Passing spreading array to function parameters should raise an error

[zanminkian]

🔎 Search Terms

spreading array function parameter

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about spreading array in function parameters.

⏯ Playground Link

No response

💻 Code

function foo(args?: string): unknown {
  return args;
}
declare const arr: string[];

foo(...arr);

🙁 Actual behavior

No compilation error.

🙂 Expected behavior

TS compilation error when calling foo(...arr)

Additional information about the issue

One

function foo(): unknown
function foo(args: string): unknown
function foo(args?: string): unknown {
  return args;
}
declare const arr: string[];

foo(...arr); // ts compilation error here as expected 🤔️

Two

Background

function getNames() {
  return ['foo', 'bar', 'foo'];
}

const uniqueNames = [...new Set(...getNames())]; // I mistakenly spreading the `getNames()`
console.log(uniqueNames) // [ 'f', 'o' ]

Once I've wrote code above. What I expect is [ 'foo', 'bar' ]. It's really hard to find out the problem in long-line codes, if TS not reports it in compilation time.

[MartinJohns]

This is working as intended. See #48575 (comment):

The behavior we actually work hard to exhibit here is that a spread is valid if all its possible arities result in valid calls, [...]

I think your additional "One" does not work because overloads are not supported for this case.
And the "Two" version works unfortunately due to #52060 / #9726.

[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.