[Sass] Fix invalid-comma errors for functions.

Closes gh-171

doc-src/SASS_CHANGELOG.md

@@ -3,6 +3,11 @@
 * Table of contents
 {:toc}
 
+## 3.0.4 (Unreleased)
+
+* Raise an informative error when function arguments have a mispaced comma,
+  as in `foo(bar, )`.
+
 ## 3.0.3
 
 [Tagged on GitHub](http://github.com/nex3/haml/commit/3.0.3).

lib/sass/script/parser.rb

@@ -265,7 +265,7 @@ RUBY
       def fn_arglist
         return unless e = equals
         return [e] unless try_tok(:comma)
-        [e, *fn_arglist]
+        [e, *assert_expr(:fn_arglist)]
       end
 
       def arglist
@@ -334,6 +334,7 @@ RUBY
         :string => "string",
         :default => "expression (e.g. 1px, bold)",
         :arglist => "mixin argument",
+        :fn_arglist => "function argument",
       }
 
       def assert_expr(name)

test/sass/script_test.rb

@@ -329,6 +329,11 @@ SASS
     assert_equal "#2", resolve('"##{1 + 1}"')
   end
 
+  def test_misplaced_comma_in_funcall
+    assert_raise(Sass::SyntaxError,
+      'Invalid CSS after "foo(bar, ": expected function argument, was ")"') {eval('foo(bar, )')}
+  end
+
   private
 
   def resolve(str, opts = {}, environment = env)