Small fixes for table line priority in headers/footers (#3602)

crates/typst/src/layout/grid/layout.rs

@@ -1731,21 +1731,44 @@ impl<'a> GridLayouter<'a> {
                     })
                     .unwrap_or(LinePosition::Before);
 
+                // FIXME: In the future, directly specify in 'self.rrows' when
+                // we place a repeated header rather than its original rows.
+                // That would let us remove most of those verbose checks, both
+                // in 'lines.rs' and here. Those checks also aren't fully
+                // accurate either, since they will also trigger when some rows
+                // have been removed between the header and what's below it.
+                let is_under_repeated_header = self
+                    .grid
+                    .header
+                    .as_ref()
+                    .and_then(Repeatable::as_repeated)
+                    .zip(prev_y)
+                    .is_some_and(|(header, prev_y)| {
+                        // Note: 'y == header.end' would mean we're right below
+                        // the NON-REPEATED header, so that case should return
+                        // false.
+                        prev_y < header.end && y > header.end
+                    });
+
                 // If some grid rows were omitted between the previous resolved
                 // row and the current one, we ensure lines below the previous
                 // row don't "disappear" and are considered, albeit with less
                 // priority. However, don't do this when we're below a header,
                 // as it must have more priority instead of less, so it is
-                // chained later instead of before.
+                // chained later instead of before. The exception is when the
+                // last row in the header is removed, in which case we append
+                // both the lines under the row above us and also (later) the
+                // lines under the header's (removed) last row.
                 let prev_lines = prev_y
                     .filter(|prev_y| {
                         prev_y + 1 != y
-                            && !self
-                                .grid
-                                .header
-                                .as_ref()
-                                .and_then(Repeatable::as_repeated)
-                                .is_some_and(|header| prev_y + 1 == header.end)
+                            && (!is_under_repeated_header
+                                || self
+                                    .grid
+                                    .header
+                                    .as_ref()
+                                    .and_then(Repeatable::as_repeated)
+                                    .is_some_and(|header| prev_y + 1 != header.end))
                     })
                     .map(|prev_y| get_hlines_at(prev_y + 1))
                     .unwrap_or(&[]);
@@ -1765,15 +1788,16 @@ impl<'a> GridLayouter<'a> {
                     &[]
                 };
 
-                // The header lines, if any, will correspond to the lines under
-                // the previous row, so they function similarly to 'prev_lines'.
-                let expected_header_line_position = expected_prev_line_position;
+                let mut expected_header_line_position = LinePosition::Before;
                 let header_hlines = if let Some((Repeatable::Repeated(header), prev_y)) =
                     self.grid.header.as_ref().zip(prev_y)
                 {
-                    if prev_y + 1 != y
-                        && prev_y + 1 == header.end
-                        && !self.grid.has_gutter
+                    if is_under_repeated_header
+                        && (!self.grid.has_gutter
+                            || matches!(
+                                self.grid.rows[prev_y],
+                                Sizing::Rel(length) if length.is_zero()
+                            ))
                     {
                         // For lines below a header, give priority to the
                         // lines originally below the header rather than
@@ -1783,10 +1807,18 @@ impl<'a> GridLayouter<'a> {
                         // lines being normally laid out then will be
                         // precisely the lines below the header.
                         //
-                        // Additionally, we don't append header lines when
-                        // gutter is enabled, since, in that case, there will
-                        // be a gutter row between header and content, so no
-                        // lines should overlap.
+                        // Additionally, we don't repeat lines above the row
+                        // below the header when gutter is enabled, since, in
+                        // that case, there will be a gutter row between header
+                        // and content, so no lines should overlap. The
+                        // exception is when the gutter at the end of the
+                        // header has a size of zero, which happens when only
+                        // column-gutter is specified, for example. In that
+                        // case, we still repeat the line under the gutter.
+                        expected_header_line_position = expected_line_position(
+                            header.end,
+                            header.end == self.grid.rows.len(),
+                        );
                         get_hlines_at(header.end)
                     } else {
                         &[]

crates/typst/src/layout/grid/lines.rs

@@ -547,7 +547,7 @@ pub(super) fn hline_stroke_at_column(
             // Ensure the row above us is a repeated header.
             // FIXME: Make this check more robust when headers at arbitrary
             // positions are added.
-            local_top_y + 1 == header.end && y != header.end
+            local_top_y < header.end && y > header.end
         });
 
     // Prioritize the footer's top stroke as well where applicable.
@@ -559,7 +559,7 @@ pub(super) fn hline_stroke_at_column(
             // Ensure the row below us is a repeated footer.
             // FIXME: Make this check more robust when footers at arbitrary
             // positions are added.
-            local_top_y.unwrap_or(0) + 1 != footer.start && y == footer.start
+            local_top_y.unwrap_or(0) + 1 < footer.start && y >= footer.start
         });
 
     let (prioritized_cell_stroke, deprioritized_cell_stroke) =

tests/typ/layout/grid-footers-5.typ

@@ -26,3 +26,16 @@
   gutter: 3pt,
   table.footer[a][b][c]
 )
+
+---
+// Test footer stroke priority edge case
+#set page(height: 10em)
+#table(
+  columns: 2,
+  stroke: black,
+  ..(table.cell(stroke: aqua)[d],) * 8,
+  table.footer(
+    table.cell(rowspan: 2, colspan: 2)[a],
+    [c], [d]
+  )
+)

tests/typ/layout/grid-headers-4.typ

@@ -56,3 +56,44 @@
   ),
   [a\ b]
 )
+
+---
+// Test header stroke priority edge case (last header row removed)
+#set page(height: 8em)
+#table(
+  columns: 2,
+  stroke: black,
+  gutter: (auto, 3pt),
+  table.header(
+    [c], [d],
+  ),
+  ..(table.cell(stroke: aqua)[d],) * 8,
+)
+
+---
+// Yellow line should be kept here
+#set text(6pt)
+#table(
+  column-gutter: 3pt,
+  inset: 1pt,
+  table.header(
+    [a],
+    table.hline(stroke: yellow),
+  ),
+  table.cell(rowspan: 2)[b]
+)
+
+---
+// Red line should be kept here
+#set page(height: 6em)
+#set text(6pt)
+#table(
+  column-gutter: 3pt,
+  inset: 1pt,
+  table.header(
+    table.hline(stroke: red, position: bottom),
+    [a],
+  ),
+  [a],
+  table.cell(stroke: aqua)[b]
+)