Issue with keyof passed to a generic with conditional types

[sharshuv-quotient]

EDIT: I wrote this completely wrong, please see comments

Bug Report

🔎 Search Terms

Issue with keyof passed to a generic with conditional types (Sorry can't think of a better description)

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

Playground link with relevant code

💻 Code

function f<G>(x: G): [G] extends [object] ? G : G {
  return x;
}

or:

function f<G>(x: G): G extends object ? G : G {
  return x;
}

🙁 Actual behavior

Fails with the following error:

Type 'G' is not assignable to type '[G] extends [object] ? G : G'

🙂 Expected behavior

G should be assignable to [G] extends [object] ? G : G.

Additional clues

Without condition it works

function f<G>(x: G): G {
  return x;
}

With condition that is always true it works:

function f<G>(x: G): [G] extends [any] ? G : G {
  return x;
}

With a condition that is always false it doesn't work:

function f<G>(x: G): [G] extends [never] ? G : G {
  return x;
}

[fatcerberus]

This is the behavior in every version I tried

Your playground is set to TS 3.5.1. Using 4.3.5 or higher makes the error go away, so this is apparently already fixed:

• https://www.typescriptlang.org/play?ts=4.5.3#code/GYVwdgxgLglg9mABMAjAHgOID4AUAPALkQwEoiBtDAXUQFM8pawATAZ0XIEMwBPGgfmKIiGRAG8AUIkQAnWlBAykeANwSAvhImhIsBMgBMmXIWJkO1OgyZsOYWgDdaMgUJHips+YuVrNQA

That being said, I have to question why someone would use a conditional type at all if they know in advance it will always take the same branch.

Also:

Issue with keyof passed to a generic with conditional types

There's no keyof in any of your examples.

[sharshuv-quotient]

This is embarrassing.
I was trying different versions to make sure that this wasn't a regression, then I found out I can simplify the minimal-reproduction even more. Apparently, with the latest version, this is the minimal reproduction of my original problem:
https://www.typescriptlang.org/play?#code/C4TwDgpgBAsiAq4IB4DiA+KBeKqoQA9gIA7AEwGcoBDEkKAflygC5cBuAKE4DMBXEgGNgASwD2JKDzToAFATYBrCCDE9cASjZxEkZMtXqMUAN6coUAE4RgfS5IJcAvpyA

type MyType<G> = [G] extends [object] ? G : G;

function f<G>(x: keyof G): MyType<keyof G> {
  return x;
}

I expect keyof G to be assianble to MyType<keyof G> as MyType is basically an identity type.
Should I create a new issue and close this one or edit this issue accordingly?

[typescript-bot]

This issue has been marked as 'Question' and has seen no recent activity. It has been automatically closed for house-keeping purposes. If you're still waiting on a response, questions are usually better suited to stackoverflow or the TypeScript Discord community.