Fix(SprocketsRenderer) support Sprockets::Manifest if assets were precompiled

Author: rmosolgo

lib/react/server_rendering/sprockets_renderer.rb

@@ -11,7 +11,7 @@ def initialize(options={})
         js_code = CONSOLE_POLYFILL.dup
 
         filenames.each do |filename|
-          js_code << ::Rails.application.assets[filename].to_s
+          js_code << get_asset_content(filename)
         end
 
         super(options.merge(code: js_code))
@@ -58,6 +58,31 @@ def after_render(component_name, props, prerender_options)
           }
         })(console.history);
       JS
+
+      # Given an asset name, return the fully-compiled body of that asset.
+      #
+      # Out of the box, it supports a Sprockets::Environment (application.assets)
+      # and a Sprockets::Manifest (application.assets_manifest), which covers the
+      # default Rails setups.
+      #
+      # Make a `server.js` which has `//= require react-server` and `//= require components`.
+      # Then add `server` to the precompile list, eg `Rails.application.config.assets.precompile += %w( server.js )`.
+      #
+      # In production, react-rails will use the precompiled file.
+      #
+      # TODO: what if the assets aren't on the local server (maybe they're on a CDN?)
+      # Can we check for asset_host configuration here?
+      def get_asset_content(asset_name)
+        if ::Rails.application.config.assets.compile
+          ::Rails.application.assets[asset_name].to_s
+        else
+          manifest = ::Rails.application.assets_manifest
+          # Find the corresponding compiled file:
+          asset_path = manifest.assets[asset_name] || raise("No compiled asset for #{asset_name}, was it precompiled?")
+          asset_full_path = ::Rails.root.join("public", manifest.directory, asset_path)
+          File.read(asset_full_path)
+        end
+      end
     end
   end
 end