Support loading transformer plugins from pub.

sdk/lib/_internal/pub/lib/src/barback/watch_sources.dart

Index: sdk/lib/_internal/pub/lib/src/barback/watch_sources.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/watch_sources.dart b/sdk/lib/_internal/pub/lib/src/barback/watch_sources.dart
new file mode 100644
index 0000000000000000000000000000000000000000..dc29294422f610a0ffd67422fcea003477d84400
--- /dev/null
+++ b/sdk/lib/_internal/pub/lib/src/barback/watch_sources.dart
@@ -0,0 +1,73 @@
+// 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.watch_sources;
+
+import 'package:barback/barback.dart';
+import 'package:path/path.dart' as path;
+import 'package:watcher/watcher.dart';
+
+import '../entrypoint.dart';
+import '../io.dart';
+import '../package_graph.dart';
+
+/// Adds all of the source assets in the provided packages to barback and
+/// then watches the public directories for changes.
+void watchSources(PackageGraph graph, Barback barback) {
+  for (var package in graph.packages.values) {
+    // Add the initial sources.
+    barback.updateSources(_listAssets(graph.entrypoint, package));
+
+    // Watch the visible package directories for changes.
+    for (var name in _getPublicDirectories(graph.entrypoint, package)) {
+      var subdirectory = path.join(package.dir, name);
+      // TODO(nweiz): close these watchers when [barback] is closed.
+      var watcher = new DirectoryWatcher(subdirectory);
+      watcher.events.listen((event) {
+        var id = new AssetId(package.name,
+            path.relative(event.path, from: package.dir));
+        if (event.type == ChangeType.REMOVE) {
+          barback.removeSources([id]);
+        } else {
+          barback.updateSources([id]);
+        }
+      });
+    }
+  }
+}
+
+/// Lists all of the visible files in [package].
+///
+/// This is the recursive contents of the "asset" and "lib" directories (if
+/// present). If [package] is the entrypoint package, it also includes the
+/// contents of "web".
+List<AssetId> _listAssets(Entrypoint entrypoint, Package package) {
+  var files = <AssetId>[];
+
+  for (var dirPath in _getPublicDirectories(entrypoint, package)) {
+    var dir = path.join(package.dir, dirPath);
+    if (!dirExists(dir)) continue;
+    for (var entry in listDir(dir, recursive: true)) {
+      // Ignore "packages" symlinks if there.
+      if (path.split(entry).contains("packages")) continue;
+
+      // Skip directories.
+      if (!fileExists(entry)) continue;
+
+      var id = new AssetId(package.name,
+          path.relative(entry, from: package.dir));
+      files.add(id);
+    }
+  }
+
+  return files;
+}
+
+/// Gets the names of the top-level directories in [package] whose contents
+/// should be provided as source assets.
+Iterable<String> _getPublicDirectories(Entrypoint entrypoint, Package package) {
+  var directories = ["asset", "lib"];
+  if (package.name == entrypoint.root.name) directories.add("web");
+  return directories;
+}