feat: add alias feature to rewrite URLs (#274)

README.md

@@ -89,6 +89,7 @@ To be compatible with existing css files (if not in CSS Module mode):
 |**`sourceMap`**|`false`|Enable/Disable Sourcemaps|
 |**`camelCase`**|`false`|Export Classnames in CamelCase|
 |**`importLoaders`**|`0`|Number of loaders applied before CSS loader|
+|**`alias`**|`{}`|Create aliases to import certain modules more easily|
 
 The following webpack config can load CSS files, embed small PNG/JPG/GIF/SVG images as well as fonts as [Data URLs](https://tools.ietf.org/html/rfc2397) and copy larger files to the output directory.
 
@@ -322,7 +323,7 @@ They are not enabled by default because they expose a runtime overhead and incre
 
 ### toString
 
-You can also use the css-loader results directly as string, such as in Angular's component style. 
+You can also use the css-loader results directly as string, such as in Angular's component style.
 
 **webpack.config.js**
 
@@ -430,6 +431,44 @@ By default, the exported JSON keys mirror the class names. If you want to cameli
 import { className } from 'file.css';
 ```
 
+### Alias
+
+Rewrite your urls with alias, this is useful when it's hard to change url paths of your input files, for example, when you're using some css / sass files in another package (bootstrap, ratchet, font-awesome, etc.).
+
+#### Possible Options
+
+css-loader's `alias` follows the same syntax as webpack's `resolve.alias`, you can see the details at: https://webpack.js.org/configuration/resolve/#resolve-alias
+
+**webpack.config.js**
+```js
+{
+  test: /\.scss$/,
+  use: [{
+    loader: "style-loader"
+  }, {
+    loader: "css-loader",
+    options: {
+      alias: {
+        "../fonts/bootstrap": "bootstrap-sass/assets/fonts/bootstrap"
+      }
+    }
+  }, {
+    loader: "sass-loader",
+    options: {
+      includePaths: [
+        path.resolve("./node_modules/bootstrap-sass/assets/stylesheets")
+      ]
+    }
+  }]
+}
+```
+
+```scss
+@charset "UTF-8";
+@import "bootstrap";
+```
+Check out this [working bootstrap example](https://github.com/bbtfr/webpack2-bootstrap-sass-sample).
+
 <h2 align="center">Maintainers</h2>
 
 <table>

lib/createResolver.js

@@ -0,0 +1,36 @@
+module.exports = function createResolver(alias) {
+	if(typeof alias !== "object" || Array.isArray(alias)) {
+		return function(url) {
+			return url
+		};
+	}
+
+	alias = Object.keys(alias).map(function(key) {
+		var onlyModule = false;
+		var obj = alias[key];
+		if(/\$$/.test(key)) {
+			onlyModule = true;
+			key = key.substr(0, key.length - 1);
+		}
+		if(typeof obj === "string") {
+			obj = {
+				alias: obj
+			};
+		}
+		obj = Object.assign({
+			name: key,
+			onlyModule: onlyModule
+		}, obj);
+		return obj;
+	});
+
+	return function(url) {
+		alias.forEach(function(obj) {
+			var name = obj.name;
+			if(url === name || (!obj.onlyModule && url.startsWith(name + "/"))) {
+				url = obj.alias + url.substr(name.length);
+			}
+		});
+		return url;
+	}
+}

lib/loader.js

@@ -6,6 +6,7 @@ var loaderUtils = require("loader-utils");
 var processCss = require("./processCss");
 var getImportPrefix = require("./getImportPrefix");
 var compileExports = require("./compile-exports");
+var createResolver = require("./createResolver");
 
 
 module.exports = function(content, map) {
@@ -15,6 +16,7 @@ module.exports = function(content, map) {
 	var root = query.root;
 	var moduleMode = query.modules || query.module;
 	var camelCaseKeys = query.camelCase || query.camelcase;
+	var resolve = createResolver(query.alias);
 
 	if(map !== null && typeof map !== "string") {
 		map = JSON.stringify(map);
@@ -69,7 +71,7 @@ module.exports = function(content, map) {
 				var match = result.urlItemRegExp.exec(item);
 				var idx = +match[1];
 				var urlItem = result.urlItems[idx];
-				var url = urlItem.url;
+				var url = resolve(urlItem.url);
 				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 { query: { 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" }));
+});