react-redux type error when only passing in only mapStateToProps on flow v0.55.0

Previously on flow v0.54.1, the following code checked out fine

// @flow
import { connect, type Connector } from 'react-redux'

type State = {
  val: string,
}
type OwnProps = {
  other: string,
}
type Props = {
  other: string,
  val: string,
}

const mapStateToProps = (state: State) => {
  return {
    val: state.val,
  }
}

const connector: Connector<OwnProps, Props> = connect(mapStateToProps)

After upgrading flow to v0.55.0, flow gives an error

Error: src/components/body/custom-events/department-transfer-container.js:29
 29: const connector: Connector<OwnProps, Props> = connect(mapStateToProps)
                                                   ^^^^^^^^^^^^^^^^^^^^^^^^ function call. Could not decide which case to select
 29: const connector: Connector<OwnProps, Props> = connect(mapStateToProps)
                                                   ^^^^^^^ intersection type
  Case 3 may work:
                                 v--------------
   78:   declare function connect<S, A, OP, SP>(
   79:     mapStateToProps: MapStateToProps<S, OP, SP>,
   80:     mapDispatchToProps: Null,
  ...:
   83:   ): Connector<OP, $Supertype<SP & { dispatch: Dispatch<A> } & OP>>
         ----------------------------------------------------------------^ polymorphic type: function type. See lib: flow-typed/npm/react-redux_v5.x.x.js:78
  But if it doesn't, case 5 looks promising too:
                                 v------------------
   92:   declare function connect<S, A, OP, SP, DP>(
   93:     mapStateToProps: MapStateToProps<S, OP, SP>,
   94:     mapDispatchToProps: MapDispatchToProps<A, OP, DP>,
  ...:
   97:   ): Connector<OP, $Supertype<SP & DP & OP>>
         -----------------------------------------^ polymorphic type: function type. See lib: flow-typed/npm/react-redux_v5.x.x.js:92
  Please provide additional annotation(s) to determine whether case 3 works (or consider merging it with case 5):
   14: const mapStateToProps = (state: Object, ownProps: OwnProps) => {
                                                                     ^ return

I can resolve the error by passing in an empty mapDispatchToProps like so

const mapDispatchToProps = (dispatch: Dispatch<*>) => {
  return {}
}
const connector: Connector<OwnProps, Props> = connect(
  mapStateToProps,
  mapDispatchToProps
)

but hoping there might be a way to adjust the libdef to support not passing in mapDispatchToProps like before.

[sporto]

Annotating mapStateToProps has worked for me.

import type { MapStateToProps } from "react-redux"

const mapStateToProps: MapStateToProps<*, *, *> = (state: StateType) => {
  return ...
}

export default connect(mapStateToProps)(...)

Flow infers what version of connect to use this way.

[adamesque]

We were wrestling with this issue, and it turned out the problem was that we weren’t declaring a return type for our mapStateToProps function. Adding a signature like

function mapStateToProps(state: State): StateProps {
    return …;
}

resolved the type error. It was just an oversight on our part.