Mapped types regression with v3.6.2

[lemoustachiste]

TypeScript Version: 3.6.2

Search Terms: Mapped Types, MappedTypes, MappedType

Code

export enum LayoutElementType {
  Image = 'image' as any
}

const layoutElementTypesMap: { [key in LayoutElementType]: string } = {
  'image': PLATFORM.moduleName('components/record/record-layout/element/image.html')
};

Expected behavior: as described here: #2491 (comment), this should be a work around to map an enum to object keys. We were using it successfully until v3.5.3 (I just installed v3.5.3 to double check and no error).

Actual behavior: Typescript complains:
Object literal may only specify known properties, and ''image'' does not exist in type '{ [x: number]: string; }'.
Looks similar to this: #2491 (comment)

Playground Link:

Related Issues: #2491

[j-oliveras]

If you remove the as any on the enum should work. I don't known the reason to use it. Typescript supports enums with string values since version 2.4. Full code:

export enum LayoutElementType {
  Image = 'image'
}

const layoutElementTypesMap: { [key in LayoutElementType]: string } = {
  'image': PLATFORM.moduleName('components/record/record-layout/element/image.html')
};

[jack-williams]

Caused by #31784.

I'm not sure why the any assertion is used in your enum, but it causes the enum to be considered a numeric enum which is in turn affected by the linked PR.

Prior to #31784, the type of layoutElementTypesMap was the empty object type and not subject to excess property checking.

[lemoustachiste]

Perfect thanks @jack-williams and @j-oliveras, this does indeed fix it.
This code is legacy and written before I worked on it and I wasn't sure why too it was there, but legacy being legacy, I tend to leave things that look weird but work. Good cleanup then.