<===> input.scss
@function test() {
  @if (false) {
    @return 0;
  } @else {
    opacity: 1;
  }
}

.my-module {
  opacity: test();
}
<===> error
Error: Functions can only contain variable declarations and control directives.
        on line 5 of input.scss
  Use --trace for backtrace.

<===> error-dart-sass
Error: @function rules may not contain declarations.
  ,
5 |     opacity: 1;
  |     ^^^^^^^^^^
  '
  input.scss 5:5  root stylesheet