Allow registering javascript/stylesheet_expansions to existing symbols

actionpack/lib/action_view/helpers/asset_tag_helper.rb

@@ -375,7 +375,10 @@ def javascript_include_tag(*sources)
       #     <script type="text/javascript" src="/javascripts/body.js"></script>
       #     <script type="text/javascript" src="/javascripts/tail.js"></script>
       def self.register_javascript_expansion(expansions)
-        @@javascript_expansions.merge!(expansions)
+        expansions.each do |key, values|
+          @@javascript_expansions[key] ||= []
+          @@javascript_expansions[key] += Array(values)
+        end
       end
 
       # Register one or more stylesheet files to be included when <tt>symbol</tt>
@@ -390,7 +393,10 @@ def self.register_javascript_expansion(expansions)
       #     <link href="/stylesheets/body.css"  media="screen" rel="stylesheet" type="text/css" />
       #     <link href="/stylesheets/tail.css"  media="screen" rel="stylesheet" type="text/css" />
       def self.register_stylesheet_expansion(expansions)
-        @@stylesheet_expansions.merge!(expansions)
+        expansions.each do |key, values|
+          @@stylesheet_expansions[key] ||= []
+          @@stylesheet_expansions[key] += Array(values)
+        end
       end
 
       def self.reset_javascript_include_default
@@ -860,7 +866,7 @@ def expand_stylesheet_sources(sources, recursive)
         def determine_source(source, collection)
           case source
           when Symbol
-            collection[source] || raise(ArgumentError, "No expansion found for #{source.inspect}")
+            collection[source].present? ? collection[source] : raise(ArgumentError, "No expansion found for #{source.inspect}")
           else
             source
           end

actionpack/test/template/asset_tag_helper_test.rb

@@ -47,13 +47,19 @@ def host_with_port() 'localhost' end
     ActionView::Helpers::AssetTagHelper::register_javascript_expansion :defaults => ['prototype', 'effects', 'dragdrop', 'controls', 'rails']
   end
 
-  def url_for(*args)
-    "http://www.example.com"
-  end
-
   def teardown
+    super
     config.perform_caching = false
     ENV.delete('RAILS_ASSET_ID')
+
+    ActionView::Helpers::AssetTagHelper.module_eval do
+      javascript_expansions.clear
+      stylesheet_expansions.clear
+    end
+  end
+
+  def url_for(*args)
+    "http://www.example.com"
   end
 
   AutoDiscoveryToTag = {
@@ -268,6 +274,13 @@ def test_custom_javascript_expansions_and_defaults_puts_application_js_at_the_en
     assert_dom_equal  %(<script src="/javascripts/controls.js" type="text/javascript"></script>\n<script src="/javascripts/prototype.js" type="text/javascript"></script>\n<script src="/javascripts/effects.js" type="text/javascript"></script>\n<script src="/javascripts/dragdrop.js" type="text/javascript"></script>\n<script src="/javascripts/controls.js" type="text/javascript"></script>\n<script src="/javascripts/rails.js" type="text/javascript"></script>\n<script src="/javascripts/bank.js" type="text/javascript"></script>\n<script src="/javascripts/robber.js" type="text/javascript"></script>\n<script src="/javascripts/effects.js" type="text/javascript"></script>\n<script src="/javascripts/application.js" type="text/javascript"></script>), javascript_include_tag('controls',:defaults, :robbery, 'effects')
   end
 
+  def test_registering_javascript_expansions_merges_with_existing_expansions
+    ENV["RAILS_ASSET_ID"] = ""
+    ActionView::Helpers::AssetTagHelper::register_javascript_expansion :can_merge => ['bank']
+    ActionView::Helpers::AssetTagHelper::register_javascript_expansion :can_merge => ['robber']
+    assert_dom_equal  %(<script src="/javascripts/bank.js" type="text/javascript"></script>\n<script src="/javascripts/robber.js" type="text/javascript"></script>), javascript_include_tag(:can_merge)
+  end
+
   def test_custom_javascript_expansions_with_undefined_symbol
     ActionView::Helpers::AssetTagHelper::register_javascript_expansion :monkey => nil
     assert_raise(ArgumentError) { javascript_include_tag('first', :monkey, 'last') }
@@ -334,6 +347,13 @@ def test_custom_stylesheet_expansions_with_undefined_symbol
     assert_raise(ArgumentError) { stylesheet_link_tag('first', :monkey, 'last') }
   end
 
+  def test_registering_stylesheet_expansions_merges_with_existing_expansions
+    ENV["RAILS_ASSET_ID"] = ""
+    ActionView::Helpers::AssetTagHelper::register_stylesheet_expansion :can_merge => ['bank']
+    ActionView::Helpers::AssetTagHelper::register_stylesheet_expansion :can_merge => ['robber']
+    assert_dom_equal  %(<link href="/stylesheets/bank.css" media="screen" rel="stylesheet" type="text/css" />\n<link href="/stylesheets/robber.css" media="screen" rel="stylesheet" type="text/css" />), stylesheet_link_tag(:can_merge)
+  end
+
   def test_image_path
     ImagePathToTag.each { |method, tag| assert_dom_equal(tag, eval(method)) }
   end