_sass/vendor/bourbon/helpers/_render-gradients.scss

// User for linear and radial gradients within background-image or border-image properties

@function _render-gradients($gradient-positions, $gradients, $gradient-type, $vendor: false) {
  $pre-spec: null;
  $spec: null;
  $vendor-gradients: null;
  @if $gradient-type == linear {
    @if $gradient-positions {
      $pre-spec: nth($gradient-positions, 1);
      $spec:     nth($gradient-positions, 2);
    }
  }
  @else if $gradient-type == radial {
    $pre-spec: nth($gradient-positions, 1);
    $spec:     nth($gradient-positions, 2);
  }

  @if $vendor {
    $vendor-gradients: -#{$vendor}-#{$gradient-type}-gradient(#{$pre-spec} $gradients);
  }
  @else if $vendor == false {
    $vendor-gradients: "#{$gradient-type}-gradient(#{$spec} #{$gradients})";
    $vendor-gradients: unquote($vendor-gradients);
  }
  @return $vendor-gradients;
}