Added .scss transform

pkg/csslib/lib/transform.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/**
+ * Code transform for pre-processing CSS files any extension of .scss is
+ * transformed to runable CSS styling (nesting, calc, var, @define, @extends,
+ * @mixin, etc).
+ */
+library csslib.transform;
+
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+import 'package:source_maps/span.dart' show SourceFile;
+import 'package:csslib/parser.dart' show parse, analyze;
+import 'package:csslib/visitor.dart' show StyleSheet, CssPrinter;
+
+class ScssTransformer extends Transformer {
+  Future<bool> isPrimary(Asset input) =>
+    new Future.value((input.id.extension == '.scss'));

[Siggi Cherem (dart-lang), 2013/09/08 20:31:33]

replace the above two lines with:

/** Only run this transformer on .scss files. */                                
                  
final String allowedExtensions = ".scss"; 

(it's a new improvement from barback :-))

+
+  Future apply(Transform transform) {
+    return transform.primaryInput.readAsString().then((content) {
+      // Generate .css output file.
+      var id = transform.primaryInput.id.changeExtension('.css');
+
+      // Parse the .scss file.
+      var sourceFile = new SourceFile.text(id.path, content);
+      var stylesheet = _parseCss(content, sourceFile, transform.logger);
+
+      analyze([stylesheet]);
+
+      transform.addOutput(new Asset.fromString(id, _prettyPrint(stylesheet)));
+    });
+  }
+}
+
+StyleSheet _parseCss(String content, SourceFile sourceFile, logger) {
+  if (content.trim().isEmpty) return null;
+
+  var errors = [];
+
+  // TODO(terry): Add --checked when fully implemented and error handling as
+  //              part of validation transform.
+  // TODO(terry): All warnings as errors.
+  var stylesheet = parse(content, errors: errors, options:
+    ['--warnings_as_errors', 'memory']);
+
+  // Note: errors aren't fatal in HTML (unless strict mode is on).
+  // So just print them as warnings.
+  for (var e in errors) {
+    logger.warning(e.message, e.span);
+  }
+
+  return stylesheet;
+}
+
+/** Pretty printer for CSS. */
+String _prettyPrint(StyleSheet ss) {
+  // Walks the style sheet tree and emits readable CSS.
+  var formatCss = (new CssPrinter()..visitTree(ss, pretty: true)).toString();
+  return "/***** Generated by SCSS transform. *****/\n\n$formatCss";
+}
+