It's incorrect to resolve spread interpolation as intersect

[gomain]

🔎 Search Terms

object spread generic intersect

🕗 Version & Regression Information

• This is a crash:
• This changed between versions ______ and _______
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about: no mention in the FAQ
• I was unable to test this on prior versions because _______

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.3.0-dev.20231005#code/GYVwdgxgLglg9mABAWwIYGsCmB1APAeUUwA8pMwATAZ0QG9FUAuBsAT0QF8AaRAIQD4AFHGb4eqAEzNeiAJR0AUIkQAnTFBAqk9AHR6445pJ4cA3ArMKFEBFSiIA7ogC8KDDkH0mdRACNmAIwMNDZgdpzcPhDMEsGIoeEcsubWtnAANpg66XAA5oIOOqg6vi7OrgHJQA

💻 Code

function makeW<O extends { a: any }, B>(o: O, a2: B ) {
  return { ...o, a: a2, };
};

const w = makeW({ a: { b: 1 as const }}, { c: 2 as const });

console.log(w.a.b === 1);

🙁 Actual behavior

Return type of makeW is resolved/inferred as O & { a: B } which is wrong.

the returned value { ...o, a: a2 } overrides any o.a.

🙂 Expected behavior

type of w is Omit<O, "a"> & { a: B }.

Additional information about the issue

Explicit typing works, but should be needed.

function makeW<O extends { a: any }, B>(o: O, a2: B ): Omit<O, "a"> & { a: B } {
  return { ...o, a: a2 };
};

const w = makeW({ a: { b: 1 as const }}, { c: 2 as const });

console.log(w.a.b === 1); // type error, no `b`.

[RyanCavanaugh]

Duplicate #10727

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.