Don't remove ResultData(s) for incrementally updated results.

pkg/analyzer/lib/src/task/dart.dart

 // Copyright (c) 2015, 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 analyzer.src.task.dart;
 
 import 'dart:collection';
 import 'dart:math' as math;
 
 import 'package:analyzer/src/context/cache.dart';
@@ skipping 1905 matching lines @@
   final Set<String> addedNames = new Set<String>();
   final Set<String> changedNames = new Set<String>();
   final Set<String> removedNames = new Set<String>();
 
   final Set<Source> invalidatedSources = new Set<Source>();
 
   DartDelta(Source source) : super(source) {
     invalidatedSources.add(source);
   }
 
+  void elementAdded(Element element) {
+    addedNames.add(element.name);
+  }
+
+  void elementChanged(Element element) {
+    changedNames.add(element.name);
+  }
+
+  void elementRemoved(Element element) {
+    removedNames.add(element.name);
+  }
+
+  bool isNameAffected(String name) {
+    return addedNames.contains(name) ||
+        changedNames.contains(name) ||
+        removedNames.contains(name);
+  }
+
+  bool nameChanged(String name) {
+    return changedNames.add(name);
+  }
+
   @override
-  bool affects(InternalAnalysisContext context, AnalysisTarget target,
+  DeltaResult validate(InternalAnalysisContext context, AnalysisTarget target,
       ResultDescriptor descriptor) {
     if (hasDirectiveChange) {
-      return true;
+      return DeltaResult.INVALIDATE;
     }
+    // Prepare target source.
     Source targetSource = null;
     if (target is Source) {
       targetSource = target;
     }
     if (target is LibrarySpecificUnit) {
       targetSource = target.library;
     }
     if (target is Element) {
       targetSource = target.source;
     }
+    // Keep results that are updated incrementally.
+    // If we want to analyze only some references to the source being changed,
+    // we need to keep the same instances of CompilationUnitElement and
+    // LibraryElement.
     if (targetSource == source) {
-      return true;
+      if (ParseDartTask.DESCRIPTOR.results.contains(descriptor)) {
+        return DeltaResult.KEEP_CONTINUE;
+      }
+      if (BuildCompilationUnitElementTask.DESCRIPTOR.results
+          .contains(descriptor)) {
+        return DeltaResult.KEEP_CONTINUE;
+      }
+      if (BuildLibraryElementTask.DESCRIPTOR.results.contains(descriptor)) {
+        return DeltaResult.KEEP_CONTINUE;
+      }
+      return DeltaResult.INVALIDATE;
     }
+    // Use the target library dependency information to decide whether
+    // the delta affects the library.
     if (targetSource != null) {
       List<Source> librarySources =
           context.getLibrariesContaining(targetSource);
       for (Source librarySource in librarySources) {
         AnalysisCache cache = context.analysisCache;
         ReferencedNames referencedNames =
             cache.getValue(librarySource, REFERENCED_NAMES);
         if (referencedNames == null) {
-          return true;
+          return DeltaResult.INVALIDATE;
         }
         referencedNames.addChangedElements(this);
         if (referencedNames.isAffectedBy(this)) {
-          return true;
+          return DeltaResult.INVALIDATE;
         }
       }
-      return false;
+      return DeltaResult.STOP;
     }
-    return true;
-  }
-
-  void elementAdded(Element element) {
-    addedNames.add(element.name);
-  }
-
-  void elementChanged(Element element) {
-    changedNames.add(element.name);
-  }
-
-  void elementRemoved(Element element) {
-    removedNames.add(element.name);
-  }
-
-  bool isNameAffected(String name) {
-    return addedNames.contains(name) ||
-        changedNames.contains(name) ||
-        removedNames.contains(name);
-  }
-
-  bool nameChanged(String name) {
-    return changedNames.add(name);
+    // We don't know what to do with the given target, invalidate it.
+    return DeltaResult.INVALIDATE;
   }
 }
 
 /**
  * A task that merges all of the errors for a single source into a single list
  * of errors.
  */
 class DartErrorsTask extends SourceBasedAnalysisTask {
   /**
    * The name of the [BUILD_DIRECTIVES_ERRORS] input.
@@ skipping 1680 matching lines @@
 
   @override
   bool moveNext() {
     if (_newSources.isEmpty) {
       return false;
     }
     currentTarget = _newSources.removeLast();
     return true;
   }
 }