Generated code when re-exporting a const enum using "preserveConstEnums": true is inconsistent

[elliottsj]

TypeScript Version: 2.8.1 and 2.9.0-dev.20180418

Search Terms: const enum import export preserveConstEnums

Code

ConstEnum.ts

const enum MyConstEnum {
  Foo,
  Bar
};
export { MyConstEnum };

ImportExport.ts

import { MyConstEnum } from './MyConstEnum';
export default MyConstEnum;

ReExport.ts

export { MyConstEnum as default } from './MyConstEnum';

Compile the above using

{
  "compilerOptions": {
    "target": "es5",
    "module": "commonjs",
    "preserveConstEnums": true
  }
}

Expected behavior:

Both ImportExport.ts and ReExport.ts compile to

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var MyConstEnum_1 = require("./MyConstEnum");
exports.default = MyConstEnum_1.MyConstEnum;

Actual behavior:

ReExport.js is as expected, but ImportExport.js is:

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.default = MyConstEnum_1.MyConstEnum;

i.e. we are missing

var MyConstEnum_1 = require("./MyConstEnum");

This results in a runtime error due to MyConstEnum_1 being undefined.

Related Issues:
#18644