<===> input.scss
@function test($from, $to) {
    @warn 'Starting loop';
    @for $i from $from through $to {
      @warn 'Step #{$i}' ;
    }
    @warn 'Finished loop';
    @return 100%;
}
body {
    width: test(0, 1);
    height: test(-1, 1);
}
<===> output.css
body {
  width: 100%;
  height: 100%;
}

<===> warning
WARNING: Starting loop
         on line 2 of input.scss

WARNING: Step 0
         on line 4 of input.scss

WARNING: Step 1
         on line 4 of input.scss

WARNING: Finished loop
         on line 6 of input.scss

WARNING: Starting loop
         on line 2 of input.scss

WARNING: Step -1
         on line 4 of input.scss

WARNING: Step 0
         on line 4 of input.scss

WARNING: Step 1
         on line 4 of input.scss

WARNING: Finished loop
         on line 6 of input.scss

<===> warning-dart-sass
WARNING: Starting loop
    input.scss 2:5    test()
    input.scss 10:12  root stylesheet

WARNING: Step 0
    input.scss 4:7    test()
    input.scss 10:12  root stylesheet

WARNING: Step 1
    input.scss 4:7    test()
    input.scss 10:12  root stylesheet

WARNING: Finished loop
    input.scss 6:5    test()
    input.scss 10:12  root stylesheet

WARNING: Starting loop
    input.scss 2:5    test()
    input.scss 11:13  root stylesheet

WARNING: Step -1
    input.scss 4:7    test()
    input.scss 11:13  root stylesheet

WARNING: Step 0
    input.scss 4:7    test()
    input.scss 11:13  root stylesheet

WARNING: Step 1
    input.scss 4:7    test()
    input.scss 11:13  root stylesheet

WARNING: Finished loop
    input.scss 6:5    test()
    input.scss 11:13  root stylesheet