Pick utility - error on excess values

[nitzcard]

Using Pick on a function argument and then giving it a defined variable with excess properties do not give error like if I write it inline.

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about

⏯ Playground Link

https://www.typescriptlang.org/play?ssl=22&ssc=1&pln=1&pc=1#code/FASwdgLgpgTgZgQwMZQAQEFUG9itQgBwIBsoAuVMAVwFsAjWAbl1ToTHYQuvqeAF9gwCAE8CaAAogkAaygATVAF5UU2QB50AGlQByNhw66AfM2BwqYJBBAB7MKiQALKLIAUCGAHMAzhTVy8gCU2ILAAPThqAC0sXHxCYlJySkJwEj2PhCoAG7K2KycHBQAjDqEJOSoJaj8zM6uMm5YhYZc1eVEpKW1IZGoAOq2MDI++GPg0GDyCuku7jkhqP0+TrZUxIpeIDlo7KiwMMOoxCBy+HS2uxFRqXf3D-FC-UMjYwgTkFDTsxlgWfh-NJAvkcHgKt09HRiAhdFoWMN2F4qgAOeFhFgsIA

💻 Code

interface A {
  apple: number;
  banana: number;
}

type Picked = Pick<A, 'banana'>;

function check(args: Picked) {}

// --------------------------------------------------
const v = { banana: 1, apple: 1 };
check({ banana: 1, apple: 1 }) // Works as intended
check(v)  // should give an error like above
// --------------------------------------------------

// Works as intended
const a: Picked = {
  apple: 'bla',
  orange: 8,
}

🙁 Actual behavior

check(v) do not raise an error

🙂 Expected behavior

check(v) should raise an error

Additional information about the issue

No response

[Andarist]

This is working as intended. Object types are not sealed in TypeScript and the excess property check is more like a lint rule than a strong type error. See the docs: https://www.typescriptlang.org/docs/handbook/2/objects.html#excess-property-checks

[nmain]

Pick<...> has no impact here and the results are exactly the same if you write:

type Picked = { banana: number };

[fatcerberus]

There’s a reason the error message specifies “Object literal can only specify known properties”; v is not an object literal. You’d need #12936 to enforce this across the board.

[typescript-bot]

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