lazy produces TypeScript error: JSX element type 'Component' does not have any construct or call signatures

[birtles]

• Check if updating to the latest Preact version resolves the issue (it does not -- 10.5.13 is fine, but 10.5.14 is broken for me)

Describe the bug

As of 10.5.14 code like the following:

const MyComponent = lazy(() =>
  import('./my-component').then((m) => {
    return {
      default: m.MyComponent,
    };
  })
);

may begin to error with: TS2604: JSX element type 'MyComponent' does not have any construct or call signatures

#3139 changed the type of lazy as follows:

- export function lazy<T>(loader: () => Promise<{ default: T }>): T;
+ export function lazy<T>(loader: () => Promise<{ default: T } | T>): T;

From what I can tell, in the above code fragment, TypeScript tries to infer the type of T by matching the return value of the function against the newly added T instead of { default: T } and hence resolves the return type of lazy as { default: React.FunctionComponent<Props> } not React.FunctionComponent<Props> as it previously did.

For the time being it seems possible to work around this by explicitly providing the generic type parameter such as follows:

import type { Props as MyComponentProps } from './my-component';

const MyComponent = lazy<React.FunctionComponent<MyComponentProps>>(() =>
  import('./my-component').then((m) => {
    return {
      default: m.MyComponent,
    };
  })
);

[JoviDeCroock]

This has been implemented in #3139

[birtles]

This has been implemented in #3139

Is that right? #3139 is the regressing issue, not the fix.

[JoviDeCroock]

You are completely right