Bootstrap/scss/mixins/_utilities.scss

// Utility generator
// Used to generate utilities & print utilities
@mixin generate-utility($utility, $infix: "", $is-rfs-media-query: false) {
  $values: map-get($utility, values);

  // If the values are a list or string, convert it into a map
  @if type-of($values) == "string" or type-of(nth($values, 1)) != "list" {
    $values: zip($values, $values);
  }

  @each $key, $value in $values {
    $properties: map-get($utility, property);

    // Multiple properties are possible, for example with vertical or horizontal margins or paddings
    @if type-of($properties) == "string" {
      $properties: append((), $properties);
    }

    // Use custom class if present
    $property-class: if(map-has-key($utility, class), map-get($utility, class), nth($properties, 1));
    $property-class: if($property-class == null, "", $property-class);

    // Use custom CSS variable name if present, otherwise default to `class`
    $css-variable-name: if(map-has-key($utility, css-variable-name), map-get($utility, css-variable-name), map-get($utility, class));

    // State params to generate pseudo-classes
    $state: if(map-has-key($utility, state), map-get($utility, state), ());

    $infix: if($property-class == "" and str-slice($infix, 1, 1) == "-", str-slice($infix, 2), $infix);

    // Don't prefix if value key is null (e.g. with shadow class)
    $property-class-modifier: if($key, if($property-class == "" and $infix == "", "", "-") + $key, "");

    @if map-get($utility, rfs) {
      // Inside the media query
      @if $is-rfs-media-query {
        $val: rfs-value($value);

        // Do not render anything if fluid and non fluid values are the same
        $value: if($val == rfs-fluid-value($value), null, $val);
      }
      @else {
        $value: rfs-fluid-value($value);
      }
    }

    $is-css-var: map-get($utility, css-var);
    $is-local-vars: map-get($utility, local-vars);
    $is-rtl: map-get($utility, rtl);

    @if $value != null {
      @if $is-rtl == false {
        /* rtl:begin:remove */
      }

      @if $is-css-var {
        .#{$property-class + $infix + $property-class-modifier} {
          --#{$prefix}#{$css-variable-name}: #{$value};
        }

        @each $pseudo in $state {
          .#{$property-class + $infix + $property-class-modifier}-#{$pseudo}:#{$pseudo} {
            --#{$prefix}#{$css-variable-name}: #{$value};
          }
        }
      } @else {
        .#{$property-class + $infix + $property-class-modifier} {
          @each $property in $properties {
            @if $is-local-vars {
              @each $local-var, $variable in $is-local-vars {
                --#{$prefix}#{$local-var}: #{$variable};
              }
            }
            #{$property}: $value if($enable-important-utilities, !important, null);
          }
        }

        @each $pseudo in $state {
          .#{$property-class + $infix + $property-class-modifier}-#{$pseudo}:#{$pseudo} {
            @each $property in $properties {
              @if $is-local-vars {
                @each $local-var, $variable in $is-local-vars {
                  --#{$prefix}#{$local-var}: #{$variable};
                }
              }
              #{$property}: $value if($enable-important-utilities, !important, null);
            }
          }
        }
      }

      @if $is-rtl == false {
        /* rtl:end:remove */
      }
    }
  }
}


//
// Helper functions and mixins for manipulating the utilities map
//

// Gets the map of options for a given utility
@function utilities-get-options($utility-name) {
  @return map-get($utilities, $utility-name);
}

// Gets the value of a specific option for a given utility
@function utilities-get-option($utility-name, $option-name) {
  $options: utilities-get-options($utility-name);

  @if ($options) {
    @return map-get(
      $options,
      $option-name
    );
  }

  @return null;
}

// Returns a map of the values for the utility
@function utilities-get-values($utility-name) {
  $values: utilities-get-option($utility-name, values);

  @if (type-of($values) != map) {
    @return map-from($values);
  }

  @return $values;
}

@function map-from($list-or-string) {
  $map: ();

  @each $item in $list-or-string {
    $map: map-merge(
      $map,
      ($item: $item)
    );
  }

  @return $map;
}

// Gets a specific value for the given utility
@function utilities-get-value($utility-name, $value-name) {
  $values: utilities-get-values($utility-name);

  @return map-get(
    $values,
    $value-name
  );
}

// Set options for a given utility, merged with the existing ones by default.
// To completely replace the existing options, set the 3rd `$merge` parameter to false
@mixin utilities-set-options($utility-name, $options, $merge: true) {
  @if ($merge) {
    $existing-options: utilities-get-options($utility-name);

    // Allow the mixin to create a new utility when setting an unknown utility name
    $options: if(
      $existing-options,
      map-merge(
        utilities-get-options($utility-name),
        $options
      ),
      $options
    );
  }

  $utilities: map-merge(
    $utilities,
    ($utility-name: $options)
  ) !global; // !global ensures we modify the global $utilities map
}

// Set a specific option to a new value for the given utility
@mixin utilities-set-option($utility-name, $option-name, $value) {
  @include utilities-set-options($utility-name, ($option-name: $value));
}

// Add new values to a given utility
//
// If you want to completely reconfigure the values use `utilities-set-option` to provide a new map for the `values` option
@mixin utilities-add-values($utility-name, $values) {
  $existing-values: utilities-get-values($utility-name);

  @include utilities-set-option(
    $utility-name,
    values,
    map-merge(
      $existing-values,
      $values
    )
  );
}

// Remove specific values from a given utility
@mixin utilities-remove-values($utility-name, $value-names...) {
  $values: utilities-get-values($utility-name);

  $updated-values: map-remove($values, $value-names...);

  @include utilities-set-option($utility-name, values, $updated-values);
}

// Add a new utility to the utilities map
@mixin utilities-add($utility-name, $utility) {
  $utilities: map-merge(
    $utilities,
    ($utility-name: $utility)
  ) !global;
}

// Remove a utility from the utilities map
@mixin utilities-remove($utility-names...) {
  $utilities: map-remove($utilities, $utility-names...) !global;
}