Payload type unknown when defining optional property?

[mcchrish]

This is for version 0.8.0.

const action = createAction<{ input?: string }>('ACTION')
type ActionType = ReturnType<typeof action> // ActionType.payload === unknown


const action = createAction<{ input?: string, input2: string }>('ACTION')
type ActionType = ReturnType<typeof action> // ActionType.payload === { input?: string | undefined; input2: string }

Somehow, if there is only one property and it's optional, it converts it type to unknown

[markerikson]

Oh dear. What version of TS are you on?

@phryneas , @Jessidhia : any ideas?

[phryneas]

Phew. Yup.

The feature detection for TS<3.5 was leaking both cases (TS<3.5 and TS>=3.5), exposing the pre-3.5 behaviour.
Back then, we could not distinguish between the empty object default case and unknown, so it would fall back to unknown behaviour if the object looked like an empty object (which is the case here).

We can fix this for TS>=3.5, but in old versions this will be the behaviour if something possibly looks like an empty object.

( fixed TS version feature detection would look like this:

export type AtLeastTS35<True, False> = [True, False][IsUnknown<ReturnType<<T>() => T>, 0, 1>]

)

Question is: is it worth it supporting old TS versions, which should be our minimum requirement? I guess we should still support 3.4, which is from march 2019, even if it hurts a little :/

[markerikson]

Yeah, 3.4 seems reasonable to support, even if it's a bit of a pain.

[phryneas]

I might be even able to fix it for pre-3.5... PR coming in.

[markerikson]

Fix published as 0.8.1. Hopefully that should resolve this - let us know if there's still an issue!