Flow freezes when 'merging inference'

[villesau]

Flow checker freezes completely with following code:

// @flow
import React from 'react';
import _ from 'lodash';

export default class Test extends React.Component {

  state: {matrix: Array<Array<boolean>>};
  state = {matrix: _.times(5, () => _.times(5, () => false))};

  toggleCell(rowIndex: number, columnIndex: number) {
    const newRow = this.state.matrix[rowIndex];
    this.setState({matrix: _.set(this.state.matrix, rowIndex, newRow)})
  }

  render() {
    return (<div onClick={() => this.toggleCell(1, 1)}></div>);
  }
}

my flow definitions for lodash looks like following:

declare module 'lodash' {
  declare function set(object?: ?Object, path?: ?Array<string>|string, value: any): Object;
  declare function set<T>(array: Array<T>, index: number, value: T): Array<T>;
  declare function times<T>(n: number, iteratee: (i: number) => T): Array<T>;
}

few ways how i can get it fixed:
(1. Move state = {matrix: _.times(5, () => _.times(5, () => false))};
to constructor:

export default class Test extends React.Component {

  state: {matrix: Array<Array<boolean>>};

  constructor() {
    super();
    this.state = {matrix: _.times(5, () => _.times(5, () => false))};
  }

  toggleCell(rowIndex: number, columnIndex: number) {
    const newRow = this.state.matrix[rowIndex];
    this.setState({matrix: _.set(this.state.matrix, rowIndex, newRow)})
  }

  render() {
    return (<div onClick={() => this.toggleCell(1, 1)}></div>);
  }
}

(2. Declare _.times to return any: declare function times<T>(n: number, iteratee: (i: number) => T): any;

(3. Remove _.set: this.setState({matrix: this.state.matrix})

  toggleCell(rowIndex: number, columnIndex: number) {
    const newRow = this.state.matrix[rowIndex];
    this.setState({matrix: this.state.matrix})
  }

Anyone of above is not optimal solution, and last of them breaks the logic. Just wanted to point it out to narrow the problem.

declaring state outside of the constructor should be valid javascript. Webpack&babel compiles it just fine and it works like expected.

[gcanti]

state: {matrix: Array<Array<boolean>>} = {matrix: _.times(5, () => _.times(5, () => false))};

[villesau]

thanks @gcanti :) Somehow my mind was stuck with approach i had since usually we define type of state and initialize it separately in the constructor.

Anyhow in my original scenario flow should either be a) error b) it should succeed without freezing.

[MoOx]

Looks similar to #1570 somehow (> "something" flow does not like make it ultra slow)

[TrySound]

Is this still relevant?

[villesau]

Not relevant to me anymore. Not sure if the issue would still exist though.

[TrySound]

This probably can be closed in favor of newer feedback.
/cc @vkurchatkin