Add ApplyChangesStatus to AnalysisContext.applyChanges() and use it in DAS.

pkg/analyzer/lib/src/generated/engine.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 engine;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:math' as math;
 
@@ skipping 434 matching lines @@
    * Apply the given [delta] to change the level of analysis that will be
    * performed for the sources known to this context.
    */
   void applyAnalysisDelta(AnalysisDelta delta);
 
   /**
    * Apply the changes specified by the given [changeSet] to this context. Any
    * analysis results that have been invalidated by these changes will be
    * removed.
    */
-  void applyChanges(ChangeSet changeSet);
+  ApplyChangesStatus applyChanges(ChangeSet changeSet);
 
   /**
    * Return the documentation comment for the given [element] as it appears in
    * the original source (complete with the beginning and ending delimiters) for
    * block documentation comments, or lines starting with `"///"` and separated
    * with `"\n"` characters for end-of-line documentation comments, or `null` if
    * the element does not have a documentation comment associated with it. This
    * can be a long-running operation if the information needed to access the
    * comment is not cached.
    *
@@ skipping 1143 matching lines @@
       if (level == AnalysisLevel.NONE) {
         changeSet.removedSource(source);
       } else {
         changeSet.addedSource(source);
       }
     });
     applyChanges(changeSet);
   }
 
   @override
-  void applyChanges(ChangeSet changeSet) {
+  ApplyChangesStatus applyChanges(ChangeSet changeSet) {
     if (changeSet.isEmpty) {
-      return;
+      return new ApplyChangesStatus(false);
     }
     //
     // First, compute the list of sources that have been removed.
     //
     List<Source> removedSources =
         new List<Source>.from(changeSet.removedSources);
     for (SourceContainer container in changeSet.removedContainers) {
       _addSourcesInContainer(removedSources, container);
     }
     //
@@ skipping 19 matching lines @@
       _contentRangeChanged(source, change.contents, change.offset,
           change.oldLength, change.newLength);
     });
     for (Source source in changeSet.deletedSources) {
       _sourceDeleted(source);
     }
     for (Source source in removedSources) {
       _sourceRemoved(source);
     }
     _onSourcesChangedController.add(new SourcesChangedEvent(changeSet));
+    return new ApplyChangesStatus(true);
   }
 
   @override
   String computeDocumentationComment(Element element) {
     if (element == null) {
       return null;
     }
     Source source = element.source;
     if (source == null) {
       return null;
@@ skipping 5124 matching lines @@
   E visitResolveHtmlTask(ResolveHtmlTask task);
 
   /**
    * Visit the given [task], returning the result of the visit. This method will
    * throw an AnalysisException if the visitor throws an exception.
    */
   E visitScanDartTask(ScanDartTask task);
 }
 
 /**
+ * The result of applying a [ChangeSet] to a [AnalysisContext].
+ */
+class ApplyChangesStatus {
+  /**
+   * Is `true` if the given [ChangeSet] caused any changes in the context.
+   */
+  final bool hasChanges;
+
+  ApplyChangesStatus(this.hasChanges);
+}
+
+/**
  * A `CachedResult` is a single analysis result that is stored in a
  * [SourceEntry].
  */
 class CachedResult<E> {
   /**
    * The state of the cached value.
    */
   CacheState state;
 
   /**
@@ skipping 5298 matching lines @@
     PendingFuture pendingFuture =
         new PendingFuture<T>(_context, source, computeValue);
     if (!pendingFuture.evaluate(sourceEntry)) {
       _context._pendingFutureSources
           .putIfAbsent(source, () => <PendingFuture>[])
           .add(pendingFuture);
     }
     return pendingFuture.future;
   }
 }