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

pkg/analyzer/test/src/dart/analysis/index_test.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 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart';
@@ skipping 458 matching lines @@
   test_isReferencedBy_CompilationUnitElement_part() async {
     provider.newFile(_p('$testProject/my_unit.dart'), 'part of my_lib;');
     await _indexTestUnit('''
 library my_lib;
 part 'my_unit.dart';
 ''');
     CompilationUnitElement element = testLibraryElement.parts[0];
     assertThat(element)..isReferencedAt("'my_unit.dart';", true, length: 14);
   }
 
+  test_isReferencedBy_CompilationUnitElement_part_inPart() async {
+    provider.newFile(_p('$testProject/a.dart'), 'part of lib;');
+    provider.newFile(
+        _p('$testProject/b.dart'),
+        '''
+library lib;
+part 'a.dart';
+''');
+    await _indexTestUnit('''
+part 'b.dart';
+''');
+    // No exception, even though a.dart is a part of b.dart part.
+  }
+
   test_isReferencedBy_ConstructorElement() async {
     await _indexTestUnit('''
 class A implements B {
   A() {}
   A.foo() {}
 }
 class B extends A {
   B() : super(); // 1
   B.foo() : super.foo(); // 2
   factory B.bar() = A.foo; // 3
@@ skipping 754 matching lines @@
   final bool isQualified;
 
   _Relation(this.kind, this.offset, this.length, this.isQualified);
 
   @override
   String toString() {
     return '_Relation{kind: $kind, offset: $offset, length: $length, '
         'isQualified: $isQualified}lified)';
   }
 }