added plugin transformer which initializers can extend to do additional post-processing during tran…

lib/plugin_transformer.dart

Index: lib/plugin_transformer.dart
diff --git a/lib/plugin_transformer.dart b/lib/plugin_transformer.dart
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+// 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 initialize.plugin_transformer;
+
+import 'dart:async';
+import 'package:analyzer/analyzer.dart';
+import 'package:barback/barback.dart';
+import 'package:source_maps/refactor.dart';
+import 'package:source_span/source_span.dart';
+
+/// Abstract transformer which will call [initEntry] for every [InitEntry]
+/// expression found in the bootstrap file. This is used to centralize logic
+/// for initializers which want to do something special at transform time.
+abstract class InitializePluginTransformer extends AggregateTransformer {
+  // Path to the bootstrap file created by the initialize transformer.
+  final String _bootstrapFile;
+
+  // All the extra assets that were found, if child classes override
+  // classifyPrimary this lets them get at the other assets easily.
+  final allAssets = <Asset>[];
+
+  TransformLogger _logger;
+
+  InitializePluginTransformer(this._bootstrapFile);
+
+  classifyPrimary(AssetId id) =>
+      _bootstrapFile == id.path ? _bootstrapFile : null;
+
+  Future apply(AggregateTransform transform) {
+    _logger = transform.logger;
+    var listener = transform.primaryInputs.listen((Asset asset) {
+      allAssets.add(asset);
+      var id = asset.id;
+      if (id.path != _bootstrapFile) return;
+      // Calls initEntry for each InitEntry expression.
+      asset.readAsString().then((dartCode) {
+        var url = id.path.startsWith('lib/')
+            ? 'package:${id.package}/${id.path.substring(4)}'
+            : id.path;
+        var source = new SourceFile(dartCode, url: url);
+        var transaction = new TextEditTransaction(dartCode, source);
+        (parseCompilationUnit(dartCode,
+                    suppressErrors: true) as dynamic).declarations.firstWhere(
+                (d) => d.name.toString() ==
+                    'main').functionExpression.body.block.statements.firstWhere(
+            (statement) {
+          return statement.expression.target.toString() == 'initializers' &&
+              statement.expression.methodName.toString() == 'addAll';
+        }).expression.argumentList.arguments[0].elements
+            .where((arg) => arg is InstanceCreationExpression)
+            .forEach((e) => initEntry(e, transaction));
+
+        // Apply any transformations.
+        if (!transaction.hasEdits) {
+          transform.addOutput(asset);
+        } else {
+          var printer = transaction.commit();
+          printer.build(url);
+          transform.addOutput(new Asset.fromString(id, printer.text));
+        }
+      });
+    });
+
+    // Make sure all the assets are read before returning.
+    return listener.asFuture();
+  }
+
+  /// Gets called once for each generated [InitEntry] expression in the
+  /// bootstrap file. A [TextEditTransaction] is supplied so that the user can
+  /// modify the expression however they see fit.
+  void initEntry(
+      InstanceCreationExpression expression, TextEditTransaction transaction);
+
+  /// Convenience method to delete an Initializer expression completely.
+  void removeInitializer(
+      InstanceCreationExpression expression, TextEditTransaction transaction) {
+    // Delete the entire line.
+    var line = transaction.file.getLine(expression.offset);
+    transaction.edit(transaction.file.getOffset(line),
+        transaction.file.getOffset(line + 1), '');
+  }
+}