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

Riproduci la discrepanza nel TypeScript Playground collegato usando gli esempi forniti distill, requiredKeyOf e requiredDeclared. Traccia come viene ridotto il tipo Mapped/Intersection calcolato e come requiredKeyOf lo valuta; il lavoro è completato quando requiredDistilledKey viene inferito come never, in corrispondenza di requiredDeclaredKey.