Redesigned template layout

Cargo.lock

@@ -932,6 +932,12 @@ version = "0.12.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7ae2f58a822f08abdaf668897e96a5656fe72f5a9ce66422423e8849384872e6"
 
+[[package]]
+name = "typed-arena"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0685c84d5d54d1c26f7d3eb96cd41550adb97baed141a761cf335d3d33bcd0ae"
+
 [[package]]
 name = "typst"
 version = "0.1.0"
@@ -962,6 +968,7 @@ dependencies = [
  "syntect",
  "tiny-skia",
  "ttf-parser",
+ "typed-arena",
  "typst-macros",
  "unicode-bidi",
  "unicode-segmentation",

Cargo.toml

@@ -24,6 +24,7 @@ fxhash = "0.2"
 itertools = "0.10"
 once_cell = "1"
 serde = { version = "1", features = ["derive"] }
+typed-arena = "2"
 
 # Text and font handling
 kurbo = "0.8"

src/eval/collapse.rs

@@ -0,0 +1,109 @@
+use super::{StyleChain, StyleVec, StyleVecBuilder};
+
+/// A wrapper around a [`StyleVecBuilder`] that allows to collapse items.
+pub struct CollapsingBuilder<'a, T> {
+    builder: StyleVecBuilder<'a, T>,
+    staged: Vec<(T, StyleChain<'a>, bool)>,
+    last: Last,
+}
+
+/// What the last non-ignorant item was.
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+enum Last {
+    Weak,
+    Destructive,
+    Supportive,
+}
+
+impl<'a, T: Merge> CollapsingBuilder<'a, T> {
+    /// Create a new style-vec builder.
+    pub fn new() -> Self {
+        Self {
+            builder: StyleVecBuilder::new(),
+            staged: vec![],
+            last: Last::Destructive,
+        }
+    }
+
+    /// Can only exist when there is at least one supportive item to its left
+    /// and to its right, with no destructive items or weak items in between to
+    /// its left and no destructive items in between to its right. There may be
+    /// ignorant items in between in both directions.
+    pub fn weak(&mut self, item: T, styles: StyleChain<'a>) {
+        if self.last == Last::Supportive {
+            self.staged.push((item, styles, true));
+            self.last = Last::Weak;
+        }
+    }
+
+    /// Forces nearby weak items to collapse.
+    pub fn destructive(&mut self, item: T, styles: StyleChain<'a>) {
+        self.flush(false);
+        self.push(item, styles);
+        self.last = Last::Destructive;
+    }
+
+    /// Allows nearby weak items to exist.
+    pub fn supportive(&mut self, item: T, styles: StyleChain<'a>) {
+        self.flush(true);
+        self.push(item, styles);
+        self.last = Last::Supportive;
+    }
+
+    /// Has no influence on other items.
+    pub fn ignorant(&mut self, item: T, styles: StyleChain<'a>) {
+        self.staged.push((item, styles, false));
+    }
+
+    /// Return the finish style vec and the common prefix chain.
+    pub fn finish(mut self) -> (StyleVec<T>, StyleChain<'a>) {
+        self.flush(false);
+        self.builder.finish()
+    }
+
+    /// Push the staged items, filtering out weak items if `supportive` is false.
+    fn flush(&mut self, supportive: bool) {
+        for (item, styles, weak) in self.staged.drain(..) {
+            if !weak || supportive {
+                push_merging(&mut self.builder, item, styles);
+            }
+        }
+    }
+
+    /// Push a new item into the style vector.
+    fn push(&mut self, item: T, styles: StyleChain<'a>) {
+        push_merging(&mut self.builder, item, styles);
+    }
+}
+
+/// Push an item into a style-vec builder, trying to merging it with the
+/// previous item.
+fn push_merging<'a, T: Merge>(
+    builder: &mut StyleVecBuilder<'a, T>,
+    item: T,
+    styles: StyleChain<'a>,
+) {
+    if let Some((prev_item, prev_styles)) = builder.last_mut() {
+        if styles == prev_styles {
+            if prev_item.merge(&item) {
+                return;
+            }
+        }
+    }
+
+    builder.push(item, styles);
+}
+
+impl<'a, T: Merge> Default for CollapsingBuilder<'a, T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+/// Defines if and how to merge two adjacent items in a [`CollapsingBuilder`].
+pub trait Merge {
+    /// Try to merge the items, returning whether they were merged.
+    ///
+    /// Defaults to not merging.
+    fn merge(&mut self, next: &Self) -> bool;
+}

src/eval/mod.rs

@@ -10,6 +10,7 @@ mod value;
 mod styles;
 mod capture;
 mod class;
+mod collapse;
 mod func;
 mod ops;
 mod scope;
@@ -18,6 +19,7 @@ mod template;
 pub use array::*;
 pub use capture::*;
 pub use class::*;
+pub use collapse::*;
 pub use dict::*;
 pub use func::*;
 pub use scope::*;

src/eval/styles.rs

@@ -3,44 +3,10 @@ use std::fmt::{self, Debug, Formatter};
 use std::hash::{Hash, Hasher};
 use std::sync::Arc;
 
-/// An item with associated styles.
-#[derive(PartialEq, Clone, Hash)]
-pub struct Styled<T> {
-    /// The item to apply styles to.
-    pub item: T,
-    /// The associated style map.
-    pub map: StyleMap,
-}
-
-impl<T> Styled<T> {
-    /// Create a new instance from an item and a style map.
-    pub fn new(item: T, map: StyleMap) -> Self {
-        Self { item, map }
-    }
-
-    /// Create a new instance with empty style map.
-    pub fn bare(item: T) -> Self {
-        Self { item, map: StyleMap::new() }
-    }
-
-    /// Map the item with `f`.
-    pub fn map<F, U>(self, f: F) -> Styled<U>
-    where
-        F: FnOnce(T) -> U,
-    {
-        Styled { item: f(self.item), map: self.map }
-    }
-}
-
-impl<T: Debug> Debug for Styled<T> {
-    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        self.map.fmt(f)?;
-        self.item.fmt(f)
-    }
-}
+use crate::library::{PageNode, ParNode};
 
 /// A map of style properties.
-#[derive(Default, Clone, Hash)]
+#[derive(Default, Clone, PartialEq, Hash)]
 pub struct StyleMap(Vec<Entry>);
 
 impl StyleMap {
@@ -93,7 +59,7 @@ impl StyleMap {
             *outer
         } else {
             StyleChain {
-                first: Link::Map(self),
+                link: Some(Link::Map(self)),
                 outer: Some(outer),
             }
         }
@@ -103,31 +69,16 @@ impl StyleMap {
     /// equivalent to the style chain created by
     /// `self.chain(StyleChain::new(outer))`.
     ///
-    /// This is useful in the evaluation phase while building nodes and their
-    /// style maps, whereas `chain` would be used during layouting to combine
-    /// immutable style maps from different levels of the hierarchy.
+    /// This is useful over `chain` when you need an owned map without a
+    /// lifetime, for example, because you want to store the style map inside a
+    /// packed node.
     pub fn apply(&mut self, outer: &Self) {
         self.0.splice(0 .. 0, outer.0.clone());
     }
 
-    /// Subtract `other` from `self` in-place, keeping only styles that are in
-    /// `self` but not in `other`.
-    pub fn erase(&mut self, other: &Self) {
-        self.0.retain(|x| !other.0.contains(x));
-    }
-
-    /// Intersect `self` with `other` in-place, keeping only styles that are
-    /// both in `self` and `other`.
-    pub fn intersect(&mut self, other: &Self) {
-        self.0.retain(|x| other.0.contains(x));
-    }
-
-    /// Whether two style maps are equal when filtered down to properties of the
-    /// node `T`.
-    pub fn compatible<T: 'static>(&self, other: &Self) -> bool {
-        let f = |entry: &&Entry| entry.is_of::<T>();
-        self.0.iter().filter(f).count() == other.0.iter().filter(f).count()
-            && self.0.iter().filter(f).all(|x| other.0.contains(x))
+    /// The highest-level interruption of the map.
+    pub fn interruption(&self) -> Option<Interruption> {
+        self.0.iter().filter_map(|entry| entry.interruption()).max()
     }
 }
 
@@ -140,10 +91,13 @@ impl Debug for StyleMap {
     }
 }
 
-impl PartialEq for StyleMap {
-    fn eq(&self, other: &Self) -> bool {
-        self.0.len() == other.0.len() && self.0.iter().all(|x| other.0.contains(x))
-    }
+/// Determines whether a style could interrupt some composable structure.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
+pub enum Interruption {
+    /// The style forces a paragraph break.
+    Par,
+    /// The style forces a page break.
+    Page,
 }
 
 /// A chain of style maps, similar to a linked list.
@@ -153,10 +107,10 @@ impl PartialEq for StyleMap {
 /// eagerly merging the maps, each access walks the hierarchy from the innermost
 /// to the outermost map, trying to find a match and then folding it with
 /// matches further up the chain.
-#[derive(Clone, Copy, Hash)]
+#[derive(Default, Clone, Copy, Hash)]
 pub struct StyleChain<'a> {
-    /// The first link in the chain.
-    first: Link<'a>,
+    /// The first link of this chain.
+    link: Option<Link<'a>>,
     /// The remaining links in the chain.
     outer: Option<&'a Self>,
 }
@@ -173,10 +127,52 @@ enum Link<'a> {
 
 impl<'a> StyleChain<'a> {
     /// Start a new style chain with a root map.
-    pub fn new(first: &'a StyleMap) -> Self {
-        Self { first: Link::Map(first), outer: None }
+    pub fn new(map: &'a StyleMap) -> Self {
+        Self { link: Some(Link::Map(map)), outer: None }
     }
 
+    /// The number of links in the chain.
+    pub fn len(self) -> usize {
+        self.links().count()
+    }
+
+    /// Convert to an owned style map.
+    ///
+    /// Panics if the chain contains barrier links.
+    pub fn to_map(self) -> StyleMap {
+        let mut suffix = StyleMap::new();
+        for link in self.links() {
+            match link {
+                Link::Map(map) => suffix.apply(map),
+                Link::Barrier(_) => panic!("chain contains barrier"),
+            }
+        }
+        suffix
+    }
+
+    /// Build a style map from the suffix (all links beyond the `len`) of the
+    /// chain.
+    ///
+    /// Panics if the suffix contains barrier links.
+    pub fn suffix(self, len: usize) -> StyleMap {
+        let mut suffix = StyleMap::new();
+        let remove = self.len().saturating_sub(len);
+        for link in self.links().take(remove) {
+            match link {
+                Link::Map(map) => suffix.apply(map),
+                Link::Barrier(_) => panic!("suffix contains barrier"),
+            }
+        }
+        suffix
+    }
+
+    /// Remove the last link from the chain.
+    pub fn pop(&mut self) {
+        *self = self.outer.copied().unwrap_or_default();
+    }
+}
+
+impl<'a> StyleChain<'a> {
     /// Get the (folded) value of a copyable style property.
     ///
     /// This is the method you should reach for first. If it doesn't work
@@ -235,17 +231,19 @@ impl<'a> StyleChain<'a> {
     pub fn barred<'b>(&'b self, node: TypeId) -> StyleChain<'b> {
         if self
             .maps()
-            .any(|map| map.0.iter().any(|entry| entry.scoped && entry.is_of_same(node)))
+            .any(|map| map.0.iter().any(|entry| entry.scoped && entry.is_of_id(node)))
         {
             StyleChain {
-                first: Link::Barrier(node),
+                link: Some(Link::Barrier(node)),
                 outer: Some(self),
             }
         } else {
             *self
         }
     }
+}
 
+impl<'a> StyleChain<'a> {
     /// Iterate over all values for the given property in the chain.
     fn values<P: Property>(self, _: P) -> impl Iterator<Item = &'a P::Value> {
         let mut depth = 0;
@@ -263,16 +261,6 @@ impl<'a> StyleChain<'a> {
         })
     }
 
-    /// Iterate over the links of the chain.
-    fn links(self) -> impl Iterator<Item = Link<'a>> {
-        let mut cursor = Some(self);
-        std::iter::from_fn(move || {
-            let Self { first, outer } = cursor?;
-            cursor = outer.copied();
-            Some(first)
-        })
-    }
-
     /// Iterate over the map links of the chain.
     fn maps(self) -> impl Iterator<Item = &'a StyleMap> {
         self.links().filter_map(|link| match link {
@@ -280,6 +268,16 @@ impl<'a> StyleChain<'a> {
             Link::Barrier(_) => None,
         })
     }
+
+    /// Iterate over the links of the chain.
+    fn links(self) -> impl Iterator<Item = Link<'a>> {
+        let mut cursor = Some(self);
+        std::iter::from_fn(move || {
+            let Self { link, outer } = cursor?;
+            cursor = outer.copied();
+            link
+        })
+    }
 }
 
 impl Debug for StyleChain<'_> {
@@ -300,6 +298,192 @@ impl Debug for Link<'_> {
     }
 }
 
+impl PartialEq for StyleChain<'_> {
+    fn eq(&self, other: &Self) -> bool {
+        let as_ptr = |s| s as *const _;
+        self.link == other.link && self.outer.map(as_ptr) == other.outer.map(as_ptr)
+    }
+}
+
+impl PartialEq for Link<'_> {
+    fn eq(&self, other: &Self) -> bool {
+        match (*self, *other) {
+            (Self::Map(a), Self::Map(b)) => std::ptr::eq(a, b),
+            (Self::Barrier(a), Self::Barrier(b)) => a == b,
+            _ => false,
+        }
+    }
+}
+
+/// A sequence of items with associated styles.
+#[derive(Hash)]
+pub struct StyleVec<T> {
+    items: Vec<T>,
+    maps: Vec<(StyleMap, usize)>,
+}
+
+impl<T> StyleVec<T> {
+    /// Whether there are any items in the sequence.
+    pub fn is_empty(&self) -> bool {
+        self.items.is_empty()
+    }
+
+    /// Iterate over the contained items.
+    pub fn items(&self) -> std::slice::Iter<'_, T> {
+        self.items.iter()
+    }
+
+    /// Iterate over the contained items and associated style maps.
+    pub fn iter(&self) -> impl Iterator<Item = (&T, &StyleMap)> + '_ {
+        let styles = self
+            .maps
+            .iter()
+            .flat_map(|(map, count)| std::iter::repeat(map).take(*count));
+        self.items().zip(styles)
+    }
+}
+
+impl<T> Default for StyleVec<T> {
+    fn default() -> Self {
+        Self { items: vec![], maps: vec![] }
+    }
+}
+
+impl<T: Debug> Debug for StyleVec<T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        f.debug_list()
+            .entries(self.iter().map(|(item, map)| {
+                crate::util::debug(|f| {
+                    map.fmt(f)?;
+                    item.fmt(f)
+                })
+            }))
+            .finish()
+    }
+}
+
+/// Assists in the construction of a [`StyleVec`].
+pub struct StyleVecBuilder<'a, T> {
+    items: Vec<T>,
+    chains: Vec<(StyleChain<'a>, usize)>,
+}
+
+impl<'a, T> StyleVecBuilder<'a, T> {
+    /// Create a new style-vec builder.
+    pub fn new() -> Self {
+        Self { items: vec![], chains: vec![] }
+    }
+
+    /// Push a new item into the style vector.
+    pub fn push(&mut self, item: T, styles: StyleChain<'a>) {
+        self.items.push(item);
+
+        if let Some((prev, count)) = self.chains.last_mut() {
+            if *prev == styles {
+                *count += 1;
+                return;
+            }
+        }
+
+        self.chains.push((styles, 1));
+    }
+
+    /// Access the last item mutably and its chain by value.
+    pub fn last_mut(&mut self) -> Option<(&mut T, StyleChain<'a>)> {
+        let item = self.items.last_mut()?;
+        let chain = self.chains.last()?.0;
+        Some((item, chain))
+    }
+
+    /// Finish building, returning a pair of two things:
+    /// - a style vector of items with the non-shared styles
+    /// - a shared prefix chain of styles that apply to all items
+    pub fn finish(self) -> (StyleVec<T>, StyleChain<'a>) {
+        let mut iter = self.chains.iter();
+        let mut trunk = match iter.next() {
+            Some(&(chain, _)) => chain,
+            None => return Default::default(),
+        };
+
+        let mut shared = trunk.len();
+        for &(mut chain, _) in iter {
+            let len = chain.len();
+            if len < shared {
+                for _ in 0 .. shared - len {
+                    trunk.pop();
+                }
+                shared = len;
+            } else if len > shared {
+                for _ in 0 .. len - shared {
+                    chain.pop();
+                }
+            }
+
+            while shared > 0 && chain != trunk {
+                trunk.pop();
+                chain.pop();
+                shared -= 1;
+            }
+        }
+
+        let maps = self
+            .chains
+            .into_iter()
+            .map(|(chain, count)| (chain.suffix(shared), count))
+            .collect();
+
+        (StyleVec { items: self.items, maps }, trunk)
+    }
+}
+
+impl<'a, T> Default for StyleVecBuilder<'a, T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+/// Style property keys.
+///
+/// This trait is not intended to be implemented manually, but rather through
+/// the `#[class]` proc-macro.
+pub trait Property: Sync + Send + 'static {
+    /// The type of value that is returned when getting this property from a
+    /// style map. For example, this could be [`Length`](crate::geom::Length)
+    /// for a `WIDTH` property.
+    type Value: Debug + Clone + PartialEq + Hash + Sync + Send + 'static;
+
+    /// The name of the property, used for debug printing.
+    const NAME: &'static str;
+
+    /// Whether the property needs folding.
+    const FOLDING: bool = false;
+
+    /// The type id of the node this property belongs to.
+    fn node_id() -> TypeId;
+
+    /// The default value of the property.
+    fn default() -> Self::Value;
+
+    /// A static reference to the default value of the property.
+    ///
+    /// This is automatically implemented through lazy-initialization in the
+    /// `#[class]` macro. This way, expensive defaults don't need to be
+    /// recreated all the time.
+    fn default_ref() -> &'static Self::Value;
+
+    /// Fold the property with an outer value.
+    ///
+    /// For example, this would fold a relative font size with an outer
+    /// absolute font size.
+    #[allow(unused_variables)]
+    fn fold(inner: Self::Value, outer: Self::Value) -> Self::Value {
+        inner
+    }
+}
+
+/// Marker trait that indicates that a property doesn't need folding.
+pub trait Nonfolding {}
+
 /// An entry for a single style property.
 #[derive(Clone)]
 struct Entry {
@@ -323,13 +507,23 @@ impl Entry {
         self.pair.node_id() == TypeId::of::<T>()
     }
 
-    fn is_of_same(&self, node: TypeId) -> bool {
+    fn is_of_id(&self, node: TypeId) -> bool {
         self.pair.node_id() == node
     }
 
     fn downcast<P: Property>(&self) -> Option<&P::Value> {
         self.pair.as_any().downcast_ref()
     }
+
+    fn interruption(&self) -> Option<Interruption> {
+        if self.is_of::<PageNode>() {
+            Some(Interruption::Page)
+        } else if self.is_of::<ParNode>() {
+            Some(Interruption::Par)
+        } else {
+            None
+        }
+    }
 }
 
 impl Debug for Entry {
@@ -356,48 +550,6 @@ impl Hash for Entry {
     }
 }
 
-/// Style property keys.
-///
-/// This trait is not intended to be implemented manually, but rather through
-/// the `#[properties]` proc-macro.
-pub trait Property: Sync + Send + 'static {
-    /// The type of value that is returned when getting this property from a
-    /// style map. For example, this could be [`Length`](crate::geom::Length)
-    /// for a `WIDTH` property.
-    type Value: Debug + Clone + PartialEq + Hash + Sync + Send + 'static;
-
-    /// The name of the property, used for debug printing.
-    const NAME: &'static str;
-
-    /// Whether the property needs folding.
-    const FOLDING: bool = false;
-
-    /// The type id of the node this property belongs to.
-    fn node_id() -> TypeId;
-
-    /// The default value of the property.
-    fn default() -> Self::Value;
-
-    /// A static reference to the default value of the property.
-    ///
-    /// This is automatically implemented through lazy-initialization in the
-    /// `#[properties]` macro. This way, expensive defaults don't need to be
-    /// recreated all the time.
-    fn default_ref() -> &'static Self::Value;
-
-    /// Fold the property with an outer value.
-    ///
-    /// For example, this would fold a relative font size with an outer
-    /// absolute font size.
-    #[allow(unused_variables)]
-    fn fold(inner: Self::Value, outer: Self::Value) -> Self::Value {
-        inner
-    }
-}
-
-/// Marker trait that indicates that a property doesn't need folding.
-pub trait Nonfolding {}
-
 /// This trait is implemented for pairs of zero-sized property keys and their
 /// value types below. Although it is zero-sized, the property `P` must be part
 /// of the implementing type so that we can use it in the methods (it must be a

src/eval/template.rs

@@ -1,11 +1,12 @@
-use std::convert::TryFrom;
 use std::fmt::Debug;
 use std::hash::Hash;
 use std::iter::Sum;
 use std::mem;
 use std::ops::{Add, AddAssign};
 
-use super::{Property, StyleMap, Styled};
+use typed_arena::Arena;
+
+use super::{CollapsingBuilder, Interruption, Property, StyleMap, StyleVecBuilder};
 use crate::diag::StrResult;
 use crate::layout::{Layout, PackedNode};
 use crate::library::prelude::*;
@@ -50,16 +51,16 @@ pub enum Template {
     Horizontal(SpacingKind),
     /// Plain text.
     Text(EcoString),
-    /// An inline node.
+    /// An inline-level node.
     Inline(PackedNode),
     /// A paragraph break.
     Parbreak,
-    /// Vertical spacing.
-    Vertical(SpacingKind),
-    /// A block node.
-    Block(PackedNode),
     /// A column break.
     Colbreak,
+    /// Vertical spacing.
+    Vertical(SpacingKind),
+    /// A block-level node.
+    Block(PackedNode),
     /// A page break.
     Pagebreak,
     /// A page node.
@@ -95,12 +96,11 @@ impl Template {
     /// Layout this template into a collection of pages.
     pub fn layout(&self, ctx: &mut Context) -> Vec<Arc<Frame>> {
         let (mut ctx, styles) = LayoutContext::new(ctx);
-        let mut packer = Packer::new(true);
-        packer.walk(self.clone(), StyleMap::new());
-        packer
-            .into_root()
+        let (pages, shared) = Builder::build_pages(self);
+        let styles = shared.chain(&styles);
+        pages
             .iter()
-            .flat_map(|styled| styled.item.layout(&mut ctx, styled.map.chain(&styles)))
+            .flat_map(|(page, map)| page.layout(&mut ctx, map.chain(&styles)))
             .collect()
     }
 
@@ -159,13 +159,13 @@ impl Debug for Template {
                 f.write_str(")")
             }
             Self::Parbreak => f.pad("Parbreak"),
+            Self::Colbreak => f.pad("Colbreak"),
             Self::Vertical(kind) => write!(f, "Vertical({kind:?})"),
             Self::Block(node) => {
                 f.write_str("Block(")?;
                 node.fmt(f)?;
                 f.write_str(")")
             }
-            Self::Colbreak => f.pad("Colbreak"),
             Self::Pagebreak => f.pad("Pagebreak"),
             Self::Page(page) => page.fmt(f),
             Self::Styled(sub, map) => {
@@ -220,338 +220,172 @@ impl Layout for Template {
         regions: &Regions,
         styles: StyleChain,
     ) -> Vec<Constrained<Arc<Frame>>> {
-        let mut packer = Packer::new(false);
-        packer.walk(self.clone(), StyleMap::new());
-        packer.into_block().layout(ctx, regions, styles)
+        let (flow, shared) = Builder::build_flow(self);
+        flow.layout(ctx, regions, shared.chain(&styles))
     }
 
     fn pack(self) -> PackedNode {
-        if let Template::Block(packed) = self {
-            packed
-        } else {
-            PackedNode::new(self)
+        match self {
+            Template::Block(node) => node,
+            other => PackedNode::new(other),
         }
     }
 }
 
-/// Packs a [`Template`] into a flow or root node.
-struct Packer {
-    /// Whether this packer produces a root node.
-    top: bool,
-    /// The accumulated page nodes.
-    pages: Vec<Styled<PageNode>>,
-    /// The accumulated flow children.
-    flow: Builder<Styled<FlowChild>>,
-    /// The accumulated paragraph children.
-    par: Builder<Styled<ParChild>>,
+/// Builds a flow or page nodes from a template.
+struct Builder<'a> {
+    /// An arena where intermediate style chains are stored.
+    arena: &'a Arena<StyleChain<'a>>,
+    /// The already built page runs.
+    pages: Option<StyleVecBuilder<'a, PageNode>>,
+    /// The currently built flow.
+    flow: CollapsingBuilder<'a, FlowChild>,
+    /// The currently built paragraph.
+    par: CollapsingBuilder<'a, ParChild>,
+    /// Whether to keep the next page even if it is empty.
+    keep_next: bool,
 }
 
-impl Packer {
-    /// Start a new template-packing session.
-    fn new(top: bool) -> Self {
+impl<'a> Builder<'a> {
+    /// Build page runs from a template.
+    fn build_pages(template: &Template) -> (StyleVec<PageNode>, StyleMap) {
+        let arena = Arena::new();
+
+        let mut builder = Builder::prepare(&arena, true);
+        builder.process(template, StyleChain::default());
+        builder.finish_page(true, false, StyleChain::default());
+
+        let (pages, shared) = builder.pages.unwrap().finish();
+        (pages, shared.to_map())
+    }
+
+    /// Build a subflow from a template.
+    fn build_flow(template: &Template) -> (FlowNode, StyleMap) {
+        let arena = Arena::new();
+
+        let mut builder = Builder::prepare(&arena, false);
+        builder.process(template, StyleChain::default());
+        builder.finish_par();
+
+        let (flow, shared) = builder.flow.finish();
+        (FlowNode(flow), shared.to_map())
+    }
+
+    /// Prepare the builder.
+    fn prepare(arena: &'a Arena<StyleChain<'a>>, top: bool) -> Self {
         Self {
-            top,
-            pages: vec![],
-            flow: Builder::default(),
-            par: Builder::default(),
+            arena,
+            pages: top.then(|| StyleVecBuilder::new()),
+            flow: CollapsingBuilder::new(),
+            par: CollapsingBuilder::new(),
+            keep_next: true,
         }
     }
 
-    /// Finish up and return the resulting flow.
-    fn into_block(mut self) -> PackedNode {
-        self.parbreak(None, false);
-        FlowNode(self.flow.children).pack()
-    }
-
-    /// Finish up and return the resulting root node.
-    fn into_root(mut self) -> Vec<Styled<PageNode>> {
-        self.pagebreak();
-        self.pages
-    }
-
-    /// Consider a template with the given styles.
-    fn walk(&mut self, template: Template, styles: StyleMap) {
+    /// Process a template.
+    fn process(&mut self, template: &'a Template, styles: StyleChain<'a>) {
         match template {
             Template::Space => {
-                // A text space is "soft", meaning that it can be eaten up by
-                // adjacent line breaks or explicit spacings.
-                self.par.last.soft(Styled::new(ParChild::text(' '), styles), false);
+                self.par.weak(ParChild::Text(' '.into()), styles);
             }
             Template::Linebreak => {
-                // A line break eats up surrounding text spaces.
-                self.par.last.hard();
-                self.push_inline(Styled::new(ParChild::text('\n'), styles));
-                self.par.last.hard();
-            }
-            Template::Parbreak => {
-                // An explicit paragraph break is styled according to the active
-                // styles (`Some(_)`) whereas paragraph breaks forced by
-                // incompatibility take their styles from the preceding
-                // paragraph.
-                self.parbreak(Some(styles), true);
-            }
-            Template::Colbreak => {
-                // Explicit column breaks end the current paragraph and then
-                // discards the paragraph break.
-                self.parbreak(None, false);
-                self.make_flow_compatible(&styles);
-                self.flow.children.push(Styled::new(FlowChild::Skip, styles));
-                self.flow.last.hard();
-            }
-            Template::Pagebreak => {
-                // We must set the flow styles after the page break such that an
-                // empty page created by two page breaks in a row has styles at
-                // all.
-                self.pagebreak();
-                self.flow.styles = styles;
-            }
-            Template::Text(text) => {
-                self.push_inline(Styled::new(ParChild::text(text), styles));
+                self.par.destructive(ParChild::Text('\n'.into()), styles);
             }
             Template::Horizontal(kind) => {
-                // Just like a line break, explicit horizontal spacing eats up
-                // surrounding text spaces.
-                self.par.last.hard();
-                self.push_inline(Styled::new(ParChild::Spacing(kind), styles));
-                self.par.last.hard();
+                let child = ParChild::Spacing(*kind);
+                if kind.is_fractional() {
+                    self.par.destructive(child, styles);
+                } else {
+                    self.par.ignorant(child, styles);
+                }
+            }
+            Template::Text(text) => {
+                self.par.supportive(ParChild::Text(text.clone()), styles);
+            }
+            Template::Inline(node) => {
+                self.par.supportive(ParChild::Node(node.clone()), styles);
+            }
+            Template::Parbreak => {
+                self.finish_par();
+                self.flow.weak(FlowChild::Parbreak, styles);
+            }
+            Template::Colbreak => {
+                self.finish_par();
+                self.flow.destructive(FlowChild::Colbreak, styles);
             }
             Template::Vertical(kind) => {
-                // Explicit vertical spacing ends the current paragraph and then
-                // discards the paragraph break.
-                self.parbreak(None, false);
-                self.make_flow_compatible(&styles);
-                self.flow.children.push(Styled::new(FlowChild::Spacing(kind), styles));
-                self.flow.last.hard();
+                self.finish_par();
+                let child = FlowChild::Spacing(*kind);
+                if kind.is_fractional() {
+                    self.flow.destructive(child, styles);
+                } else {
+                    self.flow.ignorant(child, styles);
+                }
             }
-            Template::Inline(inline) => {
-                self.push_inline(Styled::new(ParChild::Node(inline), styles));
+            Template::Block(node) => {
+                self.finish_par();
+                let child = FlowChild::Node(node.clone());
+                if node.is::<PlaceNode>() {
+                    self.flow.ignorant(child, styles);
+                } else {
+                    self.flow.supportive(child, styles);
+                }
             }
-            Template::Block(block) => {
-                self.push_block(Styled::new(block, styles));
+            Template::Pagebreak => {
+                self.finish_page(true, true, styles);
             }
             Template::Page(page) => {
-                if self.top {
-                    self.pagebreak();
-                    self.pages.push(Styled::new(page, styles));
-                } else {
-                    self.push_block(Styled::new(page.0, styles));
+                self.finish_page(false, false, styles);
+                if let Some(pages) = &mut self.pages {
+                    pages.push(page.clone(), styles);
                 }
             }
-            Template::Styled(template, mut map) => {
-                map.apply(&styles);
-                self.walk(*template, map);
+            Template::Styled(sub, map) => {
+                let interruption = map.interruption();
+                match interruption {
+                    Some(Interruption::Page) => self.finish_page(false, true, styles),
+                    Some(Interruption::Par) => self.finish_par(),
+                    None => {}
+                }
+
+                let outer = self.arena.alloc(styles);
+                let styles = map.chain(outer);
+                self.process(sub, styles);
+
+                match interruption {
+                    Some(Interruption::Page) => self.finish_page(true, false, styles),
+                    Some(Interruption::Par) => self.finish_par(),
+                    None => {}
+                }
             }
             Template::Sequence(seq) => {
-                // For a list of templates, we apply the list's styles to each
-                // templates individually.
-                for item in seq {
-                    self.walk(item, styles.clone());
+                for sub in seq {
+                    self.process(sub, styles);
                 }
             }
         }
     }
 
-    /// Insert an inline-level element into the current paragraph.
-    fn push_inline(&mut self, child: Styled<ParChild>) {
-        // The child's map must be both compatible with the current page and the
-        // current paragraph.
-        self.make_flow_compatible(&child.map);
-        self.make_par_compatible(&child.map);
-
-        if let Some(styled) = self.par.last.any() {
-            self.push_coalescing(styled);
+    /// Finish the currently built paragraph.
+    fn finish_par(&mut self) {
+        let (par, shared) = mem::take(&mut self.par).finish();
+        if !par.is_empty() {
+            let node = ParNode(par).pack();
+            self.flow.supportive(FlowChild::Node(node), shared);
         }
-
-        self.push_coalescing(child);
-        self.par.last.any();
     }
 
-    /// Push a paragraph child, coalescing text nodes with compatible styles.
-    fn push_coalescing(&mut self, child: Styled<ParChild>) {
-        if let ParChild::Text(right) = &child.item {
-            if let Some(Styled { item: ParChild::Text(left), map }) =
-                self.par.children.last_mut()
-            {
-                if child.map.compatible::<TextNode>(map) {
-                    left.0.push_str(&right.0);
-                    return;
-                }
+    /// Finish the currently built page run.
+    fn finish_page(&mut self, keep_last: bool, keep_next: bool, styles: StyleChain<'a>) {
+        self.finish_par();
+        if let Some(pages) = &mut self.pages {
+            let (flow, shared) = mem::take(&mut self.flow).finish();
+            if !flow.is_empty() || (keep_last && self.keep_next) {
+                let styles = if flow.is_empty() { styles } else { shared };
+                let node = PageNode(FlowNode(flow).pack());
+                pages.push(node, styles);
             }
         }
-
-        self.par.children.push(child);
-    }
-
-    /// Insert a block-level element into the current flow.
-    fn push_block(&mut self, node: Styled<PackedNode>) {
-        let placed = node.item.is::<PlaceNode>();
-
-        self.parbreak(Some(node.map.clone()), false);
-        self.make_flow_compatible(&node.map);
-        self.flow.children.extend(self.flow.last.any());
-        self.flow.children.push(node.map(FlowChild::Node));
-        self.parbreak(None, false);
-
-        // Prevent paragraph spacing between the placed node and the paragraph
-        // below it.
-        if placed {
-            self.flow.last.hard();
-        }
-    }
-
-    /// Advance to the next paragraph.
-    fn parbreak(&mut self, break_styles: Option<StyleMap>, important: bool) {
-        // Erase any styles that will be inherited anyway.
-        let Builder { mut children, styles, .. } = mem::take(&mut self.par);
-        for Styled { map, .. } in &mut children {
-            map.erase(&styles);
-        }
-
-        // We don't want empty paragraphs.
-        if !children.is_empty() {
-            // The paragraph's children are all compatible with the page, so the
-            // paragraph is too, meaning we don't need to check or intersect
-            // anything here.
-            let par = ParNode(children).pack();
-            self.flow.children.extend(self.flow.last.any());
-            self.flow.children.push(Styled::new(FlowChild::Node(par), styles));
-        }
-
-        // Actually styled breaks have precedence over whatever was before.
-        if break_styles.is_some() {
-            if let Last::Soft(_, false) = self.flow.last {
-                self.flow.last = Last::Any;
-            }
-        }
-
-        // For explicit paragraph breaks, `break_styles` is already `Some(_)`.
-        // For page breaks due to incompatibility, we fall back to the styles
-        // of the preceding thing.
-        let break_styles = break_styles
-            .or_else(|| self.flow.children.last().map(|styled| styled.map.clone()))
-            .unwrap_or_default();
-
-        // Insert paragraph spacing.
-        self.flow
-            .last
-            .soft(Styled::new(FlowChild::Break, break_styles), important);
-    }
-
-    /// Advance to the next page.
-    fn pagebreak(&mut self) {
-        if self.top {
-            self.parbreak(None, false);
-
-            // Take the flow and erase any styles that will be inherited anyway.
-            let Builder { mut children, styles, .. } = mem::take(&mut self.flow);
-            for Styled { map, .. } in &mut children {
-                map.erase(&styles);
-            }
-
-            let flow = FlowNode(children).pack();
-            self.pages.push(Styled::new(PageNode(flow), styles));
-        }
-    }
-
-    /// Break to a new paragraph if the `styles` contain paragraph styles that
-    /// are incompatible with the current paragraph.
-    fn make_par_compatible(&mut self, styles: &StyleMap) {
-        if self.par.children.is_empty() {
-            self.par.styles = styles.clone();
-            return;
-        }
-
-        if !self.par.styles.compatible::<ParNode>(styles) {
-            self.parbreak(Some(styles.clone()), false);
-            self.par.styles = styles.clone();
-            return;
-        }
-
-        self.par.styles.intersect(styles);
-    }
-
-    /// Break to a new page if the `styles` contain page styles that are
-    /// incompatible with the current flow.
-    fn make_flow_compatible(&mut self, styles: &StyleMap) {
-        if self.flow.children.is_empty() && self.par.children.is_empty() {
-            self.flow.styles = styles.clone();
-            return;
-        }
-
-        if self.top && !self.flow.styles.compatible::<PageNode>(styles) {
-            self.pagebreak();
-            self.flow.styles = styles.clone();
-            return;
-        }
-
-        self.flow.styles.intersect(styles);
-    }
-}
-
-/// Container for building a flow or paragraph.
-struct Builder<T> {
-    /// The intersection of the style properties of all `children`.
-    styles: StyleMap,
-    /// The accumulated flow or paragraph children.
-    children: Vec<T>,
-    /// The kind of thing that was last added.
-    last: Last<T>,
-}
-
-impl<T> Default for Builder<T> {
-    fn default() -> Self {
-        Self {
-            styles: StyleMap::new(),
-            children: vec![],
-            last: Last::None,
-        }
-    }
-}
-
-/// The kind of child that was last added to a flow or paragraph. A small finite
-/// state machine used to coalesce spaces.
-///
-/// Soft children can only exist when surrounded by `Any` children. Not at the
-/// start, end or next to hard children. This way, spaces at start and end of
-/// paragraphs and next to `#h(..)` goes away.
-enum Last<N> {
-    /// Start state, nothing there.
-    None,
-    /// Text or a block node or something.
-    Any,
-    /// Hard children: Linebreaks and explicit spacing.
-    Hard,
-    /// Soft children: Word spaces and paragraph breaks. These are saved here
-    /// temporarily and then applied once an `Any` child appears. The boolean
-    /// says whether this soft child is "important" and preferrable to other soft
-    /// nodes (that is the case for explicit paragraph breaks).
-    Soft(N, bool),
-}
-
-impl<N> Last<N> {
-    /// Transition into the `Any` state and return a soft child to really add
-    /// now if currently in `Soft` state.
-    fn any(&mut self) -> Option<N> {
-        match mem::replace(self, Self::Any) {
-            Self::Soft(soft, _) => Some(soft),
-            _ => None,
-        }
-    }
-
-    /// Transition into the `Soft` state, but only if in `Any`. Otherwise, the
-    /// soft child is discarded.
-    fn soft(&mut self, soft: N, important: bool) {
-        if matches!(
-            (&self, important),
-            (Self::Any, _) | (Self::Soft(_, false), true)
-        ) {
-            *self = Self::Soft(soft, important);
-        }
-    }
-
-    /// Transition into the `Hard` state, discarding a possibly existing soft
-    /// child and preventing further soft nodes from being added.
-    fn hard(&mut self) {
-        *self = Self::Hard;
+        self.keep_next = keep_next;
     }
 }

src/library/flow.rs

@@ -1,16 +1,27 @@
 //! A flow of paragraphs and other block-level nodes.
 
-use std::fmt::{self, Debug, Formatter};
-
 use super::prelude::*;
 use super::{AlignNode, ParNode, PlaceNode, SpacingKind, TextNode};
 
-/// A vertical flow of content consisting of paragraphs and other layout nodes.
+/// Arrange spacing, paragraphs and other block-level nodes into a flow.
 ///
 /// This node is reponsible for layouting both the top-level content flow and
 /// the contents of boxes.
 #[derive(Hash)]
-pub struct FlowNode(pub Vec<Styled<FlowChild>>);
+pub struct FlowNode(pub StyleVec<FlowChild>);
+
+/// A child of a flow node.
+#[derive(Hash)]
+pub enum FlowChild {
+    /// A paragraph / block break.
+    Parbreak,
+    /// A column / region break.
+    Colbreak,
+    /// Vertical spacing between other children.
+    Spacing(SpacingKind),
+    /// An arbitrary block-level node.
+    Node(PackedNode),
+}
 
 impl Layout for FlowNode {
     fn layout(
@@ -19,45 +30,58 @@ impl Layout for FlowNode {
         regions: &Regions,
         styles: StyleChain,
     ) -> Vec<Constrained<Arc<Frame>>> {
-        FlowLayouter::new(self, regions.clone()).layout(ctx, styles)
+        let mut layouter = FlowLayouter::new(regions);
+
+        for (child, map) in self.0.iter() {
+            let styles = map.chain(&styles);
+            match child {
+                FlowChild::Parbreak => {
+                    let em = styles.get(TextNode::SIZE).abs;
+                    let amount = styles.get(ParNode::SPACING).resolve(em);
+                    layouter.layout_spacing(SpacingKind::Linear(amount.into()));
+                }
+                FlowChild::Colbreak => {
+                    layouter.finish_region();
+                }
+                FlowChild::Spacing(kind) => {
+                    layouter.layout_spacing(*kind);
+                }
+                FlowChild::Node(ref node) => {
+                    layouter.layout_node(ctx, node, styles);
+                }
+            }
+        }
+
+        layouter.finish()
+    }
+}
+
+impl Merge for FlowChild {
+    fn merge(&mut self, _: &Self) -> bool {
+        false
     }
 }
 
 impl Debug for FlowNode {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         f.write_str("Flow ")?;
-        f.debug_list().entries(&self.0).finish()
+        self.0.fmt(f)
     }
 }
 
-/// A child of a flow node.
-#[derive(Hash)]
-pub enum FlowChild {
-    /// A paragraph/block break.
-    Break,
-    /// Skip the rest of the region and move to the next.
-    Skip,
-    /// Vertical spacing between other children.
-    Spacing(SpacingKind),
-    /// An arbitrary node.
-    Node(PackedNode),
-}
-
 impl Debug for FlowChild {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         match self {
-            Self::Break => f.pad("Break"),
-            Self::Skip => f.pad("Skip"),
-            Self::Spacing(kind) => kind.fmt(f),
+            Self::Parbreak => f.pad("Parbreak"),
+            Self::Colbreak => f.pad("Colbreak"),
+            Self::Spacing(kind) => write!(f, "{:?}", kind),
             Self::Node(node) => node.fmt(f),
         }
     }
 }
 
 /// Performs flow layout.
-struct FlowLayouter<'a> {
-    /// The children of the flow.
-    children: &'a [Styled<FlowChild>],
+pub struct FlowLayouter {
     /// The regions to layout children into.
     regions: Regions,
     /// Whether the flow should expand to fill the region.
@@ -69,6 +93,8 @@ struct FlowLayouter<'a> {
     used: Size,
     /// The sum of fractional ratios in the current region.
     fr: Fractional,
+    /// Whether to add leading before the next node.
+    leading: bool,
     /// Spacing and layouted nodes.
     items: Vec<FlowItem>,
     /// Finished frames for previous regions.
@@ -87,98 +113,64 @@ enum FlowItem {
     Placed(Arc<Frame>),
 }
 
-impl<'a> FlowLayouter<'a> {
+impl FlowLayouter {
     /// Create a new flow layouter.
-    fn new(flow: &'a FlowNode, mut regions: Regions) -> Self {
+    pub fn new(regions: &Regions) -> Self {
         let expand = regions.expand;
         let full = regions.current;
 
         // Disable vertical expansion for children.
+        let mut regions = regions.clone();
         regions.expand.y = false;
 
         Self {
-            children: &flow.0,
             regions,
             expand,
             full,
             used: Size::zero(),
             fr: Fractional::zero(),
+            leading: false,
             items: vec![],
             finished: vec![],
         }
     }
 
-    /// Layout all children.
-    fn layout(
-        mut self,
-        ctx: &mut LayoutContext,
-        styles: StyleChain,
-    ) -> Vec<Constrained<Arc<Frame>>> {
-        for styled in self.children {
-            let styles = styled.map.chain(&styles);
-            match styled.item {
-                FlowChild::Break => {
-                    let em = styles.get(TextNode::SIZE).abs;
-                    let amount = styles.get(ParNode::SPACING).resolve(em);
-                    self.layout_absolute(amount.into());
-                }
-                FlowChild::Skip => {
-                    self.finish_region();
-                }
-                FlowChild::Spacing(kind) => {
-                    self.layout_spacing(kind);
-                }
-                FlowChild::Node(ref node) => {
-                    if self.regions.is_full() {
-                        self.finish_region();
-                    }
-
-                    self.layout_node(ctx, node, styles);
-                }
-            }
-        }
-
-        if self.expand.y {
-            while self.regions.backlog.len() > 0 {
-                self.finish_region();
-            }
-        }
-
-        self.finish_region();
-        self.finished
-    }
-
     /// Layout spacing.
-    fn layout_spacing(&mut self, spacing: SpacingKind) {
+    pub fn layout_spacing(&mut self, spacing: SpacingKind) {
         match spacing {
-            SpacingKind::Linear(v) => self.layout_absolute(v),
+            SpacingKind::Linear(v) => {
+                // Resolve the linear and limit it to the remaining space.
+                let resolved = v.resolve(self.full.y);
+                let limited = resolved.min(self.regions.current.y);
+                self.regions.current.y -= limited;
+                self.used.y += limited;
+                self.items.push(FlowItem::Absolute(resolved));
+            }
             SpacingKind::Fractional(v) => {
                 self.items.push(FlowItem::Fractional(v));
                 self.fr += v;
+                self.leading = false;
             }
         }
     }
 
-    /// Layout absolute spacing.
-    fn layout_absolute(&mut self, amount: Linear) {
-        // Resolve the linear, limiting it to the remaining available space.
-        let resolved = amount.resolve(self.full.y);
-        let limited = resolved.min(self.regions.current.y);
-        self.regions.current.y -= limited;
-        self.used.y += limited;
-        self.items.push(FlowItem::Absolute(resolved));
-    }
-
     /// Layout a node.
-    fn layout_node(
+    pub fn layout_node(
         &mut self,
         ctx: &mut LayoutContext,
         node: &PackedNode,
         styles: StyleChain,
     ) {
+        // Don't even try layouting into a full region.
+        if self.regions.is_full() {
+            self.finish_region();
+        }
+
         // Placed nodes that are out of flow produce placed items which aren't
         // aligned later.
+        let mut is_placed = false;
         if let Some(placed) = node.downcast::<PlaceNode>() {
+            is_placed = true;
             if placed.out_of_flow() {
                 let frame = node.layout(ctx, &self.regions, styles).remove(0);
                 self.items.push(FlowItem::Placed(frame.item));
@@ -186,6 +178,13 @@ impl<'a> FlowLayouter<'a> {
             }
         }
 
+        // Add leading.
+        if self.leading {
+            let em = styles.get(TextNode::SIZE).abs;
+            let amount = styles.get(ParNode::LEADING).resolve(em);
+            self.layout_spacing(SpacingKind::Linear(amount.into()));
+        }
+
         // How to align the node.
         let aligns = Spec::new(
             // For non-expanding paragraphs it is crucial that we align the
@@ -211,10 +210,12 @@ impl<'a> FlowLayouter<'a> {
                 self.finish_region();
             }
         }
+
+        self.leading = !is_placed;
     }
 
     /// Finish the frame for one region.
-    fn finish_region(&mut self) {
+    pub fn finish_region(&mut self) {
         // Determine the size of the flow in this region dependening on whether
         // the region expands.
         let mut size = self.expand.select(self.full, self.used);
@@ -263,6 +264,19 @@ impl<'a> FlowLayouter<'a> {
         self.full = self.regions.current;
         self.used = Size::zero();
         self.fr = Fractional::zero();
+        self.leading = false;
         self.finished.push(output.constrain(cts));
     }
+
+    /// Finish layouting and return the resulting frames.
+    pub fn finish(mut self) -> Vec<Constrained<Arc<Frame>>> {
+        if self.expand.y {
+            while self.regions.backlog.len() > 0 {
+                self.finish_region();
+            }
+        }
+
+        self.finish_region();
+        self.finished
+    }
 }

src/library/mod.rs

@@ -68,8 +68,8 @@ prelude! {
 
     pub use crate::diag::{At, TypResult};
     pub use crate::eval::{
-        Args, Construct, EvalContext, Template, Property, Scope, Set, Smart, StyleChain,
-        StyleMap, Styled, Value,
+        Args, Construct, EvalContext, Merge, Property, Scope, Set, Smart, StyleChain,
+        StyleMap, StyleVec, Template, Value,
     };
     pub use crate::frame::*;
     pub use crate::geom::*;

src/library/par.rs

@@ -1,6 +1,5 @@
 //! Paragraph layout.
 
-use std::fmt::{self, Debug, Formatter};
 use std::sync::Arc;
 
 use itertools::Either;
@@ -11,9 +10,20 @@ use super::prelude::*;
 use super::{shape, ShapedText, SpacingKind, TextNode};
 use crate::util::{ArcExt, EcoString, RangeExt, SliceExt};
 
-/// Arrange text, spacing and inline nodes into a paragraph.
+/// Arrange text, spacing and inline-level nodes into a paragraph.
 #[derive(Hash)]
-pub struct ParNode(pub Vec<Styled<ParChild>>);
+pub struct ParNode(pub StyleVec<ParChild>);
+
+/// A uniformly styled atomic piece of a paragraph.
+#[derive(Hash)]
+pub enum ParChild {
+    /// A chunk of text.
+    Text(EcoString),
+    /// Horizontal spacing between other children.
+    Spacing(SpacingKind),
+    /// An arbitrary inline-level node.
+    Node(PackedNode),
+}
 
 #[class]
 impl ParNode {
@@ -23,8 +33,8 @@ impl ParNode {
     pub const ALIGN: Align = Align::Left;
     /// The spacing between lines (dependent on scaled font size).
     pub const LEADING: Linear = Relative::new(0.65).into();
-    /// The spacing between paragraphs (dependent on scaled font size).
-    pub const SPACING: Linear = Relative::new(1.2).into();
+    /// The extra spacing between paragraphs (dependent on scaled font size).
+    pub const SPACING: Linear = Relative::new(0.55).into();
 
     fn construct(_: &mut EvalContext, args: &mut Args) -> TypResult<Template> {
         // The paragraph constructor is special: It doesn't create a paragraph
@@ -116,9 +126,9 @@ impl ParNode {
 
     /// The string representation of each child.
     fn strings(&self) -> impl Iterator<Item = &str> {
-        self.0.iter().map(|styled| match &styled.item {
+        self.0.items().map(|child| match child {
+            ParChild::Text(text) => text,
             ParChild::Spacing(_) => " ",
-            ParChild::Text(text) => &text.0,
             ParChild::Node(_) => "\u{FFFC}",
         })
     }
@@ -127,38 +137,31 @@ impl ParNode {
 impl Debug for ParNode {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         f.write_str("Par ")?;
-        f.debug_list().entries(&self.0).finish()
-    }
-}
-
-/// A child of a paragraph node.
-#[derive(Hash)]
-pub enum ParChild {
-    /// Spacing between other nodes.
-    Spacing(SpacingKind),
-    /// A run of text and how to align it in its line.
-    Text(TextNode),
-    /// Any child node and how to align it in its line.
-    Node(PackedNode),
-}
-
-impl ParChild {
-    /// Create a text child.
-    pub fn text(text: impl Into<EcoString>) -> Self {
-        Self::Text(TextNode(text.into()))
+        self.0.fmt(f)
     }
 }
 
 impl Debug for ParChild {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
         match self {
-            Self::Spacing(kind) => kind.fmt(f),
-            Self::Text(text) => text.fmt(f),
+            Self::Text(text) => write!(f, "Text({:?})", text),
+            Self::Spacing(kind) => write!(f, "{:?}", kind),
             Self::Node(node) => node.fmt(f),
         }
     }
 }
 
+impl Merge for ParChild {
+    fn merge(&mut self, next: &Self) -> bool {
+        if let (Self::Text(left), Self::Text(right)) = (self, next) {
+            left.push_str(right);
+            true
+        } else {
+            false
+        }
+    }
+}
+
 /// A paragraph break.
 pub struct ParbreakNode;
 
@@ -222,20 +225,9 @@ impl<'a> ParLayouter<'a> {
         let mut ranges = vec![];
 
         // Layout the children and collect them into items.
-        for (range, styled) in par.ranges().zip(&par.0) {
-            let styles = styled.map.chain(styles);
-            match styled.item {
-                ParChild::Spacing(kind) => match kind {
-                    SpacingKind::Linear(v) => {
-                        let resolved = v.resolve(regions.current.x);
-                        items.push(ParItem::Absolute(resolved));
-                        ranges.push(range);
-                    }
-                    SpacingKind::Fractional(v) => {
-                        items.push(ParItem::Fractional(v));
-                        ranges.push(range);
-                    }
-                },
+        for (range, (child, map)) in par.ranges().zip(par.0.iter()) {
+            let styles = map.chain(styles);
+            match child {
                 ParChild::Text(_) => {
                     // TODO: Also split by language and script.
                     let mut cursor = range.start;
@@ -249,7 +241,18 @@ impl<'a> ParLayouter<'a> {
                         ranges.push(subrange);
                     }
                 }
-                ParChild::Node(ref node) => {
+                ParChild::Spacing(kind) => match *kind {
+                    SpacingKind::Linear(v) => {
+                        let resolved = v.resolve(regions.current.x);
+                        items.push(ParItem::Absolute(resolved));
+                        ranges.push(range);
+                    }
+                    SpacingKind::Fractional(v) => {
+                        items.push(ParItem::Fractional(v));
+                        ranges.push(range);
+                    }
+                },
+                ParChild::Node(node) => {
                     let size = Size::new(regions.current.x, regions.base.y);
                     let pod = Regions::one(size, regions.base, Spec::splat(false));
                     let frame = node.layout(ctx, &pod, styles).remove(0);

src/library/spacing.rs

@@ -31,6 +31,13 @@ pub enum SpacingKind {
     Fractional(Fractional),
 }
 
+impl SpacingKind {
+    /// Whether this is fractional spacing.
+    pub fn is_fractional(self) -> bool {
+        matches!(self, Self::Fractional(_))
+    }
+}
+
 castable! {
     SpacingKind,
     Expected: "linear or fractional",

src/library/text.rs

@@ -19,7 +19,7 @@ use crate::util::{EcoString, SliceExt};
 
 /// A single run of text with the same style.
 #[derive(Hash)]
-pub struct TextNode(pub EcoString);
+pub struct TextNode;
 
 #[class]
 impl TextNode {
@@ -144,12 +144,6 @@ impl TextNode {
     }
 }
 
-impl Debug for TextNode {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        write!(f, "Text({:?})", self.0)
-    }
-}
-
 /// Strong text, rendered in boldface.
 pub struct StrongNode;
 

tests/typ/coma.typ

@@ -6,11 +6,10 @@ Sekretariat MA \
 Dr. Max Mustermann \
 Ola Nordmann, John Doe
 
-#v(6mm)
+#v(2mm)
 #align(center)[
-  ==== 3. Übungsblatt Computerorientierte Mathematik II
-  #v(4mm)
-  *Abgabe: 03.05.2019* (bis 10:10 Uhr in MA 001) #v(4mm)
+  ==== 3. Übungsblatt Computerorientierte Mathematik II #v(1mm)
+  *Abgabe: 03.05.2019* (bis 10:10 Uhr in MA 001) #v(1mm)
   *Alle Antworten sind zu beweisen.*
 ]
 
@@ -21,5 +20,4 @@ Die Tiefe eines Knotens _v_ ist die Länge des eindeutigen Weges von der Wurzel
 zu _v_, und die Höhe von _v_ ist die Länge eines längsten (absteigenden) Weges
 von _v_ zu einem Blatt. Die Höhe des Baumes ist die Höhe der Wurzel.
 
-#v(6mm)
 #align(center, image("../res/graph.png", width: 75%))

tests/typ/layout/box-block.typ

@@ -15,6 +15,7 @@ Apart
 #set page(height: 60pt)
 
 First!
+
 #block[
   But, soft! what light through yonder window breaks? It is the east, and Juliet
   is the sun.

tests/typ/layout/page-box.typ

@@ -0,0 +1,14 @@
+// Test that you can't do page related stuff in a container.
+
+---
+A
+#box[
+  B
+  #pagebreak()
+  #set page("a4")
+]
+C
+
+// No consequences from the page("A4") call here.
+#pagebreak()
+D

tests/typ/layout/page-margin.typ

@@ -0,0 +1,20 @@
+// Test page margins.
+
+---
+// Set all margins at once.
+[
+  #set page(height: 20pt, margins: 5pt)
+  #place(top + left)[TL]
+  #place(bottom + right)[BR]
+]
+
+---
+// Set individual margins.
+#set page(height: 40pt)
+[#set page(left: 0pt); #align(left)[Left]]
+[#set page(right: 0pt); #align(right)[Right]]
+[#set page(top: 0pt); #align(top)[Top]]
+[#set page(bottom: 0pt); #align(bottom)[Bottom]]
+
+// Ensure that specific margins override general margins.
+[#set page(margins: 0pt, left: 20pt); Overriden]

tests/typ/layout/page-style.typ

@@ -0,0 +1,28 @@
+// Test setting page styles.
+
+---
+// Empty with styles
+// Should result in one conifer-colored A11 page.
+#set page("a11", flipped: true, fill: conifer)
+
+---
+// Empty with styles and then pagebreak
+// Should result in two forest-colored pages.
+#set page(fill: forest)
+#pagebreak()
+
+---
+// Empty with multiple page styles.
+// Should result in a small white page.
+#set page("a4")
+#set page("a5")
+#set page(width: 1cm, height: 1cm)
+
+---
+// Empty with multiple page styles.
+// Should result in one eastern-colored A11 page.
+#set page("a4")
+#set page("a5")
+#set page("a11", flipped: true, fill: eastern)
+#set text("Roboto", white, smallcaps: true)
+Typst

tests/typ/layout/page.typ

@@ -1,34 +1,33 @@
-// Test configuring page sizes and margins.
+// Test the page class.
+
+---
+// Just empty page.
+// Should result in auto-sized page, just like nothing.
+#page[]
+
+---
+// Just empty page with styles.
+// Should result in one conifer-colored A11 page.
+#page("a11", flipped: true, fill: conifer)[]
 
 ---
 // Set width and height.
+// Should result in one high and one wide page.
 #set page(width: 80pt, height: 80pt)
 [#set page(width: 40pt);High]
 [#set page(height: 40pt);Wide]
 
-// Set all margins at once.
-[
-  #set page(margins: 5pt)
-  #place(top + left)[TL]
-  #place(bottom + right)[BR]
-]
-
-// Set individual margins.
-#set page(height: 40pt)
-[#set page(left: 0pt); #align(left)[Left]]
-[#set page(right: 0pt); #align(right)[Right]]
-[#set page(top: 0pt); #align(top)[Top]]
-[#set page(bottom: 0pt); #align(bottom)[Bottom]]
-
-// Ensure that specific margins override general margins.
-[#set page(margins: 0pt, left: 20pt); Overriden]
-
 // Flipped predefined paper.
 [#set page(paper: "a11", flipped: true);Flipped A11]
 
 ---
+// Test page fill.
 #set page(width: 80pt, height: 40pt, fill: eastern)
 #text(15pt, "Roboto", fill: white, smallcaps: true)[Typst]
+#page(width: 40pt, fill: none, margins: auto, top: 10pt)[Hi]
 
-#set page(width: 40pt, fill: none, margins: auto, top: 10pt)
-Hi
+---
+// Just page followed by pagebreak.
+// Should result in one forest-colored A11 page and one auto-sized page.
+#page("a11", flipped: true, fill: forest)[]
+#pagebreak()

tests/typ/layout/pagebreak.typ

@@ -1,35 +1,23 @@
 // Test forced page breaks.
 
 ---
-First of two
+// Just a pagebreak.
+// Should result in two auto-sized pages.
 #pagebreak()
-#set page(height: 40pt)
-Second of two
 
 ---
-// Make sure that you can't do page related stuff in a container.
-A
-#box[
-  B
-  #pagebreak()
-  #set page("a4")
-]
-C
-
-// No consequences from the page("A4") call here.
+// Pagebreak, empty with styles and then pagebreak
+// Should result in one auto-sized page and two conifer-colored A11 pages.
+#pagebreak()
+#set page(width: 2cm, fill: conifer)
 #pagebreak()
-D
 
 ---
-// Test a combination of pages with bodies and normal content.
-
+// Test a combination of pagebreaks, styled pages and pages with bodies.
 #set page(width: 80pt, height: 30pt)
-
-[#set page(width: 80pt); First]
+[#set page(width: 60pt); First]
 #pagebreak()
 #pagebreak()
-#pagebreak()
-Fourth
-#page(height: 20pt)[]
-Sixth
-[#set page(); Seventh]
+Third
+#page(height: 20pt, fill: forest)[]
+Fif[#set page();th]

tests/typ/layout/spacing.typ

@@ -1,38 +1,27 @@
 // Test the `h` and `v` functions.
 
 ---
-// Ends paragraphs.
-Tightly #v(0pt) packed
+// Linebreak and v(0pt) are equivalent.
+#box[A \ B] #box[A #v(0pt) B]
 
 // Eating up soft spacing.
-Inv #h(0pt) isible
+Inv#h(0pt)isible
 
 // Multiple spacings in a row.
 Add #h(10pt) #h(10pt) up
 
 // Relative to area.
 #let x = 25% - 4pt
-| #h(x) | #h(x) | #h(x) | #h(x) |
+|#h(x)|#h(x)|#h(x)|#h(x)|
 
 // Fractional.
 | #h(1fr) | #h(2fr) | #h(1fr) |
 
 ---
-// Test spacing collapsing with parbreaks.
-#v(0pt)
-A
-#v(0pt)
-B
-#v(0pt)
-
-C #parbreak() D
-
----
-// Test that spacing can carry paragraph and page style properties.
-
-A[#set par(align: right);#h(1cm)]B
-[#set page(height: 20pt);#v(1cm)]
-B
+// Test spacing collapsing before spacing.
+#set par(align: right)
+A #h(0pt) B #h(0pt) \
+A B
 
 ---
 // Missing spacing.

tests/typ/layout/stack-1.typ

@@ -31,7 +31,7 @@
 ---
 // Test spacing.
 #set page(width: 50pt, margins: 0pt)
-#set par(spacing: 5pt)
+#set par(leading: 5pt)
 
 #let x = square(size: 10pt, fill: eastern)
 #stack(dir: rtl, spacing: 5pt, x, x, x)

tests/typ/markup/enums.typ

@@ -8,6 +8,7 @@
 ---
 1. First.
    2. Second.
+
 1. Back to first.
 
 ---

tests/typ/markup/lists.typ

@@ -14,13 +14,15 @@ paragraphs.
 
 ---
 - First level.
+
   - Second level.
 
     There are multiple paragraphs.
     - Third level.
-
     Still the same bullet point.
+
   - Still level 2.
+
 - At the top.
 
 ---

tests/typ/style/construct.typ

@@ -2,7 +2,7 @@
 
 ---
 // Ensure that constructor styles aren't passed down the tree.
-#set par(spacing: 2pt)
+#set par(leading: 2pt)
 #list(
   body-indent: 20pt,
   [First],

tests/typ/style/set-site.typ

@@ -8,7 +8,6 @@ Hello *{x}*
 
 ---
 // Test that lists are affected by correct indents.
-#set par(spacing: 4pt)
 #let fruit = [
   - Apple
   - Orange
@@ -23,7 +22,7 @@ Hello *{x}*
 ---
 // Test that that par spacing and text style are respected from
 // the outside, but the more specific fill is respected.
-#set par(spacing: 4pt)
+#set par(spacing: 0pt)
 #set text(style: "italic", fill: eastern)
 #let x = [And the forest #parbreak() lay silent!]
 #text(fill: forest, x)

tests/typ/text/par.typ

@@ -7,11 +7,11 @@ To the right! Where the sunlight peeks behind the mountain.
 
 ---
 // Test that explicit paragraph break respects active styles.
-#set par(spacing: 7pt)
+#set par(spacing: 0pt)
 [#set par(spacing: 100pt);First]
 
 [#set par(spacing: 100pt);Second]
-#set par(spacing: 20pt)
+#set par(spacing: 13.5pt)
 
 Third
 
@@ -21,32 +21,26 @@ Hello
 
 #set par(spacing: 100pt)
 World
-#set par(spacing: 0pt)
+#set par(spacing: 0pt, leading: 0pt)
 
 You
 
 ---
 // Test that paragraphs break due to incompatibility has correct spacing.
-A #set par(spacing: 0pt); B #parbreak() C
+A #set par(spacing: 0pt, leading: 0pt); B #parbreak() C
 
 ---
 // Test that paragraph breaks due to block nodes have the correct spacing.
+#set par(spacing: 10pt)
 - A
 
-#set par(spacing: 0pt)
+#set par(leading: 0pt)
 - B
 - C
-#set par(spacing: 5pt)
+#set par(leading: 5pt)
 - D
 - E
 
----
-// Test that paragraph break due to incompatibility respects
-// spacing defined by the two adjacent paragraphs.
-#let a = [#set par(spacing: 40pt);Hello]
-#let b = [#set par(spacing: 10pt);World]
-{a}{b}
-
 ---
 // Test weird metrics.
 #set par(spacing: 100%, leading: 0pt)