Introduce polymer transformers (inlined code extraction, inlining html imports,

pkg/polymer/lib/src/transform/common.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.
+
+/** Common methods used by transfomers. */
+library polymer.src.transform.common;
+
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+import 'package:html5lib/dom.dart' show Document;
+import 'package:html5lib/parser.dart' show HtmlParser;
+import 'package:path/path.dart' as path;
+import 'package:source_maps/span.dart' show Span;
+
+// TODO(sigmund): delete this function (see dartbug.com/12515 and
+// dartbug.com/12516)
+Future<String> getPrimaryContent(Transform transform) =>
+  transform.primaryInput.then((asset) => asset.readAsString());
+
+// TODO(sigmund): delete this function (see dartbug.com/12515)
+Future<String> getContent(Transform transform, AssetId id) =>
+  transform.getInput(id).then((asset) => asset.readAsString());
+
+/**
+ * Parses an HTML file [contents] and returns a DOM-like tree. Adds emitted
+ * error/warning to [logger].
+ */
+Document parseHtml(String contents, String sourcePath, TransformLogger logger,
+    {bool checkDocType: true}) {
+  // TODO(jmesserly): make HTTP encoding configurable
+  var parser = new HtmlParser(contents, encoding: 'utf8', generateSpans: true,
+      sourceUrl: sourcePath);
+  var document = parser.parse();
+
+  // Note: errors aren't fatal in HTML (unless strict mode is on).
+  // So just print them as warnings.
+  for (var e in parser.errors) {
+    if (checkDocType || e.errorCode != 'expected-doctype-but-got-start-tag') {
+      logger.warning(e.message, e.span);
+    }
+  }
+  return document;
+}
+
+/** Create an [AssetId] for a [url] seen in the [source] asset. */
+// TODO(sigmund): delete once this is part of barback (dartbug.com/12610)
+AssetId resolve(AssetId source, String url, TransformLogger logger, Span span) {
+  if (url == null || url == '') return null;
+  var uri = Uri.parse(url);
+  if (uri.host != '' || uri.scheme != '' || path.isAbsolute(url)) {
+    logger.error('absolute paths not allowed: "$url"', span);
+    return null;
+  }
+
+  var package;
+  var targetPath;
+  var segments = path.split(url);
+  if (segments[0] == 'packages') {
+    if (segments.length < 3) {
+      logger.error("incomplete packages/ path. It should have at least 3 "
+          "segments packages/name/path-from-name's-lib-dir", span);
+      return null;
+    }
+    package = segments[1];
+    targetPath = path.join('lib', path.joinAll(segments.sublist(2)));
+  } else if (segments[0] == 'assets') {
+    if (segments.length < 3) {
+      logger.error("incomplete assets/ path. It should have at least 3 "
+          "segments assets/name/path-from-name's-asset-dir", span);
+    }
+    package = segments[1];
+    targetPath = path.join('asset', path.joinAll(segments.sublist(2)));
+  } else {
+    package = source.package;
+    targetPath = path.normalize(path.join(path.dirname(source.path), url));
+  }
+  return new AssetId(package, targetPath);
+}