Improve Flow types

[migueloller]

Adds better Flow support. Now, if the return type of the recipe never returns undefined, it can be guaranteed that produce won't return undefined. This allows compatibility with other types, like Redux's Reducer type.

i.e.,

import type { Reducer } from 'redux'

type State = {| count: number |}

type Action = {| type: 'INCREMENT' |} | {| type: 'DECREMENT' |}

const reducer: Reducer<State, Action> = (state: State = { count: 0 }, action) => {
  switch(action.type) {
    case 'INCREMENT':
      state.count++
      break

    case 'DECREMENT':
      state.count--
  }

  return state
}

// This is now possible! Before it would fail, as the return type of
// produce would be `State | void`.
const initialState: State = produce(reducer)(undefined, { type: 'INCREMENT' })

[migueloller]

Seems to be failing tests that fail in master as well. Looks like #231 fixes it. Will rebase once #231 is merged.

[aleclarson]

You shouldn't need to rebase, since you're not touching any of the same files as #231

[migueloller]

@aleclarson, sweet! Let me know if there's anything else you need from me 😄

[aleclarson]

@mweststrate won't be maintaining much in the next 2 weeks, and we need him to review this PR. Therefore, I moved this PR to v1.7.5 instead of v1.7.4.

[mweststrate]

The CI failed, I guess this still needs rebasing?

[mweststrate]

• Flow type updates look correct to me, approved that part
• Build is failing, needs to be rebased on master?
• The changes in this MR are more than just the flow typings, was this PR based on a not-yet-merged branch? If so, we need to make sure that one get's first

[aleclarson]

@mweststrate This PR was put up before I removed failing tests from master with a rebase (naughty, I know).

[migueloller]

@mweststrate, thanks for the review! Rebasing now.

[coveralls]

Coverage remained the same at 96.393% when pulling 46d9db7 on migueloller:flow-type-definitions into 4613b06 on mweststrate:master.

[mweststrate]

@migueloller, some tests are failing in the CI. Probably locally as well. Could you look into this?

[migueloller]

@mweststrate, I spent a bit looking at the failing test and realized a few things.

• There are other regressions on the Flow types
• $ExpectError tests weren't even working at all
• The currently proposed types seem to break down in some use cases

I want to spend some more time to address these issues but I'm extremely busy with my day job at the moment. I will push new changes ASAP.

[mweststrate]

Merged into 3.0 branch

[mweststrate]

Undid that :)

[mweststrate]

Closing for inactivity