TS 3.4: Error when passing dynamically imported generic type as a function argument

TypeScript Version: 3.4.0-dev.201xxxxx

Search Terms: TS2322, dynamic import, dynamic import never, dynamic import generic

Code

 .\node_modules\.bin\tsc --jsx react --lib es2017 --strict index.tsx

// ===== page.tsx ======
import * as React from 'react'

export interface PageProps {
    title: string
}

export class Page extends React.Component<PageProps> {
    render() {
        return <div>{this.props.title}</div>
    }
}

// ===== index.tsx =====
import * as React from 'react'
import{ PageProps, Page } from './page'

export function myFunction<TProps>(loader: () => Promise<React.ComponentType<TProps>>) {

}

// No error
myFunction(() => Promise.resolve(Page))

// No error
const loader: () => Promise<React.ComponentType<PageProps>> = () => import('./page').then(m => m.Page)

// Error
myFunction(() => import('./page').then(m => m.Page))

Expected behavior:

No compile error. This was the behavior in TS 3.3 and earlier.

Actual behavior:

There is an error after upgrading to TS 3.4:

index.tsx:14:18 - error TS2322: Type 'Promise<typeof Page | ComponentClass<never, any> | FunctionComponen
t<never>>' is not assignable to type 'Promise<ComponentType<PageProps>>'.
  Type 'typeof Page | ComponentClass<never, any> | FunctionComponent<never>' is not assignable to type 'C
omponentType<PageProps>'.
    Type 'ComponentClass<never, any>' is not assignable to type 'ComponentType<PageProps>'.
      Type 'ComponentClass<never, any>' is not assignable to type 'ComponentClass<PageProps, any>'.
        Type 'PageProps' is not assignable to type 'never'.

14 myFunction(() => import('./page').then(m => m.Page))
                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  index.tsx:4:44
    4 export function myFunction<TProps>(loader: () => Promise<React.ComponentType<TProps>>) {
                                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    The expected type comes from the return type of this signature.

Repro here: https://github.com/srmagura/ts-import-repro

Reproduisez l’erreur avec la commande tsc sur index.tsx et page.tsx, en utilisant l’import dynamique et la fonction générique présentés dans l’issue. Comparez le comportement avec TypeScript 3.3 et 3.4, puis suivez l’inférence générique pour le type de retour Promise<ComponentType>. La tâche est terminée lorsque l’appel signalé compile sans l’erreur TS2322, tandis que les exemples existants continuent de fonctionner correctement.