change type

Author: phryneas

etc/redux-toolkit.api.md

@@ -7,10 +7,10 @@
 import { Action } from 'redux';
 import { ActionCreator } from 'redux';
 import { AnyAction } from 'redux';
+import { CombinedState } from 'redux';
 import { default as createNextState } from 'immer';
 import { createSelector } from 'reselect';
 import { current } from 'immer';
-import { DeepPartial } from 'redux';
 import { Dispatch } from 'redux';
 import { Draft } from 'immer';
 import { freeze } from 'immer';
@@ -20,6 +20,7 @@ import { original } from 'immer';
 import { OutputParametricSelector } from 'reselect';
 import { OutputSelector } from 'reselect';
 import { ParametricSelector } from 'reselect';
+import { PreloadedState } from 'redux';
 import { Reducer } from 'redux';
 import { ReducersMapObject } from 'redux';
 import { Selector } from 'reselect';
@@ -127,7 +128,7 @@ export interface ConfigureStoreOptions<S = any, A extends Action = AnyAction, M
     devTools?: boolean | EnhancerOptions;
     enhancers?: StoreEnhancer[] | ConfigureEnhancersCallback;
     middleware?: ((getDefaultMiddleware: CurriedGetDefaultMiddleware<S>) => M) | M;
-    preloadedState?: DeepPartial<S extends any ? S : S>;
+    preloadedState?: PreloadedState<CombinedState<NoInfer<S>>>;
     reducer: Reducer<S, A> | ReducersMapObject<S, A>;
 }
 

src/configureStore.ts

@@ -11,7 +11,8 @@ import {
   StoreEnhancer,
   Store,
   Dispatch,
-  PreloadedState
+  PreloadedState,
+  CombinedState
 } from 'redux'
 import {
   composeWithDevTools,
@@ -74,7 +75,16 @@ export interface ConfigureStoreOptions<
    * function (either directly or indirectly by passing an object as `reducer`),
    * this must be an object with the same shape as the reducer map keys.
    */
-  preloadedState?: PreloadedState<NoInfer<S>>
+  /* 
+  Not 100% correct but the best approximation we can get:
+  - if S is a `CombinedState` we know it is from a `combineReducers` call and we can just apply `PreloadedState` on it.
+  - if it is not, there could be two cases:
+    - `ReducersMapObject<S, A>` is being passed in. In this case, we will call `combineReducers` on it and `Partial<S>` is correct
+    - `Reducer<S, A>` is being passed in. In this case, actually `Partial<S>` is wrong and `S` would be correct.
+    As we cannot distinguish between those two cases without adding another generic paramter, 
+    we just make the pragmatic assumption that the latter almost never happens.
+  */
+  preloadedState?: PreloadedState<CombinedState<NoInfer<S>>>
 
   /**
    * The store enhancers to apply. See Redux's `createStore()`.
@@ -169,5 +179,9 @@ export function configureStore<
 
   const composedEnhancer = finalCompose(...storeEnhancers) as any
 
-  return createStore(rootReducer, preloadedState, composedEnhancer)
+  return createStore(
+    rootReducer,
+    preloadedState as PreloadedState<S> | undefined,
+    composedEnhancer
+  )
 }