1 files changed, 93 insertions, 0 deletions
diff --git a/actionview/lib/action_view/dependency_tracker.rb b/actionview/lib/action_view/dependency_tracker.rb
new file mode 100644
index 0000000000..b2e8334077
--- /dev/null
+++ b/actionview/lib/action_view/dependency_tracker.rb
@@ -0,0 +1,93 @@
+require 'thread_safe'
+
+module ActionView
+  class DependencyTracker
+    @trackers = ThreadSafe::Cache.new
+
+    def self.find_dependencies(name, template)
+      tracker = @trackers[template.handler]
+
+      if tracker.present?
+        tracker.call(name, template)
+      else
+        []
+      end
+    end
+
+    def self.register_tracker(extension, tracker)
+      handler = Template.handler_for_extension(extension)
+      @trackers[handler] = tracker
+    end
+
+    def self.remove_tracker(handler)
+      @trackers.delete(handler)
+    end
+
+    class ERBTracker
+      EXPLICIT_DEPENDENCY = /# Template Dependency: (\S+)/
+
+      # Matches:
+      #   render partial: "comments/comment", collection: commentable.comments
+      #   render "comments/comments"
+      #   render 'comments/comments'
+      #   render('comments/comments')
+      #
+      #   render(@topic)         => render("topics/topic")
+      #   render(topics)         => render("topics/topic")
+      #   render(message.topics) => render("topics/topic")
+      RENDER_DEPENDENCY = /
+        render\s*                     # render, followed by optional whitespace
+        \(?                           # start an optional parenthesis for the render call
+        (partial:|:partial\s+=>)?\s*  # naming the partial, used with collection -- 1st capture
+        ([@a-z"'][@\w\/\."']+)        # the template name itself -- 2nd capture
+      /x
+
+      def self.call(name, template)
+        new(name, template).dependencies
+      end
+
+      def initialize(name, template)
+        @name, @template = name, template
+      end
+
+      def dependencies
+        render_dependencies + explicit_dependencies
+      end
+
+      attr_reader :name, :template
+      private :name, :template
+
+      private
+
+        def source
+          template.source
+        end
+
+        def directory
+          name.split("/")[0..-2].join("/")
+        end
+
+        def render_dependencies
+          source.scan(RENDER_DEPENDENCY).
+            collect(&:second).uniq.
+
+            # render(@topic)         => render("topics/topic")
+            # render(topics)         => render("topics/topic")
+            # render(message.topics) => render("topics/topic")
+            collect { |name| name.sub(/\A@?([a-z_]+\.)*([a-z_]+)\z/) { "#{$2.pluralize}/#{$2.singularize}" } }.
+
+            # render("headline") => render("message/headline")
+            collect { |name| name.include?("/") ? name : "#{directory}/#{name}" }.
+
+            # replace quotes from string renders
+            collect { |name| name.gsub(/["']/, "") }
+        end
+
+        def explicit_dependencies
+          source.scan(EXPLICIT_DEPENDENCY).flatten.uniq
+        end
+    end
+
+    register_tracker :erb, ERBTracker
+  end
+end