Add support for negative augment indexes (#2372)

3 files changed, 26 insertions, 15 deletions

diff --git a/crates/typst-library/src/math/matrix.rs b/crates/typst-library/src/math/matrix.rs
index 91310ed3..333a5706 100644
--- a/crates/typst-library/src/math/matrix.rs
+++ b/crates/typst-library/src/math/matrix.rs
@@ -97,7 +97,7 @@ pub struct MatElem {
     ///
     /// - `{none}`: No lines are drawn.
     /// - A single number: A vertical augmentation line is drawn
-    ///   after the specified column number.
+    ///   after the specified column number. Negative numbers start from the end.
     /// - A dictionary: With a dictionary, multiple augmentation lines can be
     ///   drawn both horizontally and vertically. Additionally, the style of the
     ///   lines can be set. The dictionary can contain the following keys:
@@ -105,17 +105,19 @@ pub struct MatElem {
     ///     For example, an offset of `2` would result in a horizontal line
     ///     being drawn after the second row of the matrix. Accepts either an
     ///     integer for a single line, or an array of integers
-    ///     for multiple lines.
+    ///     for multiple lines. Like for a single number, negative numbers start from the end.
     ///   - `vline`: The offsets at which vertical lines should be drawn.
     ///     For example, an offset of `2` would result in a vertical line being
     ///     drawn after the second column of the matrix. Accepts either an
     ///     integer for a single line, or an array of integers
-    ///     for multiple lines.
+    ///     for multiple lines. Like for a single number, negative numbers start from the end.
     ///   - `stroke`: How to [stroke]($stroke) the line. If set to `{auto}`,
     ///     takes on a thickness of 0.05em and square line caps.
     ///
     /// ```example
     /// $ mat(1, 0, 1; 0, 1, 2; augment: #2) $
+    /// // Equivalent to:
+    /// $ mat(1, 0, 1; 0, 1, 2; augment: #(-1)) $
     /// ```
     ///
     /// ```example
@@ -200,15 +202,16 @@ impl LayoutMath for MatElem {
         // validate inputs
 
         let augment = self.augment(ctx.styles());
+        let rows = self.rows();
 
         if let Some(aug) = &augment {
             for &offset in &aug.hline.0 {
-                if offset == 0 || offset >= self.rows().len() {
+                if offset == 0 || offset.unsigned_abs() >= rows.len() {
                     bail!(
                         self.span(),
                         "cannot draw a horizontal line after row {} of a matrix with {} rows",
-                        offset,
-                        self.rows().len()
+                        if offset < 0 { rows.len() as isize + offset } else { offset },
+                        rows.len()
                     );
                 }
             }
@@ -216,11 +219,11 @@ impl LayoutMath for MatElem {
             let ncols = self.rows().first().map_or(0, |row| row.len());
 
             for &offset in &aug.vline.0 {
-                if offset == 0 || offset >= ncols {
+                if offset == 0 || offset.unsigned_abs() >= ncols {
                     bail!(
                         self.span(),
                         "cannot draw a vertical line after column {} of a matrix with {} columns",
-                        offset,
+                        if offset < 0 { ncols as isize + offset } else { offset },
                         ncols
                     );
                 }
@@ -230,7 +233,7 @@ impl LayoutMath for MatElem {
         let delim = self.delim(ctx.styles());
         let frame = layout_mat_body(
             ctx,
-            &self.rows(),
+            &rows,
             augment,
             Axes::new(self.column_gap(ctx.styles()), self.row_gap(ctx.styles())),
             self.span(),
@@ -472,7 +475,9 @@ fn layout_mat_body(
         x += rcol;
 
         // If a vertical line should be inserted after this column
-        if vline.0.contains(&(index + 1)) {
+        if vline.0.contains(&(index as isize + 1))
+            || vline.0.contains(&(1 - ((ncols - index) as isize)))
+        {
             frame.push(
                 Point::with_x(x + half_gap.x),
                 line_item(total_height, true, stroke.clone(), span),
@@ -488,8 +493,10 @@ fn layout_mat_body(
 
     // This allows the horizontal lines to be laid out
     for line in hline.0 {
-        let offset = (heights[0..line].iter().map(|&(a, b)| a + b).sum::<Abs>()
-            + gap.y * (line - 1) as f64)
+        let real_line =
+            if line < 0 { nrows - line.unsigned_abs() } else { line as usize };
+        let offset = (heights[0..real_line].iter().map(|&(a, b)| a + b).sum::<Abs>()
+            + gap.y * (real_line - 1) as f64)
             + half_gap.y;
 
         frame.push(
@@ -605,7 +612,7 @@ cast! {
 
         d.into_value()
     },
-    v: usize => Augment {
+    v: isize => Augment {
         hline: Offsets::default(),
         vline: Offsets(vec![v]),
         stroke: Smart::Auto,
@@ -632,11 +639,11 @@ cast! {
 /// The offsets at which augmentation lines
 /// should be drawn on a matrix.
 #[derive(Debug, Default, Clone, Hash)]
-pub struct Offsets(Vec<usize>);
+pub struct Offsets(Vec<isize>);
 
 cast! {
     Offsets,
     self => self.0.into_value(),
-    v: usize => Self(vec![v]),
+    v: isize => Self(vec![v]),
     v: Array => Self(v.into_iter().map(Value::cast).collect::<StrResult<_>>()?),
 }
diff --git a/tests/ref/math/matrix.png b/tests/ref/math/matrix.png
index 530c2b5a..32181c69 100644
--- a/tests/ref/math/matrix.png
+++ b/tests/ref/math/matrix.png
diff --git a/tests/typ/math/matrix.typ b/tests/typ/math/matrix.typ
index efcde1eb..57ecd85f 100644
--- a/tests/typ/math/matrix.typ
+++ b/tests/typ/math/matrix.typ
@@ -72,9 +72,13 @@ $ mat(#1, #(foo: "bar")) $
   gutter: 10pt,
 
   $ mat(10, 2, 3, 4; 5, 6, 7, 8; augment: #3) $,
+  $ mat(10, 2, 3, 4; 5, 6, 7, 8; augment: #(-1)) $,
   $ mat(100, 2, 3; 4, 5, 6; 7, 8, 9; augment: #(hline: 2)) $,
+  $ mat(100, 2, 3; 4, 5, 6; 7, 8, 9; augment: #(hline: -1)) $,
   $ mat(100, 2, 3; 4, 5, 6; 7, 8, 9; augment: #(hline: 1, vline: 1)) $,
+  $ mat(100, 2, 3; 4, 5, 6; 7, 8, 9; augment: #(hline: -2, vline: -2)) $,
   $ mat(100, 2, 3; 4, 5, 6; 7, 8, 9; augment: #(vline: 2, stroke: 1pt + blue)) $,
+  $ mat(100, 2, 3; 4, 5, 6; 7, 8, 9; augment: #(vline: -1, stroke: 1pt + blue)) $,
 )
 
 ---