Mobx flow type hinting using observable function around a map creates incorrect type

[paul23-git]

Intended outcome:

When creating a new map and making it observable using the function, the returned type is of a map without specifying the key type, or

Actual outcome:
The type of the key is "lost", and the type of the value is converted to V|undefined. - Or when not giving an initial value to the map the type of the value is just V

How to reproduce the issue:

The following line to a store, or anywhere (ps: how can I create a flow test on codesandbox?):
const someMap: ObservableMap<number, string> = observable(new Map());

Some extra discovery:

This seems to be due line 254 of mobx.js.flow:

export interface IObservableFactory {
    // observable overloads
    (target: Object, key: string, baseDescriptor?: PropertyDescriptor<*>): any;
    <T>(value: Array<T>): IObservableArray<T>;
    <T>(value: null | void): IObservableValue<T>;
    (value: null | void): IObservableValue<any>;
    <T>(value: IMap<string | number | boolean, T>): ObservableMap<T>;
    <T: Object>(value: T): T;
}

Versions
mobx: 5.15.3
flow: 0.124

[danielkcz]

Can you please set up a simple reproduction with a Flow playground?

[mweststrate]

Note that the flow types aren't actively maintained but a community effort, feel free to submit a PR to improve things.

…

On Wed, May 13, 2020 at 5:39 AM Daniel K. ***@***.***> wrote: Can you please set up a simple reproduction with a Flow playground <https://flow.org/try>? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#2355 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAN4NBA6XX7WRIQFMB7NMLDRRIP7VANCNFSM4M7HDKZA> .

[danielkcz]

Closing for inactivity.