4 files changed, 188 insertions, 108 deletions

diff --git a/src/eval/class.rs b/src/eval/class.rs
index b7b4d012..307bebcc 100644
--- a/src/eval/class.rs
+++ b/src/eval/class.rs
@@ -66,7 +66,7 @@ impl Class {
         let mut styles = StyleMap::new();
         self.set(args, &mut styles)?;
         let node = (self.construct)(ctx, args)?;
-        Ok(node.styled_with_map(styles))
+        Ok(node.styled_with_map(styles.scoped()))
     }
 
     /// Execute the class's set rule.
diff --git a/src/eval/node.rs b/src/eval/node.rs
index 37f230ee..ecbee8ee 100644
--- a/src/eval/node.rs
+++ b/src/eval/node.rs
@@ -302,7 +302,7 @@ impl Packer {
             if let Some(Styled { item: ParChild::Text(left), map }) =
                 self.par.children.last_mut()
             {
-                if child.map.compatible(map, TextNode::has_property) {
+                if child.map.compatible::<TextNode>(map) {
                     left.0.push_str(&right.0);
                     return;
                 }
@@ -380,7 +380,7 @@ impl Packer {
             return;
         }
 
-        if !self.par.styles.compatible(styles, ParNode::has_property) {
+        if !self.par.styles.compatible::<ParNode>(styles) {
             self.parbreak(None);
             self.par.styles = styles.clone();
             return;
@@ -397,7 +397,7 @@ impl Packer {
             return;
         }
 
-        if self.top && !self.flow.styles.compatible(styles, PageNode::has_property) {
+        if self.top && !self.flow.styles.compatible::<PageNode>(styles) {
             self.pagebreak();
             self.flow.styles = styles.clone();
             return;
diff --git a/src/eval/styles.rs b/src/eval/styles.rs
index 0f3d694a..bdc01f1f 100644
--- a/src/eval/styles.rs
+++ b/src/eval/styles.rs
@@ -100,6 +100,16 @@ impl StyleMap {
         self.0.push(Entry::new(key, true));
     }
 
+    /// Mark all contained properties as _scoped_. This means that they only
+    /// apply to the first descendant node (of their type) in the hierarchy and
+    /// not its children, too. This is used by class constructors.
+    pub fn scoped(mut self) -> Self {
+        for entry in &mut self.0 {
+            entry.scoped = true;
+        }
+        self
+    }
+
     /// Make `self` the first link of the style chain `outer`.
     ///
     /// The resulting style chain contains styles from `self` as well as
@@ -109,7 +119,10 @@ impl StyleMap {
         if self.is_empty() {
             *outer
         } else {
-            StyleChain { inner: self, outer: Some(outer) }
+            StyleChain {
+                first: Link::Map(self),
+                outer: Some(outer),
+            }
         }
     }
 
@@ -122,9 +135,7 @@ impl StyleMap {
     /// immutable style maps from different levels of the hierarchy.
     pub fn apply(&mut self, outer: &Self) {
         for outer in &outer.0 {
-            if let Some(inner) =
-                self.0.iter_mut().find(|inner| inner.style_id() == outer.style_id())
-            {
+            if let Some(inner) = self.0.iter_mut().find(|inner| inner.is_same(outer)) {
                 *inner = inner.fold(outer);
                 continue;
             }
@@ -145,13 +156,10 @@ impl StyleMap {
         self.0.retain(|x| other.0.contains(x));
     }
 
-    /// Whether two style maps are equal when filtered down to the given
-    /// properties.
-    pub fn compatible<F>(&self, other: &Self, filter: F) -> bool
-    where
-        F: Fn(StyleId) -> bool,
-    {
-        let f = |entry: &&Entry| filter(entry.style_id());
+    /// 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))
     }
@@ -168,7 +176,7 @@ impl Debug for StyleMap {
 
 impl PartialEq for StyleMap {
     fn eq(&self, other: &Self) -> bool {
-        self.compatible(other, |_| true)
+        self.0.len() == other.0.len() && self.0.iter().all(|x| other.0.contains(x))
     }
 }
 
@@ -182,15 +190,22 @@ impl PartialEq for StyleMap {
 #[derive(Clone, Copy, Hash)]
 pub struct StyleChain<'a> {
     /// The first map in the chain.
-    inner: &'a StyleMap,
+    first: Link<'a>,
     /// The remaining maps in the chain.
     outer: Option<&'a Self>,
 }
 
+/// The two kinds of links in the chain.
+#[derive(Clone, Copy, Hash)]
+enum Link<'a> {
+    Map(&'a StyleMap),
+    Barrier(TypeId),
+}
+
 impl<'a> StyleChain<'a> {
     /// Start a new style chain with a root map.
     pub fn new(map: &'a StyleMap) -> Self {
-        Self { inner: map, outer: None }
+        Self { first: Link::Map(map), outer: None }
     }
 
     /// Get the (folded) value of a copyable style property.
@@ -205,7 +220,7 @@ impl<'a> StyleChain<'a> {
     where
         P::Value: Copy,
     {
-        self.get_cloned(key)
+        self.get_impl(key, 0)
     }
 
     /// Get a reference to a style property's value.
@@ -220,13 +235,7 @@ impl<'a> StyleChain<'a> {
     where
         P: Nonfolding,
     {
-        if let Some(value) = self.find(key) {
-            value
-        } else if let Some(outer) = self.outer {
-            outer.get_ref(key)
-        } else {
-            P::default_ref()
-        }
+        self.get_ref_impl(key, 0)
     }
 
     /// Get the (folded) value of any style property.
@@ -238,35 +247,87 @@ impl<'a> StyleChain<'a> {
     /// Returns the property's default value if no map in the chain contains an
     /// entry for it.
     pub fn get_cloned<P: Property>(self, key: P) -> P::Value {
-        if let Some(value) = self.find(key).cloned() {
-            if !P::FOLDABLE {
-                return value;
+        self.get_impl(key, 0)
+    }
+
+    /// Insert a barrier into the style chain.
+    ///
+    /// Barriers interact with [scoped](StyleMap::scoped) styles: A scoped style
+    /// can still be read through a single barrier (the one of the node it
+    /// _should_ apply to), but a second barrier will make it invisible.
+    pub fn barred<'b>(&'b self, node: TypeId) -> StyleChain<'b> {
+        if self.needs_barrier(node) {
+            StyleChain {
+                first: Link::Barrier(node),
+                outer: Some(self),
             }
+        } else {
+            *self
+        }
+    }
+}
 
-            match self.outer {
-                Some(outer) => P::fold(value, outer.get_cloned(key)),
-                None => P::fold(value, P::default()),
+impl<'a> StyleChain<'a> {
+    fn get_impl<P: Property>(self, key: P, depth: usize) -> P::Value {
+        let (value, depth) = self.process(key, depth);
+        if let Some(value) = value.cloned() {
+            if P::FOLDABLE {
+                if let Some(outer) = self.outer {
+                    P::fold(value, outer.get_cloned(key))
+                } else {
+                    P::fold(value, P::default())
+                }
+            } else {
+                value
             }
         } else if let Some(outer) = self.outer {
-            outer.get_cloned(key)
+            outer.get_impl(key, depth)
         } else {
             P::default()
         }
     }
 
-    /// Find a property directly in the localmost map.
-    fn find<P: Property>(self, _: P) -> Option<&'a P::Value> {
-        self.inner
-            .0
-            .iter()
-            .find(|entry| entry.is::<P>())
-            .and_then(|entry| entry.downcast::<P>())
+    fn get_ref_impl<P: Property>(self, key: P, depth: usize) -> &'a P::Value
+    where
+        P: Nonfolding,
+    {
+        let (value, depth) = self.process(key, depth);
+        if let Some(value) = value {
+            value
+        } else if let Some(outer) = self.outer {
+            outer.get_ref_impl(key, depth)
+        } else {
+            P::default_ref()
+        }
+    }
+
+    fn process<P: Property>(self, _: P, depth: usize) -> (Option<&'a P::Value>, usize) {
+        match self.first {
+            Link::Map(map) => (
+                map.0
+                    .iter()
+                    .find(|entry| entry.is::<P>() && (!entry.scoped || depth <= 1))
+                    .and_then(|entry| entry.downcast::<P>()),
+                depth,
+            ),
+            Link::Barrier(node) => (None, depth + (P::node_id() == node) as usize),
+        }
+    }
+
+    fn needs_barrier(self, node: TypeId) -> bool {
+        if let Link::Map(map) = self.first {
+            if map.0.iter().any(|entry| entry.is_of_same(node)) {
+                return true;
+            }
+        }
+
+        self.outer.map_or(false, |outer| outer.needs_barrier(node))
     }
 }
 
 impl Debug for StyleChain<'_> {
     fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        self.inner.fmt(f)?;
+        self.first.fmt(f)?;
         if let Some(outer) = self.outer {
             outer.fmt(f)?;
         }
@@ -274,14 +335,67 @@ impl Debug for StyleChain<'_> {
     }
 }
 
-/// A unique identifier for a style property.
-#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
-pub struct StyleId(TypeId);
+impl Debug for Link<'_> {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        match self {
+            Self::Map(map) => map.fmt(f),
+            Self::Barrier(id) => writeln!(f, "Barrier({:?})", id),
+        }
+    }
+}
+
+/// An entry for a single style property.
+#[derive(Clone)]
+struct Entry {
+    p: Rc<dyn Bounds>,
+    scoped: bool,
+}
+
+impl Entry {
+    fn new<P: Property>(key: P, value: P::Value) -> Self {
+        Self { p: Rc::new((key, value)), scoped: false }
+    }
+
+    fn is<P: Property>(&self) -> bool {
+        self.p.style_id() == TypeId::of::<P>()
+    }
+
+    fn is_same(&self, other: &Self) -> bool {
+        self.p.style_id() == other.p.style_id()
+    }
+
+    fn is_of<T: 'static>(&self) -> bool {
+        self.p.node_id() == TypeId::of::<T>()
+    }
+
+    fn is_of_same(&self, node: TypeId) -> bool {
+        self.p.node_id() == node
+    }
+
+    fn downcast<P: Property>(&self) -> Option<&P::Value> {
+        self.p.as_any().downcast_ref()
+    }
+
+    fn fold(&self, outer: &Self) -> Self {
+        self.p.fold(outer)
+    }
+}
+
+impl Debug for Entry {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        self.p.dyn_fmt(f)
+    }
+}
+
+impl PartialEq for Entry {
+    fn eq(&self, other: &Self) -> bool {
+        self.p.dyn_eq(other)
+    }
+}
 
-impl StyleId {
-    /// The style id of the property.
-    pub fn of<P: Property>() -> Self {
-        Self(TypeId::of::<P>())
+impl Hash for Entry {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        state.write_u64(self.p.hash64());
     }
 }
 
@@ -298,6 +412,12 @@ pub trait Property: Copy + 'static {
     /// The name of the property, used for debug printing.
     const NAME: &'static str;
 
+    /// Whether the property needs folding.
+    const FOLDABLE: 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;
 
@@ -308,9 +428,6 @@ pub trait Property: Copy + 'static {
     /// recreated all the time.
     fn default_ref() -> &'static Self::Value;
 
-    /// Whether the property needs folding.
-    const FOLDABLE: bool = false;
-
     /// Fold the property with an outer value.
     ///
     /// For example, this would fold a relative font size with an outer
@@ -324,74 +441,21 @@ pub trait Property: Copy + 'static {
 /// 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(Rc<dyn Bounds>);
-
-impl Entry {
-    fn new<P: Property>(key: P, value: P::Value) -> Self {
-        Self(Rc::new((key, value)))
-    }
-
-    fn style_id(&self) -> StyleId {
-        self.0.style_id()
-    }
-
-    fn is<P: Property>(&self) -> bool {
-        self.style_id() == StyleId::of::<P>()
-    }
-
-    fn downcast<P: Property>(&self) -> Option<&P::Value> {
-        self.0.as_any().downcast_ref()
-    }
-
-    fn fold(&self, outer: &Self) -> Self {
-        self.0.fold(outer)
-    }
-}
-
-impl Debug for Entry {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        self.0.dyn_fmt(f)
-    }
-}
-
-impl PartialEq for Entry {
-    fn eq(&self, other: &Self) -> bool {
-        self.0.dyn_eq(other)
-    }
-}
-
-impl Hash for Entry {
-    fn hash<H: Hasher>(&self, state: &mut H) {
-        state.write_u64(self.0.hash64());
-    }
-}
-
 /// 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
 /// constrained type parameter).
 trait Bounds: 'static {
-    fn style_id(&self) -> StyleId;
-    fn fold(&self, outer: &Entry) -> Entry;
     fn as_any(&self) -> &dyn Any;
     fn dyn_fmt(&self, f: &mut Formatter) -> fmt::Result;
     fn dyn_eq(&self, other: &Entry) -> bool;
     fn hash64(&self) -> u64;
+    fn node_id(&self) -> TypeId;
+    fn style_id(&self) -> TypeId;
+    fn fold(&self, outer: &Entry) -> Entry;
 }
 
 impl<P: Property> Bounds for (P, P::Value) {
-    fn style_id(&self) -> StyleId {
-        StyleId::of::<P>()
-    }
-
-    fn fold(&self, outer: &Entry) -> Entry {
-        let outer = outer.downcast::<P>().unwrap();
-        let combined = P::fold(self.1.clone(), outer.clone());
-        Entry::new(self.0, combined)
-    }
-
     fn as_any(&self) -> &dyn Any {
         &self.1
     }
@@ -401,7 +465,7 @@ impl<P: Property> Bounds for (P, P::Value) {
     }
 
     fn dyn_eq(&self, other: &Entry) -> bool {
-        self.style_id() == other.style_id()
+        self.style_id() == other.p.style_id()
             && if let Some(other) = other.downcast::<P>() {
                 &self.1 == other
             } else {
@@ -415,4 +479,18 @@ impl<P: Property> Bounds for (P, P::Value) {
         self.1.hash(&mut state);
         state.finish()
     }
+
+    fn node_id(&self) -> TypeId {
+        P::node_id()
+    }
+
+    fn style_id(&self) -> TypeId {
+        TypeId::of::<P>()
+    }
+
+    fn fold(&self, outer: &Entry) -> Entry {
+        let outer = outer.downcast::<P>().unwrap();
+        let combined = P::fold(self.1.clone(), outer.clone());
+        Entry::new(self.0, combined)
+    }
 }
diff --git a/src/layout/mod.rs b/src/layout/mod.rs
index a00687eb..6935afc2 100644
--- a/src/layout/mod.rs
+++ b/src/layout/mod.rs
@@ -197,6 +197,8 @@ impl Layout for PackedNode {
         regions: &Regions,
         styles: StyleChain,
     ) -> Vec<Constrained<Rc<Frame>>> {
+        let styles = styles.barred(self.node.as_any().type_id());
+
         #[cfg(not(feature = "layout-cache"))]
         return self.node.layout(ctx, regions, styles);