treat Directive like a Ruleset

lib/less/tree/directive.js

@@ -3,21 +3,28 @@ if (typeof(require) !== 'undefined') { var tree = require('less/tree') }
 tree.Directive = function Directive(name, value) {
     this.name = name;
     if (Array.isArray(value)) {
-        this.rules = new(tree.Ruleset)([], value);
+        this.ruleset = new(tree.Ruleset)([], value);
     } else {
         this.value = value;
     }
 };
-tree.Directive.prototype.toCSS = function (ctx, env) {
-    if (this.rules) {
-        this.rules.root = true;
-        return this.name + ' {\n  ' +
-               this.rules.toCSS(ctx, env).trim().replace(/\n/g, '\n  ') + '\n}\n';
-    } else {
-        return this.name + ' ' + this.value.toCSS() + ';\n';
-    }
+tree.Directive.prototype = {
+    toCSS: function (ctx, env) {
+        if (this.ruleset) {
+            this.ruleset.root = true;
+            return this.name + ' {\n  ' +
+                   this.ruleset.toCSS(ctx, env).trim().replace(/\n/g, '\n  ') + '\n}\n';
+        } else {
+            return this.name + ' ' + this.value.toCSS() + ';\n';
+        }
+    },
+    eval: function (env) {
+        env.frames.unshift(this);
+        this.ruleset && this.ruleset.evalRules(env);
+        env.frames.shift();
+        return this;
+    },
+    variable: function (name) { return tree.Ruleset.prototype.variable.call(this.ruleset, name) },
+    find: function () { return tree.Ruleset.prototype.find.apply(this.ruleset, arguments) },
+    rulesets: function () { return tree.Ruleset.prototype.rulesets.apply(this.ruleset) }
 };
-tree.Directive.prototype.eval = function (env) {
-    this.rules && this.rules.evalRules(env);
-    return this;
-}

test/less/media.less

@@ -15,7 +15,7 @@
     }
 }
 
-@base: 8;
 @media screen {
+    @base: 8;
     body { max-width: @base * 60; }
 }