Either CombineEpics typing is misleading or I don't understand something

Do you want to request a feature or report a bug?
I want to report a bug.

Here’s the problem. I have a bunch of modules (store/state, actions, reducer, epic(s), views). If I combine reducers like this:

type Module1State = { .... }
...
type Module2State = { .... }
...
type RootState = {
  m1: Module1State
  m2: Module2State
}
...
const rootReducer: Reducer<RootState> = combineReducers<RootState>({
  m1: module1reducer,
  m2: module2reducer
});

… I get my RootState just like it is shown above.

Now, each module has its own Epic:

type Module1Action = ... | ... | ...
type Module1State = { .... }
...
const m1Epic: Epic<Module1Action, Module1State>

Okay. The problem appears when I want to combine such Epics:

import { m1Epic, m1ActionType, m1State } from './m1';
import { m2Epic, m2ActionType, m2State } from './m2';
...
type RootAction = m1ActionType | m2ActionType
type RootState = {
  m1: m1State
  m2: m2State
}
...
const store = createStore<RootAction>(
  rootReducer,
  applyMiddleware(
    createEpicMiddleware(
      combineEpics<RootAction, RootState>(m1Epic, m2Epic)
    )
  )
);

This will not compile because according to https://github.com/redux-observable/redux-observable/blob/master/index.d.ts#L51 combineEpics takes type S for Root State Type. Therefor, RootState is not assignable to m1State or m1State

Therefore, it’s either me being stupid and doing something wrong or there’s an issue with the type signatures…

[rgbkrk]

In the above example it’s:

CONTENTS_ACTION = LOAD_ACTION | SAVE_ACTION

Whereas in the current code it’s ALL_ACTIONS.

[rgbkrk]

Yeah, that’s correct. What I end up doing, at least because I’m using FlowType is:

export function loadEpic(
  action$: ActionsObservable<CONTENTS_ACTION>,
  store: Store<*, *>
) {
  return action$
    .ofType("LOAD")
    .do((action: LOAD_ACTION) => {
      // If there isn't a filename, save-as it instead
      if (!action.filename) {
        throw new Error("save needs a filename");
      }
    })

since it lets me carve out the types within the operators just fine.

The reason it tends to be useful to have the action$ all available is that you can use other actions to end certain streams.

.takeUntil(action$.ofType('CANCEL_LOAD').filter(action => action.id === someID))