Provide initialize_on_precompile which, when set to false, does not initialize the app for precompilation. Defaults to true.

actionpack/lib/sprockets/assets.rake

@@ -54,7 +54,11 @@ namespace :assets do
   end
 
   task :environment do
-    Rails.application.initialize!(:assets)
-    Sprockets::Bootstrap.new(Rails.application).run
+    if Rails.application.config.assets.initialize_on_precompile
+      Rake::Task["environment"].invoke
+    else
+      Rails.application.initialize!(:assets)
+      Sprockets::Bootstrap.new(Rails.application).run
+    end
   end
 end

railties/CHANGELOG

@@ -17,7 +17,8 @@
 
 * Add jquery-rails to Gemfile of plugins, test/dummy app needs it. Closes #3091. [Santiago Pastorino]
 
-* `rake assets:precompile` loads the application but does not initialize it.
+* Add config.assets.initialize_on_precompile which, when set to false, forces
+  `rake assets:precompile` to load the application but does not initialize it.
 
   To the app developer, this means configuration add in
   config/initializers/* will not be executed.

railties/lib/rails/application/configuration.rb

@@ -37,19 +37,20 @@ module Rails
         @cache_store                 = [ :file_store, "#{root}/tmp/cache/" ]
 
         @assets = ActiveSupport::OrderedOptions.new
-        @assets.enabled         = false
-        @assets.paths           = []
-        @assets.precompile      = [ Proc.new{ |path| !File.extname(path).in?(['.js', '.css']) },
-                                    /(?:\/|\\|\A)application\.(css|js)$/ ]
-        @assets.prefix          = "/assets"
-        @assets.version         = ''
-        @assets.debug           = false
-        @assets.compile         = true
-        @assets.digest          = false
-        @assets.manifest        = nil
-        @assets.cache_store     = [ :file_store, "#{root}/tmp/cache/assets/" ]
-        @assets.js_compressor   = nil
-        @assets.css_compressor  = nil
+        @assets.enabled                  = false
+        @assets.paths                    = []
+        @assets.precompile               = [ Proc.new{ |path| !File.extname(path).in?(['.js', '.css']) },
+                                             /(?:\/|\\|\A)application\.(css|js)$/ ]
+        @assets.prefix                   = "/assets"
+        @assets.version                  = ''
+        @assets.debug                    = false
+        @assets.compile                  = true
+        @assets.digest                   = false
+        @assets.manifest                 = nil
+        @assets.cache_store              = [ :file_store, "#{root}/tmp/cache/assets/" ]
+        @assets.js_compressor            = nil
+        @assets.css_compressor           = nil
+        @assets.initialize_on_precompile = true
       end
 
       def compiled_asset_path

railties/test/application/assets_test.rb

@@ -395,7 +395,30 @@ module ApplicationTests
       assert_match(/<script src="\/assets\/xmlhr-([0-z]+)\.js\?body=1" type="text\/javascript"><\/script>/, last_response.body)
     end
 
+    test "assets can access model information when precompiling" do
+      app_file "app/models/post.rb", "class Post; end"
+      app_file "app/assets/javascripts/application.js", "//= require_tree ."
+      app_file "app/assets/javascripts/xmlhr.js.erb", "<%= Post.name %>"
+
+      add_to_config "config.assets.digest = false"
+      precompile!
+      assert_equal "Post;\n", File.read("#{app_path}/public/assets/application.js")
+    end
+
+    test "assets can't access model information when precompiling if not initializing the app" do
+      app_file "app/models/post.rb", "class Post; end"
+      app_file "app/assets/javascripts/application.js", "//= require_tree ."
+      app_file "app/assets/javascripts/xmlhr.js.erb", "<%= defined?(Post) || :NoPost %>"
+
+      add_to_config "config.assets.digest = false"
+      add_to_config "config.assets.initialize_on_precompile = false"
+
+      precompile!
+      assert_equal "NoPost;\n", File.read("#{app_path}/public/assets/application.js")
+    end
+
     private
+
     def app_with_assets_in_view
       app_file "app/assets/javascripts/application.js", "//= require_tree ."
       app_file "app/assets/javascripts/xmlhr.js", "function f1() { alert(); }"