Clear definitions cache after file change

When the `elements.yml` or `page_layouts.yml` files change
the memoiziation gets resetted, so that the next app reload
includes the latest changes to these files.

This removes the need to restart the Rails server after one
changed an element definition or page layout.

lib/alchemy/element_definition.rb

@@ -42,6 +42,16 @@ def get(name)
         all.detect { |a| a["name"] == name }
       end
 
+      def reset!
+        @definitions = nil
+      end
+
+      # The absolute +elements.yml+ file path
+      # @return [Pathname]
+      def definitions_file_path
+        Rails.root.join("config", "alchemy", "elements.yml")
+      end
+
       private
 
       # Reads the element definitions from +config/alchemy/elements.yml+.
@@ -58,12 +68,6 @@ def read_definitions_file
             "Could not find elements.yml file! Please run `rails generate alchemy:install`"
         end
       end
-
-      # Returns the elements.yml file path
-      #
-      def definitions_file_path
-        Rails.root.join "config/alchemy/elements.yml"
-      end
     end
   end
 end

lib/alchemy/engine.rb

@@ -35,6 +35,23 @@ class Engine < Rails::Engine
       end
     end
 
+    initializer "alchemy.watch_definition_changes" do |app|
+      elements_reloader = app.config.file_watcher.new([ElementDefinition.definitions_file_path]) do
+        Rails.logger.info "[#{engine_name}] Reloading Element Definitions."
+        ElementDefinition.reset!
+      end
+      page_layouts_reloader = app.config.file_watcher.new([PageLayout.layouts_file_path]) do
+        Rails.logger.info "[#{engine_name}] Reloading Page Layouts."
+        PageLayout.reset!
+      end
+      [elements_reloader, page_layouts_reloader].each do |reloader|
+        app.reloaders << reloader
+        app.reloader.to_run do
+          reloader.execute_if_updated
+        end
+      end
+    end
+
     # Gutentag downcases all tags before save
     # and Gutentag validations are not case sensitive.
     # But we support having tags with uppercase characters.

lib/alchemy/page_layout.rb

@@ -41,6 +41,16 @@ def get(name)
         all.detect { |a| a["name"].casecmp(name).zero? }
       end
 
+      def reset!
+        @definitions = nil
+      end
+
+      # The absolute +page_layouts.yml+ file path
+      # @return [Pathname]
+      def layouts_file_path
+        Rails.root.join("config", "alchemy", "page_layouts.yml")
+      end
+
       private
 
       # Reads the layout definitions from +config/alchemy/page_layouts.yml+.
@@ -58,12 +68,6 @@ def read_definitions_file
           raise LoadError, "Could not find page_layouts.yml file! Please run `rails generate alchemy:install`"
         end
       end
-
-      # Returns the page_layouts.yml file path
-      #
-      def layouts_file_path
-        Rails.root.join "config/alchemy/page_layouts.yml"
-      end
     end
   end
 end

spec/libraries/element_definition_spec.rb

@@ -35,5 +35,13 @@ module Alchemy
         expect(ElementDefinition.get("default")).to eq({"name" => "default"})
       end
     end
+
+    describe ".reset!" do
+      it "sets @definitions to nil" do
+        ElementDefinition.all
+        ElementDefinition.reset!
+        expect(ElementDefinition.instance_variable_get(:@definitions)).to be_nil
+      end
+    end
   end
 end

spec/libraries/page_layout_spec.rb

@@ -67,5 +67,13 @@ module Alchemy
         expect(PageLayout.get("default")).to eq({"name" => "default"})
       end
     end
+
+    describe ".reset!" do
+      it "sets @definitions to nil" do
+        PageLayout.all
+        PageLayout.reset!
+        expect(PageLayout.instance_variable_get(:@definitions)).to be_nil
+      end
+    end
   end
 end