Support `React.ElementProps`

[rsolomon]

Flow provides a method for obtaining a component's prop types called React.ElementProps (documentation here).

babel-plugin-flow-react-proptypes does not recognize usage, resulting in a transpilation error along these lines:

ERROR in <COMPONENT_PATH>
Module build failed: TypeError: <COMPONENT_PATH>: Cannot read property 'forEach' of undefined
    at convertToPropTypes (/node_modules/babel-plugin-flow-react-proptypes/lib/convertToPropTypes.js:77:19)
    at /node_modules/babel-plugin-flow-react-proptypes/lib/convertToPropTypes.js:31:20
    at Array.forEach (<anonymous>)
    at convertToPropTypes (/node_modules/babel-plugin-flow-react-proptypes/lib/convertToPropTypes.js:27:21)
    at convertToPropTypes (/node_modules/babel-plugin-flow-react-proptypes/lib/convertToPropTypes.js:51:13)
    at /node_modules/babel-plugin-flow-react-proptypes/lib/convertToPropTypes.js:31:20
    at Array.forEach (<anonymous>)
    at convertToPropTypes (/node_modules/babel-plugin-flow-react-proptypes/lib/convertToPropTypes.js:27:21)
    at convertNodeToPropTypes (/node_modules/babel-plugin-flow-react-proptypes/lib/index.js:31:43)
    at PluginPass.TypeAlias (/node_modules/babel-plugin-flow-react-proptypes/lib/index.js:175:25)

[brigand]

@rsolomon thanks for the report!

I'm not quite sure what we should do in this case. Could you give an example of how you're using this type in your code?

[rsolomon]

For example, the material-ui library uses the withStyles HoC for most components. This HoC modifies the exported component's properties. For example:

https://github.com/mui-org/material-ui/blob/v1-beta/src/Menu/MenuItem.js

The component itself takes in Props and ProvidedProps, but the output only requires a diff of Props and DefaultProps. Using React.ElementProps<typeof MenuItem> would get the correctly diffed props, but using the exported Props would mean the user would incorrectly need to provide props that are already provided by either DefaultProps or ProvidedProps.

[brigand]

@rsolomon does this look right?

Input:

import MenuItem from 'whatever';

type Props = {
  foo: React.ElementProps<typeof MenuItem>,
};
const C = (props: Props) => {};

Output:

import MenuItem from 'whatever';

const C = (props) => {};

C.propTypes = {
  foo: MenuItem.propTypes
    ? PropTypes.shape(MenuItem.propTypes).isRequired,
    : PropTypes.any.isRequired,
};

Are there other situations I'm missing?

[rsolomon]

That's correct in that scenario, though usually I've been using the props for compositions. Ex:

import MenuItem from 'whatever';

type Props = React.ElementProps<typeof MenuItem> & {
  foo: string,
};
const C = (props: Props) => {};

With the expected output being:

import MenuItem from 'whatever';

const C = (props) => {};

C.propTypes = {
  ...MenuItem.propTypes,
  foo: PropTypes.string.isRequired,
};

[brigand]

@rsolomon I implemented it for this case:

const React = require('react');
const MenuItem = require('./MenuItem');
type Props = {
  foo: React.ElementProps<typeof MenuItem>,
};
const C = (props: Props) => <div />;

Published as 9.2.0. I don't know when I'll have time to implement the intersection case. If you're interested in implementing this, a PR would be great!

If you take it on, you can use ./scripts/runOnFile example.js while developing.