Fix generating ignore list when one exists already

lib/standard/runners/genignore.rb

@@ -12,6 +12,7 @@ def call(config)
           # Run Rubocop to generate the files with errors into the temp file.
           config.rubocop_options[:formatters] = [["json", temp_file.path]]
           config.rubocop_options[:out] = temp_file.path
+          remove_project_files_from_ignore_list(config)
           exit_code = Runners::Rubocop.new.call(config)
 
           result = JSON.parse(temp_file.read)
@@ -39,6 +40,14 @@ def call(config)
           temp_file.unlink
         end
       end
+
+      # FIXME: This will also remove files which are in
+      # `Standard::CreatesConfigStore::ConfiguresIgnoredPaths::DEFAULT_IGNORES`.
+      def remove_project_files_from_ignore_list(config)
+        options_config = config.rubocop_config_store.instance_variable_get("@options_config")
+        options_config["AllCops"] ||= []
+        options_config["AllCops"]["Exclude"] = []
+      end
     end
   end
 end

test/standard/runners/genignore_test.rb

@@ -30,6 +30,17 @@ def test_todo_generated
   def create_config(config_path)
     store = RuboCop::ConfigStore.new.tap do |config_store|
       config_store.options_config = config_path
+
+      # Simulate a `.standard_todo.yml` that contains an ignore file:
+      #
+      #   ---
+      #   ignore:
+      #     - errors_one.rb
+      #
+      options_config = config_store.instance_variable_get("@options_config")
+      options_config["AllCops"] ||= []
+      options_config["AllCops"]["Exclude"] ||= []
+      options_config["AllCops"]["Exclude"] |= [path("errors_one.rb")]
     end
 
     Standard::Config.new(nil, ["."], {}, store)