Fix undefined children does not update children in state

[istarkov]

If at first render you have children props, and at second not
(this.props does not contain children element),
this.state contains previous version of children.

[istarkov]

And it look's like the problem is deeper
for any component props which is gone
you can't use setState because of it's merge nature,
it's need something like replaceState

[gaearon]

Can you add a failing test case instead? I don't understand the problem yet.

[istarkov]

Ok i'll add, the problem is that setState merges newState with old state.
And if at first rendering step you have some prop, and at next rendering step this prop is not exists,
connector state still contains prop from first rendering.
As example

render () {
  const obj = this.props.a ? {someProp: 1} : {};
  <ReduxConnectedComponent {...obj} />
}

if this.props.a was true, and becomes false, ReduxConnectedComponent still contains this.props.someProp equal to 1

[istarkov]

So recomputeState must be like

        recomputeState(props = this.props) {
          const nextState = this.computeNextState(props);
          if (!shallowEqual(nextState, this.state)) {
            this.setState({
              ...Object.keys(this.state)
                .reduce((r, k) => ({
                  [k]: undefined
                }), {}),
              ...nextState,
            });
          }
        }

[istarkov]

I've add failing test, (without @connect it works as expected)

[gaearon]

I got it now, thanks a lot!

[gaearon]

This is out in 0.8.1, if you see any use cases that aren't covered yet, feel free to add more tests ;-)