"Cannot create property 'modifierFlagsCache'" when using string-based enums

First of all: I’m not sure if this is an issue with ng-packagr or maybe tsickle or even typescript itself. However, I didn’t know how to reproduce this issue without ng-packagr, so I thought it would be best to start here. Feel free to point me in the right direction.

Type of Issue

[x] Bug Report
[ ] Feature Request

Description

Whenever I use a string-based enum (available since TypeScript 2.4) in my project, the build process fails with this error message:

> ng-packagr -p ng-package.json

Building Angular library
Generating bundle for mfc-issue

BUILD ERROR
Cannot create property 'modifierFlagsCache' on string 'some string'
TypeError: Cannot create property 'modifierFlagsCache' on string 'some string'
    at Object.getModifierFlags (C:\Users\mal\Projekte\mfc-issue\node_modules\typescript\lib\typescript.js:9685:33)
    at Object.getCombinedModifierFlags (C:\Users\mal\Projekte\mfc-issue\node_modules\typescript\lib\typescript.js:10388:24)
    at hasModifierFlag (C:\Users\mal\Projekte\mfc-issue\node_modules\tsickle\build\src\tsickle.js:72:16)
    at Annotator.maybeProcess (C:\Users\mal\Projekte\mfc-issue\node_modules\tsickle\build\src\tsickle.js:538:13)
    at Annotator.Rewriter.visit (C:\Users\mal\Projekte\mfc-issue\node_modules\tsickle\build\src\rewriter.js:52:19)
    at Annotator.maybeProcessEnum (C:\Users\mal\Projekte\mfc-issue\node_modules\tsickle\build\src\tsickle.js:1188:22)
    at Annotator.maybeProcess (C:\Users\mal\Projekte\mfc-issue\node_modules\tsickle\build\src\tsickle.js:676:29)
    at Annotator.Rewriter.visit (C:\Users\mal\Projekte\mfc-issue\node_modules\tsickle\build\src\rewriter.js:52:19)
    at C:\Users\mal\Projekte\mfc-issue\node_modules\tsickle\build\src\rewriter.js:84:19
    at visitNodes (C:\Users\mal\Projekte\mfc-issue\node_modules\typescript\lib\typescript.js:11911:30)

How To Reproduce

Put a string-based enum in your project:

export enum MyEnum {
    StrVal = 'some string'
}

I created a simple project with for reproduction: https://github.com/luchsamapparat/mfc-issue

Expected Behaviour

no error 😃

Version Information

ng-packagr: v1.5.0-rc.0
node: v8.0.0
typescript: 2.5.3
@angular: n/a
rxjs: n/a
zone.js: n/a

[ghiscoding]

I have the same problem and it’s worth to know that setting strings on Enum are available only since TypeScript version 2.4 and ng-packagr is set to ~2.3.3 in package.json. However, updating TypeScript to latest still throws the error on build.

After some googling, there seem to be 2 options available to bypass this issue (as shown in this SO question). 1- Change enum to a class and add static in front of each enum property

export class Order { 
  static Asc = 'Asc'; 
  static Desc = 'Desc' 
}

2- Use enum as usual but simply add <any> in front of each enum property

export enum Order { 
  Asc = <any>'Asc', 
  Desc = <any>'Desc' 
}

I decided to use the 2nd option since it remains as an Enum, even though it’s a little bit hacky. This is still a hack, so if someone finds the correct way to fix it, then please advise.

[dherges]

Closing this issue as v2 now supports typescript 2.5+ an onwards.