conditional generic Type assignable Error

[iahu]

Bug Report

🔎 Search Terms

conditional

🕗 Version & Regression Information

• This changed between versions 4.4.4 and 4.5.2

⏯ Playground Link

Playground link with relevant code

💻 Code

type KonvaEventObject<T> = {

}

export type GetMultiType<T extends string> = T extends `${infer A} ${infer B}`
  ? GetMultiType<A> | GetMultiType<B>
  : T extends `${infer C}.${string}`
  ? GetMultiType<C>
  : T extends keyof DocumentEventMap
  ? KonvaEventObject<DocumentEventMap[T]>
  : T extends 'tap' | 'touchstart' | 'touchmove' | 'touchcancel' | 'touchend'
  ? KonvaEventObject<TouchEvent>
  : KonvaEventObject<Event>


type Handler  = (e: KonvaEventObject<any>) => void
const on = (type: string, handler: Handler) => {

}
const off = (type: string, handler: Handler) => {

}

export const KAD_ACTION_NS = 'kadAction'
export const withKadActionNS = (s: string) => (s.includes('.') ? s : `${s}.${KAD_ACTION_NS}`)
export const ensureWithNS = (type: string) => type.split(' ').map(withKadActionNS).join(' ')
export const onceOn = <T extends string>(target: Node, type: T, lisenter: (event: GetMultiType<T>) => void) => {
  const typeWithNS = ensureWithNS(type)
  const handler = (event: GetMultiType<T>) => {
    lisenter(event)
    // throw an error
    off(typeWithNS, handler)
  }
  // also throw an error here
  return on(typeWithNS, handler)
}

🙁 Actual behavior

Type 'KonvaEventObject' is not assignable to type 'GetMultiType'

🙂 Expected behavior

can assign type 'KonvaEventObject<NodeEventMap[T]>' to type 'GetMultiType'

[RyanCavanaugh]

Bisect to #46429

[RyanCavanaugh]

Simplified

type EventWrapper<T> = {
  event: T;
}

export type GetEventType<T extends string> =
  T extends `${infer A} ${string}` ?
    GetEventType<A>
    : T extends keyof DocumentEventMap ?
      EventWrapper<DocumentEventMap[T]>
    : EventWrapper<Event>

function go<T extends string>(type: T, lisenter: (event: GetEventType<T>) => void) {
  const src: EventWrapper<any> = null as any;
  // OK in 4.4, error in 4.5
  // Should be OK [?]; all terminuses of GetEventType<T> are EventWrapper<any>'s
  const dst: GetEventType<T> = src;
}

[RyanCavanaugh]

This was an announced breaking change:

https://devblogs.microsoft.com/typescript/announcing-typescript-4-5/#restrictions-on-assignability-to-conditional-types

[RyanCavanaugh]

FYI @ahejlsberg for visibility anyway

[typescript-bot]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.