Issue 23573. Catch exception during indexing.

pkg/analysis_server/lib/src/operation/operation_analysis.dart

Index: pkg/analysis_server/lib/src/operation/operation_analysis.dart
diff --git a/pkg/analysis_server/lib/src/operation/operation_analysis.dart b/pkg/analysis_server/lib/src/operation/operation_analysis.dart
index 6ac3935af247e1b5f5f534d45a16aa86c61dae12..918deb8f710dd72d834a28b258eacc6f6d3f7705 100644
--- a/pkg/analysis_server/lib/src/operation/operation_analysis.dart
+++ b/pkg/analysis_server/lib/src/operation/operation_analysis.dart
@@ -326,8 +326,12 @@ class _DartIndexOperation extends _SingleFileOperation {
   @override
   void perform(AnalysisServer server) {
     ServerPerformanceStatistics.indexOperation.makeCurrentWhile(() {
-      Index index = server.index;
-      index.indexUnit(context, unit);
+      try {
+        Index index = server.index;
+        index.indexUnit(context, unit);
+      } catch (exception, stackTrace) {
+        server.sendServerErrorNotification(exception, stackTrace);
+      }
     });
   }
 }