Fix dynamic mixins with nested rules

Dynamic mixins with more than one level of nesting wouldn't work.
This is now fixed. Also refactored mixin.definition.eval a little.

lib/less/tree/mixin.js

@@ -45,13 +45,8 @@ tree.mixin.Definition.prototype = {
         context = { frames: [this, frame].concat(env.frames) };
 
         return new(tree.Ruleset)(null, this.rules.map(function (rule) {
-            if (rule.rules) {
-                return new(tree.Ruleset)(rule.selectors, rule.rules.map(function (r) {
-                    return new(tree.Rule)(r.name, r.value.eval(context));
-                }));
-            } else {
-                return new(tree.Rule)(rule.name, rule.value.eval(context));
-            }
+            if (rule.evalRules) return rule.evalRules(context);
+            else                return rule.eval(context);
         }));
     }
 };

lib/less/tree/rule.js

@@ -16,6 +16,10 @@ tree.Rule.prototype.toCSS = function (env) {
     }
 };
 
+tree.Rule.prototype.eval = function (context) {
+    return new(tree.Rule)(this.name, this.value.eval(context));
+};
+
 tree.Value = function Value(value) {
     this.value = value;
     this.is = 'value';

lib/less/tree/ruleset.js

@@ -7,6 +7,12 @@ tree.Ruleset = function Ruleset(selectors, rules) {
 };
 tree.Ruleset.prototype = {
     eval: function () { return this },
+    evalRules: function (context) {
+        return new(tree.Ruleset)(this.selectors, this.rules.map(function (r) {
+            if (r.evalRules) return r.evalRules(context);
+            else             return r.eval(context);
+        }));
+    },
     variables: function () {
         if (this._variables) { return this._variables }
         else {

test/css/mixins-nested.css

@@ -0,0 +1,6 @@
+.class .inner {
+  height: 300;
+}
+.class .inner .innest {
+  width: 30;
+}

test/less/mixins-nested.less

@@ -0,0 +1,13 @@
+.mix (@a: 10) {
+  .inner {
+    height: @a * 10;
+
+    .innest {
+      width: @a;  
+    }  
+  }
+}
+
+.class {
+  .mix(30);
+}