Error when use spread arguments twice

[KSXGitHub]

TypeScript Version: 3.5.1

Search Terms:

Code

declare function fn (a: string, b: string, ...c: string[]): void
declare const foo: [string, string, ...string[]]
declare const bar: string[]
fn(...foo) // ok
fn(...foo, ...bar) // error
fn(...foo, ...foo) // error
fn(...bar, ...foo) // error

Expected behavior:

No errors

Actual behavior:

Expected at least 2 arguments, but got 1 or more

Playground Link: link

Related Issues:

[sandersn]

@elibarzilay I think your tuple PR recently fixed this bug. Can you confirm?

[elibarzilay]

#33069 is fixing one aspect of this issue, but there is an additional issue with typechecking the arguments. An example of this:

declare function s2n_ (a: string, b: string, ...c: number[]): void
declare const s2: [string, string]
declare const n_: number[]
s2n_(...s2, ...n_);

fails with

error TS2345: Argument of type 'number' is not assignable to parameter of type 'string'.

which is bogus due to code that does not handle spreaded tuples properly. (A fix for that is probably in the loop which is around the middle of getSignatureApplicabilityError.)