<===> input.scss
$bar: true;

@mixin mixin() {
    mix: in;
}

@mixin include() {
    @content;
}

p {
    @at-root {
        @if $bar {
            #if {
                height: 100px;
            }
        }
        @if (not $bar) {
        } @else if($bar) {
            #elseif {
                width: 100px;
            }
        }
        @if (not $bar) {
        } @else {
            #else {
                width: 100px;
            }
        }
        @for $i from 1 through 1 {
            #for {
                foo: bar#{$i};
            }
        }
        $i: 0;
        @while ($i == 0) {
            $i: $i + 1;
            #while {
                foo: bar#{$i};
            }
        }
        @each $i in (1) {
            #each {
                foo: bar#{$i};
            }
        }
        #inc {
            @include mixin();
            @include include() {
                inc: lude;
            }
        }
        @supports (display: flex) {
            a {display: flex}
        }
        @foo {
           bar: bat;
        }
    }
}
<===> output.css
#if {
  height: 100px;
}

#elseif {
  width: 100px;
}

#else {
  width: 100px;
}

#for {
  foo: bar1;
}

#while {
  foo: bar1;
}

#each {
  foo: bar1;
}

#inc {
  mix: in;
  inc: lude;
}

@supports (display: flex) {
  a {
    display: flex;
  }
}
@foo {
  bar: bat;
}