Open Vim/MacVim or other $EDITOR on each offense in RuboCop

editor.rb

require "rubocop"

class OpenEditor < RuboCop::Formatter::ProgressFormatter
  VimFamily = %w{vim gvim mvim}

  def report_file file, offenses
    super

    if editor_supports_lines?
      offenses.each do |offense|
        run_editor file, offense unless offense.corrected?
      end
    else
      run_editor file
    end
  end

  def editor
    ENV["EDITOR"]
  end

  def editor_supports_lines?
    VimFamily.include? editor
  end

  def run_editor file, offense = nil
    if offense
      args = args_with_offense file, offense
    else
      args = args_without_offense file
    end

    original_modification_time = File.mtime file

    system editor, *args

    return if original_modification_time != File.mtime(file)

    output.puts "No changes made to the file. Aborting."
    exit 1
  end

  def args_with_offense file, offense
    case editor
    when *VimFamily
      # Text vim will hide our console output, so we need to echo the message again
      # inside vim.
      message = offense.message.to_s
        .gsub('"', "double quote")
        .gsub("'", "quote")

      [
        "+#{offense.line}",           # go to line
        "-f",                         # gvim/mvim will not detach from shell
        "-c", "echomsg '#{message}'",
        file
      ]
    else
      [file]
    end
  end

  def args_without_offense file
    [file]
  end
end

usage.sh

rubocop -r ./editor.rb -f OpenEditor