Allow aliases for directories and resolve aliased paths normally

This changes the `alias` option to apply to the directories of imported
files (such as alias the `utils` directory in `@import "utils/other";`).
It also allows aliased paths to be processed with the full resolve
algorithm, for example importing an aliased directory will search for
the `index.css` file in the directory.

Also expanded the options documentation

Author: conradz

README.md

@@ -49,22 +49,91 @@ console.log(output);
 
 Creates a new plugin for rework that will import files from NPM.
 
-Valid options:
-
- * `root`: The root directory for the source files. This is used for source maps
-   to make imported file names relative to this directory, and for finding the
-   absolute path for the top level source file. Example: `root: 'src/client'`
- * `shim`: If you need to import packages that do not specify a `style`
-   property in their `package.json` or provide their styles in `index.css`,
-   you can provide a shim config option to access them. This is specified as a
-   hash whose keys are the names of packages to shim and whose values are the
-   path, relative to that package's `package.json` file, where styles can be
-   found. Example: `shim: { 'leaflet': 'dist/leaflet.css' }`
- * `alias`: You can provide aliases for arbitrary file paths using the same
-   format as the `shim` option. These files must be complete file paths,
-   relative to the `root` directory. Example:
-   `alias: { 'tree': './deep/tree/index.css' }`
- * `prefilter`: A function that will be called before an imported file is
-   parsed. This function will be called with the file contents and the full file
-   path. This option can be used to convert other languages such as SCSS to CSS
-   before importing. Example: `prefilter: function(src, file) { return src; }`
+## Options
+
+### root
+The root directory for the source files. This is used for source maps to make
+imported file names relative to this directory, and for finding the absolute
+path for the top level source file.
+
+Example:
+
+```js
+// Uses `<dir>/src/index.css` as the file path for the top level file. Also all
+// file paths in the source map will be relative to the `<dir>/src` folder.
+rework('@import "./abc";', { source: 'index.css' })
+    .use(reworkNPM({ root: path.join(__dirname, 'src') }))
+    .toString();
+```
+
+### shim
+If you need to import packages that do not specify a `style` property in their
+`package.json` or provide their styles in `index.css`, you can provide a shim
+config option to access them. This is specified as a hash whose keys are the
+names of packages to shim and whose values are the path, relative to that
+package's `package.json` file, where styles can be found.
+
+Example:
+
+```js
+// Imports the `dist/leaflet.css` file from the `leaflet` package
+rework('@import "leaflet";', { source: 'index.css' })
+    .use(reworkNPM({ shim: { 'leaflet': 'dist/leaflet.css' } }))
+    .toString();
+```
+
+### alias
+
+You can provide aliases for arbitrary import paths, including files and
+directories. When importing a file, it will search all directories in the path
+for aliases also. Note that relative imports are never aliased.
+
+This is specified as an object where the keys are the name of the import path to
+alias, and the values are the file or directory path for the destination,
+relative to the `root` option.
+
+Example:
+
+```js
+// Imports the `styles/util.css` file
+rework('@import "util";', { source: 'index.css' })
+    .use(reworkNPM({ alias: { 'util': 'styles/util.css' } }))
+    .toString();
+```
+
+```js
+// Imports the `styles/index.css` file if there is a `styles` directory,
+// otherwise the `styles.css` file.
+rework('@import "util";', { source: 'index.css' })
+    .use(reworkNPM({ alias: { 'util': 'styles' } }))
+    .toString();
+```
+
+```js
+// Imports the `styles/other.css` file
+rework('@import "util/other";', { source: 'index.css' })
+    .use(reworkNPM({ alias: { 'util': 'styles' } }))
+    .toString();
+```
+
+### prefilter
+A function that will be called before an imported file is parsed. This function
+will be called with the file contents and the full file path. This option can be
+used to convert other languages such as SCSS to CSS before importing.
+
+Example:
+
+```js
+// Process SCSS files
+rework('@import "./some-file.scss";', { source: 'index.css' })
+    .use(reworkNPM({ prefilter: compile }))
+    .toString();
+
+function compile(src, file) {
+    if (path.extname(file) === '.scss') {
+        return compileScss(src);
+    }
+
+    return src;
+}
+```

index.js

@@ -5,8 +5,10 @@ var path = require('path');
 var parse = require('css').parse;
 var fs = require('fs');
 
-var ABS_URL = /^url\(|:\/\//,
-    QUOTED = /^['"]|['"]$/g;
+var ABS_URL = /^url\(|:\/\//;
+var QUOTED = /^['"]|['"]$/g;
+var RELATIVE = /^\./;
+var SEPARATOR = '/';
 
 module.exports = reworkNPM;
 
@@ -51,8 +53,8 @@ function reworkNPM(opts) {
             return null;
         }
 
-        if (hasOwn(alias, name)) {
-            return path.resolve(root, alias[name]);
+        if (!RELATIVE.test(name)) {
+            name = resolveAlias(name) || name;
         }
 
         var source = rule.position.source;
@@ -67,6 +69,23 @@ function reworkNPM(opts) {
         return path.normalize(file);
     }
 
+    function resolveAlias(name) {
+        if (hasOwn(alias, name)) {
+            return path.resolve(root, alias[name]);
+        }
+
+        var segments = name.split(SEPARATOR);
+        if (segments.length > 1) {
+            var current = segments.pop();
+            var parent = resolveAlias(segments.join(SEPARATOR));
+            if (parent) {
+                return path.join(parent, current);
+            }
+        }
+
+        return null;
+    }
+
     function processPackage(pkg) {
         pkg.main =
             (hasOwn(shim, pkg.name) && shim[pkg.name]) ||

test.js

@@ -192,6 +192,27 @@ test('Use alias config option', function(t) {
     t.end();
 });
 
+test('Import index file in aliased directory', function(t) {
+    var source = '@import "util";';
+    var alias = { 'util': 'test/styles' };
+    var output = rework(source, { source: 'test/index.css' })
+        .use(reworkNPM({ alias: alias }))
+        .toString();
+
+    t.equal(output, '.test {\n  content: "Test file";\n}');
+    t.end();
+});
+
+test('Import file in aliased directory', function(t) {
+    var source = '@import "util/index";';
+    var alias = { 'util': 'test/styles' };
+    var output = rework(source, { source: 'test/index.css' })
+        .use(reworkNPM({ alias: alias }))
+        .toString();
+    t.equal(output, '.test {\n  content: "Test file";\n}');
+    t.end();
+});
+
 test('Allow prefiltering input CSS (e.g. css-whitespace)', function(t) {
     var input = '@import "./styles/index-unfiltered.css";';
     var output = rework(input, { source: 'test/index.css' })