Set config.action_view.warn_cache_misses = true to receive a warning if you perform an action that results in an expensive disk operation that could be cached

3 files changed, 34 insertions, 5 deletions

diff --git a/actionpack/lib/action_controller/base.rb b/actionpack/lib/action_controller/base.rb
index 6926941396..df94f78f18 100755
--- a/actionpack/lib/action_controller/base.rb
+++ b/actionpack/lib/action_controller/base.rb
@@ -431,7 +431,7 @@ module ActionController #:nodoc:
       end
 
       def view_paths=(value)
-        @view_paths = ActionView::PathSet.new(Array(value)) if value
+        @view_paths = ActionView::Base.process_view_paths(value) if value
       end
 
       # Adds a view_path to the front of the view_paths array.
@@ -652,7 +652,7 @@ module ActionController #:nodoc:
       end
 
       def view_paths=(value)
-        @template.view_paths = PathSet.new(value)
+        @template.view_paths = ActionView::Base.process_view_paths(value)
       end
 
       # Adds a view_path to the front of the view_paths array.
diff --git a/actionpack/lib/action_view/base.rb b/actionpack/lib/action_view/base.rb
index 9d4d897dbc..989e92a890 100644
--- a/actionpack/lib/action_view/base.rb
+++ b/actionpack/lib/action_view/base.rb
@@ -185,6 +185,10 @@ module ActionView #:nodoc:
     @@debug_rjs = false
     cattr_accessor :debug_rjs
 
+    # A warning will be displayed whenever an action results in a cache miss on your view paths.
+    @@warn_cache_misses = false
+    cattr_accessor :warn_cache_misses
+
     attr_internal :request
 
     delegate :request_forgery_protection_token, :template, :params, :session, :cookies, :response, :headers,
@@ -212,6 +216,10 @@ module ActionView #:nodoc:
       return helpers
     end
 
+    def self.process_view_paths(value)
+      ActionView::PathSet.new(Array(value))
+    end
+
     def initialize(view_paths = [], assigns_for_first_render = {}, controller = nil)#:nodoc:
       @assigns = assigns_for_first_render
       @assigns_added = nil
@@ -222,7 +230,7 @@ module ActionView #:nodoc:
     attr_reader :view_paths
 
     def view_paths=(paths)
-      @view_paths = PathSet.new(Array(paths))
+      @view_paths = self.class.process_view_paths(paths)
     end
 
     # Renders the template present at <tt>template_path</tt> (relative to the view_paths array).
@@ -311,7 +319,17 @@ module ActionView #:nodoc:
         @template_format = :html
         template
       else
-        Template.new(template_path, view_paths)
+        template = Template.new(template_path, view_paths)
+
+        if self.class.warn_cache_misses && logger = ActionController::Base.logger
+          logger.debug "[PERFORMANCE] Rendering a template that was " +
+            "not found in view path. Templates outside the view path are " +
+            "not cached and result in expensive disk operations. Move this " + 
+            "file into #{view_paths.join(':')} or add the folder to your " + 
+            "view path list"
+        end
+
+        template
       end
     end
 
diff --git a/actionpack/lib/action_view/paths.rb b/actionpack/lib/action_view/paths.rb
index 0fa7d3dad3..b0ab7d0c67 100644
--- a/actionpack/lib/action_view/paths.rb
+++ b/actionpack/lib/action_view/paths.rb
@@ -1,7 +1,18 @@
 module ActionView #:nodoc:
   class PathSet < Array #:nodoc:
     def self.type_cast(obj)
-      obj.is_a?(String) ? Path.new(obj) : obj
+      if obj.is_a?(String)
+        if Base.warn_cache_misses && defined?(Rails) && Rails.initialized?
+          Rails.logger.debug "[PERFORMANCE] Processing view path during a " +
+            "request. This an expense disk operation that should be done at " +
+            "boot. You can manually process this view path with " +
+            "ActionView::Base.process_view_paths(#{obj.inspect}) and set it " +
+            "as your view path"
+        end
+        Path.new(obj)
+      else
+        obj
+      end
     end
 
     class Path #:nodoc: