Track context (#3623)

28 files changed, 108 insertions, 67 deletions

diff --git a/crates/typst-ide/src/analyze.rs b/crates/typst-ide/src/analyze.rs
index 1fef1b49..9d67b322 100644
--- a/crates/typst-ide/src/analyze.rs
+++ b/crates/typst-ide/src/analyze.rs
@@ -67,8 +67,12 @@ pub fn analyze_import(world: &dyn World, source: &LinkedNode) -> Option<Value> {
     };
 
     let context = Context::none();
-    let mut vm =
-        Vm::new(engine, &context, Scopes::new(Some(world.library())), Span::detached());
+    let mut vm = Vm::new(
+        engine,
+        context.track(),
+        Scopes::new(Some(world.library())),
+        Span::detached(),
+    );
     typst::eval::import(&mut vm, source, Span::detached(), true)
         .ok()
         .map(Value::Module)
diff --git a/crates/typst/src/eval/call.rs b/crates/typst/src/eval/call.rs
index 97ca6c2c..ddc05416 100644
--- a/crates/typst/src/eval/call.rs
+++ b/crates/typst/src/eval/call.rs
@@ -278,7 +278,7 @@ pub(crate) fn call_closure(
     route: Tracked<Route>,
     locator: Tracked<Locator>,
     tracer: TrackedMut<Tracer>,
-    context: &Context,
+    context: Tracked<Context>,
     mut args: Args,
 ) -> SourceResult<Value> {
     let (name, params, body) = match closure.node.cast::<ast::Closure>() {
diff --git a/crates/typst/src/eval/mod.rs b/crates/typst/src/eval/mod.rs
index 07d27021..3622c012 100644
--- a/crates/typst/src/eval/mod.rs
+++ b/crates/typst/src/eval/mod.rs
@@ -63,7 +63,7 @@ pub fn eval(
     let context = Context::none();
     let scopes = Scopes::new(Some(world.library()));
     let root = source.root();
-    let mut vm = Vm::new(engine, &context, scopes, root.span());
+    let mut vm = Vm::new(engine, context.track(), scopes, root.span());
 
     // Check for well-formedness unless we are in trace mode.
     let errors = root.errors();
@@ -131,7 +131,7 @@ pub fn eval_string(
     // Prepare VM.
     let context = Context::none();
     let scopes = Scopes::new(Some(world.library()));
-    let mut vm = Vm::new(engine, &context, scopes, root.span());
+    let mut vm = Vm::new(engine, context.track(), scopes, root.span());
     vm.scopes.scopes.push(scope);
 
     // Evaluate the code.
diff --git a/crates/typst/src/eval/vm.rs b/crates/typst/src/eval/vm.rs
index 27d141cc..be43b5ba 100644
--- a/crates/typst/src/eval/vm.rs
+++ b/crates/typst/src/eval/vm.rs
@@ -21,14 +21,14 @@ pub struct Vm<'a> {
     /// A span that is currently under inspection.
     pub(crate) inspected: Option<Span>,
     /// Data that is contextually made accessible to code behind the scenes.
-    pub(crate) context: &'a Context<'a>,
+    pub(crate) context: Tracked<'a, Context<'a>>,
 }
 
 impl<'a> Vm<'a> {
     /// Create a new virtual machine.
     pub fn new(
         engine: Engine<'a>,
-        context: &'a Context<'a>,
+        context: Tracked<'a, Context<'a>>,
         scopes: Scopes<'a>,
         target: Span,
     ) -> Self {
@@ -55,6 +55,6 @@ impl<'a> Vm<'a> {
     pub fn trace(&mut self, value: Value) {
         self.engine
             .tracer
-            .value(value.clone(), self.context.styles.map(|s| s.to_map()));
+            .value(value.clone(), self.context.styles().ok().map(|s| s.to_map()));
     }
 }
diff --git a/crates/typst/src/foundations/array.rs b/crates/typst/src/foundations/array.rs
index a1e93d7b..8f5703bb 100644
--- a/crates/typst/src/foundations/array.rs
+++ b/crates/typst/src/foundations/array.rs
@@ -3,6 +3,7 @@ use std::fmt::{Debug, Formatter};
 use std::num::{NonZeroI64, NonZeroUsize};
 use std::ops::{Add, AddAssign};
 
+use comemo::Tracked;
 use ecow::{eco_format, EcoString, EcoVec};
 use serde::{Deserialize, Serialize};
 use smallvec::SmallVec;
@@ -301,7 +302,7 @@ impl Array {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The function to apply to each item. Must return a boolean.
         searcher: Func,
     ) -> SourceResult<Option<Value>> {
@@ -325,7 +326,7 @@ impl Array {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The function to apply to each item. Must return a boolean.
         searcher: Func,
     ) -> SourceResult<Option<i64>> {
@@ -402,7 +403,7 @@ impl Array {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The function to apply to each item. Must return a boolean.
         test: Func,
     ) -> SourceResult<Array> {
@@ -427,7 +428,7 @@ impl Array {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The function to apply to each item.
         mapper: Func,
     ) -> SourceResult<Array> {
@@ -536,7 +537,7 @@ impl Array {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The initial value to start with.
         init: Value,
         /// The folding function. Must have two parameters: One for the
@@ -598,7 +599,7 @@ impl Array {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The function to apply to each item. Must return a boolean.
         test: Func,
     ) -> SourceResult<bool> {
@@ -618,7 +619,7 @@ impl Array {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The function to apply to each item. Must return a boolean.
         test: Func,
     ) -> SourceResult<bool> {
@@ -765,7 +766,7 @@ impl Array {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The callsite span.
         span: Span,
         /// If given, applies this function to the elements in the array to
@@ -815,7 +816,7 @@ impl Array {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// If given, applies this function to the elements in the array to
         /// determine the keys to deduplicate by.
         #[named]
diff --git a/crates/typst/src/foundations/content.rs b/crates/typst/src/foundations/content.rs
index 83e94d30..6184f4cf 100644
--- a/crates/typst/src/foundations/content.rs
+++ b/crates/typst/src/foundations/content.rs
@@ -6,6 +6,7 @@ use std::marker::PhantomData;
 use std::ops::{Add, AddAssign, Deref, DerefMut};
 use std::sync::Arc;
 
+use comemo::Tracked;
 use ecow::{eco_format, EcoString};
 use serde::{Serialize, Serializer};
 use smallvec::smallvec;
@@ -345,7 +346,7 @@ impl Content {
     pub fn styled_with_recipe(
         self,
         engine: &mut Engine,
-        context: &Context,
+        context: Tracked<Context>,
         recipe: Recipe,
     ) -> SourceResult<Self> {
         if recipe.selector.is_none() {
diff --git a/crates/typst/src/foundations/context.rs b/crates/typst/src/foundations/context.rs
index 41fdbfec..bf4bdcd2 100644
--- a/crates/typst/src/foundations/context.rs
+++ b/crates/typst/src/foundations/context.rs
@@ -1,3 +1,5 @@
+use comemo::Track;
+
 use crate::diag::{bail, Hint, HintedStrResult, SourceResult};
 use crate::engine::Engine;
 use crate::foundations::{
@@ -28,7 +30,10 @@ impl<'a> Context<'a> {
     pub fn new(location: Option<Location>, styles: Option<StyleChain<'a>>) -> Self {
         Self { location, styles }
     }
+}
 
+#[comemo::track]
+impl<'a> Context<'a> {
     /// Try to extract the location.
     pub fn location(&self) -> HintedStrResult<Location> {
         require(self.location)
@@ -75,6 +80,6 @@ impl Show for Packed<ContextElem> {
     fn show(&self, engine: &mut Engine, styles: StyleChain) -> SourceResult<Content> {
         let loc = self.location().unwrap();
         let context = Context::new(Some(loc), Some(styles));
-        Ok(self.func.call::<[Value; 0]>(engine, &context, [])?.display())
+        Ok(self.func.call::<[Value; 0]>(engine, context.track(), [])?.display())
     }
 }
diff --git a/crates/typst/src/foundations/func.rs b/crates/typst/src/foundations/func.rs
index 7871e297..70fbea77 100644
--- a/crates/typst/src/foundations/func.rs
+++ b/crates/typst/src/foundations/func.rs
@@ -1,7 +1,7 @@
 use std::fmt::{self, Debug, Formatter};
 use std::sync::Arc;
 
-use comemo::TrackedMut;
+use comemo::{Tracked, TrackedMut};
 use ecow::{eco_format, EcoString};
 use once_cell::sync::Lazy;
 
@@ -261,7 +261,7 @@ impl Func {
     pub fn call<A: IntoArgs>(
         &self,
         engine: &mut Engine,
-        context: &Context,
+        context: Tracked<Context>,
         args: A,
     ) -> SourceResult<Value> {
         self.call_impl(engine, context, args.into_args(self.span))
@@ -272,7 +272,7 @@ impl Func {
     fn call_impl(
         &self,
         engine: &mut Engine,
-        context: &Context,
+        context: Tracked<Context>,
         mut args: Args,
     ) -> SourceResult<Value> {
         match &self.repr {
@@ -440,7 +440,7 @@ pub trait NativeFunc {
 /// Defines a native function.
 #[derive(Debug)]
 pub struct NativeFuncData {
-    pub function: fn(&mut Engine, &Context, &mut Args) -> SourceResult<Value>,
+    pub function: fn(&mut Engine, Tracked<Context>, &mut Args) -> SourceResult<Value>,
     pub name: &'static str,
     pub title: &'static str,
     pub docs: &'static str,
diff --git a/crates/typst/src/foundations/selector.rs b/crates/typst/src/foundations/selector.rs
index 92bfa823..4dc8ab3b 100644
--- a/crates/typst/src/foundations/selector.rs
+++ b/crates/typst/src/foundations/selector.rs
@@ -304,7 +304,7 @@ impl LocatableSelector {
     pub fn resolve_unique(
         &self,
         introspector: Tracked<Introspector>,
-        context: &Context,
+        context: Tracked<Context>,
     ) -> HintedStrResult<Location> {
         match &self.0 {
             Selector::Location(loc) => Ok(*loc),
diff --git a/crates/typst/src/foundations/str.rs b/crates/typst/src/foundations/str.rs
index e1c5d8b0..897ca45b 100644
--- a/crates/typst/src/foundations/str.rs
+++ b/crates/typst/src/foundations/str.rs
@@ -3,6 +3,7 @@ use std::fmt::{self, Debug, Display, Formatter};
 use std::hash::{Hash, Hasher};
 use std::ops::{Add, AddAssign, Deref, Range};
 
+use comemo::Tracked;
 use ecow::EcoString;
 use serde::{Deserialize, Serialize};
 use unicode_segmentation::UnicodeSegmentation;
@@ -425,7 +426,7 @@ impl Str {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The pattern to search for.
         pattern: StrPattern,
         /// The string to replace the matches with or a function that gets a
diff --git a/crates/typst/src/foundations/styles.rs b/crates/typst/src/foundations/styles.rs
index 469cad1a..dd09b605 100644
--- a/crates/typst/src/foundations/styles.rs
+++ b/crates/typst/src/foundations/styles.rs
@@ -3,6 +3,7 @@ use std::fmt::{self, Debug, Formatter};
 use std::hash::{Hash, Hasher};
 use std::{mem, ptr};
 
+use comemo::{Track, Tracked};
 use ecow::{eco_vec, EcoString, EcoVec};
 use smallvec::SmallVec;
 
@@ -57,7 +58,10 @@ impl Show for Packed<StyleElem> {
     #[typst_macros::time(name = "style", span = self.span())]
     fn show(&self, engine: &mut Engine, styles: StyleChain) -> SourceResult<Content> {
         let context = Context::new(self.location(), Some(styles));
-        Ok(self.func().call(engine, &context, [styles.to_map()])?.display())
+        Ok(self
+            .func()
+            .call(engine, context.track(), [styles.to_map()])?
+            .display())
     }
 }
 
@@ -385,7 +389,7 @@ impl Recipe {
     pub fn apply(
         &self,
         engine: &mut Engine,
-        context: &Context,
+        context: Tracked<Context>,
         content: Content,
     ) -> SourceResult<Content> {
         let mut content = match &self.transform {
diff --git a/crates/typst/src/introspection/counter.rs b/crates/typst/src/introspection/counter.rs
index 4a9bae03..dd2fdcff 100644
--- a/crates/typst/src/introspection/counter.rs
+++ b/crates/typst/src/introspection/counter.rs
@@ -1,7 +1,7 @@
 use std::num::NonZeroUsize;
 use std::str::FromStr;
 
-use comemo::{Tracked, TrackedMut};
+use comemo::{Track, Tracked, TrackedMut};
 use ecow::{eco_format, eco_vec, EcoString, EcoVec};
 use smallvec::{smallvec, SmallVec};
 
@@ -271,7 +271,7 @@ impl Counter {
         let context = Context::new(Some(loc), Some(styles));
         Ok(self
             .at_loc(engine, loc)?
-            .display(engine, &context, numbering)?
+            .display(engine, context.track(), numbering)?
             .display())
     }
 
@@ -392,7 +392,7 @@ impl Counter {
         };
 
         let context = Context::new(Some(location), styles);
-        state.display(engine, &context, &numbering)
+        state.display(engine, context.track(), &numbering)
     }
 }
 
@@ -425,7 +425,7 @@ impl Counter {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The callsite span.
         span: Span,
     ) -> SourceResult<CounterState> {
@@ -446,7 +446,7 @@ impl Counter {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The call span of the display.
         span: Span,
         /// A [numbering pattern or a function]($numbering), which specifies how
@@ -468,8 +468,8 @@ impl Counter {
         #[default(false)]
         both: bool,
     ) -> SourceResult<Value> {
-        if let Some(loc) = context.location {
-            self.display_impl(engine, loc, numbering, both, context.styles)
+        if let Ok(loc) = context.location() {
+            self.display_impl(engine, loc, numbering, both, context.styles().ok())
         } else {
             Ok(CounterDisplayElem::new(self, numbering, both)
                 .pack()
@@ -494,7 +494,7 @@ impl Counter {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The callsite span.
         span: Span,
         /// The place at which the counter's value should be retrieved.
@@ -512,7 +512,7 @@ impl Counter {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The callsite span.
         span: Span,
         /// _Compatibility:_ This argument only exists for compatibility with
@@ -669,7 +669,7 @@ impl CounterState {
             CounterUpdate::Step(level) => self.step(level, 1),
             CounterUpdate::Func(func) => {
                 *self = func
-                    .call(engine, &Context::none(), self.0.iter().copied())?
+                    .call(engine, Context::none().track(), self.0.iter().copied())?
                     .cast()
                     .at(func.span())?
             }
@@ -700,7 +700,7 @@ impl CounterState {
     pub fn display(
         &self,
         engine: &mut Engine,
-        context: &Context,
+        context: Tracked<Context>,
         numbering: &Numbering,
     ) -> SourceResult<Value> {
         numbering.apply(engine, context, &self.0)
diff --git a/crates/typst/src/introspection/here.rs b/crates/typst/src/introspection/here.rs
index ac6b5335..e921079b 100644
--- a/crates/typst/src/introspection/here.rs
+++ b/crates/typst/src/introspection/here.rs
@@ -1,3 +1,5 @@
+use comemo::Tracked;
+
 use crate::diag::HintedStrResult;
 use crate::foundations::{func, Context};
 use crate::introspection::Location;
@@ -44,7 +46,7 @@ use crate::introspection::Location;
 #[func(contextual)]
 pub fn here(
     /// The callsite context.
-    context: &Context,
+    context: Tracked<Context>,
 ) -> HintedStrResult<Location> {
     context.location()
 }
diff --git a/crates/typst/src/introspection/locate.rs b/crates/typst/src/introspection/locate.rs
index 1ce3ae38..373b1fe2 100644
--- a/crates/typst/src/introspection/locate.rs
+++ b/crates/typst/src/introspection/locate.rs
@@ -1,3 +1,5 @@
+use comemo::{Track, Tracked};
+
 use crate::diag::{HintedStrResult, SourceResult};
 use crate::engine::Engine;
 use crate::foundations::{
@@ -37,7 +39,7 @@ pub fn locate(
     /// The engine.
     engine: &mut Engine,
     /// The callsite context.
-    context: &Context,
+    context: Tracked<Context>,
     /// The span of the `locate` call.
     span: Span,
     /// A selector that should match exactly one element. This element will be
@@ -106,6 +108,6 @@ impl Show for Packed<LocateElem> {
     fn show(&self, engine: &mut Engine, styles: StyleChain) -> SourceResult<Content> {
         let location = self.location().unwrap();
         let context = Context::new(Some(location), Some(styles));
-        Ok(self.func().call(engine, &context, [location])?.display())
+        Ok(self.func().call(engine, context.track(), [location])?.display())
     }
 }
diff --git a/crates/typst/src/introspection/query.rs b/crates/typst/src/introspection/query.rs
index a6ddb815..eb2b9df4 100644
--- a/crates/typst/src/introspection/query.rs
+++ b/crates/typst/src/introspection/query.rs
@@ -1,3 +1,5 @@
+use comemo::Tracked;
+
 use crate::diag::HintedStrResult;
 use crate::engine::Engine;
 use crate::foundations::{func, Array, Context, LocatableSelector, Value};
@@ -135,7 +137,7 @@ pub fn query(
     /// The engine.
     engine: &mut Engine,
     /// The callsite context.
-    context: &Context,
+    context: Tracked<Context>,
     /// Can be
     /// - an element function like a `heading` or `figure`,
     /// - a `{<label>}`,
diff --git a/crates/typst/src/introspection/state.rs b/crates/typst/src/introspection/state.rs
index 228fbab2..c4c95137 100644
--- a/crates/typst/src/introspection/state.rs
+++ b/crates/typst/src/introspection/state.rs
@@ -1,4 +1,4 @@
-use comemo::{Tracked, TrackedMut};
+use comemo::{Track, Tracked, TrackedMut};
 use ecow::{eco_format, eco_vec, EcoString, EcoVec};
 
 use crate::diag::{bail, At, SourceResult};
@@ -249,7 +249,7 @@ impl State {
             match elem.update() {
                 StateUpdate::Set(value) => state = value.clone(),
                 StateUpdate::Func(func) => {
-                    state = func.call(&mut engine, &Context::none(), [state])?
+                    state = func.call(&mut engine, Context::none().track(), [state])?
                 }
             }
             stops.push(state.clone());
@@ -287,7 +287,7 @@ impl State {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The callsite span.
         span: Span,
     ) -> SourceResult<Value> {
@@ -310,7 +310,7 @@ impl State {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The callsite span.
         span: Span,
         /// The place at which the state's value should be retrieved.
@@ -327,7 +327,7 @@ impl State {
         /// The engine.
         engine: &mut Engine,
         /// The callsite context.
-        context: &Context,
+        context: Tracked<Context>,
         /// The callsite span.
         span: Span,
         /// _Compatibility:_ This argument only exists for compatibility with
@@ -451,7 +451,7 @@ impl Show for Packed<StateDisplayElem> {
         let context = Context::new(Some(location), Some(styles));
         let value = self.state().at_loc(engine, location)?;
         Ok(match self.func() {
-            Some(func) => func.call(engine, &context, [value])?.display(),
+            Some(func) => func.call(engine, context.track(), [value])?.display(),
             None => value.display(),
         })
     }
diff --git a/crates/typst/src/layout/grid/layout.rs b/crates/typst/src/layout/grid/layout.rs
index 20b2ddc8..6d89b73c 100644
--- a/crates/typst/src/layout/grid/layout.rs
+++ b/crates/typst/src/layout/grid/layout.rs
@@ -3,6 +3,7 @@ use std::hash::Hash;
 use std::num::NonZeroUsize;
 use std::sync::Arc;
 
+use comemo::Track;
 use ecow::eco_format;
 
 use super::lines::{
@@ -50,7 +51,7 @@ impl<T: Default + Clone + FromValue> Celled<T> {
         Ok(match self {
             Self::Value(value) => value.clone(),
             Self::Func(func) => func
-                .call(engine, &Context::new(None, Some(styles)), [x, y])?
+                .call(engine, Context::new(None, Some(styles)).track(), [x, y])?
                 .cast()
                 .at(func.span())?,
             Self::Array(array) => x
@@ -151,7 +152,7 @@ where
         Ok(match &self.0 {
             Celled::Value(value) => value.clone(),
             Celled::Func(func) => func
-                .call(engine, &Context::new(None, Some(styles)), [x, y])?
+                .call(engine, Context::new(None, Some(styles)).track(), [x, y])?
                 .cast::<T>()
                 .at(func.span())?
                 .resolve(styles),
diff --git a/crates/typst/src/layout/layout.rs b/crates/typst/src/layout/layout.rs
index 27942f80..01fb9092 100644
--- a/crates/typst/src/layout/layout.rs
+++ b/crates/typst/src/layout/layout.rs
@@ -1,3 +1,5 @@
+use comemo::Track;
+
 use crate::diag::SourceResult;
 use crate::engine::Engine;
 use crate::foundations::{
@@ -84,7 +86,7 @@ impl LayoutMultiple for Packed<LayoutElem> {
         let context = Context::new(Some(loc), Some(styles));
         let result = self
             .func()
-            .call(engine, &context, [dict! { "width" => x, "height" => y }])?
+            .call(engine, context.track(), [dict! { "width" => x, "height" => y }])?
             .display();
         result.layout(engine, styles, regions)
     }
diff --git a/crates/typst/src/layout/length.rs b/crates/typst/src/layout/length.rs
index ecc7a954..0e6176c0 100644
--- a/crates/typst/src/layout/length.rs
+++ b/crates/typst/src/layout/length.rs
@@ -2,6 +2,7 @@ use std::cmp::Ordering;
 use std::fmt::{self, Debug, Formatter};
 use std::ops::{Add, Div, Mul, Neg};
 
+use comemo::Tracked;
 use ecow::{eco_format, EcoString};
 
 use crate::diag::{At, Hint, HintedStrResult, SourceResult};
@@ -151,7 +152,7 @@ impl Length {
     /// ]
     /// ```
     #[func]
-    pub fn to_absolute(&self, context: &Context) -> HintedStrResult<Length> {
+    pub fn to_absolute(&self, context: Tracked<Context>) -> HintedStrResult<Length> {
         Ok(self.resolve(context.styles()?).into())
     }
 }
diff --git a/crates/typst/src/layout/measure.rs b/crates/typst/src/layout/measure.rs
index b2d78665..89054925 100644
--- a/crates/typst/src/layout/measure.rs
+++ b/crates/typst/src/layout/measure.rs
@@ -1,3 +1,5 @@
+use comemo::Tracked;
+
 use crate::diag::{At, SourceResult};
 use crate::engine::Engine;
 use crate::foundations::{dict, func, Content, Context, Dict, StyleChain, Styles};
@@ -43,7 +45,7 @@ pub fn measure(
     /// The engine.
     engine: &mut Engine,
     /// The callsite context.
-    context: &Context,
+    context: Tracked<Context>,
     /// The callsite span.
     span: Span,
     /// The content whose size to measure.
diff --git a/crates/typst/src/layout/page.rs b/crates/typst/src/layout/page.rs
index f5727d57..f6221887 100644
--- a/crates/typst/src/layout/page.rs
+++ b/crates/typst/src/layout/page.rs
@@ -3,6 +3,8 @@ use std::num::NonZeroUsize;
 use std::ptr;
 use std::str::FromStr;
 
+use comemo::Track;
+
 use crate::diag::{bail, SourceResult};
 use crate::engine::Engine;
 use crate::foundations::{
@@ -691,7 +693,7 @@ impl Marginal {
         Ok(match self {
             Self::Content(content) => Cow::Borrowed(content),
             Self::Func(func) => Cow::Owned(
-                func.call(engine, &Context::new(None, Some(styles)), [page])?
+                func.call(engine, Context::new(None, Some(styles)).track(), [page])?
                     .display(),
             ),
         })
diff --git a/crates/typst/src/math/cancel.rs b/crates/typst/src/math/cancel.rs
index 36f56160..405b0351 100644
--- a/crates/typst/src/math/cancel.rs
+++ b/crates/typst/src/math/cancel.rs
@@ -1,3 +1,5 @@
+use comemo::Track;
+
 use crate::diag::{At, SourceResult};
 use crate::foundations::{
     cast, elem, Content, Context, Func, Packed, Resolve, Smart, StyleChain,
@@ -204,7 +206,7 @@ fn draw_cancel_line(
             CancelAngle::Angle(v) => *v,
             // This specifies a function that takes the default angle as input.
             CancelAngle::Func(func) => func
-                .call(ctx.engine, &Context::new(None, Some(styles)), [default])?
+                .call(ctx.engine, Context::new(None, Some(styles)).track(), [default])?
                 .cast()
                 .at(span)?,
         },
diff --git a/crates/typst/src/model/enum.rs b/crates/typst/src/model/enum.rs
index ba0b697a..98402057 100644
--- a/crates/typst/src/model/enum.rs
+++ b/crates/typst/src/model/enum.rs
@@ -1,5 +1,6 @@
 use std::str::FromStr;
 
+use comemo::Track;
 use smallvec::{smallvec, SmallVec};
 
 use crate::diag::{bail, SourceResult};
@@ -247,7 +248,8 @@ impl LayoutMultiple for Packed<EnumElem> {
             let context = Context::new(None, Some(styles));
             let resolved = if full {
                 parents.push(number);
-                let content = numbering.apply(engine, &context, &parents)?.display();
+                let content =
+                    numbering.apply(engine, context.track(), &parents)?.display();
                 parents.pop();
                 content
             } else {
@@ -255,7 +257,7 @@ impl LayoutMultiple for Packed<EnumElem> {
                     Numbering::Pattern(pattern) => {
                         TextElem::packed(pattern.apply_kth(parents.len(), number))
                     }
-                    other => other.apply(engine, &context, &[number])?.display(),
+                    other => other.apply(engine, context.track(), &[number])?.display(),
                 }
             };
 
diff --git a/crates/typst/src/model/list.rs b/crates/typst/src/model/list.rs
index 6d53b6d7..665575e8 100644
--- a/crates/typst/src/model/list.rs
+++ b/crates/typst/src/model/list.rs
@@ -1,3 +1,5 @@
+use comemo::Track;
+
 use crate::diag::{bail, SourceResult};
 use crate::engine::Engine;
 use crate::foundations::{
@@ -218,7 +220,7 @@ impl ListMarker {
                 list.get(depth % list.len()).cloned().unwrap_or_default()
             }
             Self::Func(func) => func
-                .call(engine, &Context::new(None, Some(styles)), [depth])?
+                .call(engine, Context::new(None, Some(styles)).track(), [depth])?
                 .display(),
         })
     }
diff --git a/crates/typst/src/model/numbering.rs b/crates/typst/src/model/numbering.rs
index 9de09046..10946ccc 100644
--- a/crates/typst/src/model/numbering.rs
+++ b/crates/typst/src/model/numbering.rs
@@ -1,6 +1,7 @@
 use std::str::FromStr;
 
 use chinese_number::{ChineseCase, ChineseCountMethod, ChineseVariant, NumberToChinese};
+use comemo::Tracked;
 use ecow::{eco_format, EcoString, EcoVec};
 
 use crate::diag::SourceResult;
@@ -36,7 +37,7 @@ pub fn numbering(
     /// The engine.
     engine: &mut Engine,
     /// The callsite context.
-    context: &Context,
+    context: Tracked<Context>,
     /// Defines how the numbering works.
     ///
     /// **Counting symbols** are `1`, `a`, `A`, `i`, `I`, `一`, `壹`, `あ`, `い`, `ア`, `イ`, `א`, `가`,
@@ -85,7 +86,7 @@ impl Numbering {
     pub fn apply(
         &self,
         engine: &mut Engine,
-        context: &Context,
+        context: Tracked<Context>,
         numbers: &[usize],
     ) -> SourceResult<Value> {
         Ok(match self {
diff --git a/crates/typst/src/model/outline.rs b/crates/typst/src/model/outline.rs
index cc3d6d6e..6fb1f601 100644
--- a/crates/typst/src/model/outline.rs
+++ b/crates/typst/src/model/outline.rs
@@ -1,6 +1,8 @@
 use std::num::NonZeroUsize;
 use std::str::FromStr;
 
+use comemo::Track;
+
 use crate::diag::{bail, At, SourceResult};
 use crate::engine::Engine;
 use crate::foundations::{
@@ -381,7 +383,7 @@ impl OutlineIndent {
             Some(Smart::Custom(OutlineIndent::Func(func))) => {
                 let depth = ancestors.len();
                 let LengthOrContent(content) = func
-                    .call(engine, &Context::new(None, Some(styles)), [depth])?
+                    .call(engine, Context::new(None, Some(styles)).track(), [depth])?
                     .cast()
                     .at(span)?;
                 if !content.is_empty() {
diff --git a/crates/typst/src/model/reference.rs b/crates/typst/src/model/reference.rs
index 4cb46617..0cdb5e30 100644
--- a/crates/typst/src/model/reference.rs
+++ b/crates/typst/src/model/reference.rs
@@ -1,3 +1,4 @@
+use comemo::Track;
 use ecow::eco_format;
 
 use crate::diag::{bail, At, Hint, SourceResult};
@@ -275,9 +276,9 @@ impl Supplement {
     ) -> SourceResult<Content> {
         Ok(match self {
             Supplement::Content(content) => content.clone(),
-            Supplement::Func(func) => {
-                func.call(engine, &Context::new(None, Some(styles)), args)?.display()
-            }
+            Supplement::Func(func) => func
+                .call(engine, Context::new(None, Some(styles)).track(), args)?
+                .display(),
         })
     }
 }
diff --git a/crates/typst/src/realize/process.rs b/crates/typst/src/realize/process.rs
index cb11686b..8d3d01a6 100644
--- a/crates/typst/src/realize/process.rs
+++ b/crates/typst/src/realize/process.rs
@@ -1,5 +1,6 @@
 use std::cell::OnceCell;
 
+use comemo::{Track, Tracked};
 use smallvec::smallvec;
 
 use crate::diag::SourceResult;
@@ -255,11 +256,11 @@ fn show(
                 // text element. This invokes special regex handling.
                 Some(Selector::Regex(regex)) => {
                     let text = target.into_packed::<TextElem>().unwrap();
-                    show_regex(engine, &text, regex, recipe, guard, &context)
+                    show_regex(engine, &text, regex, recipe, guard, context.track())
                 }
 
                 // Just apply the recipe.
-                _ => recipe.apply(engine, &context, target.guarded(guard)),
+                _ => recipe.apply(engine, context.track(), target.guarded(guard)),
             }
         }
 
@@ -276,7 +277,7 @@ fn show_regex(
     regex: &Regex,
     recipe: &Recipe,
     index: RecipeIndex,
-    context: &Context,
+    context: Tracked<Context>,
 ) -> SourceResult<Content> {
     let make = |s: &str| {
         let mut fresh = target.clone();