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

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

Index: pkg/analyzer/lib/src/task/dart.dart
diff --git a/pkg/analyzer/lib/src/task/dart.dart b/pkg/analyzer/lib/src/task/dart.dart
index 62fed3be1866d76cfc386fb077736ee9e2474424..04baefa1a3c857ec68765cb33837a7fc6fd5cd0e 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -1923,12 +1923,35 @@ class DartDelta extends Delta {
     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;
@@ -1939,9 +1962,25 @@ class DartDelta extends Delta {
     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);
@@ -1950,38 +1989,17 @@ class DartDelta extends Delta {
         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;
   }
 }