Report changed assets through build daemon (#3273)

Report a list of changed assets (outputs + changed inputs from watcher) through the build daemon. Because this list can be rather large, the changes are only reported to clients actually interested in them.

Closes #3268.

build_daemon/CHANGELOG.md

@@ -1,5 +1,7 @@
-## 3.0.3-dev
+## 3.1.0-dev
 
+- Add `BuildResults.changedAssets` containing asset URIs changed during a
+  build.
 - Updated the example to use `dart pub` instead of `pub`.
 
 ## 3.0.2

build_daemon/lib/data/build_status.dart

@@ -6,6 +6,8 @@ import 'package:built_collection/built_collection.dart';
 import 'package:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';
 
+import 'build_target.dart';
+
 part 'build_status.g.dart';
 
 class BuildStatus extends EnumClass {
@@ -59,4 +61,16 @@ abstract class BuildResults
   BuildResults._();
 
   BuiltList<BuildResult> get results;
+
+  /// A list of asset URIs that were modified since the last build.
+  ///
+  /// This includes both sources that were updated and affected generated assets
+  /// that were rebuilt.
+  ///
+  /// To avoid communication overhead for clients not interested in this field,
+  /// it is not set by default. To enable it, register at least one target with
+  /// [DefaultBuildTarget.reportChangedAssets].
+  /// However, build implementations can unconditionally set this field as it
+  /// is stripped out in the daemon server implementation.
+  BuiltList<Uri>? get changedAssets;
 }

build_daemon/lib/data/build_target.dart

@@ -2,6 +2,8 @@ import 'package:built_collection/built_collection.dart';
 import 'package:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';
 
+import 'build_status.dart';
+
 part 'build_target.g.dart';
 
 /// The string representation of a build target, e.g. folder path.
@@ -16,6 +18,10 @@ abstract class DefaultBuildTarget
   static Serializer<DefaultBuildTarget> get serializer =>
       _$defaultBuildTargetSerializer;
 
+  @BuiltValueHook(initializeBuilder: true)
+  static void _setDefaults(DefaultBuildTargetBuilder b) =>
+      b.reportChangedAssets = false;
+
   factory DefaultBuildTarget([void Function(DefaultBuildTargetBuilder) b]) =
       _$DefaultBuildTarget;
 
@@ -38,6 +44,13 @@ abstract class DefaultBuildTarget
   /// - package:*/**
   /// - $target/**
   BuiltSet<String>? get buildFilters;
+
+  /// Whether the [BuildResults] events emitted for this target should report a
+  /// list of assets invalidated in a build.
+  ///
+  /// This defaults to `false` to reduce the serialization overhead when this
+  /// information is not required.
+  bool get reportChangedAssets;
 }
 
 /// The location to write the build outputs.

build_daemon/lib/src/fakes/fake_test_builder.dart

@@ -15,14 +15,16 @@ class FakeTestDaemonBuilder implements DaemonBuilder {
   static final buildCompletedMessage = 'Build Completed';
 
   final _outputStreamController = StreamController<ServerLog>();
+  final _buildsController = StreamController<BuildResults>.broadcast();
+
   late final Stream<ServerLog> _logs;
 
   FakeTestDaemonBuilder() {
     _logs = _outputStreamController.stream.asBroadcastStream();
   }
 
   @override
-  Stream<BuildResults> get builds => Stream.empty();
+  Stream<BuildResults> get builds => _buildsController.stream;
 
   @override
   Stream<ServerLog> get logs => _logs;
@@ -34,8 +36,16 @@ class FakeTestDaemonBuilder implements DaemonBuilder {
       ..loggerName = loggerName
       ..level = Level.INFO
       ..message = buildCompletedMessage));
+
+    _buildsController.add(BuildResults(
+        (b) => b.changedAssets.add(Uri.parse('package:foo/bar.dart'))));
   }
 
   @override
-  Future<void> stop() => _outputStreamController.close();
+  Future<void> stop() {
+    return Future.wait([
+      _outputStreamController.close(),
+      _buildsController.close(),
+    ]);
+  }
 }

build_daemon/lib/src/managers/build_target_manager.dart

@@ -19,6 +19,7 @@ bool _shouldBuild(BuildTarget target, Iterable<WatchEvent> changes) =>
 /// the Dart Build Daemon.
 class BuildTargetManager {
   var _buildTargets = <BuildTarget, Set<WebSocketChannel>>{};
+  final _channelSubscriptions = <WebSocketChannel, Set<BuildTarget>>{};
 
   bool Function(BuildTarget, Iterable<WatchEvent>) shouldBuild;
 
@@ -37,16 +38,24 @@ class BuildTargetManager {
   /// Adds a tracked build target with corresponding interested channel.
   void addBuildTarget(BuildTarget target, WebSocketChannel channel) {
     _buildTargets.putIfAbsent(target, () => <WebSocketChannel>{}).add(channel);
+    _channelSubscriptions.putIfAbsent(channel, () => {}).add(target);
   }
 
   /// Returns channels that are interested in the provided target.
   Set<WebSocketChannel> channels(BuildTarget target) =>
       _buildTargets[target] ?? <WebSocketChannel>{};
 
-  void removeChannel(WebSocketChannel channel) =>
-      _buildTargets = Map.fromEntries(_buildTargets.entries
-          .map((e) => MapEntry(e.key, e.value..remove(channel)))
-          .where((e) => e.value.isNotEmpty));
+  /// Returns build targets that the [channel] has added.
+  Iterable<BuildTarget> targetsFor(WebSocketChannel channel) {
+    return _channelSubscriptions[channel] ?? const Iterable.empty();
+  }
+
+  void removeChannel(WebSocketChannel channel) {
+    _buildTargets = Map.fromEntries(_buildTargets.entries
+        .map((e) => MapEntry(e.key, e.value..remove(channel)))
+        .where((e) => e.value.isNotEmpty));
+    _channelSubscriptions.remove(channel);
+  }
 
   Set<BuildTarget> targetsForChanges(List<WatchEvent> changes) =>
       targets.where((target) => shouldBuild(target, changes)).toSet();