Add a generic type for getters too.

[mat813]

This allows you to write something like this, for example, in a vuex
module, that lives in a subdirectory of the store, where it is most
interesting:

import { GetterTree } from 'vuex';

import type { State as RootState, Getters as RootGetters } from '../';
import type { State } from './state';

export type Getters = {
  loggedIn: boolean;
  roles: string[];
  isAdmin: boolean;
};

export const getters: GetterTree<State, RootState, Getters, RootGetters> = {

And you get correct type inference in your editor.

[mat813]

And then, in your actual store that only imports modules, you would do something like:

import { createStore } from 'vuex';

import * as auth from './auth';

export type State = {
  auth: auth.State;
};

// This needs typescript 4.1
type Namespaced<T, N extends string> = {
  [P in keyof T & string as `${N}/${P}`]: T[P];
};

// Other getters are appended with a `&`
export type Getters = Namespaced<auth.Getters, 'auth'>;

export const store = createStore<State, Getters>({
  modules: {
    auth,
  },
});

(fun fact, with that, the compiler found a typo in some of my code that passed tests anyway, a new test case has been written.)