typescript version 7 complains about unused generic type even though version 6 does not

[sudo-barun]

🔎 Search Terms

"TS6196", "is declared but never used", "unused generic", "noUnusedParameters"

🕗 Version & Regression Information

• This changed between versions 6.0.3 and 7.0.2

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/C4TwDgpgBAShBmAeAKgPigXigbwFAEgA3AQwBsBXCALimQBpcBfXXecgOwGNgBLAe3ZROAJwjFgEOEnoBVKBAAeE9gBMAzlEJ8eK1AAoSFapu0qAlDSkpUAblYdu-QSLESraA2Uo1kF2Ams7Ni5eASFRcUkAj0NvWj93dDx8UWByYUFkoi8IBnxGO2ZcTgE1YChReABGTHDXKPg9MzsS9jU+UggAOlI+AHM9Sqrm4tLyyoAmWpdIq3ZyAFsAIwhhOhMdfRHW9s6e-sGECe2xioQAZmmItwD55dX9KvOTto7u3oHK57sgA

💻 Code

type Ref<T> = {
	value: T,
}

function createRef<T,U extends void>(value: void): Ref<T>;
function createRef<T>(value: T): Ref<T>;
function createRef<T>(value: T): Ref<T> {
	return {
		value,
	};
}

const ref1 = createRef();
console.log(ref1);
const ref2 = createRef<number, void>();
console.log(ref2);
const ref3 = createRef<number>(13);
console.log(ref3);

🙁 Actual behavior

The typescript compiler version 7 fails with following error message:

code.ts:5:22 - error TS6196: 'U' is declared but never used.

5 function createRef<T,U extends void>(value: void): Ref<T>;
                       ~~~~~~~~~~~~~~


Found 1 error in code.ts:5

The typescript compiler version 6 succeeds without any errors.

🙂 Expected behavior

The typescript compiler version 7 should behave exactly like version 6 i.e. not fail.

Additional information about the issue

This error only occurs with noUnusedParameters set to true.

[MartinJohns]

But.. it is unused. So it's actually a bugfix.

[jakebailey]

Yes, this is a bug that was noticed in the port.