Rule: no-event-calls-in-reducers

[AlexandrHoroshih]

Event or effect calls inside reducers or other supposed-to-be-pure functions like fn of sample or combine rule is a violation of current declared rules of effector, because it makes those functions calls observable "from the outside"

So code like this is technically wrong:

// this code must be either rewritten to operators or written in the same way, but inside `.watch`
$store.on(someEvent, (state, payload) => { 
 // store reducer meant to update stored value
 if (payload.some) {
   // but there is some control flow happening instead, which is wrong
   someEffect(state)
 } else {
  someOtherEvent(payload)
 }
 // next state is never returned - plain wrong usage of `.on`
})

Even though effector still can handle that, breaking this rule may lead to problems in next releases of effector

It looks like that check for such calls at the core adds more issues than profit (see: effector/effector#541 (comment)), so eslint-rule is preferred

[igorkamyshev]

Yeah, good idea. I think we also should ban effects.

related #6