reuse utility and test preparedReducer

Author: ben.durrant

packages/toolkit/src/createAction.ts

@@ -50,26 +50,6 @@ export type PrepareAction<P> =
   | ((...args: any[]) => { payload: P; error: any })
   | ((...args: any[]) => { payload: P; meta: any; error: any })
 
-export type _PayloadActionForPrepare<
-  PA extends PrepareAction<any>,
-  T extends string = string
-> = PA extends PrepareAction<infer P>
-  ? PayloadAction<
-      P,
-      T,
-      ReturnType<PA> extends {
-        meta: infer M
-      }
-        ? M
-        : never,
-      ReturnType<PA> extends {
-        error: infer E
-      }
-        ? E
-        : never
-    >
-  : never
-
 /**
  * Internal version of `ActionCreatorWithPreparedPayload`. Not to be used externally.
  *

packages/toolkit/src/createSlice.ts

@@ -5,7 +5,6 @@ import type {
   PayloadActionCreator,
   PrepareAction,
   _ActionCreatorWithPreparedPayload,
-  _PayloadActionForPrepare,
 } from './createAction'
 import { createAction } from './createAction'
 import type {
@@ -373,11 +372,17 @@ interface ReducerCreators<State> {
 
   preparedReducer<Prepare extends PrepareAction<any>>(
     prepare: Prepare,
-    reducer: CaseReducer<State, _PayloadActionForPrepare<Prepare>>
+    reducer: CaseReducer<
+      State,
+      ReturnType<_ActionCreatorWithPreparedPayload<Prepare>>
+    >
   ): {
     [reducerDefinitionType]: ReducerType.reducerWithPrepare
     prepare: Prepare
-    reducer: CaseReducer<State, _PayloadActionForPrepare<Prepare>>
+    reducer: CaseReducer<
+      State,
+      ReturnType<_ActionCreatorWithPreparedPayload<Prepare>>
+    >
   }
 }
 

packages/toolkit/src/tests/createSlice.typetest.ts

@@ -17,7 +17,7 @@ import type {
 } from '@reduxjs/toolkit'
 import { configureStore } from '@reduxjs/toolkit'
 import { createAction, createSlice } from '@reduxjs/toolkit'
-import { expectType, expectUnknown } from './helpers'
+import { expectExactType, expectType, expectUnknown } from './helpers'
 
 /*
  * Test: Slice name is strongly typed.
@@ -597,6 +597,19 @@ const value = actionCreators.anyKey
           expectType<TestState>(state)
           expectType<string>(action.payload)
         }),
+        preparedReducer: create.preparedReducer(
+          (payload: string) => ({
+            payload,
+            meta: 'meta' as const,
+            error: 'error' as const,
+          }),
+          (state, action) => {
+            expectType<TestState>(state)
+            expectType<string>(action.payload)
+            expectExactType('meta' as const)(action.meta)
+            expectExactType('error' as const)(action.error)
+          }
+        ),
         testInfer: create.asyncThunk(
           function payloadCreator(arg: TestArg, api) {
             return Promise.resolve<TestReturned>({ payload: 'foo' })
@@ -688,6 +701,15 @@ const value = actionCreators.anyKey
   type StoreDispatch = typeof store.dispatch
 
   expectType<PayloadActionCreator<string>>(slice.actions.normalReducer)
+  expectType<
+    ActionCreatorWithPreparedPayload<
+      [string],
+      string,
+      'test/preparedReducer',
+      'error',
+      'meta'
+    >
+  >(slice.actions.preparedReducer)
   expectType<AsyncThunk<TestReturned, TestArg, {}>>(slice.actions.testInfer)
   expectType<AsyncThunk<TestReturned, TestArg, { rejectValue: TestReject }>>(
     slice.actions.testExplicitType