Add Sass like extend

lib/less/tree/extend.js

@@ -0,0 +1,51 @@
+(function (tree) {
+
+tree.Extend = function Extend(elements, index) {
+    this.selector = new(tree.Selector)(elements);
+    this.index = index;
+};
+
+tree.Extend.prototype.eval = function Extend_eval(env) {
+    var selfSelectors = findSelfSelectors(env.selectors);
+        targetValue = this.selector.elements[0].value;
+
+    env.frames.forEach(function(frame) {
+        frame.rulesets().forEach(function(rule) {
+            rule.selectors.forEach(function(selector) {
+                selector.elements.forEach(function(element, idx) {
+                    if (element.value === targetValue) {
+                        selfSelectors.forEach(function(_selector) {
+                            rule.selectors.push(new tree.Selector(
+                                selector.elements
+                                    .slice(0, idx)
+                                    .concat(_selector.elements)
+                                    .concat(selector.elements.slice(idx + 1))
+                            ));
+                        });
+                    }
+                });
+            });
+        });
+    });
+    return this;
+};
+
+function findSelfSelectors(selectors) {
+    var ret = [];
+
+    (function loop(elem, i) {
+        if (selectors[i] && selectors[i].length) {
+            selectors[i].forEach(function(s) {
+                loop(s.elements.concat(elem), i + 1);
+            });
+        }
+        else {
+            ret.push({ elements: elem });
+        }
+    })([], 0);
+
+    return ret;
+}
+
+
+})(require('../tree'));