Fix bug with --auto-gen-config and a file that does not exist (#3239)

CHANGELOG.md

@@ -55,6 +55,7 @@
 * [#3056](https://github.com/bbatsov/rubocop/issues/3056): Fix `Style/StringLiterals` to register offenses on non-ascii strings. ([@deivid-rodriguez][])
 * [#2986](https://github.com/bbatsov/rubocop/issues/2986): Fix `RedundantBlockCall` to not report calls that pass block arguments, or where the block has been overridden. ([@owst][])
 * [#3223](https://github.com/bbatsov/rubocop/issues/3223): Return can take many arguments. ([@ptarjan][])
+* [#3239](https://github.com/bbatsov/rubocop/pull/3239): Fix bug with --auto-gen-config and a file that does not exist. ([@meganemura][])
 
 ### Changes
 

lib/rubocop/formatter/disabled_config_formatter.rb

@@ -25,6 +25,12 @@ class << self
         attr_accessor :config_to_allow_offenses, :detected_styles
       end
 
+      def initialize(output, options = {})
+        super
+        @cops_with_offenses ||= Hash.new(0)
+        @files_with_offenses ||= {}
+      end
+
       def file_started(_file, _file_info)
         @exclude_limit_option = @options[:exclude_limit]
         @exclude_limit = (
@@ -34,8 +40,6 @@ def file_started(_file, _file_info)
       end
 
       def file_finished(file, offenses)
-        @cops_with_offenses ||= Hash.new(0)
-        @files_with_offenses ||= {}
         offenses.each do |o|
           @cops_with_offenses[o.cop_name] += 1
           @files_with_offenses[o.cop_name] ||= []

spec/rubocop/cli/cli_auto_gen_config_spec.rb

@@ -490,5 +490,9 @@ def abs(path)
                 '  Enabled: false',
                 ''].join("\n"))
     end
+
+    it 'can be called when there are no files to inspection' do
+      expect(cli.run(['--auto-gen-config'])).to eq(0)
+    end
   end
 end

spec/rubocop/formatter/disabled_config_formatter_spec.rb

@@ -125,6 +125,14 @@ def o.path
                                        ''].flatten.join("\n"))
         end
 
+        it 'creates a .rubocop_todo.yml even if RuboCop does not inspect ' \
+           'any files' do
+          formatter.finished([])
+          expect(output.string).to eq(format(described_class::HEADING,
+                                             'rubocop --auto-gen-config') +
+                                      "\n")
+        end
+
         context 'when exclude_limit option is passed into constructor' do
           let(:formatter) { described_class.new(output, exclude_limit: 5) }