Exhaustive type checking not working when class field to match on is a union #40160

class Either<T> {
  public static Left<T>(value: T): Either<T> {
    return new Either('left', value);
  }

  public static Right<T>(value: T): Either<T> {
    return new Either('right', value);
  }

  private constructor(
    public readonly kind: 'left' | 'right',
    public readonly value: T
  ) {}
}

function doSomething(): string {
  const e = Either.Left('foo');

  // e.kind: 'left' | 'right';
  switch (e.kind) {
    case 'left':
      return e.value;
    case 'right':
      return e.value;
    // case 'foo':      as expected, this doesn't work
    //   break;
    default:
      const _exhaustiveCheck: never = e;        // even though we've matched against all the possible cases of `kind`, compiler still complains here
      throw new Error("How did we get here?");
  }

}

interface Left {
  kind: 'left';
  value: string;
}
interface Right {
  kind: 'right';
  value: string;
}
type Either = Left | Right;