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

pkg/polymer/lib/src/transform/script_compactor.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.
+
+/** Transfomer that combines multiple dart script tags into a single one. */
+library polymer.src.transform.script_compactor;
+
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+import 'package:html5lib/parser.dart' show parseFragment;
+import 'package:path/path.dart' as path;
+
+import 'code_extractor.dart'; // import just for documentation.
+import 'common.dart';
+
+/**
+ * Combines Dart script tags into a single script tag, and creates a new Dart
+ * file that calls the main function of each of the original script tags.
+ *
+ * This transformer assumes that all script tags point to external files. To
+ * support script tags with inlined code, use this transformer after running
+ * [InlineCodeExtractor] on an earlier phase.
+ *
+ * Internally, this transformer will convert each script tag into an import
+ * statement to a library, and then uses `initPolymer` (see polymer.dart)  to
+ * invoke the main method on each of these libraries and register any polymer
+ * elements annotated with `@CustomTag`.
+ */
+class ScriptCompactor extends Transformer {
+  Future<bool> isPrimary(Asset input) =>
+      new Future.value(input.id.extension == ".html");
+
+  Future apply(Transform transform) {
+    var id = transform.primaryId;
+    var logger = transform.logger;
+    return getPrimaryContent(transform).then((content) {
+      var document = parseHtml(content, id.path, logger);
+      var libraries = [];
+      bool changed = false;
+      for (var tag in document.queryAll('script')) {
+        if (tag.attributes['type'] != 'application/dart') continue;
+        tag.remove();
+        changed = true;
+        var src = tag.attributes['src'];
+        if (src == null) {
+          logger.warning('unexpected script without a src url. The '
+            'ScriptCompactor transformer should run after running the '
+            'InlineCodeExtractor', tag.sourceSpan);
+          continue;
+        }
+        var libraryId = resolve(id, src, logger, tag.sourceSpan);
+
+        // TODO(sigmund): should we detect/remove duplicates?
+        if (libraryId == null) continue;
+        libraries.add(libraryId);
+      }
+
+      if (!changed) {
+        transform.addOutput(new Asset.fromString(id, content));
+        return;
+      }
+
+      var bootstrapId = id.addExtension('_bootstrap.dart');
+      var filename = path.basename(bootstrapId.path);
+      document.body.nodes.add(parseFragment(
+            '<script type="application/dart" src="$filename"></script>'));
+
+      var urls = libraries.map((id) => importUrlFor(id, bootstrapId, logger))
+          .where((url) => url != null).toList();
+      var buffer = new StringBuffer()..write(_header);
+      for (int i = 0; i < urls.length; i++) {
+        buffer.writeln("import '${urls[i]}' as i$i;");
+      }
+      buffer..write(_mainPrefix)
+          ..writeAll(urls.map((url) => "      '$url',\n"))
+          ..write(_mainSuffix);
+
+      transform.addOutput(new Asset.fromString(bootstrapId, buffer.toString()));
+      transform.addOutput(new Asset.fromString(id, document.outerHtml));
+    });
+  }
+
+  /**
+   * Generate the import url for a file described by [id], referenced by a file
+   * with [sourceId].
+   */
+  String importUrlFor(AssetId id, AssetId sourceId, TransformLogger logger) {
+    // use package: urls if possible
+    if (id.path.startsWith('lib/')) {
+      return 'package:${id.package}/${id.path.substring(4)}';
+    }
+    
+    // Use relative urls only if it's possible.
+    if (id.package != sourceId.package) {
+      logger.error("don't know how to import $id from $sourceId");
+      return null;
+    }
+
+    var upPath = path.joinAll(path.split(sourceId.path).map((_) => '..'));
+    return path.normalize(path.join(sourceId.path, upPath, id.path));
+  }
+}
+
+const _header = """
+library app_bootstrap;
+
+import 'package:polymer/polymer.dart';
+import 'dart:mirrors' show currentMirrorSystem;
+
+""";
+
+const _mainPrefix = """
+
+void main() {
+  initPolymer([
+""";
+
+// TODO(sigmund): investigate alternative to get the baseUri (dartbug.com/12612)
+const _mainSuffix = """
+    ],
+    currentMirrorSystem().findLibrary(const Symbol('app_bootstrap'))
+        .first.uri.toString());
+}
+""";