Allow function declarations inside rulesets

src/function.rs

@@ -64,7 +64,7 @@ impl Function {
                 return Err("unexpected EOF (TODO: better error message)".into());
             }
         }
-
+        devour_whitespace(toks);
         Ok((name, Function::new(scope, args, body)))
     }
 

tests/functions.rs

@@ -53,3 +53,13 @@ test!(
     "$x: 0;\na {\n  color: if($x != 0, a, b);\n}\n",
     "a {\n  color: b;\n}\n"
 );
+test!(
+    function_decl_in_ruleset,
+    "a {\n  @function foo() {\n    @return 3;\n  }\n  color: foo();\n}\n",
+    "a {\n  color: 3;\n}\n"
+);
+test!(
+    function_decl_in_foreign_ruleset,
+    "a {\n  @function foo() {\n    @return 3;\n  }\n}\nb {\n  color: foo();\n}\n",
+    "b {\n  color: foo();\n}\n"
+);