Bug Report

This is a sequel to #41966.

🔎 Search Terms

keyof, key remapping, index signature, symbol, known keys

🕗 Version & Regression Information

• This is the behavior in every version I tried since key remapping was introduced in TS4.1

⏯ Playground Link

Playground link with relevant code

💻 Code

const sym = Symbol("")
type Orig = { [k: string]: any, str: any, [sym]: any }

type Okay = Exclude<keyof Orig, never>
// type Okay = string | number | typeof sym

type Remapped = { [K in keyof Orig as {} extends Record<K, any> ? never : K]: any }
/* type Remapped = {
    str: any;
    [sym]: any;
} */
// no string index signature, right?

type Oops = Exclude<keyof Remapped, never>
// type Oops = typeof sym <-- what happened to "str"?

🙁 Actual behavior

keyof Remapped is typeof sym.

🙂 Expected behavior

keyof Remapped should be typeof sym | "str" because Remapped is {str: any, [sym]: any}.

It looks like the bug reported in #41966 was fixed for most cases, but not when the object type being remapped has a symbol-valued key. Not sure why. I ran into this when answering this Stack Overflow question.