Fixed typings for makeStyles return function

[bartekczyz]

Return function accepts optional props argument. Fixed TS typings. See https://github.com/mui-org/material-ui/blob/master/packages/material-ui-styles/src/makeStyles.js#L30

• I have followed (at least) the PR section of the contributing guide.

[eps1lon]

Would like add a typings test for that. Isn't it possible now to call it without props when the actual styling function accesses those props? That would possibly throw at runtime, no?

[bartekczyz]

Sorry mate, I have totally no idea what are you asking, could you please elaborate more on that?

[eps1lon]

Sorry mate, I have totally no idea what are you asking, could you please elaborate more on that?

This throws at runtime:

const useStyles = makeStyles({ root: props => ({ color: props.nested.value }) });

function Component(props) {
  const classes = useStyles(); // cannot read property value of undefined
  return <div className={classes.root}>Hello, World!</div>
}

<Component nested={{ value: 'green' }} />

but would be accepted at compile time now.

There is a little bit more work involved. I think you should start with Styles and then work up. Start by writing code that should be valid at compile time (i.e. in a TS file) and code that should error at compile time. Then change the declarations accordingly.

[eps1lon]

@bartekczyz See #13815 for my solution. 734018b includes tests (the $ExpectError are responsible for that) and ca668d5 the fixes.