TS4082 occurs when using `composite: true`

Bug Report

🔎 Search Terms

TS4082, composite

🕗 Version & Regression Information

• I was unable to test this on prior versions because composite is a new feature added to typescript (not actually)

⏯ Playground Link

Playground link with relevant code

💻 Code

// This throws
export default (
	a = () => {
		interface Props {}
		return {} as Props
	},
) => {};

// This works
let a = () => {
	interface Props {}
	return {} as Props
}

🙁 Actual behavior

When composite is enabled, the export default statement throws TS4082. And disabling composite fixes this issue.

🙂 Expected behavior

They should both throw, or both not throw :(

This issue only occurs when using an interface. Using a type alias won't cause this issue.

Start by running the linked TypeScript Playground reproduction with composite enabled, then compare the exported and local callbacks and the interface and type-alias cases. Trace the compiler path that reports TS4082 and add a regression test; done means the two equivalent callback forms have consistent behavior without regressing the existing type-alias case.