Ensure changing RAILS_GROUPS will load the proper dependencies.

actionpack/lib/sprockets/assets.rake

@@ -1,18 +1,21 @@
 namespace :assets do
-  task :ensure_env do
-    ENV["RAILS_GROUPS"] ||= "assets"
-    ENV["RAILS_ENV"]    ||= "production"
-  end
-
   desc "Compile all the assets named in config.assets.precompile"
-  task :precompile => :ensure_env do
-    Rake::Task["environment"].invoke
-    Sprockets::Helpers::RailsHelper
+  task :precompile do
+    # We need to do this dance because RAILS_GROUPS is used
+    # too early in the boot process and changing here is already too late.
+    if ENV["RAILS_GROUPS"].to_s.empty?
+      ENV["RAILS_GROUPS"] = "assets"
+      ENV["RAILS_ENV"]  ||= "production"
+      Kernel.exec $0, *ARGV
+    else
+      Rake::Task["environment"].invoke
+      Sprockets::Helpers::RailsHelper
 
-    assets = Rails.application.config.assets.precompile
-    # Always perform caching so that asset_path appends the timestamps to file references.
-    Rails.application.config.action_controller.perform_caching = true
-    Rails.application.assets.precompile(*assets)
+      assets = Rails.application.config.assets.precompile
+      # Always perform caching so that asset_path appends the timestamps to file references.
+      Rails.application.config.action_controller.perform_caching = true
+      Rails.application.assets.precompile(*assets)
+    end
   end
 
   desc "Remove compiled assets"
@@ -21,4 +24,4 @@ namespace :assets do
     public_asset_path = Rails.public_path + assets.prefix
     rm_rf public_asset_path, :secure => true
   end
-end
+end