count header rows in each region

- Currently also includes non-repeatable header row heights, which will lead to bugs on rowspans; needs fix

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

@@ -46,8 +46,21 @@ pub struct GridLayouter<'a> {
     pub(super) rowspans: Vec<Rowspan>,
     /// The initial size of the current region before we started subtracting.
     pub(super) initial: Size,
+    /// The amount of header rows at the start of the current region. Note that
+    /// `repeating_headers` and `pending_headers` can change if we find a new
+    /// header inside the region, so this has to be stored separately for each
+    /// new region - we can't just reuse those.
+    ///
+    /// This is used for orphan prevention checks (if there are no rows other
+    /// than header rows upon finishing a region, we'd have an orphan). In
+    /// addition, this information is stored for each finished region so
+    /// rowspans placed later can know which rows to skip at the top of the
+    /// region when spanning more than one page.
+    pub(super) current_header_rows: usize,
     /// Frames for finished regions.
     pub(super) finished: Vec<Frame>,
+    /// The height of header rows on each finished region.
+    pub(super) finished_header_rows: Vec<Abs>,
     /// Whether this is an RTL grid.
     pub(super) is_rtl: bool,
     /// Currently repeating headers, one per level.
@@ -131,7 +144,9 @@ impl<'a> GridLayouter<'a> {
             unbreakable_rows_left: 0,
             rowspans: vec![],
             initial: regions.size,
+            current_header_rows: 0,
             finished: vec![],
+            finished_header_rows: vec![],
             is_rtl: TextElem::dir_in(styles) == Dir::RTL,
             repeating_headers: vec![],
             upcoming_headers: &grid.headers,
@@ -979,16 +994,8 @@ impl<'a> GridLayouter<'a> {
             let frame = self.layout_single_row(engine, disambiguator, first, y)?;
             self.push_row(frame, y, true);
 
-            if self
-                .grid
-                .header
-                .as_ref()
-                .and_then(Repeatable::as_repeated)
-                .is_some_and(|header| y < header.end)
-            {
+            if self.lrows.len() < self.current_header_rows {
                 // Add to header height, as we are in a header row.
-                // TODO: Should we only bump from upcoming_headers to
-                // repeating_headers AFTER the header height calculation?
                 self.header_height += first;
             }
 
@@ -1221,14 +1228,9 @@ impl<'a> GridLayouter<'a> {
         let resolved = v.resolve(self.styles).relative_to(self.regions.base().y);
         let frame = self.layout_single_row(engine, disambiguator, resolved, y)?;
 
-        if self
-            .grid
-            .header
-            .as_ref()
-            .and_then(Repeatable::as_repeated)
-            .is_some_and(|header| y < header.end)
-        {
-            // Add to header height.
+        if self.lrows.len() < self.current_header_rows {
+            // Add to header height (not all headers were laid out yet, so this
+            // must be a repeated or pending header at the top of the region).
             self.header_height += resolved;
         }
 
@@ -1389,20 +1391,20 @@ impl<'a> GridLayouter<'a> {
             self.lrows.pop().unwrap();
         }
 
-        let footer_would_be_widow = if let Some(last_header) = self
-            .pending_headers
-            .last()
-            .map(Repeatable::unwrap)
-            .or_else(|| self.repeating_headers.last().map(|h| *h))
+        let footer_would_be_widow = if let Some(last_header_row) = self
+            .current_header_rows
+            .checked_sub(1)
+            .and_then(|last_header_index| self.lrows.get(last_header_index))
         {
-            if self.grid.rows.len() > last_header.end
+            let last_header_end = last_header_row.index();
+            if self.grid.rows.len() > last_header_end
                 && self
                     .grid
                     .footer
                     .as_ref()
                     .and_then(Repeatable::as_repeated)
-                    .is_none_or(|footer| footer.start != last_header.end)
-                && self.lrows.last().is_some_and(|row| row.index() < last_header.end)
+                    .is_none_or(|footer| footer.start != last_header_end)
+                && self.lrows.last().is_some_and(|row| row.index() < last_header_end)
                 && !in_last_with_offset(
                     self.regions,
                     self.header_height + self.footer_height,
@@ -1471,9 +1473,10 @@ impl<'a> GridLayouter<'a> {
         let mut pos = Point::zero();
         let mut rrows = vec![];
         let current_region = self.finished.len();
+        let mut header_row_height = Abs::zero();
 
         // Place finished rows and layout fractional rows.
-        for row in std::mem::take(&mut self.lrows) {
+        for (i, row) in std::mem::take(&mut self.lrows).into_iter().enumerate() {
             let (frame, y, is_last) = match row {
                 Row::Frame(frame, y, is_last) => (frame, y, is_last),
                 Row::Fr(v, y, disambiguator) => {
@@ -1484,6 +1487,9 @@ impl<'a> GridLayouter<'a> {
             };
 
             let height = frame.height();
+            if i < self.current_header_rows {
+                header_row_height += height;
+            }
 
             // Ensure rowspans which span this row will have enough space to
             // be laid out over it later.
@@ -1562,7 +1568,11 @@ impl<'a> GridLayouter<'a> {
                     // we have to check the same index again in the next
                     // iteration.
                     let rowspan = self.rowspans.remove(i);
-                    self.layout_rowspan(rowspan, Some((&mut output, &rrows)), engine)?;
+                    self.layout_rowspan(
+                        rowspan,
+                        Some((&mut output, header_row_height)),
+                        engine,
+                    )?;
                 } else {
                     i += 1;
                 }
@@ -1573,9 +1583,10 @@ impl<'a> GridLayouter<'a> {
             pos.y += height;
         }
 
-        self.finish_region_internal(output, rrows);
+        self.finish_region_internal(output, rrows, header_row_height);
 
         if !last {
+            self.current_header_rows = 0;
             let disambiguator = self.finished.len();
             if let Some(Repeatable::Repeated(footer)) = &self.grid.footer {
                 self.prepare_footer(footer, engine, disambiguator)?;
@@ -1602,11 +1613,16 @@ impl<'a> GridLayouter<'a> {
         &mut self,
         output: Frame,
         resolved_rows: Vec<RowPiece>,
+        header_row_height: Abs,
     ) {
         self.finished.push(output);
         self.rrows.push(resolved_rows);
         self.regions.next();
         self.initial = self.regions.size;
+
+        if !self.grid.headers.is_empty() {
+            self.finished_header_rows.push(header_row_height);
+        }
     }
 }
 

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

@@ -189,7 +189,11 @@ impl<'a> GridLayouter<'a> {
         {
             // Advance regions without any output until we can place the
             // header and the footer.
-            self.finish_region_internal(Frame::soft(Axes::splat(Abs::zero())), vec![]);
+            self.finish_region_internal(
+                Frame::soft(Axes::splat(Abs::zero())),
+                vec![],
+                Abs::zero(),
+            );
 
             // TODO: re-calculate heights of headers and footers on each region
             // if 'full'changes? (Assuming height doesn't change for now...)
@@ -250,9 +254,18 @@ impl<'a> GridLayouter<'a> {
         // TODO: maybe extract this into a function to share code with multiple
         // footers.
         if matches!(headers, HeadersToLayout::RepeatingAndPending) || skipped_region {
-            self.unbreakable_rows_left +=
+            let repeating_header_rows =
                 total_header_row_count(self.repeating_headers.iter().map(Deref::deref));
 
+            let pending_header_rows = total_header_row_count(
+                self.pending_headers.into_iter().map(Repeatable::unwrap),
+            );
+
+            // Include both repeating and pending header rows as this number is
+            // used for orphan prevention.
+            self.current_header_rows = repeating_header_rows + pending_header_rows;
+            self.unbreakable_rows_left += repeating_header_rows + pending_header_rows;
+
             // Use indices to avoid double borrow. We don't mutate headers in
             // 'layout_row' so this is fine.
             let mut i = 0;
@@ -336,7 +349,11 @@ impl<'a> GridLayouter<'a> {
         {
             // Advance regions without any output until we can place the
             // footer.
-            self.finish_region_internal(Frame::soft(Axes::splat(Abs::zero())), vec![]);
+            self.finish_region_internal(
+                Frame::soft(Axes::splat(Abs::zero())),
+                vec![],
+                Abs::zero(),
+            );
             skipped_region = true;
         }
 

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

@@ -5,7 +5,7 @@ use typst_library::layout::grid::resolve::Repeatable;
 use typst_library::layout::{Abs, Axes, Frame, Point, Region, Regions, Size, Sizing};
 use typst_utils::MaybeReverseIter;
 
-use super::layouter::{in_last_with_offset, points, Row, RowPiece};
+use super::layouter::{in_last_with_offset, points, Row};
 use super::{layout_cell, Cell, GridLayouter};
 
 /// All information needed to layout a single rowspan.
@@ -87,10 +87,10 @@ pub struct CellMeasurementData<'layouter> {
 
 impl GridLayouter<'_> {
     /// Layout a rowspan over the already finished regions, plus the current
-    /// region's frame and resolved rows, if it wasn't finished yet (because
-    /// we're being called from `finish_region`, but note that this function is
-    /// also called once after all regions are finished, in which case
-    /// `current_region_data` is `None`).
+    /// region's frame and height of resolved header rows, if it wasn't
+    /// finished yet (because we're being called from `finish_region`, but note
+    /// that this function is also called once after all regions are finished,
+    /// in which case `current_region_data` is `None`).
     ///
     /// We need to do this only once we already know the heights of all
     /// spanned rows, which is only possible after laying out the last row
@@ -98,7 +98,7 @@ impl GridLayouter<'_> {
     pub fn layout_rowspan(
         &mut self,
         rowspan_data: Rowspan,
-        current_region_data: Option<(&mut Frame, &[RowPiece])>,
+        current_region_data: Option<(&mut Frame, Abs)>,
         engine: &mut Engine,
     ) -> SourceResult<()> {
         let Rowspan {
@@ -142,11 +142,31 @@ impl GridLayouter<'_> {
 
         // Push the layouted frames directly into the finished frames.
         let fragment = layout_cell(cell, engine, disambiguator, self.styles, pod)?;
-        let (current_region, current_rrows) = current_region_data.unzip();
-        for ((i, finished), frame) in self
+        let (current_region, current_header_row_height) = current_region_data.unzip();
+
+        // Clever trick to process finished header rows:
+        // - If there are grid headers, the vector will be filled with one
+        // finished header row height per region, so, chaining with the height
+        // for the current one, we get the header row height for each region.
+        //
+        // - But if there are no grid headers, the vector will be empty, so in
+        // theory the regions and resolved header row heights wouldn't match.
+        // But that's fine - 'current_header_row_height' can only be either
+        // 'Some(zero)' or 'None' in such a case, and for all other rows we
+        // append infinite zeros. That is, in such a case, the resolved header
+        // row height is always zero, so that's our fallback.
+        let finished_header_rows = self
+            .finished_header_rows
+            .iter()
+            .copied()
+            .chain(current_header_row_height)
+            .chain(std::iter::repeat(Abs::zero()));
+
+        for ((i, (finished, header_dy)), frame) in self
             .finished
             .iter_mut()
             .chain(current_region.into_iter())
+            .zip(finished_header_rows)
             .skip(first_region)
             .enumerate()
             .zip(fragment)
@@ -158,25 +178,9 @@ impl GridLayouter<'_> {
             } else {
                 // The rowspan continuation starts after the header (thus,
                 // at a position after the sum of the laid out header
-                // rows).
-                if let Some(Repeatable::Repeated(header)) = &self.grid.header {
-                    // TODO: Need a way to distinguish header 'rrows' for each
-                    // region, as this calculation - i.e., header height at
-                    // each region - will change depending on'i'.
-                    let header_rows = self
-                        .rrows
-                        .get(i)
-                        .map(Vec::as_slice)
-                        .or(current_rrows)
-                        .unwrap_or(&[])
-                        .iter()
-                        .take_while(|row| row.y < header.end);
-
-                    header_rows.map(|row| row.height).sum()
-                } else {
-                    // Without a header, start at the very top of the region.
-                    Abs::zero()
-                }
+                // rows). Without a header, this is zero, so the rowspan can
+                // start at the very top of the region as usual.
+                header_dy
             };
 
             finished.push_frame(Point::new(dx, dy), frame);