Merge pull request #275 from jeremy/defer-asset-precompile-from-initialization

Speed up app boot by deferring asset precompile

Author: jeremy

lib/sprockets/rails/helper.rb

@@ -21,7 +21,7 @@ def initialize(source)
       include Sprockets::Rails::Utils
 
       VIEW_ACCESSORS = [:assets_environment, :assets_manifest,
-                        :assets_precompile, :precompiled_assets,
+                        :assets_precompile, :precompiled_asset_checker,
                         :assets_prefix, :digest_assets, :debug_assets]
 
       def self.included(klass)
@@ -82,7 +82,7 @@ def asset_digest_path(path, options = {})
         if environment = assets_environment
           if asset = environment[path]
             unless options[:debug]
-              if !precompiled_assets.include?(asset.logical_path)
+              if !precompiled_asset_checker.call(asset.logical_path)
                 raise AssetNotPrecompiled.new(asset.logical_path)
               end
             end
@@ -220,7 +220,7 @@ def lookup_debug_asset(path, options = {})
 
           if asset = env[path, pipeline: :debug]
             original_path = asset.logical_path.gsub('.debug', '')
-            unless precompiled_assets.include?(original_path)
+            unless precompiled_asset_checker.call(original_path)
               raise AssetNotPrecompiled.new(original_path)
             end
           end

lib/sprockets/rails/utils.rb

@@ -6,11 +6,6 @@ module Utils
       def using_sprockets4?
         Gem::Version.new(Sprockets::VERSION) >= Gem::Version.new('4.0.0')
       end
-
-      # Internal: Generate a Set of all precompiled assets logical paths.
-      def build_precompiled_list(manifest, assets)
-        manifest.find(assets || []).map(&:logical_path)
-      end
     end
   end
 end

lib/sprockets/railtie.rb

@@ -27,8 +27,18 @@ class Configuration
     # Returns Sprockets::Manifest for app config.
     attr_accessor :assets_manifest
 
-    # Returns array of already precompiled assets
-    attr_accessor :precompiled_assets
+    # Called from asset helpers to alert you if you reference an asset URL that
+    # isn't precompiled and hence won't be available in production.
+    def asset_precompiled?(logical_path)
+      precompiled_assets.include? logical_path
+    end
+
+    # Lazy-load the precompile list so we don't cause asset compilation at app
+    # boot time, but ensure we cache the list so we don't recompute it for each
+    # request or test case.
+    def precompiled_assets
+      @precompiled_assets ||= assets_manifest.find(config.assets.precompile).map(&:logical_path)
+    end
   end
 
   class Engine < Railtie
@@ -155,11 +165,8 @@ def self.build_manifest(app)
         app.routes.prepend do
           mount app.assets => config.assets.prefix
         end
-        app.assets_manifest = build_manifest(app)
-        app.precompiled_assets = build_precompiled_list(app.assets_manifest, config.assets.precompile)
-      else
-        app.assets_manifest = build_manifest(app)
       end
+      app.assets_manifest = build_manifest(app)
 
       ActionDispatch::Routing::RouteWrapper.class_eval do
         class_attribute :assets_prefix
@@ -184,7 +191,9 @@ def self.build_manifest(app)
 
         self.assets_environment = app.assets
         self.assets_manifest = app.assets_manifest
-        self.precompiled_assets = app.precompiled_assets
+
+        # Expose the app precompiled asset check to the view
+        self.precompiled_asset_checker = -> logical_path { app.asset_precompiled? logical_path }
       end
     end
   end

test/test_helper.rb

@@ -25,7 +25,8 @@ def setup
     @view.assets_manifest    = @manifest
     @view.assets_prefix      = "/assets"
     @view.assets_precompile  = %w( manifest.js )
-    @view.precompiled_assets = @view.build_precompiled_list(@manifest, @view.assets_precompile)
+    precompiled_assets = @manifest.find(@view.assets_precompile).map(&:logical_path)
+    @view.precompiled_asset_checker = -> logical_path { precompiled_assets.include? logical_path }
     @view.request = ActionDispatch::Request.new({
       "rack.url_scheme" => "https"
     })
@@ -730,7 +731,8 @@ def test_stylesheet_link_tag_integrity
 class AssetUrlHelperLinksTarget < HelperTest
   def test_precompile_allows_links
     @view.assets_precompile = ["url.css"]
-    @view.precompiled_assets = @view.build_precompiled_list(@manifest, @view.assets_precompile)
+    precompiled_assets = @manifest.find(@view.assets_precompile).map(&:logical_path)
+    @view.precompiled_asset_checker = -> logical_path { precompiled_assets.include? logical_path }
     assert @view.asset_path("url.css")
     assert @view.asset_path("logo.png")