Use union types instead of enums

Description

Instead of generating enum types I would like to have an option to generate union types instead. If you like the idea I am very happy to implement this and create a PR.

Example

YAML model:

    [...]
    schemas:
        Rating:
            type: object
            properties:
                id:
                    type: string
                value:
                    type: string
                    enum:
                        - negative
                        - neutral
                        - positive

Current behaviour

Generated model

export interface Rating {
    id?: string;
    value?: Rating.value;
}

export namespace Rating {
    export enum value {
        NEGATIVE = 'negative',
        NEUTRAL = 'neutral',
        POSITIVE = 'positive',
    }
}

Usage

If I want to use this in my code I have to do this:

const exampleRating: Rating = {
  id: '364363313',
  value: Rating.value.NEUTRAL,
}

Proposed change

Generated model

export interface Rating {
    id?: string;
    value?: 'positive' | 'neutral'  | 'negative'; // no enum anymore, instead we use union types
}

Usage

If I want to use this in my code I can do it much simpler now:

const exampleRating: Rating = {
  id: '364363313',
  value: 'neutral', // much simpler in my opinion, TS would still complain if I would use something that is not allowed
}

Explanation

Of course this would be behind a feature flag. At the beginning I thought useUnionTypes is doing that, but it is not, so I have to find another name for my feature. I thought about useUnionTypesForEnums, but I’m open for better suggestions.

[ferdikoomen]

@KevinHerklotz @nandorojo there is a new version 0.5.0-alpha that should resolve this issue, if you have time them please do check. More info on the flag here: https://github.com/ferdikoomen/openapi-typescript-codegen#enums-vs-union-types---useuniontypes and https://github.com/ferdikoomen/openapi-typescript-codegen#babel-support

[ferdikoomen]

Thanks for testing. Just pushed 0.5.0 to NPM, closing this ticket.