Allow the use of a module JSX namespace

[ceymard]

Since JSX is a global namespace, it is not possible to use typings declared in a module for its Element or ElementClass.

When writing a module, it would then be convenient to write something like ;

import {MyEltType, JSX}  from 'my-custom-jsx-lib'

var myelt = <div> ...</div>

and have typescript check Element, ElementClass and so on on its local JSX instance.

Also, when not providing any JSX namespace but having a factory that has a return type, the compiler crashes nastily with a

/usr/lib/node_modules/typescript/lib/tsc.js:33078
                throw e;
                ^

TypeError: Cannot read property 'flags' of undefined
    at isRelatedTo (/usr/lib/node_modules/typescript/lib/tsc.js:16013:32)
    at checkTypeRelatedTo (/usr/lib/node_modules/typescript/lib/tsc.js:15941:26)
    at checkTypeAssignableTo (/usr/lib/node_modules/typescript/lib/tsc.js:15819:20)
    at isTypeAssignableTo (/usr/lib/node_modules/typescript/lib/tsc.js:15813:20)
    at getJsxElementAttributesType (/usr/lib/node_modules/typescript/lib/tsc.js:18463:47)
    at checkJsxOpeningLikeElement (/usr/lib/node_modules/typescript/lib/tsc.js:18564:40)
    at checkJsxSelfClosingElement (/usr/lib/node_modules/typescript/lib/tsc.js:18265:13)
    at checkExpressionWorker (/usr/lib/node_modules/typescript/lib/tsc.js:20439:28)
    at checkExpression (/usr/lib/node_modules/typescript/lib/tsc.js:20349:42)
    at checkExpressionCached (/usr/lib/node_modules/typescript/lib/tsc.js:20310:38)

[RyanCavanaugh]

Regarding the first point, you can now do this using the declare global { syntax.

I'll take a look at the crash

[ceymard]

By doing

declare global {

  namespace JSX {

  }

}

I get an error TS2665: Module augmentation cannot introduce new names in the top level scope.

Is there something I'm not seeing ?

[ceymard]

Does this mean I have to have a .d.ts file declaring the namespace to be able to augment it ?

If so, would that mean that I would be limited to extending the JSX.Element, rather than define it altogether ?

[RyanCavanaugh]

That error and restriction has been removed

[ceymard]

Should I use a nightly build then ?

By the way I have tried to make a simple reproduction for the mentioned bug, but couldn't. The library that explodes as such is on github and I'd be delighted to show you how to reproduce if you wish.

[RyanCavanaugh]

Yea, the nightly build should make that error go away.

A github repo for the bug would be great, always happy to look at those.

[ceymard]

I just tested with [email protected] and the crash is no longer present.

There is a way of reproducing with 1.8.10 (I started a branch for this), are you still interested or do you consider this as resolved ?

[RyanCavanaugh]

If it's fixed in the nightly then it's probably a duplicate of #7286

[ceymard]

Since everything is working fine for me, shouldn't we mark this as closed ?

[ellisonbg]

We have a large extensible application where different extension authors might use different virtual dom libraries underneath TSX. Right now because JSX is expected to be global that is difficult. Allowing the JSX namespace to be resolved locally in a module would help a ton.

[mhegazy]

@ellisonbg please see #15386