A little less route nesting

crates/typst/src/engine.rs

@@ -8,9 +8,6 @@ use crate::introspection::{Introspector, Locator};
 use crate::syntax::FileId;
 use crate::World;
 
-/// The maxmium stack nesting depth.
-const MAX_DEPTH: usize = 64;
-
 /// Holds all data needed during compilation.
 pub struct Engine<'a> {
     /// The compilation environment.
@@ -69,26 +66,28 @@ pub struct Route<'a> {
     upper: Cell<usize>,
 }
 
+/// The maximum nesting depths. They are different so that even if show rule and
+/// call checks are interleaved, show rule problems we always get the show rule.
+/// The lower the max depth for a kind of error, the higher its precedence
+/// compared to the others.
+impl Route<'_> {
+    /// The maximum stack nesting depth.
+    pub const MAX_SHOW_RULE_DEPTH: usize = 64;
+
+    /// The maxmium layout nesting depth.
+    pub const MAX_LAYOUT_DEPTH: usize = 72;
+
+    /// The maxmium function call nesting depth.
+    pub const MAX_CALL_DEPTH: usize = 80;
+}
+
 impl<'a> Route<'a> {
     /// Create a new, empty route.
     pub fn root() -> Self {
         Self { id: None, outer: None, len: 0, upper: Cell::new(0) }
     }
 
-    /// Insert a new id into the route.
-    ///
-    /// You must guarantee that `outer` lives longer than the resulting
-    /// route is ever used.
-    pub fn insert(outer: Tracked<'a, Self>, id: FileId) -> Self {
-        Route {
-            outer: Some(outer),
-            id: Some(id),
-            len: 0,
-            upper: Cell::new(usize::MAX),
-        }
-    }
-
-    /// Extend the route without another id.
+    /// Extend the route with another segment with a default length of 1.
     pub fn extend(outer: Tracked<'a, Self>) -> Self {
         Route {
             outer: Some(outer),
@@ -98,6 +97,16 @@ impl<'a> Route<'a> {
         }
     }
 
+    /// Attach a file id to the route segment.
+    pub fn with_id(self, id: FileId) -> Self {
+        Self { id: Some(id), ..self }
+    }
+
+    /// Set the length of the route segment to zero.
+    pub fn unnested(self) -> Self {
+        Self { len: 0, ..self }
+    }
+
     /// Start tracking this route.
     ///
     /// In comparison to [`Track::track`], this method skips this chain link
@@ -118,11 +127,6 @@ impl<'a> Route<'a> {
     pub fn decrease(&mut self) {
         self.len -= 1;
     }
-
-    /// Check whether the nesting depth exceeds the limit.
-    pub fn exceeding(&self) -> bool {
-        !self.within(MAX_DEPTH)
-    }
 }
 
 #[comemo::track]

crates/typst/src/eval/call.rs

@@ -28,7 +28,7 @@ impl Eval for ast::FuncCall<'_> {
         let args = self.args();
         let trailing_comma = args.trailing_comma();
 
-        if vm.engine.route.exceeding() {
+        if !vm.engine.route.within(Route::MAX_CALL_DEPTH) {
             bail!(span, "maximum function call depth exceeded");
         }
 

crates/typst/src/eval/mod.rs

@@ -53,7 +53,7 @@ pub fn eval(
     let introspector = Introspector::default();
     let engine = Engine {
         world,
-        route: Route::insert(route, id),
+        route: Route::extend(route).with_id(id),
         introspector: introspector.track(),
         locator: &mut locator,
         tracer,

crates/typst/src/introspection/counter.rs

@@ -277,7 +277,7 @@ impl Counter {
         let mut engine = Engine {
             world,
             introspector,
-            route: Route::extend(route),
+            route: Route::extend(route).unnested(),
             locator: &mut locator,
             tracer,
         };

crates/typst/src/introspection/state.rs

@@ -228,7 +228,7 @@ impl State {
         let mut engine = Engine {
             world,
             introspector,
-            route: Route::extend(route),
+            route: Route::extend(route).unnested(),
             locator: &mut locator,
             tracer,
         };

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

@@ -28,7 +28,7 @@ use crate::text::{
 use crate::util::Numeric;
 use crate::World;
 
-/// Layout's content inline.
+/// Layouts content inline.
 pub(crate) fn layout_inline(
     children: &[Prehashed<Content>],
     engine: &mut Engine,

crates/typst/src/layout/mod.rs

@@ -182,7 +182,7 @@ impl LayoutRoot for Content {
             let mut engine = Engine {
                 world,
                 introspector,
-                route: Route::extend(route),
+                route: Route::extend(route).unnested(),
                 locator: &mut locator,
                 tracer,
             };
@@ -237,7 +237,7 @@ impl Layout for Content {
                 tracer,
             };
 
-            if engine.route.exceeding() {
+            if !engine.route.within(Route::MAX_LAYOUT_DEPTH) {
                 bail!(
                     content.span(), "maximum layout depth exceeded";
                     hint: "try to reduce the amount of nesting in your layout",

crates/typst/src/realize/mod.rs

@@ -11,7 +11,7 @@ use smallvec::smallvec;
 use typed_arena::Arena;
 
 use crate::diag::{bail, SourceResult};
-use crate::engine::Engine;
+use crate::engine::{Engine, Route};
 use crate::foundations::{
     Content, Finalize, Guard, NativeElement, Recipe, Selector, Show, StyleChain,
     StyleVecBuilder, Styles, Synthesize,
@@ -307,7 +307,7 @@ impl<'a, 'v, 't> Builder<'a, 'v, 't> {
 
         if let Some(realized) = realize(self.engine, content, styles)? {
             self.engine.route.increase();
-            if self.engine.route.exceeding() {
+            if !self.engine.route.within(Route::MAX_SHOW_RULE_DEPTH) {
                 bail!(
                     content.span(), "maximum show rule depth exceeded";
                     hint: "check whether the show rule matches its own output";

tests/typ/compiler/recursion.typ

@@ -44,8 +44,8 @@
 
 ---
 // Test cyclic imports during layout.
-// Error: 2-38 maximum layout depth exceeded
-// Hint: 2-38 try to reduce the amount of nesting in your layout
+// Error: 14-37 maximum layout depth exceeded
+// Hint: 14-37 try to reduce the amount of nesting in your layout
 #layout(_ => include "recursion.typ")
 
 ---