Extend cache busting to allow for path manipulation

lib/compass/configuration/data.rb

@@ -71,8 +71,10 @@ module Compass
       end
 
       # When called with a block, defines the cache buster strategy to be used.
-      # The block must return nil or a string that can be appended to a url as a query parameter.
-      # The returned string must not include the starting '?'.
+      # If the block returns nil or a string, then it is appended to the url as a query parameter.
+      # In this case, the returned string must not include the starting '?'.
+      # The block may also return a full path (i.e. /images/grid-BUSTED.png) and it
+      # will replace the original path and query string with the busted path returned.
       # The block will be passed the root-relative url of the asset.
       # If the block accepts two arguments, it will also be passed a File object
       # that points to the asset on disk -- which may or may not exist.

lib/compass/sass_extensions/functions/urls.rb

@@ -91,9 +91,7 @@ module Compass::SassExtensions::Functions::Urls
       if cache_buster.is_a?(Sass::Script::String)
         path += "?#{cache_buster.value}"
       else
-        if buster = compute_cache_buster(path, real_path)
-          path += "?#{buster}"
-        end
+        path = cache_busted_path(path, real_path)
       end
     end
 
@@ -137,6 +135,17 @@ module Compass::SassExtensions::Functions::Urls
     end
   end
 
+  def cache_busted_path(path, real_path)
+    cache_buster = compute_cache_buster(path, real_path)
+    if cache_buster.nil?
+      path
+    elsif cache_buster =~ %r{/}
+      cache_buster
+    else
+      "%s?%s" % [path, cache_buster]
+    end
+  end
+
   def compute_cache_buster(path, real_path)
     if Compass.configuration.asset_cache_buster
       args = [path]

test/compass_test.rb

@@ -71,6 +71,17 @@ class CompassTest < Test::Unit::TestCase
     end
   end
 
+  def test_busted_image_urls
+    within_project('busted_image_urls') do |proj|
+      each_css_file(proj.css_path) do |css_file|
+        assert_no_errors css_file, 'busted_image_urls'
+      end
+      each_sass_file do |sass_file|
+        assert_renders_correctly sass_file
+      end
+    end
+  end
+
   def test_image_urls
     within_project('image_urls') do |proj|
       each_css_file(proj.css_path) do |css_file|

test/fixtures/stylesheets/busted_image_urls/config.rb

@@ -0,0 +1,20 @@
+# Require any additional compass plugins here.
+project_type = :stand_alone
+css_dir = "tmp"
+sass_dir = "sass"
+images_dir = "images"
+output_style = :compact
+# To enable relative image paths using the images_url() function:
+# http_images_path = :relative
+http_images_path = "/images"
+line_comments = false
+
+asset_cache_buster do |path, file|
+  pathname = Pathname.new(path)
+  "%s/%s-BUSTED%s" % [pathname.dirname, pathname.basename(pathname.extname), pathname.extname]
+end
+
+
+asset_host do |path|
+  "http://assets%d.example.com" % (path.size % 4)
+end

test/fixtures/stylesheets/busted_image_urls/css/screen.css

@@ -0,0 +1,5 @@
+.showgrid { background-image: url('http://assets0.example.com/images/grid-BUSTED.png'); }
+
+.inlinegrid { background-image: url('data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACgAAAAUEAYAAACv1qP4AAAABmJLR0T///////8JWPfcAAAACXBIWXMAAABIAAAASABGyWs+AAAAZ0lEQVRYw+3QwQ2AIBAFUTEUwI3+uzN7gDscsIgxEuO8An52J11X73OudfxMraXkzHfO3Y98nQEhA0IGhAwIGRAyIGRAyICQASEDQgaEDAgZEDIgZEDIgJABoZzSGK3tPuN9ERFP7Nw4fg+c5g8V1wAAAABJRU5ErkJggg=='); }
+
+.no-buster { background-image: url('http://assets0.example.com/images/grid.png'); }

test/fixtures/stylesheets/busted_image_urls/sass/screen.sass

@@ -0,0 +1,8 @@
+.showgrid
+  background-image: image-url(unquote("grid.png"))
+
+.inlinegrid
+  background-image: inline-image(unquote("grid.png"))
+
+.no-buster
+  background-image: image-url("grid.png", $only-path: false, $cache-buster: false)