default.yml
Inspecting 1 file
Scanning ~/Code/linebreak_heredoc/test.rb
W

Offenses:

test.rb:8:1: C: [Corrected] Layout/TrailingWhitespace: Trailing whitespace detected.
test.rb:8:5: W: [Corrected] Lint/EmptyInterpolation: Empty interpolation detected.
    #{}
    ^^^

0 files inspected, 2 offenses detected, 2 offenses corrected
Infinite loop detected in ~/Code/linebreak_heredoc/test.rb and caused by Layout/TrailingWhitespace -> Lint/EmptyInterpolation
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:304:in `check_for_infinite_loop'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:287:in `block in iterate_until_no_changes'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:286:in `loop'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:286:in `iterate_until_no_changes'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:255:in `do_inspection_loop'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:132:in `block in file_offenses'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:157:in `file_offense_cache'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:131:in `file_offenses'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:122:in `process_file'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:101:in `block in each_inspected_file'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:100:in `each'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:100:in `reduce'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:100:in `each_inspected_file'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:86:in `inspect_files'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/runner.rb:47:in `run'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/cli/command/execute_runner.rb:25:in `execute_runner'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/cli/command/execute_runner.rb:17:in `run'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/cli/command.rb:11:in `run'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/cli/environment.rb:18:in `run'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/cli.rb:65:in `run_command'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/cli.rb:72:in `execute_runners'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/lib/rubocop/cli.rb:41:in `run'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/exe/rubocop:13:in `block in <top (required)>'
~/.rbenv/versions/2.7.0/lib/ruby/2.7.0/benchmark.rb:308:in `realtime'
~/.rbenv/versions/2.7.0/lib/ruby/gems/2.7.0/gems/rubocop-1.0.0/exe/rubocop:12:in `<top (required)>'
~/.rbenv/versions/2.7.0/bin/rubocop:23:in `load'
~/.rbenv/versions/2.7.0/bin/rubocop:23:in `<main>'
Finished in 0.1126139999832958 seconds

Steps to reproduce the problem

This is test.rb from the above output – note that the first empty line contains 4 spaces.

#! /usr/bin/env ruby -w

# frozen_string_literal: true

def testcase
  puts <<-TXT
    empty breaking lines
    
    looping infinitely on

    each rubocop run
  TXT
end

testcase

RuboCop version

$ rubocop -V
1.0.0 (using Parser 2.7.2.0, rubocop-ast 1.0.1, running on ruby 2.7.0 x86_64-darwin19)

[marcandre]

Sorry about this. This has been fixed with #8914, expect a release in the next few days.

Until the next bugfix release, you can either fix them manually, or set your config with:

Layout/TrailingWhitespace:
  AllowInHeredoc: true

To fix them manually, either remove the trailing whitespaces, or replace them with #{' '}

[bpo]

Still fails for me in 1.1.0, with the slightly modified error:

Infinite loop detected in /linebreak_heredoc/test.rb and caused by Layout/HeredocIndentation, Layout/TrailingWhitespace, Lint/LiteralInInterpolation

edited to add: looks like #8975 is already tracking the new error