Add reversed numbering (#5563)

crates/typst-layout/src/lists.rs

@@ -74,6 +74,7 @@ pub fn layout_enum(
     regions: Regions,
 ) -> SourceResult<Fragment> {
     let numbering = elem.numbering(styles);
+    let reversed = elem.reversed(styles);
     let indent = elem.indent(styles);
     let body_indent = elem.body_indent(styles);
     let gutter = elem.spacing(styles).unwrap_or_else(|| {
@@ -86,7 +87,9 @@ pub fn layout_enum(
 
     let mut cells = vec![];
     let mut locator = locator.split();
-    let mut number = elem.start(styles);
+    let mut number =
+        elem.start(styles)
+            .unwrap_or_else(|| if reversed { elem.children.len() } else { 1 });
     let mut parents = EnumElem::parents_in(styles);
 
     let full = elem.full(styles);
@@ -127,7 +130,8 @@ pub fn layout_enum(
             item.body.clone().styled(EnumElem::set_parents(smallvec![number])),
             locator.next(&item.body.span()),
         ));
-        number = number.saturating_add(1);
+        number =
+            if reversed { number.saturating_sub(1) } else { number.saturating_add(1) };
     }
 
     let grid = CellGrid::new(

crates/typst-library/src/model/enum.rs

@@ -9,7 +9,7 @@ use crate::foundations::{
     cast, elem, scope, Array, Content, NativeElement, Packed, Show, Smart, StyleChain,
     Styles, TargetElem,
 };
-use crate::html::{attr, tag, HtmlElem};
+use crate::html::{attr, tag, HtmlAttr, HtmlElem};
 use crate::layout::{Alignment, BlockElem, Em, HAlignment, Length, VAlignment, VElem};
 use crate::model::{ListItemLike, ListLike, Numbering, NumberingPattern, ParElem};
 
@@ -127,8 +127,7 @@ pub struct EnumElem {
     ///   [Ahead],
     /// )
     /// ```
-    #[default(1)]
-    pub start: usize,
+    pub start: Smart<usize>,
 
     /// Whether to display the full numbering, including the numbers of
     /// all parent enumerations.
@@ -144,6 +143,17 @@ pub struct EnumElem {
     #[default(false)]
     pub full: bool,
 
+    /// Whether to reverse the numbering for this enumeration.
+    ///
+    /// ```example
+    /// #set enum(reversed: true)
+    /// + Coffee
+    /// + Tea
+    /// + Milk
+    /// ```
+    #[default(false)]
+    pub reversed: bool,
+
     /// The indentation of each item.
     #[resolve]
     pub indent: Length,
@@ -217,7 +227,12 @@ impl EnumElem {
 impl Show for Packed<EnumElem> {
     fn show(&self, engine: &mut Engine, styles: StyleChain) -> SourceResult<Content> {
         if TargetElem::target_in(styles).is_html() {
-            return Ok(HtmlElem::new(tag::ol)
+            let mut elem = HtmlElem::new(tag::ol);
+            if self.reversed(styles) {
+                elem =
+                    elem.with_attr(const { HtmlAttr::constant("reversed") }, "reversed");
+            }
+            return Ok(elem
                 .with_body(Some(Content::sequence(self.children.iter().map(|item| {
                     let mut li = HtmlElem::new(tag::li);
                     if let Some(nr) = item.number(styles) {

tests/suite/model/enum.typ

@@ -71,6 +71,23 @@ a + 0.
 + First
   + Nested
 
+--- enum-numbering-reversed ---
+// Test reverse numbering.
+#set enum(reversed: true)
++ Coffee
++ Tea
++ Milk
+
+--- enum-numbering-reversed-overriden ---
+// Test reverse numbering with overriden numbers.
+#set enum(reversed: true)
++ A
++ B
++ C
+9. D
++ E
++ F
+
 --- enum-numbering-closure ---
 // Test numbering with closure.
 #enum(