Can't define a props interface extending DayPickerProps

[ts-web]

I am creating a Calendar component that wraps DayPicker and forwards ...props, so I want to create an interface that extends from DayPickerProps:

interface ICalendarProps extends DayPickerProps {
  ...
}

However, it produces this typescript warning:

error TS2312: An interface can only extend an object type or intersection of object types with statically known members.

To reproduce

Note: I needed to create a Codesandbox "dev box" because the in-browser IDE didn't show typescript errors. In the dev box, in the terminal you can run pnpm tsc to see the typescript error.

CodeSandbox: https://codesandbox.io/p/devbox/q4qy2h?migrateFrom=m2j7fr

Actual Behavior

It produces this typescript warning:

error TS2312: An interface can only extend an object type or intersection of object types with statically known members.

Expected Behavior

It should be possible to extend from DayPickerProps.

Screenshots

[rodgobbi]

Hi @ts-web, it's not possible to use the extends keyword with DayPickerProps because it's a Discriminated Union, that is why the TS error happens.
You need to use Intersections to extend the DayPickerProps type the way you want.

E.g.:

type CalendarProps = DayPickerProps & { bla: string };

[ts-web]

Good point. There can be a way to support extends if the discriminated union members were extended from:

export interface CalendarProps extends PropsMulti {
  bla: string;
}

However, PropsMulti is missing things because it doesn't extend PropsBase. Would it make sense to have these interfaces extend PropsBase so they can be extended from?

[rodgobbi]

The idea is to keep them separate and compose as needed.
You can compose the types for your use case like:

type FullPropsSingle = PropsBase & PropsSingle;

export interface CalendarProps extends FullPropsSingle {
  bla: string;
}