Get memento objects from tasks, remember in cache and pass back to tasks.

pkg/analyzer/lib/src/context/cache.dart

Index: pkg/analyzer/lib/src/context/cache.dart
diff --git a/pkg/analyzer/lib/src/context/cache.dart b/pkg/analyzer/lib/src/context/cache.dart
index 4ef2814a792dabf89efce162db140f8391556782..5d8354f6b41b58f4dccbc97580e48eeb6003697a 100644
--- a/pkg/analyzer/lib/src/context/cache.dart
+++ b/pkg/analyzer/lib/src/context/cache.dart
@@ -331,6 +331,17 @@ class CacheEntry {
   }
 
   /**
+   * Return the memento of the result represented by the given [descriptor].
+   */
+  dynamic getMemento(ResultDescriptor descriptor) {
+    ResultData data = _resultMap[descriptor];
+    if (data == null) {
+      return null;
+    }
+    return data.memento;
+  }
+
+  /**
    * Return the state of the result represented by the given [descriptor].
    */
   CacheState getState(ResultDescriptor descriptor) {
@@ -441,10 +452,11 @@ class CacheEntry {
 
   /**
    * Set the value of the result represented by the given [descriptor] to the
-   * given [value].
+   * given [value]. The optional [memento] may help to recompute [value] more
+   * efficiently after invalidation.
    */
   /*<V>*/ void setValue(ResultDescriptor /*<V>*/ descriptor, dynamic /*V*/
-      value, List<TargetedResult> dependedOn) {
+      value, List<TargetedResult> dependedOn, [dynamic memento]) {
     _validateStateChange(descriptor, CacheState.VALID);
     ResultData data = _getResultData(descriptor);
     {
@@ -454,6 +466,7 @@ class CacheEntry {
     }
     data.state = CacheState.VALID;
     data.value = value == null ? descriptor.defaultValue : value;
+    data.memento = memento;
   }
 
   @override
@@ -821,6 +834,12 @@ class ResultData {
   Object value;
 
   /**
+   * The optional data that is remembered with [value] and, when [value] is
+   * invalidated, may help to recompute it more efficiently.
+   */
+  dynamic memento;

[Brian Wilkerson, 2015/05/04 16:22:09]

nit: I generally prefer 'Object' over 'dynamic' as an explicit type.

+
+  /**
    * A list of the results on which this result depends.
    */
   List<TargetedResult> dependedOnResults = <TargetedResult>[];