Add a @debug directive (that needs documentation).

lib/sass/engine.rb

@@ -11,6 +11,7 @@ require 'sass/tree/mixin_node'
 require 'sass/tree/if_node'
 require 'sass/tree/while_node'
 require 'sass/tree/for_node'
+require 'sass/tree/debug_node'
 require 'sass/tree/file_node'
 require 'sass/environment'
 require 'sass/script'
@@ -334,6 +335,10 @@ END
       elsif directive == "if"
         offset = line.offset + line.text.index(value).to_i
         Tree::IfNode.new(parse_script(value, :line => line.index, :offset => offset), @options)
+      elsif directive == "debug"
+        raise SyntaxError.new("Illegal nesting: Nothing may be nested beneath debug directives.", @line + 1) unless line.children.empty?
+        offset = line.offset + line.text.index(value).to_i
+        Tree::DebugNode.new(parse_script(value, :line => line.index, :offset => offset), @options)
       else
         Tree::DirectiveNode.new(line.text, @options)
       end

lib/sass/tree/debug_node.rb

@@ -0,0 +1,22 @@
+module Sass
+  module Tree
+    class DebugNode < Node
+      def initialize(expr, options)
+        @expr = expr
+        super(options)
+      end
+
+      protected
+
+      def _perform(environment)
+        res = @expr.perform(environment)
+        if filename
+          puts "#{filename}:#{line} DEBUG: #{res}"
+        else
+          puts "Line #{line} DEBUG: #{res}"
+        end
+        []
+      end
+    end
+  end
+end