Add a grid layouter

17 files changed, 665 insertions, 2 deletions

diff --git a/src/eval/mod.rs b/src/eval/mod.rs
index 5bc2f101..80be2e82 100644
--- a/src/eval/mod.rs
+++ b/src/eval/mod.rs
@@ -18,6 +18,7 @@ use std::rc::Rc;
 use crate::cache::Cache;
 use crate::color::Color;
 use crate::diag::{Diag, DiagSet, Pass};
+use crate::geom::TrackSizing;
 use crate::geom::{Angle, Fractional, Length, Relative};
 use crate::loading::{FileHash, Loader};
 use crate::parse::parse;
@@ -251,6 +252,7 @@ impl Eval for Expr {
             Self::Angle(_, v, unit) => Value::Angle(Angle::with_unit(v, unit)),
             Self::Percent(_, v) => Value::Relative(Relative::new(v / 100.0)),
             Self::Fractional(_, v) => Value::Fractional(Fractional::new(v)),
+            Self::Auto(_) => Value::TrackSizing(TrackSizing::Auto),
             Self::Color(_, v) => Value::Color(Color::Rgba(v)),
             Self::Str(_, ref v) => Value::Str(v.clone()),
             Self::Ident(ref v) => match ctx.scopes.get(&v) {
diff --git a/src/eval/value.rs b/src/eval/value.rs
index 498403e6..fa7993ed 100644
--- a/src/eval/value.rs
+++ b/src/eval/value.rs
@@ -8,7 +8,7 @@ use std::rc::Rc;
 use super::EvalContext;
 use crate::color::{Color, RgbaColor};
 use crate::exec::ExecContext;
-use crate::geom::{Angle, Fractional, Length, Linear, Relative};
+use crate::geom::{Angle, Fractional, Length, Linear, Relative, TrackSizing};
 use crate::syntax::{Expr, Span, Spanned, Tree};
 
 /// A computational value.
@@ -32,6 +32,8 @@ pub enum Value {
     Fractional(Fractional),
     /// A combination of an absolute length and a relative value: `20% + 5cm`.
     Linear(Linear),
+    /// One of the units that can appear in a grid definition.
+    TrackSizing(TrackSizing),
     /// A color value: `#f79143ff`.
     Color(Color),
     /// A string: `"string"`.
@@ -79,6 +81,7 @@ impl Value {
             Self::Relative(_) => Relative::TYPE_NAME,
             Self::Fractional(_) => Fractional::TYPE_NAME,
             Self::Linear(_) => Linear::TYPE_NAME,
+            Self::TrackSizing(_) => TrackSizing::TYPE_NAME,
             Self::Color(_) => Color::TYPE_NAME,
             Self::Str(_) => String::TYPE_NAME,
             Self::Array(_) => ArrayValue::TYPE_NAME,
@@ -97,6 +100,14 @@ impl Value {
             (&Self::Float(a), &Self::Int(b)) => a == b as f64,
             (&Self::Length(a), &Self::Linear(b)) => a == b.abs && b.rel.is_zero(),
             (&Self::Relative(a), &Self::Linear(b)) => a == b.rel && b.abs.is_zero(),
+            (&Self::Length(a), &Self::TrackSizing(b)) => TrackSizing::from(a) == b,
+            (&Self::Relative(a), &Self::TrackSizing(b)) => TrackSizing::from(a) == b,
+            (&Self::Linear(a), &Self::TrackSizing(b)) => TrackSizing::from(a) == b,
+            (&Self::Fractional(a), &Self::TrackSizing(b)) => TrackSizing::from(a) == b,
+            (&Self::TrackSizing(a), &Self::Length(b)) => TrackSizing::from(b) == a,
+            (&Self::TrackSizing(a), &Self::Relative(b)) => TrackSizing::from(b) == a,
+            (&Self::TrackSizing(a), &Self::Linear(b)) => TrackSizing::from(b) == a,
+            (&Self::TrackSizing(a), &Self::Fractional(b)) => TrackSizing::from(b) == a,
             (&Self::Linear(a), &Self::Length(b)) => a.abs == b && a.rel.is_zero(),
             (&Self::Linear(a), &Self::Relative(b)) => a.rel == b && a.abs.is_zero(),
             (Self::Array(a), Self::Array(b)) => {
@@ -611,6 +622,14 @@ primitive! {
     Value::Length(v) => v.into(),
     Value::Relative(v) => v.into(),
 }
+primitive! {
+    TrackSizing: "GridUnit",
+    Value::TrackSizing,
+    Value::Length(v) => v.into(),
+    Value::Relative(v) => v.into(),
+    Value::Linear(v) => v.into(),
+    Value::Fractional(v) => v.into(),
+}
 primitive! { Color: "color", Value::Color }
 primitive! { String: "string", Value::Str }
 primitive! { ArrayValue: "array", Value::Array }
diff --git a/src/geom/gridu.rs b/src/geom/gridu.rs
new file mode 100644
index 00000000..70fc17e4
--- /dev/null
+++ b/src/geom/gridu.rs
@@ -0,0 +1,73 @@
+use super::*;
+
+/// An enum with the length that a grid cell may have.
+#[derive(Copy, Clone, PartialEq, Hash)]
+pub enum TrackSizing {
+    /// A length stated in absolute values and fractions of the parent's size.
+    Linear(Linear),
+    /// A length that is the fraction of the remaining free space in the parent.
+    Fractional(Fractional),
+    /// The cell will fit its contents.
+    Auto,
+}
+
+impl TrackSizing {
+    pub fn is_zero(&self) -> bool {
+        match self {
+            Self::Linear(l) => l.is_zero(),
+            Self::Fractional(f) => f.is_zero(),
+            Self::Auto => false,
+        }
+    }
+
+    pub fn preliminary_length(&self, resolve: Length) -> Length {
+        match self {
+            Self::Linear(l) => l.resolve(resolve),
+            _ => resolve,
+        }
+    }
+}
+
+impl Display for TrackSizing {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        match self {
+            Self::Linear(x) => <Linear as Display>::fmt(x, f),
+            Self::Fractional(x) => <Fractional as Display>::fmt(x, f),
+            Self::Auto => write!(f, "auto"),
+        }
+    }
+}
+
+impl Debug for TrackSizing {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        match self {
+            Self::Linear(x) => <Linear as Debug>::fmt(x, f),
+            Self::Fractional(x) => <Fractional as Debug>::fmt(x, f),
+            Self::Auto => write!(f, "auto"),
+        }
+    }
+}
+
+impl From<Length> for TrackSizing {
+    fn from(abs: Length) -> Self {
+        Self::Linear(abs.into())
+    }
+}
+
+impl From<Relative> for TrackSizing {
+    fn from(rel: Relative) -> Self {
+        Self::Linear(rel.into())
+    }
+}
+
+impl From<Linear> for TrackSizing {
+    fn from(lin: Linear) -> Self {
+        Self::Linear(lin)
+    }
+}
+
+impl From<Fractional> for TrackSizing {
+    fn from(fr: Fractional) -> Self {
+        Self::Fractional(fr)
+    }
+}
diff --git a/src/geom/mod.rs b/src/geom/mod.rs
index ce8a7276..fdc3980e 100644
--- a/src/geom/mod.rs
+++ b/src/geom/mod.rs
@@ -7,6 +7,7 @@ mod angle;
 mod dir;
 mod fr;
 mod gen;
+mod gridu;
 mod length;
 mod linear;
 mod path;
@@ -21,6 +22,7 @@ pub use angle::*;
 pub use dir::*;
 pub use fr::*;
 pub use gen::*;
+pub use gridu::*;
 pub use length::*;
 pub use linear::*;
 pub use path::*;
diff --git a/src/layout/frame.rs b/src/layout/frame.rs
index 6cecc7a3..f1dc07e6 100644
--- a/src/layout/frame.rs
+++ b/src/layout/frame.rs
@@ -35,6 +35,14 @@ impl Frame {
             self.push(pos + subpos, element);
         }
     }
+
+    /// Translate the positions of all elements in the frame by adding the
+    /// argument to their position.
+    pub fn translate(&mut self, amount: Point) {
+        for (pos, _) in &mut self.elements {
+            *pos += amount;
+        }
+    }
 }
 
 /// The building block frames are composed of.
diff --git a/src/layout/grid.rs b/src/layout/grid.rs
new file mode 100644
index 00000000..9c4c2e0e
--- /dev/null
+++ b/src/layout/grid.rs
@@ -0,0 +1,372 @@
+use std::usize;
+
+use super::*;
+use crate::library::GridUnits;
+
+/// A node that stacks its children.
+#[derive(Debug, Clone, PartialEq, Hash)]
+pub struct GridNode {
+    /// The `main` and `cross` directions of this stack.
+    ///
+    /// The children are stacked along the `main` direction. The `cross`
+    /// direction is required for aligning the children.
+    pub dir: Dir,
+    /// The nodes to be stacked.
+    pub children: Vec<AnyNode>,
+    pub tracks: Gen<GridUnits>,
+    pub gutter: Gen<GridUnits>,
+}
+
+impl Layout for GridNode {
+    fn layout(&self, ctx: &mut LayoutContext, regions: &Regions) -> Vec<Frame> {
+        let layout = GridLayouter::new(self, regions).layout(ctx);
+        layout
+    }
+}
+
+#[derive(Debug)]
+enum GridItem<'a> {
+    Node(&'a AnyNode),
+    Gutter,
+}
+
+#[derive(Debug)]
+struct GridLayouter<'a> {
+    items: Vec<GridItem<'a>>,
+    cols: Vec<TrackSizing>,
+    rows: Vec<TrackSizing>,
+    region: Regions,
+    dir: Dir,
+    rrows: Vec<(usize, Option<Length>)>,
+    rcols: Vec<Length>,
+    frames: Vec<Frame>,
+}
+
+impl<'a> GridLayouter<'a> {
+    fn new(
+        grid: &'a GridNode,
+        regions: &Regions,
+    ) -> Self {
+        let mut items = vec![];
+        let mut col_sizes = vec![];
+        let mut row_sizes = vec![];
+        let cols = grid.tracks.cross.0.len();
+        // Create at least as many rows as specified and a row to fit every item.
+        let rows = if cols > 0 {
+            let res = grid
+            .tracks
+            .main
+            .0
+            .len()
+            .max(grid.children.len() / cols + (grid.children.len() % cols).clamp(0, 1));
+            res
+        } else {
+            0
+        };
+
+        for (i, col_size) in grid.tracks.cross.0.iter().enumerate() {
+            let last = i == cols - 1;
+            col_sizes.push(*col_size);
+
+            if !last {
+                let gutter = grid.gutter.cross.get(i);
+                col_sizes.push(gutter);
+            }
+        }
+
+        for (i, row_size) in (0 .. rows).map(|i| (i, grid.tracks.main.get(i))) {
+            let last = i == rows - 1;
+            row_sizes.push(row_size);
+
+            if !last {
+                let gutter = grid.gutter.main.get(i);
+                row_sizes.push(gutter);
+            }
+        }
+
+        for (i, item) in grid.children.iter().enumerate() {
+            if cols == 0 {
+                break;
+            }
+
+            let row = i / cols;
+            let col = i % cols;
+
+            items.push(GridItem::Node(item));
+
+            if col != cols - 1 {
+                // Push gutter
+                items.push(GridItem::Gutter);
+            } else if row != rows - 1 {
+                // Push gutter row.
+                for _ in 0 .. col_sizes.len() {
+                    items.push(GridItem::Gutter);
+                }
+            }
+        }
+
+        // Fill the thing up
+        while items.len() < col_sizes.len() * row_sizes.len() {
+            items.push(GridItem::Gutter)
+        }
+
+        GridLayouter {
+            cols: col_sizes,
+            rows: row_sizes,
+            region: regions.clone(),
+            dir: grid.dir,
+            items,
+            rrows: vec![],
+            rcols: vec![],
+            frames: vec![],
+        }
+    }
+
+    fn get(&self, x: usize, y: usize) -> &GridItem<'_> {
+        assert!(x < self.cols.len());
+        assert!(y < self.rows.len());
+        let row_cmp = y * self.cols.len();
+
+        self.items.get(row_cmp + x).unwrap()
+    }
+
+    fn main(&self) -> SpecAxis {
+        self.dir.axis().other()
+    }
+
+    fn cross(&self) -> SpecAxis {
+        self.dir.axis()
+    }
+
+    fn finish_region(&mut self, ctx: &mut LayoutContext, total_frs: f64) {
+        let mut pos = Gen::splat(Length::zero());
+        let pos2point = |mut pos: Gen<Length>| {
+            if !self.dir.is_positive() {
+                pos.cross = -pos.cross;
+            }
+            pos.switch(self.main()).to_point()
+        };
+        let mut frame = Frame::new(Size::zero(), Length::zero());
+        let mut total_cross = Length::zero();
+        let mut total_main = Length::zero();
+
+        for (x, &w) in self.rcols.iter().enumerate() {
+            let total: Length = self.rrows.iter().filter_map(|(_, x)| *x).sum();
+            let available = self.region.current.get(self.main()) - total;
+            total_cross += w;
+
+            for (y, h) in self.rrows.iter() {
+                let element = self.get(x, *y);
+                let h = if let Some(len) = h {
+                    *len
+                } else {
+                    if let TrackSizing::Fractional(f) = self.rows[*y] {
+                        if total_frs > 0.0 {
+                            let res = available * (f.get() / total_frs);
+                            if res.is_finite() {
+                                res
+                            } else {
+                                Length::zero()
+                            }
+                        } else {
+                            Length::zero()
+                        }
+                    } else {
+                        unreachable!()
+                    }
+                };
+                if x == 0 {
+                    total_main += h;
+                }
+
+                if let GridItem::Node(n) = element {
+                    let item = n.layout(ctx, &Regions::one(Gen::new(w, h).switch(self.main()).to_size(), Spec::splat(false))).remove(0);
+                    frame.push_frame(pos2point(pos), item);
+                }
+
+                pos.main += h;
+            }
+            pos.main = Length::zero();
+            pos.cross += self.dir.factor() as f64 * w;
+        }
+
+        if !self.dir.is_positive() {
+            frame.translate(Gen::new(total_cross, Length::zero()).switch(self.main()).to_point());
+        }
+
+        frame.size = Gen::new(total_cross, total_main).switch(self.main()).to_size();
+        frame.baseline = frame.size.height;
+
+        self.frames.push(frame);
+
+        self.rrows.clear();
+        self.region.next();
+    }
+
+    fn layout(mut self, ctx: &mut LayoutContext) -> Vec<Frame> {
+        // Shrink area by linear sizing.
+        let mut available = self.region.current.get(self.cross());
+        available -= self
+            .cols
+            .iter()
+            .filter_map(|x| match x {
+                TrackSizing::Linear(l) => Some(l.resolve(self.region.base.get(self.cross()))),
+                _ => None,
+            })
+            .sum();
+
+        let col_frac: f64 = self
+            .cols
+            .iter()
+            .filter_map(|x| match x {
+                TrackSizing::Fractional(f) => Some(f.get()),
+                _ => None,
+            })
+            .sum();
+
+        let auto_columns = self
+            .cols
+            .iter()
+            .enumerate()
+            .filter_map(|(i, x)| (x == &TrackSizing::Auto).then(|| i));
+
+        let mut col_width = vec![];
+
+        // For each of the auto columns, lay out all elements with `preliminary_length`
+        // rows and build max.
+        for x in auto_columns {
+            let mut max = Length::zero();
+            for (y, row_height) in
+                self.rows.iter().enumerate().map(|(y, s)| {
+                    (y, s.preliminary_length(self.region.base.get(self.main())))
+                })
+            {
+                let item = self.get(x, y);
+                let size =
+                    Gen::new(self.region.current.get(self.cross()), row_height).switch(self.main()).to_size();
+                let region = Regions::one(size, Spec::splat(false));
+                match item {
+                    GridItem::Node(n) => {
+                        max = max.max(
+                            n.layout(ctx, &region).first().unwrap().size.get(self.cross()),
+                        )
+                    }
+                    GridItem::Gutter => {}
+                }
+            }
+
+            col_width.push((x, max));
+        }
+
+        // If accumulated auto column size exceeds available size, redistribute space
+        // proportionally amongst elements that exceed their size allocation.
+        let mut total: Length = col_width.iter().map(|(_, x)| *x).sum();
+        if total > available {
+            let alloc = available / col_width.len() as f64;
+
+            let mut count: usize = 0;
+            let mut redistributable = Length::zero();
+
+            for &(_, l) in &col_width {
+                if l > alloc {
+                    redistributable += l;
+                    count += 1;
+                }
+            }
+
+            let x = (available - total + redistributable) / count as f64;
+
+            if !redistributable.is_zero() {
+                for (_, l) in &mut col_width {
+                    if *l > alloc {
+                        *l = x;
+                    }
+                }
+            }
+
+            total = available;
+        }
+
+        // Build rcols
+        for (x, len) in col_width.into_iter().map(|(x, s)| (x, Some(s))).chain(std::iter::once((self.cols.len(), None))) {
+            for i in self.rcols.len() .. x {
+                let len = match self.cols[i] {
+                    TrackSizing::Linear(l) => l.resolve(self.region.base.get(self.cross())),
+                    TrackSizing::Fractional(f) => {
+                        if col_frac == 0.0 {
+                            Length::zero()
+                        } else {
+                            let res: Length = (available - total) * (f.get() / col_frac);
+                            if res.is_finite() {
+                                res
+                            } else {
+                                Length::zero()
+                            }
+                        }
+                    }
+                    TrackSizing::Auto => unreachable!(),
+                };
+
+                self.rcols.push(len);
+            }
+
+            if let Some(len) = len {
+                self.rcols.push(len);
+            }
+        }
+
+        // Determine non-`fr` row heights
+        let mut total_frs = 0.0;
+        let mut current = self.region.current.get(self.main());
+
+        for y in 0..self.rows.len() {
+            let height = &self.rows[y];
+            let resolved = match height {
+                TrackSizing::Linear(l) => Some(l.resolve(self.region.base.get(self.main()))),
+                TrackSizing::Auto => {
+                    let mut max = Length::zero();
+                    for (x, len) in self.rcols.iter().enumerate() {
+                        let node = self.get(x, y);
+                        if let GridItem::Node(node) = node {
+                            let frames = node.layout(
+                                ctx,
+                                &Regions::one(
+                                    Gen::new(*len, current)
+                                        .switch(self.main())
+                                        .to_size(),
+                                    Spec::splat(false),
+                                ),
+                            );
+                            max = max.max(frames.first().unwrap().size.get(self.main()));
+                        }
+                    }
+                    Some(max)
+                }
+                TrackSizing::Fractional(f) => {
+                    total_frs += f.get();
+                    None
+                },
+            };
+
+            if let Some(resolved) = resolved {
+                while !current.fits(resolved) && !self.region.in_full_last() {
+                    self.finish_region(ctx, total_frs);
+                    current = self.region.current.get(self.main());
+                    total_frs = 0.0;
+                }
+                current -= resolved;
+            }
+
+            self.rrows.push((y, resolved));
+        }
+
+        self.finish_region(ctx, total_frs);
+        self.frames
+    }
+}
+
+impl From<GridNode> for AnyNode {
+    fn from(grid: GridNode) -> Self {
+        Self::new(grid)
+    }
+}
diff --git a/src/layout/mod.rs b/src/layout/mod.rs
index 9d5ccdc0..9d8549e6 100644
--- a/src/layout/mod.rs
+++ b/src/layout/mod.rs
@@ -3,6 +3,7 @@
 mod background;
 mod fixed;
 mod frame;
+mod grid;
 mod pad;
 mod par;
 mod shaping;
@@ -11,6 +12,7 @@ mod stack;
 pub use background::*;
 pub use fixed::*;
 pub use frame::*;
+pub use grid::*;
 pub use pad::*;
 pub use par::*;
 pub use shaping::*;
diff --git a/src/library/grid.rs b/src/library/grid.rs
new file mode 100644
index 00000000..0aa1fc9d
--- /dev/null
+++ b/src/library/grid.rs
@@ -0,0 +1,76 @@
+use crate::layout::GridNode;
+
+use super::*;
+
+/// `stack`: Stack children along an axis.
+///
+/// # Positional parameters
+/// - Children: variadic, of type `template`.
+///
+/// # Named parameters
+/// - Column widths: `columns`, of type `Array<GridUnit>`.
+/// - Row widths: `rows`, of type `Array<GridUnit>`.
+/// - Gutter: `gutter-vertical` and `gutter-horizontal` for individual track axis or `gutter` for both, of type `Array<GridUnit>` respectively.
+/// - Stacking direction: `dir`, of type `direction`.
+///
+/// # Return value
+/// A template that arranges its children along the specified grid cells.
+///
+/// # Relevant types and constants
+/// - Type `direction`
+///   - `ltr`
+///   - `rtl`
+///   - `ttb`
+///   - `btt`
+pub fn grid(ctx: &mut EvalContext, args: &mut FuncArgs) -> Value {
+    let cols = args.eat_named::<GridUnits>(ctx, "columns").unwrap_or_default();
+    let rows = args.eat_named::<GridUnits>(ctx, "rows").unwrap_or_default();
+
+    let gutter = args.eat_named(ctx, "gutter");
+    let gutter_vertical = args
+        .eat_named::<GridUnits>(ctx, "gutter-col")
+        .or_else(|| gutter.clone())
+        .unwrap_or_default();
+    let gutter_horizontal = args
+        .eat_named::<GridUnits>(ctx, "gutter-row")
+        .or(gutter)
+        .unwrap_or_default();
+
+    let dir = args.eat_named(ctx, "dir");
+    let children = args.eat_all::<TemplateValue>(ctx);
+
+    Value::template("grid", move |ctx| {
+        let children =
+            children.iter().map(|child| ctx.exec_template_stack(child).into()).collect();
+        ctx.push(GridNode {
+            dir: dir.unwrap_or_else(|| ctx.state.lang.dir),
+            children,
+            gutter: Gen::new(gutter_vertical.clone(), gutter_horizontal.clone()),
+            tracks: Gen::new(cols.clone(), rows.clone()),
+        })
+    })
+}
+
+/// A list of [`GridUnit`]s.
+#[derive(Default, Debug, Clone, PartialEq, Hash)]
+pub struct GridUnits(pub Vec<TrackSizing>);
+
+impl GridUnits {
+    pub fn get(&self, index: usize) -> TrackSizing {
+        if self.0.is_empty() {
+            TrackSizing::Auto
+        } else {
+            *self.0.get(index).unwrap_or(self.0.last().unwrap())
+        }
+    }
+}
+
+value! {
+    GridUnits: "array of fractional values, lengths, and the `auto` keyword",
+    Value::TrackSizing(value) => Self(vec![value]),
+    Value::Array(values) => Self(values
+        .into_iter()
+        .filter_map(|v| v.cast().ok())
+        .collect()
+    ),
+}
diff --git a/src/library/mod.rs b/src/library/mod.rs
index f9e4f68a..8caddc4c 100644
--- a/src/library/mod.rs
+++ b/src/library/mod.rs
@@ -6,6 +6,7 @@
 mod align;
 mod basic;
 mod font;
+mod grid;
 mod image;
 mod lang;
 mod math;
@@ -20,6 +21,7 @@ pub use self::image::*;
 pub use align::*;
 pub use basic::*;
 pub use font::*;
+pub use grid::*;
 pub use lang::*;
 pub use math::*;
 pub use pad::*;
@@ -47,6 +49,7 @@ pub fn new() -> Scope {
     std.def_func("circle", circle);
     std.def_func("ellipse", ellipse);
     std.def_func("font", font);
+    std.def_func("grid", grid);
     std.def_func("h", h);
     std.def_func("image", image);
     std.def_func("lang", lang);
diff --git a/src/parse/mod.rs b/src/parse/mod.rs
index 3d4cc2ac..1f14f36f 100644
--- a/src/parse/mod.rs
+++ b/src/parse/mod.rs
@@ -314,6 +314,11 @@ fn primary(p: &mut Parser, atomic: bool) -> Option<Expr> {
         Some(Token::For) => expr_for(p),
         Some(Token::Import) => expr_import(p),
         Some(Token::Include) => expr_include(p),
+        Some(Token::Auto) => {
+            let start = p.next_start();
+            p.assert(Token::Auto);
+            Some(Expr::Auto(p.span(start)))
+        }
 
         // Nothing.
         _ => {
diff --git a/src/parse/tokens.rs b/src/parse/tokens.rs
index 9d3cbc9a..f82d0ae4 100644
--- a/src/parse/tokens.rs
+++ b/src/parse/tokens.rs
@@ -474,6 +474,7 @@ fn keyword(id: &str) -> Option<Token<'static>> {
         "for" => Token::For,
         "in" => Token::In,
         "while" => Token::While,
+        "auto" => Token::Auto,
         "break" => Token::Break,
         "continue" => Token::Continue,
         "return" => Token::Return,
@@ -758,6 +759,12 @@ mod tests {
             ("for", For),
             ("in", In),
             ("import", Import),
+            ("while", While),
+            ("break", Break),
+            ("continue", Continue),
+            ("using", Using),
+            ("auto", Auto),
+            ("return", Return),
         ];
 
         for &(s, t) in &list {
diff --git a/src/pretty.rs b/src/pretty.rs
index df1d844c..82e81ce6 100644
--- a/src/pretty.rs
+++ b/src/pretty.rs
@@ -4,7 +4,7 @@ use std::fmt::{self, Arguments, Write};
 
 use crate::color::{Color, RgbaColor};
 use crate::eval::*;
-use crate::geom::{Angle, Fractional, Length, Linear, Relative};
+use crate::geom::{Angle, Fractional, Length, Linear, Relative, TrackSizing};
 use crate::syntax::*;
 
 /// Pretty print an item and return the resulting string.
@@ -186,6 +186,7 @@ impl Pretty for Expr {
     fn pretty(&self, p: &mut Printer) {
         match self {
             Self::None(_) => p.push_str("none"),
+            Self::Auto(_) => p.push_str("auto"),
             Self::Bool(_, v) => v.pretty(p),
             Self::Int(_, v) => v.pretty(p),
             Self::Float(_, v) => v.pretty(p),
@@ -459,6 +460,7 @@ impl Pretty for Value {
             Value::Relative(v) => v.pretty(p),
             Value::Fractional(v) => v.pretty(p),
             Value::Linear(v) => v.pretty(p),
+            Value::TrackSizing(v) => v.pretty(p),
             Value::Color(v) => v.pretty(p),
             Value::Str(v) => v.pretty(p),
             Value::Array(v) => v.pretty(p),
@@ -579,6 +581,7 @@ pretty_display! {
     Relative,
     Fractional,
     Linear,
+    TrackSizing,
     RgbaColor,
     Color,
     AnyValue,
@@ -656,6 +659,7 @@ mod tests {
     fn test_pretty_print_expr() {
         // Basic expressions.
         roundtrip("{none}");
+        roundtrip("{auto}");
         roundtrip("{true}");
         roundtrip("{10}");
         roundtrip("{3.14}");
diff --git a/src/syntax/expr.rs b/src/syntax/expr.rs
index 4dac9c59..17e4a196 100644
--- a/src/syntax/expr.rs
+++ b/src/syntax/expr.rs
@@ -9,6 +9,8 @@ use crate::geom::{AngularUnit, LengthUnit};
 pub enum Expr {
     /// The none literal: `none`.
     None(Span),
+    /// The `auto` constant.
+    Auto(Span),
     /// A boolean literal: `true`, `false`.
     Bool(Span, bool),
     /// An integer literal: `120`.
@@ -69,6 +71,7 @@ impl Expr {
     pub fn span(&self) -> Span {
         match *self {
             Self::None(span) => span,
+            Self::Auto(span) => span,
             Self::Bool(span, _) => span,
             Self::Int(span, _) => span,
             Self::Float(span, _) => span,
diff --git a/src/syntax/token.rs b/src/syntax/token.rs
index 56ab3dd6..26c01fbb 100644
--- a/src/syntax/token.rs
+++ b/src/syntax/token.rs
@@ -100,6 +100,8 @@ pub enum Token<'s> {
     Include,
     /// The `using` keyword.
     Using,
+    /// The `auto` keyword.
+    Auto,
     /// One or more whitespace characters.
     ///
     /// The contained `usize` denotes the number of newlines that were contained
@@ -248,6 +250,7 @@ impl<'s> Token<'s> {
             Self::Import => "keyword `import`",
             Self::Include => "keyword `include`",
             Self::Using => "keyword `using`",
+            Self::Auto => "keyword `auto`",
             Self::Space(_) => "space",
             Self::Text(_) => "text",
             Self::UnicodeEscape(_) => "unicode escape sequence",
diff --git a/src/syntax/visit.rs b/src/syntax/visit.rs
index ba7555f2..97e8d4ed 100644
--- a/src/syntax/visit.rs
+++ b/src/syntax/visit.rs
@@ -74,6 +74,7 @@ visit! {
     fn visit_expr(v, node: &Expr) {
         match node {
             Expr::None(_) => {}
+            Expr::Auto(_) => {}
             Expr::Bool(_, _) => {}
             Expr::Int(_, _) => {}
             Expr::Float(_, _) => {}
diff --git a/tests/ref/library/grid.png b/tests/ref/library/grid.png
new file mode 100644
index 00000000..278ead89
--- /dev/null
+++ b/tests/ref/library/grid.png
diff --git a/tests/typ/library/grid.typ b/tests/typ/library/grid.typ
new file mode 100644
index 00000000..dcc0797f
--- /dev/null
+++ b/tests/typ/library/grid.typ
@@ -0,0 +1,83 @@
+// Test the `grid` function.
+
+---
+#page(width: 100pt, height: 140pt)
+#let rect(width, color) = rect(width: width, height: 2cm, fill: color)
+#grid(
+    columns: (auto, 1fr, 3fr, 0.25cm, 3%, 2mm + 10%),
+    rect(0.5cm, #2a631a),
+    rect(100%, forest),
+    rect(100%, conifer),
+    rect(100%, #ff0000),
+    rect(100%, #00ff00),
+    rect(80%, #00faf0),
+    rect(1cm, #00ff00),
+    rect(0.5cm, #2a631a),
+    rect(100%, forest),
+    rect(100%, conifer),
+    rect(100%, #ff0000),
+    rect(100%, #00ff00),
+)
+
+#grid()
+
+---
+
+#grid(
+    columns: (auto, auto, 40%),
+    gutter: (1fr,),
+    rect(fill: eastern)[dddaa aaa aaa],
+    rect(fill: conifer)[ccc],
+    rect(width: 100%, fill: #dddddd)[aaa],
+)
+
+#grid(
+    columns: (auto, auto, 40%),
+    gutter: (1fr,),
+    rect(fill: eastern)[dddaa aaa aaa],
+    rect(fill: conifer)[ccc],
+    rect(width: 100%, fill: #dddddd)[aaa],
+)
+
+
+---
+
+#page(width: 12cm, height: 2.5cm)
+#grid(
+    columns: (auto, auto, auto, auto, auto),
+    gutter-col: (2fr, 1fr, 1fr),
+    gutter-row: (6pt, 6pt, 6pt, 6pt),
+    [*Quarter*],
+    [Expenditure],
+    [External Revenue],
+    [Financial ROI],
+    [_total_],
+    [*Q1*],
+    [173,472.57 \$],
+    [472,860.91 \$],
+    [51,286.84 \$],
+    [_350,675.18 \$_],
+    [*Q2*],
+    [93,382.12 \$],
+    [439,382.85 \$],
+    [-1,134.30 \$],
+    [_344,866.43 \$_],
+    [*Q3*],
+    [96,421.49 \$],
+    [238,583.54 \$],
+    [3,497.12 \$],
+    [_145,659.17 \$_],
+)
+
+---
+#page(height: 3cm, width: 2cm)
+#grid(
+    dir: ttb,
+    columns: (1fr, 1cm, 1fr, 1fr),
+    rows: (auto, 1fr),
+    rect(height: 100%, fill: #222222)[foo],
+    rect(height: 100%, fill: #547d0a)[bar],
+    rect(height: 100%, fill: eastern)[hab],
+    rect(height: 100%, fill: conifer)[baz],
+    rect(height: 100%, width: 100%, fill: #547d0a)[bar],
+)