Added 'SafePromise' branded Promises for createAsyncThunk

Author: JoshuaKGoldberg

packages/toolkit/src/createAsyncThunk.ts

@@ -11,6 +11,7 @@ import type {
   Id,
   IsAny,
   IsUnknown,
+  SafePromise,
   TypeGuard,
 } from './tsHelpers'
 import { nanoid } from './nanoid'
@@ -242,7 +243,7 @@ export type AsyncThunkAction<
   dispatch: GetDispatch<ThunkApiConfig>,
   getState: () => GetState<ThunkApiConfig>,
   extra: GetExtra<ThunkApiConfig>
-) => Promise<
+) => SafePromise<
   | ReturnType<AsyncThunkFulfilledActionCreator<Returned, ThunkArg>>
   | ReturnType<AsyncThunkRejectedActionCreator<ThunkArg, ThunkApiConfig>>
 > & {
@@ -676,7 +677,7 @@ export const createAsyncThunk = /* @__PURE__ */ (() => {
           }
           return finalAction
         })()
-        return Object.assign(promise as Promise<any>, {
+        return Object.assign(promise as SafePromise<any>, {
           abort,
           requestId,
           arg,

packages/toolkit/src/index.ts

@@ -203,6 +203,6 @@ export { combineSlices } from './combineSlices'
 
 export type { WithSlice } from './combineSlices'
 
-export type { ExtractDispatchExtensions as TSHelpersExtractDispatchExtensions } from './tsHelpers'
+export type { ExtractDispatchExtensions as TSHelpersExtractDispatchExtensions, SafePromise } from './tsHelpers'
 
 export { formatProdErrorMessage } from './formatProdErrorMessage'

packages/toolkit/src/tsHelpers.ts

@@ -207,3 +207,11 @@ export type Tail<T extends any[]> = T extends [any, ...infer Tail]
   : never
 
 export type UnknownIfNonSpecific<T> = {} extends T ? unknown : T
+
+/**
+ * A Promise that will never reject.
+ * @see https://github.com/reduxjs/redux-toolkit/issues/4101
+ */
+export type SafePromise<T> = Promise<T> & {
+  __brand: 'SafePromise'
+}