Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/barback/src/graph/transform_node.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 barback.graph.transform_node;
+
+import 'dart:async';
+
+import '../asset/asset.dart';
+import '../asset/asset_id.dart';
+import '../asset/asset_node.dart';
+import '../asset/asset_node_set.dart';
+import '../errors.dart';
+import '../log.dart';
+import '../transformer/aggregate_transform.dart';
+import '../transformer/aggregate_transformer.dart';
+import '../transformer/declaring_aggregate_transform.dart';
+import '../transformer/declaring_aggregate_transformer.dart';
+import '../transformer/lazy_aggregate_transformer.dart';
+import '../utils.dart';
+import 'node_status.dart';
+import 'node_streams.dart';
+import 'phase.dart';
+import 'transformer_classifier.dart';
+
+/// Describes a transform on a set of assets and its relationship to the build
+/// dependency graph.
+///
+/// Keeps track of whether it's dirty and needs to be run and which assets it
+/// depends on.
+class TransformNode {
+  /// The aggregate key for this node.
+  final String key;
+
+  /// The [TransformerClassifier] that [this] belongs to.
+  final TransformerClassifier classifier;
+
+  /// The [Phase] that this transform runs in.
+  Phase get phase => classifier.phase;
+
+  /// The [AggregateTransformer] to apply to this node's inputs.
+  final AggregateTransformer transformer;
+
+  /// The primary asset nodes this transform runs on.
+  final _primaries = new AssetNodeSet();
+
+  /// A string describing the location of [this] in the transformer graph.
+  final String _location;
+
+  /// The subscription to the [_primaries]' [AssetNode.onStateChange] streams.
+  final _primarySubscriptions = new Map<AssetId, StreamSubscription>();
+
+  /// The subscription to [phase]'s [Phase.onAsset] stream.
+  StreamSubscription<AssetNode> _phaseAssetSubscription;
+
+  /// The subscription to [phase]'s [Phase.onStatusChange] stream.
+  StreamSubscription<NodeStatus> _phaseStatusSubscription;
+
+  /// How far along [this] is in processing its assets.
+  NodeStatus get status {
+    if (_state == _State.APPLIED || _state == _State.DECLARED) {
+      return NodeStatus.IDLE;
+    }
+
+    if (_declaring && _state != _State.DECLARING &&
+        _state != _State.NEEDS_DECLARE) {
+      return NodeStatus.MATERIALIZING;
+    } else {
+      return NodeStatus.RUNNING;
+    }
+  }
+
+  /// The [TransformInfo] describing this node.
+  ///
+  /// [TransformInfo] is the publicly-visible representation of a transform
+  /// node.
+  TransformInfo get info => new TransformInfo(transformer,
+      new AssetId(phase.cascade.package, key));
+
+  /// Whether this is a declaring transform.
+  ///
+  /// This is usually identical to `transformer is
+  /// DeclaringAggregateTransformer`, but if a declaring and non-lazy
+  /// transformer emits an error during `declareOutputs` it's treated as though
+  /// it wasn't declaring.
+  bool get _declaring => transformer is DeclaringAggregateTransformer &&
+      (_state == _State.DECLARING || _declaredOutputs != null);
+
+  /// Whether this transform has been forced since it last finished applying.
+  ///
+  /// A transform being forced means it should run until it generates outputs
+  /// and is no longer dirty. This is always true for non-declaring
+  /// transformers, since they always need to eagerly generate outputs.
+  bool _forced;
+
+  /// The subscriptions to each secondary input's [AssetNode.onStateChange]
+  /// stream.
+  final _secondarySubscriptions = new Map<AssetId, StreamSubscription>();
+
+  /// The controllers for the asset nodes emitted by this node.
+  final _outputControllers = new Map<AssetId, AssetNodeController>();
+
+  /// The ids of inputs the transformer tried and failed to read last time it
+  /// ran.
+  final _missingInputs = new Set<AssetId>();
+
+  /// The controllers that are used to pass each primary input through [this] if
+  /// it's not consumed or overwritten.
+  ///
+  /// This needs an intervening controller to ensure that the output can be
+  /// marked dirty when determining whether [this] will consume or overwrite it,
+  /// and be marked removed if it does. No pass-through controller will exist
+  /// for primary inputs that are not being passed through.
+  final _passThroughControllers = new Map<AssetId, AssetNodeController>();
+
+  /// The asset node for this transform.
+  final _streams = new NodeStreams();
+  Stream<NodeStatus> get onStatusChange => _streams.onStatusChange;
+  Stream<AssetNode> get onAsset => _streams.onAsset;
+  Stream<LogEntry> get onLog => _streams.onLog;
+
+  /// The current state of [this].
+  var _state = _State.DECLARED;
+
+  /// Whether [this] has been marked as removed.
+  bool get _isRemoved => _streams.onAssetController.isClosed;
+
+  // If [transformer] is declaring but not lazy and [primary] is available, we
+  // can run [apply] even if [force] hasn't been called, since [transformer]
+  // should run eagerly if possible.
+  bool get _canRunDeclaringEagerly =>
+      _declaring && transformer is! LazyAggregateTransformer &&
+      _primaries.every((input) => input.state.isAvailable);
+
+  /// Which primary inputs the most recent run of this transform has declared
+  /// that it consumes.
+  ///
+  /// This starts out `null`, indicating that the transform hasn't declared
+  /// anything yet. This is not meaningful unless [_state] is [_State.APPLIED]
+  /// or [_State.DECLARED].
+  Set<AssetId> _consumedPrimaries;
+
+  /// The set of output ids that [transformer] declared it would emit.
+  ///
+  /// This is only non-null if [transformer] is a
+  /// [DeclaringAggregateTransformer] and its [declareOutputs] has been run
+  /// successfully.
+  Set<AssetId> _declaredOutputs;
+
+  /// The controller for the currently-running
+  /// [DeclaringAggregateTransformer.declareOutputs] call's
+  /// [DeclaringAggregateTransform].
+  ///
+  /// This will be non-`null` when
+  /// [DeclaringAggregateTransformer.declareOutputs] is running. This means that
+  /// it's always non-`null` when [_state] is [_State.DECLARING], sometimes
+  /// non-`null` when it's [_State.NEEDS_DECLARE], and always `null` otherwise.
+  DeclaringAggregateTransformController _declareController;
+
+  /// The controller for the currently-running [AggregateTransformer.apply]
+  /// call's [AggregateTransform].
+  ///
+  /// This will be non-`null` when [AggregateTransform.apply] is running, which
+  /// means that it's always non-`null` when [_state] is [_State.APPLYING] or
+  /// [_State.NEEDS_APPLY], sometimes non-`null` when it's
+  /// [_State.NEEDS_DECLARE], and always `null` otherwise.
+  AggregateTransformController _applyController;
+
+  /// The number of secondary inputs that have been requested but not yet
+  /// produced.
+  int _pendingSecondaryInputs = 0;
+
+  /// A stopwatch that tracks the total time spent in a transformer's `apply`
+  /// function.
+  final _timeInTransformer = new Stopwatch();
+
+  /// A stopwatch that tracks the time in a transformer's `apply` function spent
+  /// waiting for [getInput] calls to complete.
+  final _timeAwaitingInputs = new Stopwatch();
+
+  TransformNode(this.classifier, this.transformer, this.key, this._location) {
+    _forced = transformer is! DeclaringAggregateTransformer;
+
+    _phaseAssetSubscription = phase.previous.onAsset.listen((node) {
+      if (!_missingInputs.contains(node.id)) return;
+      if (_forced) node.force();
+      _dirty();
+    });
+
+    _phaseStatusSubscription = phase.previous.onStatusChange.listen((status) {
+      if (status == NodeStatus.RUNNING) return;
+
+      _maybeFinishDeclareController();
+      _maybeFinishApplyController();
+    });
+
+    classifier.onDoneClassifying.listen((_) {
+      _maybeFinishDeclareController();
+      _maybeFinishApplyController();
+    });
+
+    _run();
+  }
+
+  /// Adds [input] as a primary input for this node.
+  void addPrimary(AssetNode input) {
+    _primaries.add(input);
+    if (_forced) input.force();
+
+    _primarySubscriptions[input.id] = input.onStateChange
+        .listen((_) => _onPrimaryStateChange(input));
+
+    if (_state == _State.DECLARING && !_declareController.isDone) {
+      // If we're running `declareOutputs` and its id stream isn't closed yet,
+      // pass this in as another id.
+      _declareController.addId(input.id);
+      _maybeFinishDeclareController();
+    } else if (_state == _State.APPLYING) {
+      // If we're running `apply`, we need to wait until [input] is available
+      // before we pass it into the stream. If it's available now, great; if
+      // not, [_onPrimaryStateChange] will handle it.
+      if (!input.state.isAvailable) {
+        // If we started running eagerly without being forced, abort that run if
+        // a new unavailable asset comes in.
+        if (input.isLazy && !_forced) _restartRun();
+        return;
+      }
+
+      _onPrimaryStateChange(input);
+      _maybeFinishApplyController();
+    } else {
+      // Otherwise, a new input means we'll need to re-run `declareOutputs`.
+      _restartRun();
+    }
+  }
+
+  /// Marks this transform as removed.
+  ///
+  /// This causes all of the transform's outputs to be marked as removed as
+  /// well. Normally this will be automatically done internally based on events
+  /// from the primary input, but it's possible for a transform to no longer be
+  /// valid even if its primary input still exists.
+  void remove() {
+    _streams.close();
+    _phaseAssetSubscription.cancel();
+    _phaseStatusSubscription.cancel();
+    if (_declareController != null) _declareController.cancel();
+    if (_applyController != null) _applyController.cancel();
+    _clearSecondarySubscriptions();
+    _clearOutputs();
+
+    for (var subscription in _primarySubscriptions.values) {
+      subscription.cancel();
+    }
+    _primarySubscriptions.clear();
+
+    for (var controller in _passThroughControllers.values) {
+      controller.setRemoved();
+    }
+    _passThroughControllers.clear();
+  }
+
+  /// If [this] is deferred, ensures that its concrete outputs will be
+  /// generated.
+  void force() {
+    if (_forced || _state == _State.APPLIED) return;
+    for (var input in _primaries) {
+      input.force();
+    }
+
+    _forced = true;
+    if (_state == _State.DECLARED) _apply();
+  }
+
+  /// Marks this transform as dirty.
+  ///
+  /// Specifically, this should be called when one of the transform's inputs'
+  /// contents change, or when a secondary input is removed. Primary inputs
+  /// being added or removed are handled by [addInput] and
+  /// [_onPrimaryStateChange].
+  void _dirty() {
+    if (_state == _State.DECLARING || _state == _State.NEEDS_DECLARE ||
+        _state == _State.NEEDS_APPLY) {
+      // If we already know that [_apply] needs to be run, there's nothing to do
+      // here.
+      return;
+    }
+
+    if (!_forced && !_canRunDeclaringEagerly) {
+      // [forced] should only ever be false for a declaring transformer.
+      assert(_declaring);
+
+      // If we've finished applying, transition to DECLARED, indicating that we
+      // know what outputs [apply] will emit but we're waiting to emit them
+      // concretely until [force] is called. If we're still applying, we'll
+      // transition to DECLARED once we finish.
+      if (_state == _State.APPLIED) _state = _State.DECLARED;
+      for (var controller in _outputControllers.values) {
+        controller.setLazy(force);
+      }
+      _emitDeclaredOutputs();
+      return;
+    }
+
+    if (_state == _State.APPLIED) {
+      if (_declaredOutputs != null) _emitDeclaredOutputs();
+      _apply();
+    } else if (_state == _State.DECLARED) {
+      _apply();
+    } else {
+      _state = _State.NEEDS_APPLY;
+    }
+  }
+
+  /// The callback called when [input]'s state changes.
+  void _onPrimaryStateChange(AssetNode input) {
+    if (input.state.isRemoved) {
+      _primarySubscriptions.remove(input.id);
+
+      if (_primaries.isEmpty) {
+        // If there are no more primary inputs, there's no more use for this
+        // node in the graph. It will be re-created by its
+        // [TransformerClassifier] if a new input with [key] is added.
+        remove();
+        return;
+      }
+
+      // Any change to the number of primary inputs requires that we re-run the
+      // transformation.
+      _restartRun();
+    } else if (input.state.isAvailable) {
+      if (_state == _State.DECLARED && _canRunDeclaringEagerly) {
+        // If [this] is fully declared but hasn't started applying, this input
+        // becoming available may mean that all inputs are available, in which
+        // case we can run apply eagerly.
+        _apply();
+        return;
+      }
+
+      // If we're not actively passing concrete assets to the transformer, the
+      // distinction between a dirty asset and an available one isn't relevant.
+      if (_state != _State.APPLYING) return;
+
+      if (_applyController.isDone) {
+        // If we get a new asset after we've closed the asset stream, we need to
+        // re-run declare and then apply.
+        _restartRun();
+      } else {
+        // If the new asset comes before the asset stream is done, we can just
+        // pass it to the stream.
+        _applyController.addInput(input.asset);
+        _maybeFinishApplyController();
+      }
+    } else {
+      if (_forced) input.force();
+      if (_state == _State.APPLYING && !_applyController.addedId(input.id) &&
+          (_forced || !input.isLazy)) {
+        // If the input hasn't yet been added to the transform's input stream,
+        // there's no need to consider the transformation dirty. However, if the
+        // input is lazy and we're running eagerly, we need to restart the
+        // transformation.
+        return;
+      }
+      _dirty();
+    }
+  }
+
+  /// Run the entire transformation, including both `declareOutputs` (if
+  /// applicable) and `apply`.
+  void _run() {
+    assert(_state != _State.DECLARING);
+    assert(_state != _State.APPLYING);
+
+    _markOutputsDirty();
+    _declareOutputs(() {
+      if (_forced || _canRunDeclaringEagerly) {
+        _apply();
+      } else {
+        _state = _State.DECLARED;
+        _streams.changeStatus(NodeStatus.IDLE);
+      }
+    });
+  }
+
+  /// Restart the entire transformation, including `declareOutputs` if
+  /// applicable.
+  void _restartRun() {
+    if (_state == _State.DECLARED || _state == _State.APPLIED) {
+      // If we're currently idle, we can restart the transformation immediately.
+      _run();
+      return;
+    }
+
+    // If we're actively running `declareOutputs` or `apply`, cancel the
+    // transforms and transition to `NEEDS_DECLARE`. Once the transformer's
+    // method returns, we'll transition to `DECLARING`.
+    if (_declareController != null) _declareController.cancel();
+    if (_applyController != null) _applyController.cancel();
+    _state = _State.NEEDS_DECLARE;
+  }
+
+  /// Runs [transform.declareOutputs] and emits the resulting assets as dirty
+  /// assets.
+  ///
+  /// Calls [callback] when it's finished. This doesn't return a future so that
+  /// [callback] is called synchronously if there are no outputs to declare. If
+  /// [this] is removed while inputs are being declared, [callback] will not be
+  /// called.
+  void _declareOutputs(void callback()) {
+    if (transformer is! DeclaringAggregateTransformer) {
+      callback();
+      return;
+    }
+
+    _state = _State.DECLARING;
+    var controller = new DeclaringAggregateTransformController(this);
+    _declareController = controller;
+    _streams.onLogPool.add(controller.onLog);
+    for (var primary in _primaries) {
+      controller.addId(primary.id);
+    }
+    _maybeFinishDeclareController();
+
+    syncFuture(() {
+      return (transformer as DeclaringAggregateTransformer)
+          .declareOutputs(controller.transform);
+    }).whenComplete(() {
+      // Cancel the controller here even if `declareOutputs` wasn't interrupted.
+      // Since the declaration is finished, we want to close out the
+      // controller's streams.
+      controller.cancel();
+      _declareController = null;
+    }).then((_) {
+      if (_isRemoved) return;
+      if (_state == _State.NEEDS_DECLARE) {
+        _declareOutputs(callback);
+        return;
+      }
+
+      if (controller.loggedError) {
+        // If `declareOutputs` fails, fall back to treating a declaring
+        // transformer as though it were eager.
+        if (transformer is! LazyAggregateTransformer) _forced = true;
+        callback();
+        return;
+      }
+
+      _consumedPrimaries = controller.consumedPrimaries;
+      _declaredOutputs = controller.outputIds;
+      var invalidIds = _declaredOutputs
+          .where((id) => id.package != phase.cascade.package).toSet();
+      for (var id in invalidIds) {
+        _declaredOutputs.remove(id);
+        // TODO(nweiz): report this as a warning rather than a failing error.
+        phase.cascade.reportError(new InvalidOutputException(info, id));
+      }
+
+      for (var primary in _primaries) {
+        if (_declaredOutputs.contains(primary.id)) continue;
+        _passThrough(primary.id);
+      }
+      _emitDeclaredOutputs();
+      callback();
+    }).catchError((error, stackTrace) {
+      if (_isRemoved) return;
+      if (transformer is! LazyAggregateTransformer) _forced = true;
+      phase.cascade.reportError(_wrapException(error, stackTrace));
+      callback();
+    });
+  }
+
+  /// Emits a dirty asset node for all outputs that were declared by the
+  /// transformer.
+  ///
+  /// This won't emit any outputs for which there already exist output
+  /// controllers. It should only be called for transforms that have declared
+  /// their outputs.
+  void _emitDeclaredOutputs() {
+    assert(_declaredOutputs != null);
+    for (var id in _declaredOutputs) {
+      if (_outputControllers.containsKey(id)) continue;
+      var controller = _forced
+          ? new AssetNodeController(id, this)
+          : new AssetNodeController.lazy(id, force, this);
+      _outputControllers[id] = controller;
+      _streams.onAssetController.add(controller.node);
+    }
+  }
+
+  //// Mark all emitted and passed-through outputs of this transform as dirty.
+  void _markOutputsDirty() {
+    for (var controller in _passThroughControllers.values) {
+      controller.setDirty();
+    }
+    for (var controller in _outputControllers.values) {
+      if (_forced) {
+        controller.setDirty();
+      } else {
+        controller.setLazy(force);
+      }
+    }
+  }
+
+  /// Applies this transform.
+  void _apply() {
+    assert(!_isRemoved);
+
+    _markOutputsDirty();
+    _clearSecondarySubscriptions();
+    _state = _State.APPLYING;
+    _streams.changeStatus(status);
+    _runApply().then((hadError) {
+      if (_isRemoved) return;
+
+      if (_state == _State.DECLARED) return;
+
+      if (_state == _State.NEEDS_DECLARE) {
+        _run();
+        return;
+      }
+
+      // If an input's contents changed while running `apply`, retry unless the
+      // transformer is deferred and hasn't been forced.
+      if (_state == _State.NEEDS_APPLY) {
+        if (_forced || _canRunDeclaringEagerly) {
+          _apply();
+        } else {
+          _state = _State.DECLARED;
+        }
+        return;
+      }
+
+      if (_declaring) _forced = false;
+
+      assert(_state == _State.APPLYING);
+      if (hadError) {
+        _clearOutputs();
+        // If the transformer threw an error, we don't want to emit the
+        // pass-through assets in case they'll be overwritten by the
+        // transformer. However, if the transformer declared that it wouldn't
+        // overwrite or consume a pass-through asset, we can safely emit it.
+        if (_declaredOutputs != null) {
+          for (var input in _primaries) {
+            if (_consumedPrimaries.contains(input.id) ||
+                _declaredOutputs.contains(input.id)) {
+              _consumePrimary(input.id);
+            } else {
+              _passThrough(input.id);
+            }
+          }
+        }
+      }
+
+      _state = _State.APPLIED;
+      _streams.changeStatus(NodeStatus.IDLE);
+    });
+  }
+
+  /// Gets the asset for an input [id].
+  ///
+  /// If an input with [id] cannot be found, throws an [AssetNotFoundException].
+  Future<Asset> getInput(AssetId id) {
+    _timeAwaitingInputs.start();
+    _pendingSecondaryInputs++;
+    return phase.previous.getOutput(id).then((node) {
+      // Throw if the input isn't found. This ensures the transformer's apply
+      // is exited. We'll then catch this and report it through the proper
+      // results stream.
+      if (node == null) {
+        _missingInputs.add(id);
+        throw new AssetNotFoundException(id);
+      }
+
+      _secondarySubscriptions.putIfAbsent(node.id, () {
+        return node.onStateChange.listen((_) => _dirty());
+      });
+
+      return node.asset;
+    }).whenComplete(() {
+      _pendingSecondaryInputs--;
+      if (_pendingSecondaryInputs != 0) _timeAwaitingInputs.stop();
+    });
+  }
+
+  /// Run [AggregateTransformer.apply].
+  ///
+  /// Returns whether or not an error occurred while running the transformer.
+  Future<bool> _runApply() {
+    var controller = new AggregateTransformController(this);
+    _applyController = controller;
+    _streams.onLogPool.add(controller.onLog);
+    for (var primary in _primaries) {
+      if (!primary.state.isAvailable) continue;
+      controller.addInput(primary.asset);
+    }
+    _maybeFinishApplyController();
+
+    return syncFuture(() {
+      _timeInTransformer.reset();
+      _timeAwaitingInputs.reset();
+      _timeInTransformer.start();
+      return transformer.apply(controller.transform);
+    }).whenComplete(() {
+      _timeInTransformer.stop();
+      _timeAwaitingInputs.stop();
+
+      // Cancel the controller here even if `apply` wasn't interrupted. Since
+      // the apply is finished, we want to close out the controller's streams.
+      controller.cancel();
+      _applyController = null;
+    }).then((_) {
+      assert(_state != _State.DECLARED);
+      assert(_state != _State.DECLARING);
+      assert(_state != _State.APPLIED);
+
+      if (!_forced && _primaries.any((node) => !node.state.isAvailable)) {
+        _state = _State.DECLARED;
+        _streams.changeStatus(NodeStatus.IDLE);
+        return false;
+      }
+
+      if (_isRemoved) return false;
+      if (_state == _State.NEEDS_APPLY) return false;
+      if (_state == _State.NEEDS_DECLARE) return false;
+      if (controller.loggedError) return true;
+
+      // If the transformer took long enough, log its duration in fine output.
+      // That way it's not always visible, but users running with "pub serve
+      // --verbose" can see it.
+      var ranLong = _timeInTransformer.elapsed > new Duration(seconds: 1);
+      var ranLongLocally =
+          _timeInTransformer.elapsed - _timeAwaitingInputs.elapsed >
+            new Duration(milliseconds: 200);
+
+      // Report the transformer's timing information if it spent more than 0.2s
+      // doing things other than waiting for its secondary inputs or if it spent
+      // more than 1s in total.
+      if (ranLongLocally || ranLong) {
+        _streams.onLogController.add(new LogEntry(
+            info, info.primaryId, LogLevel.FINE,
+            "Took ${niceDuration(_timeInTransformer.elapsed)} "
+              "(${niceDuration(_timeAwaitingInputs.elapsed)} awaiting "
+              "secondary inputs).",
+            null));
+      }
+
+      _handleApplyResults(controller);
+      return false;
+    }).catchError((error, stackTrace) {
+      // If the transform became dirty while processing, ignore any errors from
+      // it.
+      if (_state == _State.NEEDS_APPLY || _isRemoved) return false;
+
+      // Catch all transformer errors and pipe them to the results stream. This
+      // is so a broken transformer doesn't take down the whole graph.
+      phase.cascade.reportError(_wrapException(error, stackTrace));
+      return true;
+    });
+  }
+
+  /// Handle the results of running [Transformer.apply].
+  ///
+  /// [controller] should be the controller for the [AggegateTransform] passed
+  /// to [AggregateTransformer.apply].
+  void _handleApplyResults(AggregateTransformController controller) {
+    _consumedPrimaries = controller.consumedPrimaries;
+
+    var newOutputs = controller.outputs;
+    // Any ids that are for a different package are invalid.
+    var invalidIds = newOutputs
+        .map((asset) => asset.id)
+        .where((id) => id.package != phase.cascade.package)
+        .toSet();
+    for (var id in invalidIds) {
+      newOutputs.removeId(id);
+      // TODO(nweiz): report this as a warning rather than a failing error.
+      phase.cascade.reportError(new InvalidOutputException(info, id));
+    }
+
+    // Remove outputs that used to exist but don't anymore.
+    for (var id in _outputControllers.keys.toList()) {
+      if (newOutputs.containsId(id)) continue;
+      _outputControllers.remove(id).setRemoved();
+    }
+
+    // Emit or stop emitting pass-through assets between removing and adding
+    // outputs to ensure there are no collisions.
+    for (var id in _primaries.map((node) => node.id)) {
+      if (_consumedPrimaries.contains(id) || newOutputs.containsId(id)) {
+        _consumePrimary(id);
+      } else {
+        _passThrough(id);
+      }
+    }
+
+    // Store any new outputs or new contents for existing outputs.
+    for (var asset in newOutputs) {
+      var controller = _outputControllers[asset.id];
+      if (controller != null) {
+        controller.setAvailable(asset);
+      } else {
+        var controller = new AssetNodeController.available(asset, this);
+        _outputControllers[asset.id] = controller;
+        _streams.onAssetController.add(controller.node);
+      }
+    }
+  }
+
+  /// Cancels all subscriptions to secondary input nodes.
+  void _clearSecondarySubscriptions() {
+    _missingInputs.clear();
+    for (var subscription in _secondarySubscriptions.values) {
+      subscription.cancel();
+    }
+    _secondarySubscriptions.clear();
+  }
+
+  /// Removes all output assets.
+  void _clearOutputs() {
+    // Remove all the previously-emitted assets.
+    for (var controller in _outputControllers.values) {
+      controller.setRemoved();
+    }
+    _outputControllers.clear();
+  }
+
+  /// Emit the pass-through node for the primary input [id] if it's not being
+  /// emitted already.
+  void _passThrough(AssetId id) {
+    assert(!_outputControllers.containsKey(id));
+
+    if (_consumedPrimaries.contains(id)) return;
+    var controller = _passThroughControllers[id];
+    var primary = _primaries[id];
+    if (controller == null) {
+      controller = new AssetNodeController.from(primary);
+      _passThroughControllers[id] = controller;
+      _streams.onAssetController.add(controller.node);
+    } else if (primary.state.isDirty) {
+      controller.setDirty();
+    } else if (!controller.node.state.isAvailable) {
+      controller.setAvailable(primary.asset);
+    }
+  }
+
+  /// Stops emitting the pass-through node for the primary input [id] if it's
+  /// being emitted.
+  void _consumePrimary(AssetId id) {
+    var controller = _passThroughControllers.remove(id);
+    if (controller == null) return;
+    controller.setRemoved();
+  }
+
+  /// If `declareOutputs` is running and all previous phases have declared their
+  /// outputs, mark [_declareController] as done.
+  void _maybeFinishDeclareController() {
+    if (_declareController == null) return;
+    if (classifier.isClassifying) return;
+    if (phase.previous.status == NodeStatus.RUNNING) return;
+    _declareController.done();
+  }
+
+  /// If `apply` is running, all previous phases have declared their outputs,
+  /// and all primary inputs are available and thus have been passed to the
+  /// transformer, mark [_applyController] as done.
+  void _maybeFinishApplyController() {
+    if (_applyController == null) return;
+    if (classifier.isClassifying) return;
+    if (_primaries.any((input) => !input.state.isAvailable)) return;
+    if (phase.previous.status == NodeStatus.RUNNING) return;
+    _applyController.done();
+  }
+
+  BarbackException _wrapException(error, StackTrace stackTrace) {
+    if (error is! AssetNotFoundException) {
+      return new TransformerException(info, error, stackTrace);
+    } else {
+      return new MissingInputException(info, error.id);
+    }
+  }
+
+  String toString() =>
+      "transform node in $_location for $transformer on ${info.primaryId} "
+      "($_state, $status, ${_forced ? '' : 'un'}forced)";
+}
+
+/// The enum of states that [TransformNode] can be in.
+class _State {
+  /// The transform is running [DeclaringAggregateTransformer.declareOutputs].
+  ///
+  /// If the set of primary inputs changes while in this state, it will
+  /// transition to [NEEDS_DECLARE]. If the [TransformNode] is still in this
+  /// state when `declareOutputs` finishes running, it will transition to
+  /// [APPLYING] if the transform is non-lazy and all of its primary inputs are
+  /// available, and [DECLARED] otherwise.
+  ///
+  /// Non-declaring transformers will transition out of this state and into
+  /// [APPLYING] immediately.
+  static const DECLARING = const _State._("declaring outputs");
+
+  /// The transform is running [AggregateTransformer.declareOutputs] or
+  /// [AggregateTransform.apply], but a primary input was added or removed after
+  /// it started, so it will need to re-run `declareOutputs`.
+  ///
+  /// The [TransformNode] will transition to [DECLARING] once `declareOutputs`
+  /// or `apply` finishes running.
+  static const NEEDS_DECLARE = const _State._("needs declare");
+
+  /// The transform is deferred and has run
+  /// [DeclaringAggregateTransformer.declareOutputs] but hasn't yet been forced.
+  ///
+  /// The [TransformNode] will transition to [APPLYING] when one of the outputs
+  /// has been forced or if the transformer is non-lazy and all of its primary
+  /// inputs become available.
+  static const DECLARED = const _State._("declared");
+
+  /// The transform is running [AggregateTransformer.apply].
+  ///
+  /// If an input's contents change or a secondary input is added or removed
+  /// while in this state, the [TransformNode] will transition to [NEEDS_APPLY].
+  /// If a primary input is added or removed, it will transition to
+  /// [NEEDS_DECLARE]. If it's still in this state when `apply` finishes
+  /// running, it will transition to [APPLIED].
+  static const APPLYING = const _State._("applying");
+
+  /// The transform is running [AggregateTransformer.apply], but an input's
+  /// contents changed or a secondary input was added or removed after it
+  /// started, so it will need to re-run `apply`.
+  ///
+  /// If a primary input is added or removed while in this state, the
+  /// [TranformNode] will transition to [NEEDS_DECLARE]. If it's still in this
+  /// state when `apply` finishes running, it will transition to [APPLYING].
+  static const NEEDS_APPLY = const _State._("needs apply");
+
+  /// The transform has finished running [AggregateTransformer.apply], whether
+  /// or not it emitted an error.
+  ///
+  /// If an input's contents change or a secondary input is added or removed,
+  /// the [TransformNode] will transition to [DECLARED] if the transform is
+  /// declaring and [APPLYING] otherwise. If a primary input is added or
+  /// removed, this will transition to [DECLARING].
+  static const APPLIED = const _State._("applied");
+
+  final String name;
+
+  const _State._(this.name);
+
+  String toString() => name;
+}