Preliminary checked mirrors (not ready for review yet)

pkg/checked_mirrors/lib/transformer.dart

Index: pkg/checked_mirrors/lib/transformer.dart
diff --git a/pkg/checked_mirrors/lib/transformer.dart b/pkg/checked_mirrors/lib/transformer.dart
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+// 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.
+
+/**
+ * Replaces uses of "package:checked_mirrors/checked_mirrors.dart" with
+ * "dart:mirrors" that contain the MirrorUsed annotation.
+ */
+library checked_mirrors.transformer;
+
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+
+/**
+ * A [Transformer] that replaces observables based on dirty-checking with an
+ * implementation based on change notifications.
+ *
+ * The transformation adds hooks for field setters and notifies the observation
+ * system of the change.
+ */
+class CheckedMirrorsTransformer extends Transformer {
+
+  final List<String> _files;
+  CheckedMirrorsTransformer() : _files = null;
+  CheckedMirrorsTransformer.asPlugin(BarbackSettings settings)
+      : _files = _readFiles(settings.configuration['files']);
+
+  static List<String> _readFiles(value) {
+    if (value == null) return null;
+    var files = [];
+    bool error;
+    if (value is List) {
+      files = value;
+      error = value.any((e) => e is! String);
+    } else if (value is String) {
+      files = [value];
+      error = false;
+    } else {
+      error = true;
+    }
+    if (error) print('Invalid value for "files" in the observe transformer.');
+    return files;
+  }
+
+  Future<bool> isPrimary(Asset input) {
+    if (input.id.extension != '.dart' ||
+        (_files != null && !_files.contains(input.id.path))) {
+      return new Future.value(false);
+    }
+    return input.readAsString().then(
+        (c) => c.contains("package:checked_mirrors.dart/checked_mirrors.dart"));
+  }
+
+  Future apply(Transform transform) {
+    return transform.primaryInput.readAsString().then((content) {
+      var id = transform.primaryInput.id;
+      // TODO(sigmund): do a real transformer that only replaces imports, not
+      // all occurrences of this string.
+      // -----
+      // TODO(sigmund): move the @MirrorUsed from the field to the import
+      // need to do this before this CL is ready.
+      // ----
+      transform.addOutput(new Asset.fromString(id, content.replaceAll(
+            "package:checked_mirrors.dart/checked_mirrors.dart",
+            "dart:mirrors")));
+    });
+  }
+}