TS 3.2 breaks type-unioned component support under certain circumstances

[bytenik]

TypeScript Version: 3.3.0-dev.20181129

Code

ex.tsx:

import * as React from 'react';
import {BrowserRouter, HashRouter, Redirect, Route, RouteProps, Switch} from 'react-router-dom';

type State = {SelectedRouter?: typeof BrowserRouter | typeof HashRouter};
export class Example extends React.Component<{}, State> {
    state: State = {};
    render() {
        const {SelectedRouter} = this.state;
        if (!SelectedRouter) return null;
        return <><SelectedRouter>asdf</SelectedRouter></>;
    }
}

package.json:

{
  "name": "temp",
  "version": "1.0.0",
  "description": "",
  "author": "",
  "license": "ISC",
  "dependencies": {},
  "devDependencies": {
    "@types/prop-types": "^15.5.6",
    "@types/react": "^16.7.11",
    "@types/react-dom": "^16.0.11",
    "@types/react-router": "^4.0.32",
    "@types/react-router-dom": "^4.3.1",
    "csstype": "^2.5.7",
    "typescript": "^3.3.0-dev.20181129"
  }
}

tsconfig.json:

{
    "compilerOptions": {
      "lib": [ "dom", "es2015" ],
      "module": "es2015",
      "moduleResolution": "node",
      "target": "es6",
      "jsx": "react",
    },
    "include": [ "*.tsx" ]
}

Expected behavior:

Successful compilation.

Actual behavior:

ex.tsx:10:19 - error TS2604: JSX element type 'SelectedRouter' does not have any construct or call signatures.

10         return <><SelectedRouter>asdf</SelectedRouter></>;
                     ~~~~~~~~~~~~~~


Found 1 error.

Notes:
This works with TypeScript 3.1.x, but breaks with 3.2.0+. I am not clear on why certain types work and certain types do not, but I imported the React Router types because they definitely break. I tried creating a test ComponentA and ComponentB with a render function that returns null, but using a union of typeof ComponentA | typeof ComponentB compiles successfully for some reason.

[rhys-vdw]

This may explain this one: #28768 (comment)

[weswigham]

Thanks for the link @rhys-vdw - that is indeed the case.

[weswigham]

I'm going to mark this as a duplicate of #7294 - go chime in how important that is there, thanks~

[bytenik]

@weswigham I'm not sure how it can be the same problem. #7294 has been an issue since 2016, whereas the issue I'm describing only began with 3.2+.

[weswigham]

With 3.2 we merged jsx resolution and normal call resolution. (Previously they were separate but similar) To deal with unions, jsx call resolution was doing some unsafe operations that could poison some caches with invalid types and had been the source of a fair set of other bugs in the jsx implementation, especially surrounding generics.

We do intend to fix it - I'm just saying we already have a more general issue tracking the problem, since the problem extends beyond jsx tags to all kinds of calls.

[typescript-bot]

This issue has been marked as a duplicate and has seen no activity in the last day. It has been closed automatic house-keeping purposes.

[bytenik]

@weswigham This issue persists in 3.3.0-rc. Is this still a dupe of #7294? That one is closed and supposed to be fixed in 3.3.

[weswigham]

Do BrowserRouter and HashRouter both have overloads or generic arguments? We still can't resolve union calls on unions of multiple generic signatures.

[bytenik]

Yep, they both have generic arguments.

Would it be appropriate to reopen this issue then? Or is there another issue tracking this, or a workaround for now? Fingers crossed for a workaround for now at least because my team is pinned to 3.1.x until we can resolve it.

[gsbelarus]

Also waiting at least for work around, although there is always retreat to typecast.