Issue 29288. Resynthesize Import/Export/PartElement for every directive.

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/standard_resolution_map.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';
@@ skipping 592 matching lines @@
     IndexRelationKind kind = element is ClassElement
         ? IndexRelationKind.IS_REFERENCED_BY
         : IndexRelationKind.IS_INVOKED_BY;
     recordRelation(element, kind, name, isQualified);
     node.target?.accept(this);
     node.argumentList?.accept(this);
   }
 
   @override
   visitPartDirective(PartDirective node) {
-    Element element = node.element;
-    recordUriReference(element, node);
+    CompilationUnitElement element = node.element;
+    if (element?.source != null) {
+      recordUriReference(element, node);
+    }
     super.visitPartDirective(node);
   }
 
   @override
   visitPostfixExpression(PostfixExpression node) {
     recordOperatorReference(node.operator, node.bestElement);
     super.visitPostfixExpression(node);
   }
 
   @override
@@ skipping 178 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);
 }