Read digests of assets from manifest.yml if config.assets.manifest is on

1 files changed, 16 insertions, 1 deletions

diff --git a/actionpack/lib/sprockets/helpers/rails_helper.rb b/actionpack/lib/sprockets/helpers/rails_helper.rb
index 062aa4dae5..8e7eb182fd 100644
--- a/actionpack/lib/sprockets/helpers/rails_helper.rb
+++ b/actionpack/lib/sprockets/helpers/rails_helper.rb
@@ -14,6 +14,7 @@ module Sprockets
           paths = RailsHelper::AssetPaths.new(config, controller)
           paths.asset_environment = asset_environment
           paths.asset_prefix      = asset_prefix
+          paths.asset_digests     = asset_digests
           paths
         end
       end
@@ -76,6 +77,10 @@ module Sprockets
         Rails.application.config.assets.prefix
       end
 
+      def asset_digests
+        Rails.application.config.assets.digests
+      end
+
       # Override to specify an alternative asset environment for asset
       # path generation. The environment should already have been mounted
       # at the prefix returned by +asset_prefix+.
@@ -84,7 +89,9 @@ module Sprockets
       end
 
       class AssetPaths < ::ActionView::AssetPaths #:nodoc:
-        attr_accessor :asset_environment, :asset_prefix
+        attr_accessor :asset_environment, :asset_prefix, :asset_digests
+
+        class AssetNotPrecompiledError < StandardError; end
 
         def compute_public_path(source, dir, ext=nil, include_host=true, protocol=nil)
           super(source, asset_prefix, ext, include_host, protocol)
@@ -103,6 +110,14 @@ module Sprockets
         end
 
         def digest_for(logical_path)
+          if asset_digests && (digest = asset_digests[logical_path])
+            return digest
+          end
+
+          if digest.nil? && Rails.application.config.assets.precompile_only
+            raise AssetNotPrecompiledError
+          end
+
           if asset = asset_environment[logical_path]
             return asset.digest_path
           end