Adds @HtmlImport with both dynamic and transformer based implementations. Still need an HtmlInliner…

lib/build/html_import_annotation_inliner.dart

+// Copyright (c) 2015, 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.
+library web_components.build.html_import_annotation_inliner;
+
+import 'dart:async';
+import 'package:analyzer/analyzer.dart';
+import 'package:barback/barback.dart';
+import 'package:html5lib/dom.dart' as dom;
+import 'package:html5lib/parser.dart';
+import 'package:initialize/plugin_transformer.dart';
+import 'package:source_maps/refactor.dart';
+import '../src/normalize_path.dart';
+
+/// Given an html entry point with a single dart bootstrap file created by the
+/// `initialize` transformer, this will open that dart file and remove all
+/// `HtmlImport` initializers from it. Then it appends those imports to the head
+/// of the html entry point.
+/// Notes: Does not inline the import, it just puts the <link rel="import"> tag.
+/// This also has a few limitations, it only supports string literals (to avoid
+/// using the analyzer to resolve references) and doesn't support const
+/// references to HtmlImport annotations (for the same reason).
+class HtmlImportAnnotationInliner extends InitializePluginTransformer {
+  final String _bootstrapFile;
+  final String _htmlEntryPoint;
+  TransformLogger _logger;
+  final Set<String> importPaths = new Set();
+
+  HtmlImportAnnotationInliner(String bootstrapFile, this._htmlEntryPoint)
+      : super(bootstrapFile),
+        _bootstrapFile = bootstrapFile;
+
+  factory HtmlImportAnnotationInliner.asPlugin(BarbackSettings settings) {
+    var bootstrapFile = settings.configuration['bootstrap_file'];
+    if (bootstrapFile is! String || !bootstrapFile.endsWith('.dart')) {
+      throw new ArgumentError(
+          '`bootstrap_file` should be a string path to a dart file');
+    }
+    var htmlEntryPoint = settings.configuration['html_entry_point'];
+    if (htmlEntryPoint is! String || !htmlEntryPoint.endsWith('.html')) {
+      throw new ArgumentError(
+          '`html_entry_point` should be a string path to an html file');
+    }
+    return new HtmlImportAnnotationInliner(bootstrapFile, htmlEntryPoint);
+  }
+
+  classifyPrimary(AssetId id) {
+    var superValue = super.classifyPrimary(id);
+    if (superValue != null) return superValue;
+    // Group it with the bootstrap file.
+    if (_htmlEntryPoint == id.path) return _bootstrapFile;
+    return null;
+  }
+
+  apply(AggregateTransform transform) {
+    _logger = transform.logger;
+    return super.apply(transform).then((_) {
+      var htmlEntryPoint =
+          allAssets.firstWhere((asset) => asset.id.path == _htmlEntryPoint);
+      return htmlEntryPoint.readAsString().then((html) {
+        var doc = parse(html);
+        for (var importPath in importPaths) {
+          var import = new dom.Element.tag('link')
+            ..attributes = {'rel': 'import', 'href': importPath,};

[Siggi Cherem (dart-lang), 2015/02/12 16:49:44]

nit: remove trailing comma `,`?

[jakemac, 2015/02/12 17:04:09]

oh I probably had these on separate lines in which case the trailing comma made
sense, and then the formatter removed it, will do

+          doc.head.append(import);
+        }
+        transform
+            .addOutput(new Asset.fromString(htmlEntryPoint.id, doc.outerHtml));
+      });
+    });
+  }
+
+  // Executed for each initializer constructor in the bootstrap file. We filter
+  // out the HtmlImport ones and inline them.
+  initEntry(
+      InstanceCreationExpression expression, TextEditTransaction transaction) {
+    // Filter out extraneous values.
+    if (expression is! InstanceCreationExpression) return;
+    var args = expression.argumentList.arguments;
+    // Only support InstanceCreationExpressions. Const references to HtmlImport
+    // annotations can't be cheaply discovered.
+    if (args[0] is! InstanceCreationExpression) return;
+    if (!'${args[0].constructorName.type.name}'.contains('.HtmlImport')) return;
+
+    // Grab the raw path supplied to the HtmlImport. Only string literals are
+    // supported for the transformer.

[Siggi Cherem (dart-lang), 2015/02/12 16:49:44]

FYI - I opened https://github.com/dart-lang/initialize/issues/22 based on our
discussions from earlier this week.

[jakemac, 2015/02/12 17:04:09]

I replied there, but basically in the new plugin architecture this isn't needed.
Plugins have access to a Resolver and can do this on their own as desired.

+    var originalPath = args[0].argumentList.arguments[0];
+    if (originalPath is SimpleStringLiteral) {
+      originalPath = originalPath.value;
+    } else {
+      _logger.warning('Found HtmlImport constructor which was supplied an '
+          'expression. Only raw strings are currently supported for the '
+          'transformer, so $originalPath will be injected dynamically');
+      return;
+    }
+
+    // Now grab the package from the LibraryIdentifier, we know its either a
+    // string or null literal.
+    var package = args[1].argumentList.arguments[1];
+    if (package is SimpleStringLiteral) {
+      package = package.value;
+    } else if (package is NullLiteral) {
+      package = null;
+    } else {
+      _logger.error('Invalid LibraryIdentifier declaration. The 2nd argument '
+          'be a literal string or null. `${args[1]}`');
+    }
+
+    // And finally get the original dart file path, this is always a string
+    // literal.
+    var dartPath = args[1].argumentList.arguments[2];
+    if (dartPath is SimpleStringLiteral) {
+      dartPath = dartPath.value;
+    } else {
+      _logger.error('Invalid LibraryIdentifier declaration. The 3rd argument '
+          'be a literal string. `${args[1]}`');
+    }
+
+    // Add the normalized path to our list and remove the expression from the
+    // bootstrap file.
+    importPaths.add(normalizeHtmlImportPath(originalPath, package, dartPath));
+    removeInitializer(expression, transaction);
+  }
+}