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

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

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/member.dart';
@@ skipping 422 matching lines @@
         elementKind == ElementKind.TYPE_PARAMETER ||
         elementKind == ElementKind.FUNCTION &&
             element is FunctionElement &&
             element.enclosingElement is ExecutableElement ||
         elementKind == ElementKind.PARAMETER &&
             element is ParameterElement &&
             element.parameterKind != ParameterKind.NAMED ||
         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);
   }
 
   /**
    * Record that [element] has a relation of the given [kind] at the location
    * of the given [token].
    */
   void recordRelationToken(
       Element element, IndexRelationKind kind, Token token) {
@@ skipping 339 matching lines @@
   final String value;
 
   /**
    * The unique id of the string.  It is set after indexing of the whole
    * package is done and we are assembling the full package index.
    */
   int id;
 
   _StringInfo(this.value);
 }