Broken keyof inference

[DScheglov]

Bug Report

🔎 Search Terms

keyof

🕗 Version & Regression Information

• This changed between versions 4.4.4 and 4.5.2

Also the bug was reproduced in the Playground with version 4.5.0-beta

⏯ Playground Link

Playground (v4.5.0-beta)

💻 Code

import React from "react";

type SetState<S> = {
    (value: S): void;
    (reducer: (currentState: S) => S): void;
};

type StateManager<S> = {
    getState(): S;
    setState: SetState<S>;
    subscribe(listener: (value: S) => void): () => void;
};

type StateType<SM> = SM extends StateManager<infer S> ? S : never;

type KeyOfType<S extends {}, T> = {
    [P in keyof S]: S[P] extends T ? P : never;
}[keyof S];

export function useStateManager<S>({ getState, setState, subscribe }: StateManager<S>): [S, SetState<S>] {
    const [, next] = React.useReducer((v: number) => v + 1, 0);
    React.useEffect(() => subscribe(() => next()), []);

    return [getState(), setState];
}

export function useStateManagerFromContext<C extends {}, N extends KeyOfType<C, StateManager<any>>>(
    context: React.Context<C>,
    stateManagerName: N
) {
    const ctx: Pick<C, KeyOfType<C, StateManager<any>>> = React.useContext(context);
    return useStateManager<StateType<C[N]>>(ctx[stateManagerName]);
}

🙁 Actual behavior

The Error reported and compilation failed:

Errors in code
Argument of type 'C[N]' is not assignable to parameter of type 'StateManager<StateType<C[N]>>'.
  Type 'C[KeyOfType<C, StateManager<any>>]' is not assignable to type 'StateManager<StateType<C[N]>>'.
    Type 'C[C[keyof C] extends StateManager<any> ? keyof C : never]' is not assignable to type 'StateManager<StateType<C[N]>>'.
      Type 'C[keyof C]' is not assignable to type 'StateManager<StateType<C[N]>>'.
        Type 'C[string] | C[number] | C[symbol]' is not assignable to type 'StateManager<StateType<C[N]>>'.
          Type 'C[string]' is not assignable to type 'StateManager<StateType<C[N]>>'.

🙂 Expected behavior

No error reported as it works before, as instance in v4.4.4:

Playground (v4.4.4)

[yseymour]

Minimal playground repro

[yseymour]

I think this is the same as #46855.

[typescript-bot]

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