Computed type key inference inconsistent with identical explicitly declared type

🔎 Search Terms

keyof required keys key evaluation reduce getReducedType

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://tsplay.dev/WKQkzN

💻 Code

type distilled = distill<{
	//   ^?
	foo: "default"
	bar?: number
}>

// incorrectly inferred as unknown
type requiredDistilledKey = requiredKeyOf<distilled>
//   ^?

// explicit declaration identical to hover of distilled
type declared = {
	bar?: number
} & {
	foo?: "default"
}

// now correctly inferred as never
type requiredDeclaredKey = requiredKeyOf<declared>
//   ^?

type requiredKeyOf<o> = {
	[k in keyof o]-?: o extends { [_ in k]-?: o[k] } ? k : never
}[keyof o]

type distill<t> = t extends object ? distillMappable<t> : t

type distillMappable<o> = {
	[k in keyof o as k extends inferredDefaultKeyOf<o> ? never : k]: distill<o[k]>
} & {
	[k in inferredDefaultKeyOf<o>]?: distill<o[k]>
}

type inferredDefaultKeyOf<o> = {
	[k in keyof o]: o[k] extends "default" ? k : never
}[keyof o]

🙁 Actual behavior

requiredDistilledKey inferred as unknown

🙂 Expected behavior

requiredDistilledKey inferred as never, consistent with the equivalent declared version

Additional information about the issue

No response

Reproduce the discrepancy in the linked TypeScript Playground using the provided distill, requiredKeyOf, and requiredDeclared examples. Trace how the computed mapped/intersection type is reduced and how requiredKeyOf evaluates it; done means requiredDistilledKey is inferred as never, matching requiredDeclaredKey.