Generic is not resolving properly in complex situation.

[kiddkai]

Hi,

I am trying to create a "middleware" api, in redux, which already has a bunch of built-in types. And I am trying to use existing types to create a new middleware. But flow is throwing this error to me:

store.dispatch({ type: 'string' });
                           ^ object literal. This type is incompatible with the expected param type of
14:     return (store: MiddlewareAPI<S, A>) => next => (action: A) => {
                                        ^ some incompatible instantiation of `A`

When I am trying to do:

/* @flow */

declare type DispatchAPI<A> = (action: A) => A;
declare type Dispatch<A: { type: $Subtype<string> }> = DispatchAPI<A>;
declare type MiddlewareAPI<S, A, D = Dispatch<A>> = {
    dispatch: D;
    getState(): S;
};
type Middleware<S, A, D = Dispatch<A>> =
    (api: MiddlewareAPI<S, A, D>) =>
      (next: D) => D;

export const createSSRMiddleware = <S, A: { type: string }>(): Middleware<S, A> => {
    return (store: MiddlewareAPI<S, A>) => next => (action: A) => {
        store.dispatch({ type: 'string' });
        return next(action);
    };
};

Below is the link to reproduce the issue:

https://flow.org/try/#0PQKgBAAgZgNg9gdzCYAoVATApgYxgQwCcswAXATwAcSARASwGdL9ScALAQQAUBJAHg4A+MAF4wACnw5SdOADsAXGA4BKUcI4BuTLgLEyVWo2as2ApQG8D1JQBIAygFcARhWp8GpQnTkBzYQC+wmL0TCzs3PxC2th4RCRuJACydBgYMFgI8ZF89gA0ygU0omChJuwCgsFgFqhg9WAYxuFsSjTaDWC+WKT2pCxY4ipK9toB2olgKWkZWcS5BRxFJWUtlcF1DZKUdErT6ZnZvAuFpYJqIoKbneJyWAAepG0Xwu3oD5RwhKRgOPKev2IA3s9gASvtZvESicOJZrFglJ5vH4wEEhntUgc5lgYcFhLVOsRSI5CHIJJ4vgippjIcQcvllOd1GA7o9mZJpLJFMoXjVrp0wBTiAA6JphUziKyJJQAciRPl8MtRKg6AvqRJJZNZpA5MnkKv541QRqAA

I also found out that even with a simple case like:

/* @flow */
const foo = <A: number>() => {
  const bar: A = 1;
}

It also producing the same error, I don't know if they are related. But looks like it's the case.