<===> input.scss
@function foo($x, $y) { @return null }

a {
  b: foo(1 2 3...);
}
<===> error-dart-sass
Error: Only 2 arguments allowed, but 3 were passed.
    ,
1   | @function foo($x, $y) { @return null }
    |           =========== declaration
... |
4   |   b: foo(1 2 3...);
    |      ^^^^^^^^^^^^^ invocation
    '
  input.scss 4:6  foo()
  input.scss 4:6  root stylesheet

<===> output.css
<===> warning
WARNING: Function foo takes 2 arguments but 3 were passed.
        on line 4 of input.scss
This will be an error in future versions of Sass.