Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/barback/src/transformer/base_transform.dart

+// Copyright (c) 2014, 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 barback.transformer.base_transform;
+
+import 'dart:async';
+
+import '../asset/asset_id.dart';
+import '../graph/transform_node.dart';
+import '../log.dart';
+import 'transform_logger.dart';
+
+/// The base class for the ephemeral transform objects that are passed to
+/// transformers.
+///
+/// This class provides the transformers with inputs, but its up to the
+/// subclasses to provide a means of emitting outputs.
+abstract class BaseTransform {
+  final TransformNode _node;
+
+  /// The ids of primary inputs that should be consumed.
+  ///
+  /// This is exposed by [BaseTransformController].
+  final _consumedPrimaries = new Set<AssetId>();
+
+  /// Whether the transformer logged an error.
+  ///
+  /// This is exposed via [BaseTransformController].
+  bool _loggedError = false;
+
+  /// The controller for the stream of log entries emitted by the transformer.
+  ///
+  /// This is exposed via [BaseTransformController].
+  ///
+  /// This is synchronous because error logs can cause the transform to fail, so
+  /// we need to ensure that their processing isn't delayed until after the
+  /// transform or build has finished.
+  final _onLogController = new StreamController<LogEntry>.broadcast(sync: true);
+
+  /// A logger so that the [Transformer] can report build details.
+  TransformLogger get logger => _logger;
+  TransformLogger _logger;
+
+  BaseTransform(this._node) {
+    _logger = new TransformLogger((asset, level, message, span) {
+      if (level == LogLevel.ERROR) _loggedError = true;
+
+      // If the log isn't already associated with an asset, use the primary.
+      if (asset == null) asset = _node.info.primaryId;
+      var entry = new LogEntry(_node.info, asset, level, message, span);
+
+      // The log controller can be closed while log entries are still coming in
+      // if the transformer is removed during [apply].
+      if (!_onLogController.isClosed) _onLogController.add(entry);
+    });
+  }
+
+  /// Consume a primary input so that it doesn't get processed by future
+  /// phases or emitted once processing has finished.
+  ///
+  /// Normally each primary input will automatically be forwarded unless the
+  /// transformer overwrites it by emitting an input with the same id. This
+  /// allows the transformer to tell barback not to forward a primary input
+  /// even if it's not overwritten.
+  void consumePrimary(AssetId id) {
+    // TODO(nweiz): throw an error if an id is consumed that wasn't listed as a
+    // primary input.
+    _consumedPrimaries.add(id);
+  }
+}
+
+/// The base class for controllers of subclasses of [BaseTransform].
+///
+/// Controllers are used so that [TransformNode]s can get values from a
+/// [BaseTransform] without exposing getters in the public API.
+abstract class BaseTransformController {
+  /// The [BaseTransform] controlled by this controller.
+  final BaseTransform transform;
+
+  /// The ids of primary inputs that should be consumed.
+  Set<AssetId> get consumedPrimaries => transform._consumedPrimaries;
+
+  /// Whether the transform logged an error.
+  bool get loggedError => transform._loggedError;
+
+  /// The stream of log entries emitted by the transformer during a run.
+  Stream<LogEntry> get onLog => transform._onLogController.stream;
+
+  /// Whether the transform's input or id stream has been closed.
+  ///
+  /// See also [done].
+  bool get isDone;
+
+  BaseTransformController(this.transform);
+
+  /// Mark this transform as finished emitting new inputs or input ids.
+  ///
+  /// This is distinct from [cancel] in that it *doesn't* indicate that the
+  /// transform is finished being used entirely. The transformer may still log
+  /// messages and load secondary inputs. This just indicates that all the
+  /// primary inputs are accounted for.
+  void done();
+
+  /// Mark this transform as canceled.
+  ///
+  /// This will close any streams and release any resources that were allocated
+  /// for the duration of the transformation. Unlike [done], this indicates that
+  /// the transformation is no longer relevant; either it has returned, or
+  /// something external has preemptively invalidated its results.
+  void cancel() {
+    done();
+    transform._onLogController.close();
+  }
+}