Refactor grid/layout.rs (#4100)

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

@@ -1,7 +1,9 @@
 use std::num::NonZeroUsize;
 use std::sync::Arc;
 
-use super::layout::{CellGrid, Repeatable, RowPiece};
+use super::cells::CellGrid;
+use super::layout::RowPiece;
+use super::repeated::Repeatable;
 use crate::foundations::{AlternativeFold, Fold};
 use crate::layout::Abs;
 use crate::visualize::Stroke;
@@ -597,7 +599,7 @@ pub(super) fn hline_stroke_at_column(
 
 #[cfg(test)]
 mod test {
-    use super::super::layout::Entry;
+    use super::super::cells::Entry;
     use super::*;
     use crate::foundations::Content;
     use crate::layout::{Axes, Cell, Sides, Sizing};

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

@@ -1,11 +1,13 @@
+mod cells;
 mod layout;
 mod lines;
+mod repeated;
 mod rowspans;
 
-pub use self::layout::{
-    Cell, CellGrid, Celled, GridLayouter, ResolvableCell, ResolvableGridChild,
-    ResolvableGridItem,
+pub use self::cells::{
+    Cell, CellGrid, Celled, ResolvableCell, ResolvableGridChild, ResolvableGridItem,
 };
+pub use self::layout::GridLayouter;
 pub use self::lines::LinePosition;
 
 use std::num::NonZeroUsize;

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

@@ -0,0 +1,178 @@
+use super::rowspans::UnbreakableRowGroup;
+use crate::diag::SourceResult;
+use crate::engine::Engine;
+use crate::layout::{Abs, Axes, Frame, GridLayouter, Regions};
+
+/// A repeatable grid header. Starts at the first row.
+pub(super) struct Header {
+    /// The index after the last row included in this header.
+    pub(super) end: usize,
+}
+
+/// A repeatable grid footer. Stops at the last row.
+pub(super) struct Footer {
+    /// The first row included in this footer.
+    pub(super) start: usize,
+}
+
+/// A possibly repeatable grid object.
+/// It still exists even when not repeatable, but must not have additional
+/// considerations by grid layout, other than for consistency (such as making
+/// a certain group of rows unbreakable).
+pub(super) enum Repeatable<T> {
+    Repeated(T),
+    NotRepeated(T),
+}
+
+impl<T> Repeatable<T> {
+    /// Gets the value inside this repeatable, regardless of whether
+    /// it repeats.
+    pub(super) fn unwrap(&self) -> &T {
+        match self {
+            Self::Repeated(repeated) => repeated,
+            Self::NotRepeated(not_repeated) => not_repeated,
+        }
+    }
+
+    /// Returns `Some` if the value is repeated, `None` otherwise.
+    pub(super) fn as_repeated(&self) -> Option<&T> {
+        match self {
+            Self::Repeated(repeated) => Some(repeated),
+            Self::NotRepeated(_) => None,
+        }
+    }
+}
+
+impl<'a> GridLayouter<'a> {
+    /// Layouts the header's rows.
+    /// Skips regions as necessary.
+    pub(super) fn layout_header(
+        &mut self,
+        header: &Header,
+        engine: &mut Engine,
+    ) -> SourceResult<()> {
+        let header_rows = self.simulate_header(header, &self.regions, engine)?;
+        let mut skipped_region = false;
+        while self.unbreakable_rows_left == 0
+            && !self.regions.size.y.fits(header_rows.height + self.footer_height)
+            && !self.regions.in_last()
+        {
+            // 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![]);
+            skipped_region = true;
+        }
+
+        // Reset the header height for this region.
+        // It will be re-calculated when laying out each header row.
+        self.header_height = Abs::zero();
+
+        if let Some(Repeatable::Repeated(footer)) = &self.grid.footer {
+            if skipped_region {
+                // Simulate the footer again; the region's 'full' might have
+                // changed.
+                self.footer_height =
+                    self.simulate_footer(footer, &self.regions, engine)?.height;
+            }
+        }
+
+        // Header is unbreakable.
+        // Thus, no risk of 'finish_region' being recursively called from
+        // within 'layout_row'.
+        self.unbreakable_rows_left += header.end;
+        for y in 0..header.end {
+            self.layout_row(y, engine)?;
+        }
+        Ok(())
+    }
+
+    /// Simulate the header's group of rows.
+    pub(super) fn simulate_header(
+        &self,
+        header: &Header,
+        regions: &Regions<'_>,
+        engine: &mut Engine,
+    ) -> SourceResult<UnbreakableRowGroup> {
+        // Note that we assume the invariant that any rowspan in a header is
+        // fully contained within that header. Therefore, there won't be any
+        // unbreakable rowspans exceeding the header's rows, and we can safely
+        // assume that the amount of unbreakable rows following the first row
+        // in the header will be precisely the rows in the header.
+        let header_row_group =
+            self.simulate_unbreakable_row_group(0, Some(header.end), regions, engine)?;
+
+        Ok(header_row_group)
+    }
+
+    /// Updates `self.footer_height` by simulating the footer, and skips to fitting region.
+    pub(super) fn prepare_footer(
+        &mut self,
+        footer: &Footer,
+        engine: &mut Engine,
+    ) -> SourceResult<()> {
+        let footer_height = self.simulate_footer(footer, &self.regions, engine)?.height;
+        let mut skipped_region = false;
+        while self.unbreakable_rows_left == 0
+            && !self.regions.size.y.fits(footer_height)
+            && !self.regions.in_last()
+        {
+            // Advance regions without any output until we can place the
+            // footer.
+            self.finish_region_internal(Frame::soft(Axes::splat(Abs::zero())), vec![]);
+            skipped_region = true;
+        }
+
+        self.footer_height = if skipped_region {
+            // Simulate the footer again; the region's 'full' might have
+            // changed.
+            self.simulate_footer(footer, &self.regions, engine)?.height
+        } else {
+            footer_height
+        };
+
+        Ok(())
+    }
+
+    /// Lays out all rows in the footer.
+    /// They are unbreakable.
+    pub(super) fn layout_footer(
+        &mut self,
+        footer: &Footer,
+        engine: &mut Engine,
+    ) -> SourceResult<()> {
+        // Ensure footer rows have their own height available.
+        // Won't change much as we're creating an unbreakable row group
+        // anyway, so this is mostly for correctness.
+        self.regions.size.y += self.footer_height;
+
+        let footer_len = self.grid.rows.len() - footer.start;
+        self.unbreakable_rows_left += footer_len;
+        for y in footer.start..self.grid.rows.len() {
+            self.layout_row(y, engine)?;
+        }
+
+        Ok(())
+    }
+
+    // Simulate the footer's group of rows.
+    pub(super) fn simulate_footer(
+        &self,
+        footer: &Footer,
+        regions: &Regions<'_>,
+        engine: &mut Engine,
+    ) -> SourceResult<UnbreakableRowGroup> {
+        // Note that we assume the invariant that any rowspan in a footer is
+        // fully contained within that footer. Therefore, there won't be any
+        // unbreakable rowspans exceeding the footer's rows, and we can safely
+        // assume that the amount of unbreakable rows following the first row
+        // in the footer will be precisely the rows in the footer.
+        let footer_row_group = self.simulate_unbreakable_row_group(
+            footer.start,
+            Some(self.grid.rows.len() - footer.start),
+            regions,
+            engine,
+        )?;
+
+        Ok(footer_row_group)
+    }
+}

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

@@ -1,3 +1,5 @@
+use super::layout::{in_last_with_offset, points, Row, RowPiece};
+use super::repeated::Repeatable;
 use crate::diag::SourceResult;
 use crate::engine::Engine;
 use crate::foundations::Resolve;
@@ -6,8 +8,6 @@ use crate::layout::{
 };
 use crate::util::MaybeReverseIter;
 
-use super::layout::{in_last_with_offset, points, Repeatable, Row, RowPiece};
-
 /// All information needed to layout a single rowspan.
 pub(super) struct Rowspan {
     /// First column of this rowspan.