Computed string literal can't be used as generic argument

[Dzmitry Tolpekin]

🔎 Search Terms

"string literal is not assignable to parameter of type", "generic string literal argument"

🕗 Version & Regression Information

• This changed between versions 5.1.6 and 5.2.2

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/GYVwdgxgLglg9mABMMAeAKgPgBQEMBOA5gFyLoCUp6iA3gFCKOL4CmUI+SBhA3HQL506EBAGcoiXIgC8iAOQBGOXxFhxiAEYzJiANTzEAJmVCU2AAYASGhv6IAzOfI8gA

💻 Code

function fn<T>(arg: T): T {
    return arg;
}

const a = '1';
const b = a + ' 2';

fn(`${b} 3`);

🙁 Actual behavior

Argument of type '`${string} 3`' is not assignable to parameter of type '"1 2 3"'.

🙂 Expected behavior

No errors are expected

Additional information about the issue

No response

[Bruce Pascoe]

That’s bizarre - it’s inferring T = "1 2 3" from the argument, but then deciding the same argument isn’t assignable to the type it just inferred.

[Joe Calzaretta]

I... what?! Somehow TS is #44905 magically almost kind of happening? What gives?

const x = "w" + "t" + "f";
// const x: string
const y = `${x}` 
// const y: "wtf"

Playground link

Did #53907 do this somehow?

[Mateusz Burzyński]

The OP's repro is quite bizarre 😱

Did #53907 do this somehow?

That was meant to be my guess but - obviously - you are already one step ahead :D