1 files changed, 141 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..e34bdd4a46
--- /dev/null
+++ b/actionview/lib/action_view/dependency_tracker.rb
@@ -0,0 +1,141 @@
+require 'thread_safe'
+
+module ActionView
+  class DependencyTracker # :nodoc:
+    @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 # :nodoc:
+      EXPLICIT_DEPENDENCY = /# Template Dependency: (\S+)/
+
+      # A valid ruby identifier - suitable for class, method and specially variable names
+      IDENTIFIER = /
+        [[:alpha:]_] # at least one uppercase letter, lowercase letter or underscore
+        [[:word:]]*  # followed by optional letters, numbers or underscores
+      /x
+
+      # Any kind of variable name. e.g. @instance, @@class, $global or local.
+      # Possibly following a method call chain
+      VARIABLE_OR_METHOD_CHAIN = /
+        (?:\$|@{1,2})?            # optional global, instance or class variable indicator
+        (?:#{IDENTIFIER}\.)*      # followed by an optional chain of zero-argument method calls
+        (?<dynamic>#{IDENTIFIER}) # and a final valid identifier, captured as DYNAMIC
+      /x
+
+      # A simple string literal. e.g. "School's out!"
+      STRING = /
+        (?<quote>['"]) # an opening quote
+        (?<static>.*?) # with anything inside, captured as STATIC
+        \k<quote>      # and a matching closing quote
+      /x
+
+      # Part of any hash containing the :partial key
+      PARTIAL_HASH_KEY = /
+        (?:\bpartial:|:partial\s*=>) # partial key in either old or new style hash syntax
+        \s*                          # followed by optional spaces
+      /x
+
+      # Part of any hash containing the :layout key
+      LAYOUT_HASH_KEY = /
+        (?:\blayout:|:layout\s*=>)   # layout key in either old or new style hash syntax
+        \s*                          # followed by optional spaces
+      /x
+
+      # Matches:
+      #   partial: "comments/comment", collection: @all_comments => "comments/comment"
+      #   (object: @single_comment, partial: "comments/comment") => "comments/comment"
+      #
+      #   "comments/comments"
+      #   'comments/comments'
+      #   ('comments/comments')
+      #
+      #   (@topic)         => "topics/topic"
+      #    topics          => "topics/topic"
+      #   (message.topics) => "topics/topic"
+      RENDER_ARGUMENTS = /\A
+        (?:\s*\(?\s*)                                  # optional opening paren surrounded by spaces
+        (?:.*?#{PARTIAL_HASH_KEY}|#{LAYOUT_HASH_KEY})? # optional hash, up to the partial or layout key declaration
+        (?:#{STRING}|#{VARIABLE_OR_METHOD_CHAIN})      # finally, the dependency name of interest
+      /xm
+
+      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
+          render_dependencies = []
+          render_calls = source.split(/\brender\b/).drop(1)
+
+          render_calls.each do |arguments|
+            arguments.scan(RENDER_ARGUMENTS) do
+              add_dynamic_dependency(render_dependencies, Regexp.last_match[:dynamic])
+              add_static_dependency(render_dependencies, Regexp.last_match[:static])
+            end
+          end
+
+          render_dependencies.uniq
+        end
+
+        def add_dynamic_dependency(dependencies, dependency)
+          if dependency
+            dependencies << "#{dependency.pluralize}/#{dependency.singularize}"
+          end
+        end
+
+        def add_static_dependency(dependencies, dependency)
+          if dependency
+            if dependency.include?('/')
+              dependencies << dependency
+            else
+              dependencies << "#{directory}/#{dependency}"
+            end
+          end
+        end
+
+        def explicit_dependencies
+          source.scan(EXPLICIT_DEPENDENCY).flatten.uniq
+        end
+    end
+
+    register_tracker :erb, ERBTracker
+  end
+end