Fix for the change/save/undo race condition.

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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine;
 
 import "dart:math" as math;
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/src/cancelable_future.dart';
 import 'package:analyzer/src/generated/incremental_resolution_validator.dart';
 import 'package:analyzer/src/services/lint.dart';
 import 'package:analyzer/src/task/task_dart.dart';
+import 'package:analyzer/src/util/lru_map.dart';
 
 import '../../instrumentation/instrumentation.dart';
 import 'ast.dart';
 import 'constant.dart';
 import 'element.dart';
 import 'error.dart';
 import 'error_verifier.dart';
 import 'html.dart' as ht;
 import 'incremental_resolver.dart' show IncrementalResolver,
     PoorMansIncrementalResolver;
@@ skipping 917 matching lines @@
    * A flag indicating whether this context is disposed.
    */
   bool _disposed = false;
 
   /**
    * A cache of content used to override the default content of a source.
    */
   ContentCache _contentCache = new ContentCache();
 
   /**
+   * A cache of content used to override the default content of a source
+   * before the corresponding override was removed from [_contentCache].
+   */
+  LRUMap<Source, String> _prevOverlayCache = new LRUMap<Source, String>(5);
+
+  /**
    * The source factory used to create the sources that can be analyzed in this context.
    */
   SourceFactory _sourceFactory;
 
   /**
    * The set of declared variables used when computing constant values.
    */
   DeclaredVariables _declaredVariables = new DeclaredVariables();
 
   /**
@@ skipping 1237 matching lines @@
     } else if (originalContents != null) {
       _incrementalAnalysisCache =
           IncrementalAnalysisCache.clear(_incrementalAnalysisCache, source);
       changed = newContents != originalContents;
       // We are removing the overlay for the file, check if the file's
       // contents is the same as it was in the overlay.
       try {
         TimestampedData<String> fileContents = getContents(source);
         String fileContentsData = fileContents.data;
         if (fileContentsData == originalContents) {
+          _prevOverlayCache.put(source, fileContentsData);
           sourceEntry.modificationTime = fileContents.modificationTime;
-          sourceEntry.setValue(SourceEntry.CONTENT, fileContentsData);
           changed = false;
         }
       } catch (e) {
       }
       // If not the same content (e.g. the file is being closed without save),
       // then force analysis.
       if (changed) {
         _sourceChanged(source);
       }
     }
@@ skipping 2746 matching lines @@
 
   /**
    * Invalidate the [source] that was changed and any sources that referenced
    * the source before it existed.
    *
    * <b>Note:</b> This method must only be invoked while we are synchronized on
    * [cacheLock].
    */
   void _sourceChanged(Source source) {
     SourceEntry sourceEntry = _cache.get(source);
-    if (sourceEntry == null ||
-        sourceEntry.modificationTime == getModificationStamp(source)) {
-      // Either we have removed this source, in which case we don't care that
-      // it is changed, or we have already invalidated the cache and don't need
-      // to invalidate it again.
+    // If the source is removed, we don't care about it.
+    if (sourceEntry == null) {
       return;
     }
+    // Check if the content of the source is the same as it was the last time.
+    String sourceContent = _prevOverlayCache.get(source);
+    if (sourceContent != null) {
+      try {
+        TimestampedData<String> fileContents = getContents(source);
+        if (fileContents.data == sourceContent) {
+          return;
+        }
+      } catch (e) {
+      }
+    }
+    // We have to invalidate the cache.
     _propagateInvalidation(source, sourceEntry);
   }
 
   /**
    * <b>Note:</b> This method must only be invoked while we are synchronized on [cacheLock].
    *
    * @param source the source that has been deleted
    */
   void _sourceDeleted(Source source) {
     SourceEntry sourceEntry = _cache.get(source);
@@ skipping 4699 matching lines @@
   set contentCache(ContentCache value);
 
   /**
    * Return an array containing all of the sources that have been marked as priority sources.
    * Clients must not modify the returned array.
    *
    * @return the sources that have been marked as priority sources
    */
   List<Source> get prioritySources;
 
+  /** A factory to override how [ResolverVisitor] is created. */
+  ResolverVisitorFactory get resolverVisitorFactory;
+
   /**
    * Returns a statistics about this context.
    */
   AnalysisContextStatistics get statistics;
 
   /**
    * Returns a type provider for this context or throws an exception if dart:core cannot be
    * resolved.
    *
    * @return the type provider (not `null`)
    * @throws AnalysisException if dart:core cannot be resolved
    */
   TypeProvider get typeProvider;
 
-  /** A factory to override how [ResolverVisitor] is created. */
-  ResolverVisitorFactory get resolverVisitorFactory;
-
   /** A factory to override how [TypeResolverVisitor] is created. */
   TypeResolverVisitorFactory get typeResolverVisitorFactory;
 
   /**
    * Add the given source with the given information to this context.
    *
    * @param source the source to be added
    * @param info the information about the source
    */
   void addSourceInfo(Source source, SourceEntry info);
@@ skipping 2713 matching lines @@
     if (element.id == _id) {
       result = element;
       throw new _ElementByIdFinderException();
     }
     super.visitElement(element);
   }
 }
 
 class _ElementByIdFinderException {
 }