Add FileSystemState.knownFilesSetChanges stream.

pkg/analyzer/lib/src/dart/analysis/file_state.dart

Index: pkg/analyzer/lib/src/dart/analysis/file_state.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/file_state.dart b/pkg/analyzer/lib/src/dart/analysis/file_state.dart
index c742f9f61b25cac1c1ebe1fbb56a978cb0e1975e..1c45917e8ef2430d05e2090cb2d36114bf6bf85b 100644
--- a/pkg/analyzer/lib/src/dart/analysis/file_state.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/file_state.dart
@@ -2,6 +2,7 @@
 // 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.
 
+import 'dart:async';
 import 'dart:convert';
 import 'dart:typed_data';
 
@@ -616,6 +617,30 @@ class FileSystemState {
   final Set<String> knownFilePaths = new Set<String>();
 
   /**
+   * The paths of files that were added to the set of known files since the
+   * last [knownFilesSetChanges] notification.
+   */
+  final Set<String> _addedKnownFiles = new Set<String>();
+
+  /**
+   * If not `null`, this delay will be awaited instead of the default one.
+   */
+  Duration _knownFilesSetChangesDelay;
+
+  /**
+   * The instance of timer that is scheduled to send a new update to the
+   * [knownFilesSetChanges] stream, or `null` if there are no changes to the
+   * set of known files to notify the stream about.
+   */
+  Timer _knownFilesSetChangesTimer;
+
+  /**
+   * The controller for the [knownFilesSetChanges] stream.
+   */
+  final StreamController<KnownFilesSetChange> _knownFilesSetChangesController =
+      new StreamController<KnownFilesSetChange>();
+
+  /**
    * Mapping from a path to the flag whether there is a URI for the path.
    */
   final Map<String, bool> _hasUriForPath = {};
@@ -659,6 +684,13 @@ class FileSystemState {
   List<FileState> get knownFiles =>
       _pathToFiles.values.map((files) => files.first).toList();
 
+  /**
+   * Return the [Stream] that is periodically notified about changes to the
+   * known files set.
+   */
+  Stream<KnownFilesSetChange> get knownFilesSetChanges =>
+      _knownFilesSetChangesController.stream;
+
   @visibleForTesting
   FileSystemStateTestView get test => _testView;
 
@@ -784,9 +816,24 @@ class FileSystemState {
       knownFilePaths.add(path);
       files = <FileState>[];
       _pathToFiles[path] = files;
+      // Schedule the stream update.
+      _addedKnownFiles.add(path);
+      _scheduleKnownFilesSetChange();
     }
     files.add(file);
   }
+
+  void _scheduleKnownFilesSetChange() {
+    Duration delay = _knownFilesSetChangesDelay ?? new Duration(seconds: 1);
+    _knownFilesSetChangesTimer ??= new Timer(delay, () {
+      Set<String> addedFiles = _addedKnownFiles.toSet();
+      Set<String> removedFiles = new Set<String>();
+      _knownFilesSetChangesController
+          .add(new KnownFilesSetChange(addedFiles, removedFiles));

[Brian Wilkerson, 2017/04/19 20:09:52]

Do we want to only add to the stream if at least one of the added and removed
sets are non-empty?

[scheglov, 2017/04/19 20:21:47]

Yes, the intention is that we send only useful notifications.

Currently this happens implicitly, because we schedule sending notifications
only when a new file is added.

+      _addedKnownFiles.clear();
+      _knownFilesSetChangesTimer = null;
+    });
+  }
 }
 
 @visibleForTesting
@@ -806,6 +853,20 @@ class FileSystemStateTestView {
         .where((f) => f._transitiveSignature == null)
         .toSet();
   }
+
+  void set knownFilesDelay(Duration value) {
+    state._knownFilesSetChangesDelay = value;
+  }
+}
+
+/**
+ * Information about changes to the known file set.
+ */
+class KnownFilesSetChange {
+  final Set<String> added;
+  final Set<String> removed;
+
+  KnownFilesSetChange(this.added, this.removed);
 }
 
 class _FastaElementProxy implements fasta.KernelClassElement {