Implement non-recursive GC tracing

core/engine/src/builtins/function/mod.rs

@@ -142,7 +142,7 @@ pub enum ClassFieldDefinition {
 }
 
 unsafe impl Trace for ClassFieldDefinition {
-    custom_trace! {this, {
+    custom_trace! {this, mark, {
         match this {
             Self::Public(_key, func) => {
                 mark(func);

core/engine/src/builtins/generator/mod.rs

@@ -45,7 +45,7 @@ pub(crate) enum GeneratorState {
 
 // Need to manually implement, since `Trace` adds a `Drop` impl which disallows destructuring.
 unsafe impl Trace for GeneratorState {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         match &this {
             Self::SuspendedStart { context } | Self::SuspendedYield { context } => mark(context),
             Self::Executing | Self::Completed => {}

core/engine/src/builtins/intl/collator/mod.rs

@@ -57,7 +57,7 @@ pub(crate) struct Collator {
 
 // SAFETY: only `bound_compare` is a traceable object.
 unsafe impl Trace for Collator {
-    custom_trace!(this, mark(&this.bound_compare));
+    custom_trace!(this, mark, mark(&this.bound_compare));
 }
 
 impl Collator {

core/engine/src/builtins/map/ordered_map.rs

@@ -42,7 +42,7 @@ pub struct OrderedMap<V> {
 }
 
 unsafe impl<V: Trace> Trace for OrderedMap<V> {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         for (k, v) in &this.map {
             if let MapKey::Key(key) = k {
                 mark(key);

core/engine/src/builtins/promise/mod.rs

@@ -42,7 +42,7 @@ pub enum PromiseState {
 }
 
 unsafe impl Trace for PromiseState {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         match this {
             Self::Fulfilled(v) | Self::Rejected(v) => mark(v),
             Self::Pending => {}
@@ -121,7 +121,7 @@ pub struct ResolvingFunctions {
 
 // Manually implementing `Trace` to allow destructuring.
 unsafe impl Trace for ResolvingFunctions {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         mark(&this.resolve);
         mark(&this.reject);
     });
@@ -176,7 +176,7 @@ pub(crate) struct PromiseCapability {
 
 // SAFETY: manually implementing `Trace` to allow destructuring.
 unsafe impl Trace for PromiseCapability {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         mark(&this.promise);
         mark(&this.functions);
     });

core/engine/src/builtins/set/ordered_set.rs

@@ -14,7 +14,7 @@ pub struct OrderedSet {
 }
 
 unsafe impl Trace for OrderedSet {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         for v in &this.inner {
             if let MapKey::Key(v) = v {
                 mark(v);

core/engine/src/environments/runtime/declarative/function.rs

@@ -161,7 +161,7 @@ pub(crate) enum ThisBindingStatus {
 }
 
 unsafe impl Trace for ThisBindingStatus {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         match this {
             Self::Initialized(obj) => mark(obj),
             Self::Lexical | Self::Uninitialized => {}

core/engine/src/error.rs

@@ -53,7 +53,7 @@ pub struct JsError {
 
 // SAFETY: just mirroring the default derive to allow destructuring.
 unsafe impl Trace for JsError {
-    custom_trace!(this, mark(&this.inner));
+    custom_trace!(this, mark, mark(&this.inner));
 }
 
 /// Internal representation of a [`JsError`].
@@ -76,6 +76,7 @@ enum Repr {
 unsafe impl Trace for Repr {
     custom_trace!(
         this,
+        mark,
         match &this {
             Self::Native(err) => mark(err),
             Self::Opaque(val) => mark(val),
@@ -549,7 +550,7 @@ impl fmt::Display for JsNativeError {
 
 // SAFETY: just mirroring the default derive to allow destructuring.
 unsafe impl Trace for JsNativeError {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         mark(&this.kind);
         mark(&this.cause);
         mark(&this.realm);
@@ -1108,6 +1109,7 @@ pub enum JsNativeErrorKind {
 unsafe impl Trace for JsNativeErrorKind {
     custom_trace!(
         this,
+        mark,
         match &this {
             Self::Aggregate(errors) => mark(errors),
             Self::Error

core/engine/src/module/source.rs

@@ -104,7 +104,7 @@ enum Status {
 // useful to have for state machines like `Status`. This is solved by manually implementing
 // `Trace`.
 unsafe impl Trace for Status {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         match this {
             Self::Unlinked | Self::Linking { info: _ } => {}
             Self::PreLinked { context, info: _ } | Self::Linked { context, info: _ } => {
@@ -239,7 +239,7 @@ impl std::fmt::Debug for SourceTextContext {
 }
 
 unsafe impl Trace for SourceTextContext {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         mark(&this.codeblock);
         mark(&this.environments);
         mark(&this.realm);

core/engine/src/native_function.rs

@@ -71,7 +71,7 @@ pub struct NativeFunctionObject {
 
 // SAFETY: this traces all fields that need to be traced by the GC.
 unsafe impl Trace for NativeFunctionObject {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         mark(&this.f);
         mark(&this.realm);
     });
@@ -125,7 +125,7 @@ enum Inner {
 // Manual implementation because deriving `Trace` triggers the `single_use_lifetimes` lint.
 // SAFETY: Only closures can contain `Trace` captures, so this implementation is safe.
 unsafe impl Trace for NativeFunction {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         if let Inner::Closure(c) = &this.inner {
             mark(c);
         }

core/engine/src/object/mod.rs

@@ -178,7 +178,9 @@ impl dyn NativeObject {
 }
 
 /// The internal representation of a JavaScript object.
-#[derive(Debug, Finalize)]
+#[derive(Debug, Finalize, Trace)]
+// SAFETY: This does not implement drop, so this is safe.
+#[boa_gc(unsafe_no_drop)]
 pub struct Object<T: ?Sized> {
     /// The collection of properties contained in the object
     pub(crate) properties: PropertyMap,
@@ -201,16 +203,6 @@ impl<T: Default> Default for Object<T> {
     }
 }
 
-unsafe impl<T: Trace + ?Sized> Trace for Object<T> {
-    boa_gc::custom_trace!(this, {
-        mark(&this.data);
-        mark(&this.properties);
-        for (_, element) in &this.private_elements {
-            mark(element);
-        }
-    });
-}
-
 /// A Private Name.
 #[derive(Clone, Debug, PartialEq, Eq, Trace, Finalize)]
 pub struct PrivateName {

core/engine/src/object/property_map.rs

@@ -25,7 +25,7 @@ impl<K: Trace> Default for OrderedHashMap<K> {
 }
 
 unsafe impl<K: Trace> Trace for OrderedHashMap<K> {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         for (k, v) in &this.0 {
             mark(k);
             mark(v);

core/engine/src/value/mod.rs

@@ -81,7 +81,7 @@ pub enum JsValue {
 }
 
 unsafe impl Trace for JsValue {
-    custom_trace! {this, {
+    custom_trace! {this, mark, {
         if let Self::Object(o) = this {
             mark(o);
         }

core/engine/src/vm/completion_record.rs

@@ -18,7 +18,7 @@ pub(crate) enum CompletionRecord {
 // SAFETY: this matches all possible variants and traces
 // their inner contents, which makes this safe.
 unsafe impl Trace for CompletionRecord {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         match this {
             Self::Normal(v) => mark(v),
             Self::Return(r) => mark(r),

core/engine/src/vm/mod.rs

@@ -86,7 +86,7 @@ pub(crate) enum ActiveRunnable {
 }
 
 unsafe impl Trace for ActiveRunnable {
-    custom_trace!(this, {
+    custom_trace!(this, mark, {
         match this {
             Self::Script(script) => mark(script),
             Self::Module(module) => mark(module),

core/engine/src/vm/tests.rs

@@ -417,3 +417,17 @@ fn cross_context_funtion_call() {
 
     assert_eq!(result, Ok(JsValue::new(100)));
 }
+
+// See: https://github.com/boa-dev/boa/issues/1848
+#[test]
+fn long_object_chain_gc_trace_stack_overflow() {
+    run_test_actions([
+        TestAction::run(indoc! {r#"
+            let old = {};
+            for (let i = 0; i < 100000; i++) {
+                old = { old };
+            }
+        "#}),
+        TestAction::inspect_context(|_| boa_gc::force_collect()),
+    ]);
+}

core/gc/src/cell.rs

@@ -1,6 +1,9 @@
 //! A garbage collected cell implementation
 
-use crate::trace::{Finalize, Trace};
+use crate::{
+    trace::{Finalize, Trace},
+    Tracer,
+};
 use std::{
     cell::{Cell, UnsafeCell},
     cmp::Ordering,
@@ -218,11 +221,11 @@ impl<T: Trace + ?Sized> Finalize for GcRefCell<T> {}
 // Implementing a Trace while the cell is being written to or incorrectly implementing Trace
 // on GcCell's value may cause Undefined Behavior
 unsafe impl<T: Trace + ?Sized> Trace for GcRefCell<T> {
-    unsafe fn trace(&self) {
+    unsafe fn trace(&self, tracer: &mut Tracer) {
         match self.flags.get().borrowed() {
             BorrowState::Writing => (),
             // SAFETY: Please see GcCell's Trace impl Safety note.
-            _ => unsafe { (*self.cell.get()).trace() },
+            _ => unsafe { (*self.cell.get()).trace(tracer) },
         }
     }