add alias feature to rewrite urls

lib/loader.js

@@ -70,6 +70,18 @@ module.exports = function(content, map) {
 				var idx = +match[1];
 				var urlItem = result.urlItems[idx];
 				var url = urlItem.url;
+				var loaderOptions = this.options.cssLoader;
+				if (loaderOptions && loaderOptions.alias) {
+					var alias = loaderOptions.alias;
+					Object.keys(alias).forEach(function(aliasName) {
+						var aliasValue = alias[aliasName];
+						var onlyModule = /\$$/.test(aliasName);
+						if (onlyModule) aliasName = aliasName.substr(0, aliasName.length - 1);
+						if ((!onlyModule && url.indexOf(aliasName + "/") === 0) || url === aliasName) {
+							url = aliasValue + url.substr(aliasName.length);
+						}
+					});
+				}
 				idx = url.indexOf("?#");
 				if(idx < 0) idx = url.indexOf("#");
 				var urlRequest;

test/aliasTest.js

@@ -0,0 +1,30 @@
+/*globals describe */
+
+var test = require("./helpers").test;
+
+describe("alias", function() {
+  var css = ".className { background: url(./path/to/file.png); }";
+  var exports = {
+    without: [
+      [1, ".className { background: url({./path/to/file.png}); }", ""]
+    ],
+    onlyModule: [
+      [1, ".className { background: url({module/file.png}); }", ""]
+    ],
+    exactMatch: [
+      [1, ".className { background: url({module/file.png}); }", ""]
+    ],
+    notExactMatch: [
+      [1, ".className { background: url({./path/to/file.png}); }", ""]
+    ]
+  };
+
+  function aliasOptions(alias) {
+    return { options: { context: "", cssLoader: { alias: alias }}}
+  }
+
+  test("without", css, exports.without);
+  test("onlyModule", css, exports.onlyModule, aliasOptions({ "./path/to": "module" }));
+  test("exactMatch", css, exports.exactMatch, aliasOptions({ "./path/to/file.png$": "module/file.png" }));
+  test("notExactMatch", css, exports.notExactMatch, aliasOptions({ "./path/to/file.jpg$": "module/file.jpg" }));
+});