I’ve added a simplified version of my problem here

type BaseAssetType = {
  z?: string
}

/** Assets */
type AssetTypeAData = {
  a : string
}

type AssetTypeBData = {
  b : string
}

interface TEventAssetTypeA extends BaseAssetType {
  assetType: 'a',
  data: AssetTypeAData
}

interface TEventAssetTypeB extends BaseAssetType {
  assetType: 'b',
  data: AssetTypeBData
}

type TEventAssetTypes = TEventAssetTypeA | TEventAssetTypeB

interface IStreamToAssetType {
  streama: TEventAssetTypeA
  streamb: TEventAssetTypeB
}

/** Logs */
interface LogsEvent extends BaseAssetType {
  logs: string
}

type Topics = 'streama' | 'streamb' | 'streamc'

interface IStreamToLogType {
  streamc: LogsEvent
}

interface IStreamsToAlLEvents {
  streama: TEventAssetTypeA
  streamb: TEventAssetTypeB
  streamc: LogsEvent
}

const publishAsssetMessageToStream = <T extends keyof IStreamToAssetType, MA extends IStreamToAssetType[T]>(topic: T, message: MA) => publishToStreamCore<T, MA>({topic, message})

const publishToStreamCore = <T extends keyof IStreamsToAlLEvents, M extends IStreamsToAlLEvents[T]>({topic, message}:{topic: T, message: M}) => {
  console.log(topic, message)
}

publishAsssetMessageToStream('streama', {
    assetType: 'a',
    data: { a: '12313'}
})

I have a core function publishToStreamCore which maps messages to specific streams.

I have a higher level function which can publish a subset of those messages to their related substreams.

However I am getting the following error:

Type 'MA' does not satisfy the constraint 'IStreamsToAlLEvents[T]'.
  Type 'IStreamToAssetType[T]' is not assignable to type 'IStreamsToAlLEvents[T]'.
    Property 'streamc' is missing in type 'IStreamToAssetType' but required in type 'IStreamsToAlLEvents'.
      Type 'MA' is not assignable to type 'never'.
        The intersection 'TEventAssetTypeA & TEventAssetTypeB' was reduced to 'never' because property 'assetType' has conflicting types in some constituents.
          Type 'IStreamToAssetType[T]' is not assignable to type 'never'.
            Type 'TEventAssetTypeA | TEventAssetTypeB' is not assignable to type 'never'.
              Type 'TEventAssetTypeA' is not assignable to type 'never'.(2344)

Regardless, what is the best way to get around this?

I’m particularly surprised by the following line:

The intersection 'TEventAssetTypeA & TEventAssetTypeB' was reduced to 'never' because property 'assetType' has conflicting types in some constituents.

Why I am ending up with an intersection for MA at publishAsssetMessageToStream when I was hoping to have a union of either TEventAssetTypeA | TEventAssetTypeB?

Ideally, I would like to be specific in the core function, but only give higher level functions to other developers that would call this with a subset of the different events/topics.