Simplify error messages against intersections of weak types

Nathan Shively-Sanders (@sandersn)

I spoke a bit with Nathan Shively-Sanders (@sandersn) about ways we can tackle the type madness issue (#14662). I noted that JSX scenarios are much more broadly applicable right now and are pretty prevalent given the sorts of type arithmetic we see a lot of in the React community. 😃

Problem: JSX optional attributes make errors too hard to read

interface FooProps {
    name: string;
    age: number;
}

class Foo extends React.Component<FooProps> {
    constructor(props: FooProps) {
        super(props)
    }
    render() {
        const {name, age} = this.props;
        return <div>I'm {name} and am {age} years old</div>;
    }
}

// Type '{ blah: number; }' is not assignable to type 'IntrinsicAttributes & IntrinsicClassAttributes<Foo> & Readonly<{ children?: ReactNode; }> & Reado...'.
//   Type '{ blah: number; }' is not assignable to type 'Readonly<FooProps>'.
//     Property 'name' is missing in type '{ blah: number; }'.
<Foo blah={10} />;

Proposal

When doing relation checks against an intersection target, if a check fails, see if relating against the same type with weak types removed would result in the same outcome. If so, use that comparison when elaborating types.

The great part is that this actually solves a broader set of problems than just JSX.

Keep in mind that this needs to be tested against an intersection that consists of nothing but intersection types. We should never fall back to never.

Daniel Rosenwasser (@DanielRosenwasser)

Daniel Rosenwasser (@DanielRosenwasser) I think you mean an intersection that consists of nothing but weak types.

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Simplify error messages against intersections of weak types #24146

Problem: JSX optional attributes make errors too hard to read

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Simplify error messages against intersections of weak types #24146

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Problem: JSX optional attributes make errors too hard to read

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DanielRosenwasser commented on May 15, 2018

sandersn commented on May 16, 2018

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