TypeScript emits d.ts file that is invalid for complex mapped type.

🔎 Search Terms

d.ts emit type error

🕗 Version & Regression Information

This is a compile error when consuming a d.ts file emitting by the same version and configuration of TypeScript
This in 3.5.1, 4.0.5, 5.4.5 and 5.5.0-dev.20240528, but NOT in 3.3.3

⏯ Playground Link

https://www.typescriptlang.org/play/?module=1&ts=5.4.5&ssl=11&ssc=1&pln=1&pc=1#code/KYDwDg9gTgLgBAMwK4DsDGMCWEVwIYAmeYMAoikgLYA8AKuVXKDMCgQM5wBKwa0B1djCiYUAcwA0cISPEA+OQAoAUAEo4Ab2UBIGAE8wwOAAU8sAIxwAvJp3aA2sagRDsPXFFwA1sD0QEcPQUlAC6AFxwiupWcoEMlI7OrvohOgC+ANw6fChCiHgY0HoA8kjwNlHWsVra2lDAMEhQuIoADPicqF4oEADuuHic+ob++YVQJWVwAGQmZjDmqvbtg3BdPf0d3r6jQVQhlelZdQ1NuAgFMEWlMFlpykA

💻 Code

export function adaptEnum<TEnum extends Record<string, string>>(
) {
	type Part1 = {
		[Property in keyof TEnum]: () => TEnum[Property]
	};
	const factoryOut = () => {
		return (0 as unknown as typeof factoryOut & Part1)[0 as unknown as keyof TEnum]() 
	};
	return factoryOut;
}

🙁 Actual behavior

Emits:

export declare function adaptEnum<TEnum extends Record<string, string>>(): () => TEnum[string] | TEnum[number] | TEnum[symbol];

Which Errors:
Type 'number' cannot be used to index type 'TEnum'.(2536)

🙂 Expected behavior

I expect TypeScript to either error when trying to emit a d.ts file, or generate a valid d.ts file it can consume without error.

Additional information about the issue

This issue report is derived from minimizing the same code that produced https://github.com/microsoft/TypeScript/issues/56718 (which is now fixed) and is similar to that issue. The same workaround I have from that case still works, so this isn't blocking anything except removing that workaround.