[BUG][typescript-angular] Enum generation with 'as const' breaks Angular FormControl generic typing

[majcen-dev]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

In OpenAPI Generator 7.13.0, the typescript-angular generator changed enum generation to use the as const pattern:

export const MyEnum = {
  ValueA: 'ValueA',
  ValueB: 'ValueB'
} as const;
export type MyEnum = typeof MyEnum[keyof typeof MyEnum];

While this improves TypeScript typing, it breaks some Angular use cases involving generics, such as:

type MyFormGroup = {
  myControl: FormControl<MyEnum>;
}

export class MyClass {
  myformGroup: FormGroup<MyFormGroup> = new FormGroup({
      myControl: new FormControl(MyEnum.ValueA),
  });
}

And produces the following error:

TS2322: Type 'FormGroup<{ myControl: FormControl<"ValueA">; }>' is not assignable to type 'FormGroup<MyFormGroup>'.
  Type 'FormControl<MyEnum>' is not assignable to type 'FormControl<"ValueA">'.
    Type 'MyEnum' is not assignable to type '"ValueA"'.
      Type '"ValueB"' is not assignable to type '"ValueA"'.

EDIT: I have updated the example above with a more relevant one. Before I tried to keep it small, but that specific snippet didn't actually trigger the error.

because MyEnum.ValueA is inferred as a string literal instead of the union type, causing TypeScript errors or forcing unsafe casts. This could be seen as a regression from the previous enum output style in certain cases.

openapi-generator version

v7.13.0

Generation Details

{
  "openAPIUrl": "...../swagger.json",
  "options": {"ngVersion": "15.1.2"},
}

Steps to reproduce

The above example will trigger a type error.

Related issues/PRs

This change was introduced in #20958, which updated enum generation to use the as const pattern for better typing.

Suggest a fix

Consider adding an optional config flag (e.g., useOldEnumStyle=true) to allow reverting to the previous enum format for compatibility.

[majcen-dev]

I have found a simple enough workaround, which makes the suggested solution not worth the effort.
For those interested:

export class MyClass {
  myformGroup: FormGroup<MyFormGroup> = new FormGroup<MyFormGroup>({
      myControl: new FormControl(MyEnum.ValueA),
  });
}