Typescript unable to infer property type with utility type's index signature

[stockson]

Bug Report

🔎 Search Terms

Signature Index with Utility Types

🕗 Version & Regression Information

This happened with all versions I've tested including nightly

⏯ Playground Link

I don't have a playground link unfortunately, except my stackoverflow question:
https://stackoverflow.com/questions/67542115/typescript-compiler-failing-with-different-property-types-on-omit-and-index-sign/67542334

💻 Code

interface Obj {
foo: number
bar: string
baz: number
}
type Sub = Omit<Obj, "baz">

const obj: Obj = {foo: 1, bar: "abc", baz: 1}

function fn (key: K, val: Sub[K]) {
obj[key] = val
}

🙁 Actual behavior

Typescript should(?) have inferred the data type like it did without the utility type, but is requiring that data types be uniform on the utility type.

🙂 Expected behavior

The compiler to still be able to compute the data type

[whzx5byb]

See #31694 (comment)

[MartinJohns]

I don't have a playground link unfortunately

1. Go to the playground: https://www.typescriptlang.org/play
2. Insert your code.
3. Click on "Share".
4. Paste the URL that has been copied to your clipboard here.

[stockson]

Just realized the angle brackets disappeared. Does that mean I can inject HTML? That's interesting.

Here's the playground link:
https://www.typescriptlang.org/play?#code/JYOwLgpgTgZghgYwgAgPICMBWyDeBYAKGWRgHtSAuZEAVwFt1pDj04oqBnMKUAc2eSsAXlVoMmBAL6EwATwAOKAMo10yALxo6wMAB4MmADTIARMJMA+QoQA2EMMlJYqBjbjKVkARmOt2puHQEE184EW9pAkIYGhAEMGBSEBJk3QBpZAgAD0gQABMOZABrCFlSGGQVdAsAChLZKjTjADc4GyoqgG00gF0ASlwBJ0xO+p63VptCSSA

[IllusionMH]

Looks like duplicate of #33014

[RyanCavanaugh]

This is the intended behavior, because this is a legal call to your function:

fn(Math.random() > 0.5 ? "foo" : "bar", 42);