[typescript] fix: enum can not receive stringified class name

[joscha]

When a discriminator is a pure enum, currently the typescript generator assigns a string to it, which is the name of the class (this.discriminator = "<ClassName>").
See:

and:

Because the stringified classname and the enum type are usually incompatible (unless there is an enum value which happens to be the class name) a type error is produced.

This pull request wraps this line in an additional guard.

Please note that the fix does not do any introspection on a potential overlap of the classname with valid enum values as any such assignment, whilst syntactically valid, would most likely not make any semantical sense.

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[joscha]

this is the meaningful change of this PR.

I can see here:

openapi-generator/modules/openapi-generator/src/main/resources/Java/pojo.mustache

Lines 95 to 99 in b4357ed

	{{#discriminator}}
	{{#discriminator.isEnum}}
	this.{{{discriminatorName}}} = this.getClass().getSimpleName();
	{{/discriminator.isEnum}}
	{{/discriminator}}

that other generators guard the opposite case. If I misunderstand what the fix is, please let me know. An alternative could also be to make the discriminator type always a string/symbol and only assign the stringified value of each enum value.

[macjohnny]

so what would be the discriminator.isEnum case?

[joscha]

The discriminator is the type member and type is of type InteractionTypeEnum, thus the template string discriminator.isEnum would evaluate to true, hence with the template negation, it would not emit the guarded class name assignment (e.g. it would omit this.{{discriminatorName}} = "{{classname}}";)

[joscha]

basically before the change we'd produce code that looks like this:

export class Interaction {
    'type': InteractionTypeEnum;
    static readonly discriminator: string | undefined = "type";
    public constructor() {
        this.type = "Interaction";
    }
}

export enum InteractionTypeEnum {
    Call = 'call',
    Email = 'email',
    Meeting = 'meeting',
    ChatMessage = 'chat-message'
}

(note how the string "Interaction" is not a valid value of InteractionTypeEnum)

After the changes in this PR it would be:

export class Interaction {
    'type': InteractionTypeEnum;
    static readonly discriminator: string | undefined = "type";
    public constructor() {
    }
}

export enum InteractionTypeEnum {
    Call = 'call',
    Email = 'email',
    Meeting = 'meeting',
    ChatMessage = 'chat-message'
}

E.g. the meaningful diff is:

export class Interaction {
    'type': InteractionTypeEnum;
    static readonly discriminator: string | undefined = "type";
    public constructor() {
-        this.type = "Interaction";
    }
}

[macjohnny]

thanks for the explanation! I wonder why there even is such a default value assigned, do you happen to know?

[joscha]

I do not, sorry, I am assuming it is a remnant from making sure each class has a sane default value to discriminate on, however the implementation of it doesn't make sense. It works fine when the discriminator is of string type, which is the majority of implementations I've seen, but it obviously doesn't work any more as soon as it's a fixed enum.

[joscha]

this is an extract of the OpenAPI spec of https://developer.affinity.co/

[joscha]

Apologies for the noise that introducing a new sample fixture produces, I couldn't find a sample OpenAPI spec that shows the issue I am trying to fix. If you know of one that has a discriminator which is an enum, please feel free to point me to it, then I might be able to use it instead and reduce the footprint of this PR a bit.

[joscha]

This is the meaningful part of the fixture (the omission of this.type = "Interaction")