<===> input.scss
@function not() {
  @return "not";
}

test {
  not: not();
}

<===> error
Error: Invalid function name "not".
        on line  of input.scss
  Use --trace for backtrace.

<===> error-dart-sass
Error: Invalid function name.
  ,
1 | @function not() {
  | ^^^^^^^^^^^^^^^
  '
  input.scss 1:1  root stylesheet