Support loading transformer plugins from pub.

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

Index: sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart b/sdk/lib/_internal/pub/lib/src/barback/load_transformers.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.
+
+library pub.serialize_transformer;
+
+import 'dart:async';
+import 'dart:isolate';
+
+import 'package:barback/barback.dart';
+import 'package:stack_trace/stack_trace.dart';
+
+import '../dart.dart' as dart;
+import '../log.dart' as log;
+import '../utils.dart';
+
+/// A Dart script to run in an isolate.
+///
+/// This script serializes one or more transformers defined in a Dart library and
+/// marhsals calls to and from them with the host isolate.
+const _TRANSFORMER_ISOLATE = """
+import 'dart:async';
+import 'dart:isolate';
+import 'dart:mirrors';
+
+import 'http://localhost:<<PORT>>/packages/barback/barback.dart';
+
+/// Sets up the initial communication with the host isolate.
+void main() {
+  port.receive((uri, replyTo) {
+    _sendFuture(replyTo, new Future.sync(() {
+      return initialize(Uri.parse(uri)).map(_serializeTransformer).toList();
+    }));
+  });
+}
+
+/// Loads all the transformers defined in [uri] and adds them to [transformers].
+///
+/// We then load the library, find any Transformer subclasses in it, instantiate
+/// them, and return them.
+Iterable<Transformer> initialize(Uri uri) {
+  var mirrors = currentMirrorSystem();
+  // TODO(nweiz): look this up by name once issue 5897 is fixed.
+  var transformerUri = Uri.parse(
+      'http://localhost:<<PORT>>/packages/barback/src/transformer.dart');
+  var transformerClass = mirrors.libraries[transformerUri]
+      .classes[const Symbol('Transformer')];
+
+  return mirrors.libraries[uri].classes.values.where((classMirror) {
+    if (classMirror.isPrivate) return false;
+    if (isAbstract(classMirror)) return false;
+    if (!classIsA(classMirror, transformerClass)) return false;
+    var constructor = classMirror.constructors[classMirror.simpleName];
+    if (constructor == null) return false;
+    if (!constructor.parameters.isEmpty) return false;
+    return true;
+  }).map((classMirror) {
+    return classMirror.newInstance(const Symbol(''), []).reflectee;
+  });
+}
+
+/// A wrapper for a [Transform] that's in the host isolate.
+///
+/// This retrieves inputs from and sends outputs and logs to the host isolate.
+class ForeignTransform implements Transform {
+  /// The port with which we communicate with the host isolate.
+  ///
+  /// This port and all messages sent across it are specific to this transform.
+  final SendPort _port;
+
+  final Asset primaryInput;
+
+  // TODO(nweiz): implement this
+  TransformLogger get logger {
+    throw new UnimplementedError('ForeignTranform.logger is not yet '
+      'implemented.');
+  }
+
+  /// Creates a transform from a serializable map sent from the host isolate.
+  ForeignTransform(Map transform)
+      : _port = transform['port'],
+        primaryInput = _deserializeAsset(transform['primaryInput']);
+
+  Future<Asset> getInput(AssetId id) {
+    return _receiveFuture(_port.call({
+      'type': 'getInput',
+      'id': _serializeId(id)
+    })).then(_deserializeAsset);
+  }
+
+  void addOutput(Asset output) {
+    _port.send({
+      'type': 'addOutput',
+      'output': _serializeAsset(output)
+    });
+  }
+}
+
+/// Returns the mirror for the root Object type.
+ClassMirror get objectMirror {
+  if (_objectMirror == null) {
+    _objectMirror = currentMirrorSystem()
+        .libraries[Uri.parse('dart:core')]
+        .classes[const Symbol('Object')];
+  }
+  return _objectMirror;
+}
+ClassMirror _objectMirror;
+
+// TODO(nweiz): get rid of this when issue 12439 is fixed.
+/// Returns whether or not [mirror] is a subtype of [superclass].
+///
+/// This includes [superclass] being mixed in to or implemented by [mirror].
+bool classIsA(ClassMirror mirror, ClassMirror superclass) {
+  if (mirror == superclass) return true;
+  if (mirror == objectMirror) return false;
+  return classIsA(mirror.superclass, superclass) ||
+      mirror.superinterfaces.any((int) => classIsA(int, superclass));
+}
+
+// TODO(nweiz): get rid of this when issue 12826 is fixed.
+/// Returns whether or not [mirror] is an abstract class.
+bool isAbstract(ClassMirror mirror) => mirror.members.values
+    .any((member) => member is MethodMirror && member.isAbstract);
+
+/// Converts [transformer] into a serializable map.
+Map _serializeTransformer(Transformer transformer) {
+  var port = new ReceivePort();
+  port.receive((message, replyTo) {
+    _sendFuture(replyTo, new Future.sync(() {
+      if (message['type'] == 'isPrimary') {
+        return transformer.isPrimary(_deserializeAsset(message['asset']));
+      } else {
+        assert(message['type'] == 'apply');
+        return transformer.apply(
+            new ForeignTransform(message['transform']));
+      }
+    }));
+  });
+
+  return {
+    'toString': transformer.toString(),
+    'port': port.toSendPort()
+  };
+}
+
+/// Converts a serializable map into an [Asset].
+Asset _deserializeAsset(Map asset) {
+  var box = new MessageBox();
+  asset['sink'].add(box.sink);
+  return new Asset.fromStream(_deserializeId(asset['id']), box.stream);
+}
+
+/// Converts a serializable map into an [AssetId].
+AssetId _deserializeId(Map id) => new AssetId(id['package'], id['path']);
+
+/// Converts [asset] into a serializable map.
+Map _serializeAsset(Asset asset) {
+  // We can't send IsolateStreams (issue 12437), so instead we send a sink and
+  // get the isolate to send us back another sink.
+  var box = new MessageBox();
+  box.stream.first.then((sink) {
+    asset.read().listen(sink.add,
+        onError: sink.addError,
+        onDone: sink.close);
+  });
+
+  return {
+    'id': _serializeId(asset.id),
+    'sink': box.sink
+  };
+}
+
+/// Converts [id] into a serializable map.
+Map _serializeId(AssetId id) => {'package': id.package, 'path': id.path};
+
+/// Sends the result of [future] through [port].
+///
+/// This should be received on the other end using [_receiveFuture]. It
+/// re-raises any exceptions on the other side as [CrossIsolateException]s.
+void _sendFuture(SendPort port, Future future) {
+  future.then((result) {
+    port.send({'success': result});
+  }).catchError((error) {
+    // TODO(nweiz): at least MissingInputException should be preserved here.
+    port.send({'error': CrossIsolateException.serialize(error)});
+  });
+}
+
+/// Receives the result of [_sendFuture] from [portCall], which should be the
+/// return value of [SendPort.call].
+Future _receiveFuture(Future portCall) {
+  return portCall.then((response) {
+    if (response.containsKey('success')) return response['success'];
+    return new Future.error(
+        new CrossIsolateException.deserialize(response['error']));
+  });
+}
+
+/// An exception that was originally raised in another isolate.
+///
+/// Exception objects can't cross isolate boundaries in general, so this class
+/// wraps as much information as can be consistently serialized.
+class CrossIsolateException implements Exception {
+  /// The name of the type of exception thrown.
+  ///
+  /// This is the return value of [error.runtimeType.toString()]. Keep in mind
+  /// that objects in different libraries may have the same type name.
+  final String type;
+
+  /// The exception's message, or its [toString] if it didn't expose a `message`
+  /// property.
+  final String message;
+
+  /// The exception's stack trace, or `null` if no stack trace was available.
+  final Trace stackTrace;
+
+  /// Loads a [CrossIsolateException] from a map.
+  ///
+  /// [error] should be the result of [CrossIsolateException.serialize].
+  CrossIsolateException.deserialize(Map error)
+      : type = error['type'],
+        message = error['message'],
+        stackTrace = error['stack'] == null ? null :
+            new Trace.parse(error['stack']);
+
+  /// Serializes [error] to a map that can safely be passed across isolate
+  /// boundaries.
+  static Map serialize(error, [StackTrace stack]) {
+    if (stack == null) stack = getAttachedStackTrace(error);
+    return {
+      'type': error.runtimeType.toString(),
+      'message': getErrorMessage(error),
+      'stack': stack == null ? null : stack.toString()
+    };
+  }
+
+  String toString() => "\$message\\n\$stackTrace";
+}
+
+// Get a string description of an exception.
+//
+// Most exception types have a "message" property. We prefer this since
+// it skips the "Exception:", "HttpException:", etc. prefix that calling
+// toString() adds. But, alas, "message" isn't actually defined in the
+// base Exception type so there's no easy way to know if it's available
+// short of a giant pile of type tests for each known exception type.
+//
+// So just try it. If it throws, default to toString().
+String getErrorMessage(error) {
+  try {
+    return error.message;
+  } on NoSuchMethodError catch (_) {
+    return error.toString();
+  }
+}
+""";
+
+/// Load and return all transformers from the library identified by [library].
+///
+/// [server] is used to serve [library] and any Dart files it imports.
+Future<Set<Transformer>> loadTransformers(BarbackServer server,
+    AssetId library) {
+  var path = library.path.replaceFirst('lib/', '');
+  // TODO(nweiz): load from a "package:" URI when issue 12474 is fixed.
+  var uri = 'http://localhost:${server.port}/packages/${library.package}/$path';
+  var code = 'import "$uri";' +
+      _TRANSFORMER_ISOLATE.replaceAll('<<PORT>>', server.port.toString());
+  log.fine("Loading transformers from $library");
+  return dart.runInIsolate(code).then((sendPort) {
+    return _receiveFuture(sendPort.call(uri)).then((transformers) {
+      transformers = transformers
+          .map((transformer) => new _ForeignTransformer(transformer))
+          .toSet();
+      log.fine("Transformers from $library: $transformers");
+      return transformers;
+    });
+  }).catchError((error) {
+    if (error is! CrossIsolateException) throw error;
+    if (error.type != 'IsolateSpawnException') throw error;
+    // TODO(nweiz): don't parse this as a string once issues 12617 and 12689 are
+    // fixed.
+    if (!error.message.split('\n')[1].startsWith('import "$uri";')) {
+      throw error;
+    }
+
+    // If there was an IsolateSpawnException and the import that actually failed
+    // was the one we were loading transformers from, throw an application
+    // exception with a more user-friendly message.
+    fail('Transformer library "package:${library.package}/$path" not found.');
+  });
+}
+
+/// A wrapper for a transformer that's in a different isolate.
+class _ForeignTransformer implements Transformer {
+  /// The port with which we communicate with the child isolate.
+  ///
+  /// This port and all messages sent across it are specific to this
+  /// transformer.
+  final SendPort _port;
+
+  /// The result of calling [toString] on the transformer in the isolate.
+  final String _toString;
+
+  _ForeignTransformer(Map map)
+      : _port = map['port'],
+        _toString = map['toString'];
+
+  Future<bool> isPrimary(Asset asset) {
+    return _receiveFuture(_port.call({
+      'type': 'isPrimary',
+      'asset': _serializeAsset(asset)
+    }));
+  }
+
+  Future apply(Transform transform) {
+    return _receiveFuture(_port.call({
+      'type': 'apply',
+      'transform': _serializeTransform(transform)
+    }));
+  }
+
+  String toString() => _toString;
+}
+
+/// Converts [transform] into a serializable map.
+Map _serializeTransform(Transform transform) {
+  var receivePort = new ReceivePort();
+  receivePort.receive((message, replyTo) {
+    if (message['type'] == 'getInput') {
+      _sendFuture(replyTo, transform.getInput(_deserializeId(message['id']))
+          .then(_serializeAsset));
+    } else {
+      assert(message['type'] == 'addOutput');
+      transform.addOutput(_deserializeAsset(message['output']));
+    }
+  });
+
+  return {
+    'port': receivePort.toSendPort(),
+    'primaryInput': _serializeAsset(transform.primaryInput)
+  };
+}
+
+/// Converts a serializable map into an [Asset].
+Asset _deserializeAsset(Map asset) {
+  var box = new MessageBox();
+  asset['sink'].add(box.sink);
+  return new Asset.fromStream(_deserializeId(asset['id']), box.stream);
+}
+
+/// Converts a serializable map into an [AssetId].
+AssetId _deserializeId(Map id) => new AssetId(id['package'], id['path']);
+
+// TODO(nweiz): add custom serialization code for assets that can be more
+// efficiently serialized.
+/// Converts [asset] into a serializable map.
+Map _serializeAsset(Asset asset) {
+  // We can't send IsolateStreams (issue 12437), so instead we send a sink and
+  // get the isolate to send us back another sink.
+  var box = new MessageBox();
+  box.stream.first.then((sink) {
+    asset.read().listen(sink.add,
+        onError: sink.addError,
+        onDone: sink.close);
+  });
+
+  return {
+    'id': _serializeId(asset.id),
+    'sink': box.sink
+  };
+}
+
+/// Converts [id] into a serializable map.
+Map _serializeId(AssetId id) => {'package': id.package, 'path': id.path};
+
+/// Sends the result of [future] through [port].
+///
+/// This should be received on the other end using [_receiveFuture]. It
+/// re-raises any exceptions on the other side as [CrossIsolateException]s.
+void _sendFuture(SendPort port, Future future) {
+  future.then((result) {
+    port.send({'success': result});
+  }).catchError((error) {
+    // TODO(nweiz): at least MissingInputException should be preserved here.
+    port.send({'error': CrossIsolateException.serialize(error)});
+  });
+}
+
+/// Receives the result of [_sendFuture] from [portCall], which should be the
+/// return value of [SendPort.call].
+Future _receiveFuture(Future portCall) {
+  return portCall.then((response) {
+    if (response.containsKey('success')) return response['success'];
+    return new Future.error(
+        new dart.CrossIsolateException.deserialize(response['error']));
+  });
+}