top hlines attach to the top of row groups

crates/typst-library/src/layout/grid/resolve.rs

@@ -1101,6 +1101,14 @@ impl<'x> CellGridResolver<'_, '_, 'x> {
         // a non-empty row.
         let mut first_available_row = 0;
 
+        // Indices of hlines at the top of the row group.
+        //
+        // These hlines were auto-positioned and appeared before any auto-pos
+        // cells, so they will appear at the first possible row (above the
+        // first row spanned by the row group).
+        let mut top_hlines_start = 0;
+        let mut top_hlines_end = None;
+
         let (header_footer_items, simple_item) = match child {
             ResolvableGridChild::Header { repeat, span, items, .. } => {
                 if header.is_some() {
@@ -1115,6 +1123,15 @@ impl<'x> CellGridResolver<'_, '_, 'x> {
                 first_available_row =
                     find_next_empty_row(resolved_cells, local_auto_index, columns);
 
+                // No hlines yet, so 'end' starts as 'None'. However, its
+                // starting bound indicates where any potential top hlines
+                // would start (they would appear after the latest hline placed
+                // in previous iterations), so we only extend the end bound as
+                // necessary once more hlines are added, until we reach the
+                // first auto-positioned cell. Then, further auto-pos hlines
+                // will NOT be at the top.
+                top_hlines_start = pending_hlines.len();
+
                 // If any cell in the header is automatically positioned,
                 // have it skip to the next empty row. This is to avoid
                 // having a header after a partially filled row just add
@@ -1141,6 +1158,8 @@ impl<'x> CellGridResolver<'_, '_, 'x> {
                 first_available_row =
                     find_next_empty_row(resolved_cells, local_auto_index, columns);
 
+                top_hlines_start = pending_hlines.len();
+
                 local_auto_index = first_available_row * columns;
 
                 (Some(items), None)
@@ -1316,6 +1335,14 @@ impl<'x> CellGridResolver<'_, '_, 'x> {
                     )
                     .at(cell_span)?,
                 );
+
+                if top_hlines_end.is_none()
+                    && local_auto_index > first_available_row * columns
+                {
+                    // Auto index was moved, so upcoming auto-pos hlines should
+                    // no longer appear at the top.
+                    top_hlines_end = Some(pending_hlines.len());
+                }
             }
 
             // Let's resolve the cell so it can determine its own fields
@@ -1428,6 +1455,19 @@ impl<'x> CellGridResolver<'_, '_, 'x> {
                 }
             };
 
+            let top_hlines_end = top_hlines_end.unwrap_or(pending_hlines.len());
+            for (_, top_hline, has_auto_y) in pending_hlines
+                .get_mut(top_hlines_start..top_hlines_end)
+                .unwrap_or(&mut [])
+            {
+                if *has_auto_y {
+                    // Move this hline to the top of the child, as it was
+                    // placed before the first automatically positioned cell
+                    // and had an automatic index.
+                    top_hline.index = group_range.start;
+                }
+            }
+
             match row_group.kind {
                 RowGroupKind::Header => {
                     if group_range.start != 0 {

tests/suite/layout/grid/footers.typ

@@ -437,6 +437,38 @@
   )
 )
 
+--- grid-footer-top-hlines-with-only-row-pos-cell ---
+// Top hlines should attach to the top of the footer.
+#set page(margin: 2pt)
+#set text(6pt)
+#table(
+  columns: 3,
+  inset: 2.5pt,
+  table.footer(
+    table.hline(stroke: red),
+    table.vline(stroke: blue),
+    table.cell(x: 2, y: 2)[a],
+    table.hline(stroke: 3pt),
+    table.vline(stroke: 3pt),
+  )
+)
+
+--- grid-footer-top-hlines-with-row-and-auto-pos-cell ---
+#set page(margin: 2pt)
+#set text(6pt)
+#table(
+  columns: 3,
+  inset: 2.5pt,
+  table.footer(
+    table.hline(stroke: red),
+    table.vline(stroke: blue),
+    table.cell(x: 2, y: 2)[a],
+    [b],
+    table.hline(stroke: 3pt),
+    table.vline(stroke: 3pt),
+  )
+)
+
 --- grid-footer-below-rowspans ---
 // Footer should go below the rowspans.
 #set page(margin: 2pt)