Resynthesize enums lazily.

pkg/analyzer/lib/src/dart/element/element.dart

 // Copyright (c) 2014, 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.
 
 library analyzer.src.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 1305 matching lines @@
 
   /**
    * A list containing all of the top-level accessors (getters and setters)
    * contained in this compilation unit.
    */
   List<PropertyAccessorElement> _accessors;
 
   /**
    * A list containing all of the enums contained in this compilation unit.
    */
-  List<ClassElement> _enums = ClassElement.EMPTY_LIST;
+  List<ClassElement> _enums;
 
   /**
    * A list containing all of the top-level functions contained in this
    * compilation unit.
    */
   List<FunctionElement> _functions;
 
   /**
    * A list containing all of the function type aliases contained in this
    * compilation unit.
@@ skipping 106 matching lines @@
   @override
   LibraryElement get enclosingElement =>
       super.enclosingElement as LibraryElement;
 
   @override
   CompilationUnitElementImpl get enclosingUnit {
     return this;
   }
 
   @override
-  List<ClassElement> get enums => _enums;
+  List<ClassElement> get enums {
+    if (_unlinkedUnit != null) {
+      _enums ??= _unlinkedUnit.enums
+          .map((e) => new EnumElementImpl.forSerialized(e, this))
+          .toList(growable: false);
+    }
+    return _enums ?? const <ClassElement>[];
+  }
 
   /**
    * Set the enums contained in this compilation unit to the given [enums].
    */
   void set enums(List<ClassElement> enums) {
+    assert(_unlinkedUnit == null);
     for (ClassElement enumDeclaration in enums) {
       (enumDeclaration as EnumElementImpl).enclosingElement = this;
     }
     this._enums = enums;
   }
 
   @override
   List<FunctionElement> get functions {
     if (_unlinkedUnit != null) {
       _functions ??= _unlinkedUnit.executables
@@ skipping 6971 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }