Support hot-reloading of feature flags

This fixes a problem where a full application
restart is required:

- for a change
- for a addition
- for an update of `definition.rb`

config/initializers/0_inject_feature_flags.rb

@@ -3,3 +3,4 @@
 
 Feature.register_feature_groups
 Feature.register_definitions
+Feature.register_hot_reloader unless Rails.configuration.cache_classes

lib/feature.rb

@@ -137,6 +137,12 @@ class Feature
       Feature::Definition.load_all!
     end
 
+    def register_hot_reloader
+      return unless check_feature_flags_definition?
+
+      Feature::Definition.register_hot_reloader!
+    end
+
     private
 
     def flipper

lib/feature/definition.rb

@@ -107,6 +107,20 @@ class Feature
         end
       end
 
+      def register_hot_reloader!
+        # Reload feature flags on change of this file or any `.yml`
+        file_watcher = Rails.configuration.file_watcher.new(reload_files, reload_directories) do
+          # We use `Feature::Definition` as on Ruby code-reload
+          # a new class definition is created
+          Feature::Definition.load_all!
+        end
+
+        Rails.application.reloaders << file_watcher
+        Rails.application.reloader.to_run { file_watcher.execute_if_updated }
+
+        file_watcher
+      end
+
       private
 
       def load_from_file(path)
@@ -130,6 +144,19 @@ class Feature
           definitions[definition.key] = definition
         end
       end
+
+      def reload_files
+        [File.expand_path(__FILE__)]
+      end
+
+      def reload_directories
+        paths.each_with_object({}) do |path, result|
+          path = File.dirname(path)
+          Dir.glob(path).each do |matching_dir|
+            result[matching_dir] = 'yml'
+          end
+        end
+      end
     end
   end
 end

spec/factories/diff_position.rb

@@ -53,7 +53,10 @@ FactoryBot.define do
     factory :image_diff_position do
       position_type { 'image' }
       x { 1 }
-      y { 1 }
+      # Fix:
+      # NoMethodError: undefined method `end_line=' for nil:NilClass
+      # from /usr/lib/ruby/2.6.0/psych/tree_builder.rb:133:in `set_end_location'
+      add_attribute(:y) { 1 }
       width { 10 }
       height { 10 }
     end