Limit cache invalidation by the updated source bounds.

pkg/analyzer/lib/plugin/task.dart

Index: pkg/analyzer/lib/plugin/task.dart
diff --git a/pkg/analyzer/lib/plugin/task.dart b/pkg/analyzer/lib/plugin/task.dart
index fd4dd7cd0d8a7c79af9bbd3be4614d076942a6e5..92a55561bb09f66a0872620722ddb124f8d05488 100644
--- a/pkg/analyzer/lib/plugin/task.dart
+++ b/pkg/analyzer/lib/plugin/task.dart
@@ -43,6 +43,12 @@ final String HTML_ERRORS_EXTENSION_POINT_ID = Plugin.join(
  * The identifier of the extension point that allows plugins to register new
  * analysis tasks with the analysis engine. The object used as an extension must
  * be a [TaskDescriptor].
+ *
+ * Contributed tasks should never extract information from Dart elements or AST
+ * (e.g. offsets) of a source and put it into results for targets in other
+ * sources. Dart elements and ASTs are updated during incremental resolution,
+ * and invalidation of results is intentionally limited by the source bounds
+ * by performance reasons.

[Brian Wilkerson, 2015/09/18 22:15:30]

"by" --> "for"

  */
 final String TASK_EXTENSION_POINT_ID = Plugin.join(
     EnginePlugin.UNIQUE_IDENTIFIER, EnginePlugin.TASK_EXTENSION_POINT);