Ensure we unwrap custom .then() (#4547)

Author: JoviDeCroock

compat/src/suspense.d.ts

@@ -3,7 +3,9 @@ import { Component, ComponentChild, ComponentChildren } from '../../src';
 //
 // Suspense/lazy
 // -----------------------------------
-export function lazy<T>(loader: () => Promise<{ default: T } | T>): T;
+export function lazy<T>(
+	loader: () => Promise<{ default: T } | T>
+): T extends { default: infer U } ? U : T;
 
 export interface SuspenseProps {
 	children?: ComponentChildren;

compat/test/ts/suspense.tsx

@@ -50,3 +50,18 @@ function ReactSuspenseListTester(_props: any) {
 		</React.SuspenseList>
 	);
 }
+
+const Comp = () => <p>Hello world</p>;
+
+const importComponent = async () => {
+	return { MyComponent: Comp };
+};
+
+const Lazy = React.lazy(() =>
+	importComponent().then(mod => ({ default: mod.MyComponent }))
+);
+
+// eslint-disable-next-line
+function App() {
+	return <Lazy />;
+}