Issue 22834. Disable 'Add type annotation' Quick Assist if the type is not accessible.

pkg/analysis_server/lib/src/services/correction/util.dart

Index: pkg/analysis_server/lib/src/services/correction/util.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/util.dart b/pkg/analysis_server/lib/src/services/correction/util.dart
index d7382bbc04200722a6d28697167372cdfdb5f8a6..0f53ef5e4419c37cd5eb76cdf5c08831d76c7112 100644
--- a/pkg/analysis_server/lib/src/services/correction/util.dart
+++ b/pkg/analysis_server/lib/src/services/correction/util.dart
@@ -1001,6 +1001,11 @@ class CorrectionUtils {
     // check if imported
     LibraryElement library = element.library;
     if (library != null && library != _library) {
+      // no source, if private
+      if (element.isPrivate) {
+        return null;
+      }
+      // ensure import
       ImportElement importElement = _getImportElement(element);
       if (importElement != null) {
         if (importElement.prefix != null) {