TSX type inference is broken when using intersection types

[iyegoroff]

TypeScript Version: 2.7.1, 2.8.0-dev.20180204

Search Terms: jsx tsx intersection

Code

import * as React from 'react';

type Props<T> = T & {prop: string};

class Component<T = {valid: string}> extends React.Component<Props<T>> {}

<>
  <Component prop={''} invalid={''} />
  <Component prop={''} valid={''} invalid={''}/>
</>

Expected behavior:
Should generate 2 errors as in 2.6.2:

main.tsx(8,14): error TS2322: Type '{ prop: ""; invalid: ""; }' is not assignable to type 'IntrinsicAttributes & IntrinsicClassAttributes<Component<{ valid: string; }>> & Readonly<{ childr...'.
  Type '{ prop: ""; invalid: ""; }' is not assignable to type 'Readonly<Props<{ valid: string; }>>'.
    Property 'valid' is missing in type '{ prop: ""; invalid: ""; }'.
main.tsx(9,35): error TS2339: Property 'invalid' does not exist on type 'IntrinsicAttributes & IntrinsicClassAttributes<Component<{ valid: string; }>> & Readonly<{ childr...'.

Actual behavior:
No errors are generated

Playground Link: -

Related Issues: maybe related #21427

[RyanCavanaugh]

@weswigham thoughts on this?

[weswigham]

I think the jsx inference/contextual typing PR I currently have open is mostly to fix exactly this, since I discovered the same issue when looking at changing formik.

[weswigham]

Also, hold on: those 2.6.2 errors are themselves erroneous. Setting a default doesn't constrain the type variable - literally any props should be be OK to pass for that component - we just messed up before and instantiated with the default like it was the constraint before.

[RyanCavanaugh]

Setting a default doesn't constraint the type variable - literally any props should be be OK to pass for that component

This was my interpretation as well. Seems useless to have a generic component if you're not allowed to infer a type from its props.

[iyegoroff]

@weswigham, so the actual behavior in 2.7.1 is correct and it will stay like this after your PR will be merged?

[weswigham]

Yeah. You should be using extends in that type definition if you actually wanted that field required.

[iyegoroff]

OK, thanks for clarification.