Don't attempt to record reference to a named parameter of a synthetic function.

pkg/analyzer/lib/src/dart/analysis/index.dart

Index: pkg/analyzer/lib/src/dart/analysis/index.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/index.dart b/pkg/analyzer/lib/src/dart/analysis/index.dart
index 6b5c09c5963ec124816cd2b82efbf8804e412e8b..8c8c132aefac169fdf9d03821f3c787c5e995dbe 100644
--- a/pkg/analyzer/lib/src/dart/analysis/index.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/index.dart
@@ -440,6 +440,13 @@ class _IndexContributor extends GeneralizingAstVisitor {
         false) {
       return;
     }
+    // Ignore named parameters of synthetic functions, e.g. created for LUB.
+    // These functions are not bound to a source, we cannot index them.
+    if (elementKind == ElementKind.PARAMETER &&
+        element is ParameterElement &&
+        element.enclosingElement.isSynthetic) {
+      return;
+    }
     // Add the relation.
     assembler.addElementRelation(element, kind, offset, length, isQualified);
   }