Generated by SassMeister.com.

SassMeister-input.scss

// ----
// libsass (v3.3.2)
// ----

@function linear-gradient($parameters...) {
  $return: linear-gradient;
  @each $parameter in $parameters {
    $return: append($return,$parameter, comma);
  }
  @return $return;
}

@function reverse-gradient-direction($directions) {
  $dirs: '';
  @for $i from 1 through length($directions) {
    @if $i > 1 {
      $dirs: $dirs + ' ';
    }
    @if nth($directions, $i) == top {
      $dirs: $dirs + bottom;
    }
    @elseif nth($directions, $i) == bottom {
      $dirs: $dirs + top;
    }
    @elseif nth($directions, $i) == left {
      $dirs: $dirs + right;
    }
    @elseif nth($directions, $i) == right {
      $dirs: $dirs + left;
    }
  }
  @return unquote($dirs);
}

@mixin background-image($parameters) {
  @if nth($parameters,1) == linear-gradient {
    $prefixed-return: ();
    $standard-return: ();

    @if nth(nth($parameters, 2), 1) == to {
      $dirs: nth($parameters, 2);
      @for $i from 1 through length($dirs) {
        $prefixed-return: append($prefixed-return, reverse-gradient-direction(nth($dirs, $i)), comma);
        $standard-return: append($standard-return, nth($dirs, $i), comma);
      }
    }

    @else {
      $dirs: nth($parameters, 2);
      $i: length($dirs);
      @while $i > 0 {
        $prefixed-return: append($prefixed-return, nth($dirs, $i),  comma);
        $standard-return: append($standard-return, reverse-gradient-direction(nth($dirs, $i)), comma);
        $i: $i - 1;
      }
    }

    $temp-pref: $prefixed-return;
    $temp-stand: $standard-return;

    @if length($temp-pref) > 1 {
      $prefixed-return: '';
      $standard-return: '';
      @for $i from 1 through length($temp-pref) {
        @if $i > 1 {
          $prefixed-return: $prefixed-return + ' ';
          $standard-return: $standard-return + ' ';
        }
        $prefixed-return: $prefixed-return + nth($temp-pref, $i);
        $standard-return: $standard-return + nth($temp-stand, $i);
      }
      $prefixed-return: unquote($prefixed-return);
      $standard-return: unquote($standard-return);
    }

    @for $i from 3 through length($parameters) {
      $prefixed-return: append($prefixed-return, nth($parameters, $i), comma);
      $standard-return: append($standard-return, nth($parameters, $i), comma);
    }
    background-image: unquote('-webkit-linear-gradient(' + $prefixed-return + ')');
    background-image: unquote('-ms-linear-gradient(' + $prefixed-return + ')');
    background-image: unquote('linear-gradient(' + $standard-return + ')');
  }
}

div {
  @include background-image(linear-gradient(top, white, black));
}

div {
  @include background-image(linear-gradient(to bottom, white, black));
}

SassMeister-output.css

div {
  background-image: -webkit-linear-gradient(top, white, black);
  background-image: -ms-linear-gradient(top, white, black);
  background-image: linear-gradient(bottom, white, black);
}

div {
  background-image: -webkit-linear-gradient( top, white, black);
  background-image: -ms-linear-gradient( top, white, black);
  background-image: linear-gradient(to bottom, white, black);
}