4 files changed, 41 insertions, 13 deletions
diff --git a/actionpack/lib/action_view/helpers/asset_tag_helpers/asset_include_tag.rb b/actionpack/lib/action_view/helpers/asset_tag_helpers/asset_include_tag.rb
index e52797042f..52eb43a1cd 100644
--- a/actionpack/lib/action_view/helpers/asset_tag_helpers/asset_include_tag.rb
+++ b/actionpack/lib/action_view/helpers/asset_tag_helpers/asset_include_tag.rb
@@ -11,7 +11,9 @@ module ActionView
         attr_reader :config, :asset_paths
 
         class_attribute :expansions
-        self.expansions = { }
+        def self.inherited(base)
+          base.expansions = { }
+        end
 
         def initialize(config, asset_paths)
           @config = config
@@ -69,9 +71,21 @@ module ActionView
             if sources.first == :all
               collect_asset_files(custom_dir, ('**' if recursive), "*.#{extension}")
             else
-              sources.collect do |source|
-                determine_source(source, expansions)
-              end.flatten
+              sources.inject([]) do |list, source|
+                determined_source = determine_source(source, expansions)
+                update_source_list(list, determined_source)
+              end
+            end
+          end
+
+          def update_source_list(list, source)
+            case source
+            when String
+              list.delete(source)
+              list << source
+            when Array
+              updated_sources = source - list
+              list.concat(updated_sources)
             end
           end
 
diff --git a/actionpack/lib/action_view/helpers/asset_tag_helpers/asset_paths.rb b/actionpack/lib/action_view/helpers/asset_tag_helpers/asset_paths.rb
index b4e61f2034..014a03c54d 100644
--- a/actionpack/lib/action_view/helpers/asset_tag_helpers/asset_paths.rb
+++ b/actionpack/lib/action_view/helpers/asset_tag_helpers/asset_paths.rb
@@ -21,7 +21,7 @@ module ActionView
           @controller = controller
         end
 
-        # Add the the extension +ext+ if not present. Return full URLs otherwise untouched.
+        # Add the extension +ext+ if not present. Return full URLs otherwise untouched.
         # Prefix with <tt>/dir/</tt> if lacking a leading +/+. Account for relative URL
         # roots. Rewrite the asset path for cache-busting asset ids. Include
         # asset host, if configured, with the correct request protocol.
diff --git a/actionpack/lib/action_view/helpers/asset_tag_helpers/javascript_tag_helpers.rb b/actionpack/lib/action_view/helpers/asset_tag_helpers/javascript_tag_helpers.rb
index 6581e1d6f2..b9126af944 100644
--- a/actionpack/lib/action_view/helpers/asset_tag_helpers/javascript_tag_helpers.rb
+++ b/actionpack/lib/action_view/helpers/asset_tag_helpers/javascript_tag_helpers.rb
@@ -33,13 +33,21 @@ module ActionView
               all_asset_files = (collect_asset_files(custom_dir, ('**' if recursive), "*.#{extension}") - ['application']) << 'application'
               ((determine_source(:defaults, expansions).dup & all_asset_files) + all_asset_files).uniq
             else
-              expanded_sources = sources.collect do |source|
-                determine_source(source, expansions)
-              end.flatten
-              expanded_sources << "application" if sources.include?(:defaults) && File.exist?(File.join(custom_dir, "application.#{extension}"))
+              expanded_sources = sources.inject([]) do |list, source|
+                determined_source = determine_source(source, expansions)
+                update_source_list(list, determined_source)
+              end
+              add_application_js(expanded_sources, sources)
               expanded_sources
             end
           end
+
+          def add_application_js(expanded_sources, sources)
+            if sources.include?(:defaults) && File.exist?(File.join(custom_dir, "application.#{extension}"))
+              expanded_sources.delete('application')
+              expanded_sources << "application"
+            end
+          end
       end
 
 
@@ -59,7 +67,10 @@ module ActionView
           #     <script type="text/javascript" src="/javascripts/body.js"></script>
           #     <script type="text/javascript" src="/javascripts/tail.js"></script>
           def register_javascript_expansion(expansions)
-            JavascriptIncludeTag.expansions.merge!(expansions)
+            js_expansions = JavascriptIncludeTag.expansions
+            expansions.each do |key, values|
+              js_expansions[key] = (js_expansions[key] || []) | Array(values) if values
+            end
           end
         end
 
@@ -170,4 +181,4 @@ module ActionView
 
     end
   end
-end
-\ No newline at end of file
+end
diff --git a/actionpack/lib/action_view/helpers/asset_tag_helpers/stylesheet_tag_helpers.rb b/actionpack/lib/action_view/helpers/asset_tag_helpers/stylesheet_tag_helpers.rb
index d02b28d7f6..f3e041de95 100644
--- a/actionpack/lib/action_view/helpers/asset_tag_helpers/stylesheet_tag_helpers.rb
+++ b/actionpack/lib/action_view/helpers/asset_tag_helpers/stylesheet_tag_helpers.rb
@@ -44,7 +44,10 @@ module ActionView
           #     <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 register_stylesheet_expansion(expansions)
-            StylesheetIncludeTag.expansions.merge!(expansions)
+            style_expansions = StylesheetIncludeTag.expansions
+            expansions.each do |key, values|
+              style_expansions[key] = (style_expansions[key] || []) | Array(values) if values
+            end
           end
         end
 
@@ -141,4 +144,4 @@ module ActionView
 
     end
   end
-end
-\ No newline at end of file
+end