closes 268 - filenames can not start with numbers the must be legal css identifiers

Gemfile.lock

@@ -7,7 +7,7 @@ GIT
 PATH
   remote: .
   specs:
-    compass (0.11.beta.4.29656ea)
+    compass (0.11.beta.5.7571d4a)
       chunky_png (~> 1.1.0)
       sass (>= 3.1.0.alpha.249)
 

lib/compass/sass_extensions/sprites/sprite_map.rb

@@ -1,7 +1,7 @@
 module Compass
   class SpriteMap
     attr_reader :uri, :options
-
+    VAILD_FILE_NAME = /\A#{Sass::SCSS::RX::IDENT}\Z/
 
     def find_relative(*args)
       nil
@@ -30,7 +30,13 @@ module Compass
 
     # Returns an Array of image names without the file extension
     def sprite_names
-      @sprite_names ||= files.collect { |file| File.basename(file, '.png') }
+      @sprite_names ||= files.collect do |file|
+        filename = File.basename(file, '.png')
+        unless VAILD_FILE_NAME =~ filename
+          raise Compass::Error, "Sprite file names must be legal css identifiers. Please rename #{File.basename(file)}"
+        end
+        filename
+      end
     end
     
     # Returns the sass options for this sprite

spec/sprites_spec.rb

@@ -496,7 +496,7 @@ describe Compass::Sprites do
     css = render <<-SCSS
       @import "selectors/*.png";
       a {
-        @include selectors_sprite(ten-by-ten)
+        @include selectors-sprite(ten-by-ten)
       }
     SCSS
     css.should == <<-CSS
@@ -519,4 +519,16 @@ describe Compass::Sprites do
     CSS
   end
   
+  it "should raise error on filenames that are not valid sass syntax" do
+    lambda do
+      render <<-SCSS
+        $sprite-file-prefix:'foo';
+        @import "prefix/*.png";
+        a {
+          @include squares-sprite(20-by-20)
+        }
+      SCSS
+    end.should raise_error Compass::Error
+  end
+
 end