Support loading transformer plugins from pub.

sdk/lib/_internal/pub/lib/src/barback.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.
+
+library pub.barback;
+
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+
+import 'barback/load_transformers.dart';
+import 'barback/pub_package_provider.dart';
+import 'barback/rewrite_import_transformer.dart';
+import 'barback/server.dart';
+import 'barback/watch_sources.dart';
+import 'utils.dart';
+
+/// Creates a [BarbackServer] serving on [host] and [port].
+///
+/// This transforms and serves all library and asset files in all packages in
+/// [graph]. It loads any transformer plugins defined in packages in [graph] and
+/// re-runs them as necessary when any input files change.
+Future<BarbackServer> createServer(String host, int port, PackageGraph graph) {
+  var provider = new PubPackageProvider(graph);
+  var barback = new Barback(provider);
+  return BarbackServer.bind(host, port, barback, graph.entrypoint.root.name)
+      .then((server) {
+    watchSources(graph, barback);
+
+    var completer = new Completer();
+
+    // If any errors get emitted either by barback or by the server, including
+    // non-programmatic barback errors, they should take down the whole program.
+    var subscriptions = [
+      server.barback.errors.listen((error) {
+        if (error is TransformerException) error = error.error;
+        if (!completer.isCompleted) completer.completeError(error);
+      }),
+      server.barback.results.listen((_) {}, onError: (error) {
+        if (!completer.isCompleted) completer.completeError(error);
+      }),
+      server.results.listen((_) {}, onError: (error) {
+        if (!completer.isCompleted) completer.completeError(error);
+      })
+    ];
+
+    _loadTransformers(server, graph).then((_) {
+      if (!completer.isCompleted) completer.complete(server);
+    }).catchError((error) {
+      if (!completer.isCompleted) completer.completeError(error);
+    });
+
+    return completer.future.whenComplete(() {
+      for (var subscription in subscriptions) {
+        subscription.cancel();
+      }
+    });
+  });
+}
+
+/// Loads all transformers depended on by packages in [graph].
+///
+/// This uses [server] to serve the Dart files from which transformers are
+/// loaded, then adds the transformers to `server.barback`.
+Future _loadTransformers(BarbackServer server, PackageGraph graph) {
+  // Add a rewrite transformer for each package, so that we can resolve
+  // "package:" imports while loading transformers.
+  var rewrite = new RewriteImportTransformer();
+  for (var package in graph.packages.values) {
+    server.barback.updateTransformers(package.name, [[rewrite]]);
+  }
+
+  // A map from each transformer id to the set of packages that use it.
+  var idsToPackages = new Map<AssetId, Set<String>>();
+  for (var package in graph.packages.values) {
+    for (var id in unionAll(package.pubspec.transformers)) {
+      idsToPackages.putIfAbsent(id, () => new Set<String>()).add(package.name);
+    }
+  }
+
+  // TODO(nweiz): support transformers that (possibly transitively)
+  // depend on other transformers.
+  var transformersForId = new Map<AssetId, Set<Transformer>>();
+  return Future.wait(idsToPackages.keys.map((id) {
+    return loadTransformers(server, id).then((transformers) {
+      if (transformers.isEmpty) {
+        var path = id.path.replaceFirst('lib/', '');
+        // Ensure that packages are listed in a deterministic order.
+        var packages = idsToPackages[id].toList();
+        packages.sort();
+        throw new ApplicationException(
+            "No transformers were defined in package:${id.package}/$path,\n"
+            "required by ${packages.join(', ')}.");
+      }
+
+      transformersForId[id] = transformers;
+    });
+  })).then((_) {
+    for (var package in graph.packages.values) {
+      var phases = package.pubspec.transformers.map((phase) {
+        return unionAll(phase.map((id) => transformersForId[id]));
+      });
+      server.barback.updateTransformers(package.name, phases);
+    }
+  });
+}