use never instead of void for PayloadAction Meta & Error (#233)

avoids `any` to take the `void` branch
fixes #224

src/createAction.ts

@@ -13,13 +13,14 @@ import { IsUnknownOrNonInferrable } from './tsHelpers'
 export type PayloadAction<
   P = void,
   T extends string = string,
-  M = void,
-  E = void
+  M = never,
+  E = never
 > = WithOptional<M, E, WithPayload<P, Action<T>>>
 
 export type PrepareAction<P> =
   | ((...args: any[]) => { payload: P })
   | ((...args: any[]) => { payload: P; meta: any })
+  | ((...args: any[]) => { payload: P; error: any })
   | ((...args: any[]) => { payload: P; meta: any; error: any })
 
 export type ActionCreatorWithPreparedPayload<
@@ -30,7 +31,7 @@ export type ActionCreatorWithPreparedPayload<
   PA extends PrepareAction<infer P>
     ? (
         ...args: Parameters<PA>
-      ) => PayloadAction<P, T, MetaOrVoid<PA>, ErrorOrVoid<PA>>
+      ) => PayloadAction<P, T, MetaOrNever<PA>, ErrorOrNever<PA>>
     : void
 >
 
@@ -157,8 +158,8 @@ type Diff<T, U> = T extends U ? never : T
 type WithPayload<P, T> = T & { payload: P }
 
 type WithOptional<M, E, T> = T &
-  ([M] extends [void] ? {} : { meta: M }) &
-  ([E] extends [void] ? {} : { error: E })
+  ([M] extends [never] ? {} : { meta: M }) &
+  ([E] extends [never] ? {} : { error: E })
 
 type WithTypeProperty<T, MergeIn> = {
   type: T
@@ -170,17 +171,17 @@ type IfPrepareActionMethodProvided<
   False
 > = PA extends (...args: any[]) => any ? True : False
 
-type MetaOrVoid<PA extends PrepareAction<any>> = ReturnType<PA> extends {
+type MetaOrNever<PA extends PrepareAction<any>> = ReturnType<PA> extends {
   meta: infer M
 }
   ? M
-  : void
+  : never
 
-type ErrorOrVoid<PA extends PrepareAction<any>> = ReturnType<PA> extends {
+type ErrorOrNever<PA extends PrepareAction<any>> = ReturnType<PA> extends {
   error: infer E
 }
   ? E
-  : void
+  : never
 
 type IfMaybeUndefined<P, True, False> = [undefined] extends [P] ? True : False
 

type-tests/files/createAction.typetest.ts

@@ -1,5 +1,6 @@
 import { Action, AnyAction, ActionCreator } from 'redux'
 import { createAction, PayloadAction, PayloadActionCreator } from '../../src'
+import { IsAny } from 'src/tsHelpers'
 
 function expectType<T>(p: T): T {
   return p
@@ -218,4 +219,23 @@ function expectType<T>(p: T): T {
   const u: number = action({input: ""}).payload.input;
   // typings:expect-error
   const v: number = action({input: 3}).payload.input;
+}
+/*
+ * regression test for https://github.com/reduxjs/redux-starter-kit/issues/224
+ */
+{
+  const oops = createAction('oops', (x: any) => ({ payload: x, error: x, meta: x }))
+
+  type Ret = ReturnType<typeof oops>;
+
+  const payload: IsAny<Ret['payload'], true, false> = true;
+  const error: IsAny<Ret['error'], true, false> = true;
+  const meta: IsAny<Ret['meta'], true, false> = true;
+
+  // typings:expect-error
+  const payloadNotAny: IsAny<Ret['payload'], true, false> = false;
+  // typings:expect-error
+  const errorNotAny: IsAny<Ret['error'], true, false> = false;
+  // typings:expect-error
+  const metaNotAny: IsAny<Ret['meta'], true, false> = false;
 }