I have this ugly looking type, which basically just removes methods and makes stack optional:

type SerializedError<T extends Error> = Omit<
  T,
  | Required<{
      [K in keyof T]: T[K] extends CallableFunction ? K : never;
    }>[keyof T]
  | 'stack'
> & {
  stack?: string | undefined;
} extends infer U
  ? { [K in keyof U]: U[K] }
  : never;

And I have this custom error class:

export class ApiError extends Error {
  public override stack: string = '';

  public constructor(reason: any) {
    const { name, message, stack } = reason;
    super(typeof message === 'string' ? message : String(reason));
    this.name = typeof name === 'string' ? name : this.constructor.name;
    typeof stack === 'string'
      ? (this.stack = stack)
      : Error.captureStackTrace(this, this.constructor);
  }

  public serialize(includeStack: boolean = false): SerializedError<this> {
    const classKeys = Object.keys(this) as (keyof this)[];
    const serializableKeys = classKeys.filter((key) => {
      const isMethod = typeof this[key] === 'function';
      const isStack = key === 'stack';
      return !isMethod && (!isStack || includeStack);
    }) as (keyof SerializedError<this>)[];

    return serializableKeys.reduce((acc, key) => {
      acc[key] = this[key]; // Type 'keyof SerializedError<this>' cannot be used to index type 'this'
      return acc;
    }, {} as SerializedError<this>);
  }
}

I wanna use SerializedError<this> for ApiError‘s serialize method, like shown above, so it would work for any class extending ApiError. But typescript doesn’t let me to do that as shown in the code snippet comment.

But when I change this with ApiError, error is gone:

public serialize(includeStack: boolean = false): SerializedError<ApiError> {
  const classKeys = Object.keys(this) as (keyof ApiError)[];
  const serializableKeys = classKeys.filter((key) => {
    const isMethod = typeof this[key] === 'function';
    const isStack = key === 'stack';
    return !isMethod && (!isStack || includeStack);
  }) as (keyof SerializedError<ApiError>)[];

  return serializableKeys.reduce((acc, key) => {
    acc[key] = this[key]; // No error
    return acc;
  }, {} as SerializedError<ApiError>);
}

So the question is why this and ApiError in the given context aren’t the same, and is there any way to make it work (maybe with different approach)?