Property 'payload' is missing in type 'AnyAction'

[huan]

Minimum reproducible code snip:

import { Reducer, AnyAction } from 'redux'

type MyAction = {
  payload: number,
  type: 'TAP',
}

const f: Reducer<any, MyAction> = (s: any, ..._: any[]) => s
const r: Reducer<any, AnyAction> = f
// r is NOT ok.
void r

The error message of r is:

Type 'Reducer<any, MyAction>' is not assignable to type 'Reducer<any, AnyAction>'.
  Types of parameters 'action' and 'action' are incompatible.
    Type 'AnyAction' is not assignable to type 'MyAction'.ts(2322)

However,

const a1: MyAction = {
  payload: 42,
  type: 'TAP',
}
const a2: AnyAction = a1
// a2 is OK
void a2

To be fixed.

Related Issues

• Redux Reducer type error Redux Reducer type error microsoft/TypeScript#17154
• Regression: 2.4.1 Generic type mismatch Regression: 2.4.1 Generic type mismatch  microsoft/TypeScript#16985 (comment)
• Super-type of T is something like <U extends T> Regression: 2.4.1 Generic type mismatch  microsoft/TypeScript#16985 (comment)

[huan]

import { Reducer } from 'redux'

const count: Reducer<number> = (state: number) => {
  return state
}

void count

The above code will yield the following error message:

error TS2322: Type '(state: number) => number' is not assignable to type 'Reducer<number, AnyAction>'.
  Types of parameters 'state' and 'state' are incompatible.
    Type 'number | undefined' is not assignable to type 'number'.
      Type 'undefined' is not assignable to type 'number'.

3 const count: Reducer<number> = (state: number) => {

It turns out that we are declaring a function that can accept the state as the undefined | number type, however, the implemented function can only accept the number type of the argument, which can not satisfy the declaration.