[API] Enhance Trace trait with trace_non_roots, run_finalizer and standard types

[shruti2522]

follow up to PR #95

• added trace_non_roots and run_finalizer to the Trace trait across mark_sweep_branded and null_collector_branded
• Implemented Trace and Finalize for standard library collections (HashMap, HashSet, BinaryHeap) and utility types (Instant, Path)
• implemented Trace and Finalize for boa specific types (boa_string::JsString, icu_locale_core, either::Either, arrayvec::ArrayVec)

[Copilot]

Pull request overview

This PR extends the GC Trace trait API (adding trace_non_roots and run_finalizer) and introduces optional Trace/Finalize implementations for additional standard-library and third-party types to broaden out-of-the-box GC compatibility.

Changes:

• Added trace_non_roots and run_finalizer to Trace across collectors (mark_sweep, mark_sweep_branded, null_collector_branded).
• Added optional Trace/Finalize impls (gated by features) for several external crates and additional std types.
• Updated dependencies/features and lockfile to support the new optional integrations.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
oscars/src/collectors/null_collector_branded/trace.rs	Expands Trace API and adds many new Trace/Finalize impls (std + external crates) under feature gates.
oscars/src/collectors/mark_sweep/trace.rs	Extends Trace trait with trace_non_roots default method.
oscars/src/collectors/mark_sweep_branded/trace.rs	Extends Trace trait with trace_non_roots and a default run_finalizer.
oscars/Cargo.toml	Adds optional dependencies and feature flags for external type support.
Cargo.lock	Updates dependency resolution to include newly added optional crates and transitive updates.

Suppressed comments (3)

oscars/src/collectors/null_collector_branded/trace.rs:351

• Trace for hashbrown::HashSet is currently a no-op. Elements can contain Gc pointers and must be visited; add a T: Trace bound and trace each element.

unsafe impl<T, S> Trace for hashbrown::hash_set::HashSet<T, S> {
    #[inline]
    unsafe fn trace(&self, _tracer: &mut Tracer) {}
}

oscars/src/collectors/null_collector_branded/trace.rs:360

• Trace for BinaryHeap is implemented as a no-op due to the lack of iter_mut(), but tracing only requires &self. This should iterate the heap and trace each element so reachable Gc pointers are not skipped.

unsafe impl<T: Trace> Trace for rust_alloc::collections::BinaryHeap<T> {
    #[inline]
    unsafe fn trace(&self, _tracer: &mut Tracer) {
        // BinaryHeap has no iter_mut(); the null collector's trace is a no-op
        // so no values need to be visited here.
    }
}

oscars/src/collectors/null_collector_branded/trace.rs:409

• Trace for std::collections::HashSet is currently a no-op. Elements can contain Gc pointers and must be traced; add a T: Trace bound and trace each element.

unsafe impl<T, S> Trace for std::collections::HashSet<T, S> {
    #[inline]
    unsafe fn trace(&self, _tracer: &mut Tracer) {}
}

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[nekevss]

Approving for now. I left one comment, and we will need to address it in the future. @shruti2522 could you file an issue to track it.

[nekevss]

Hmmmm, we will probably need to look into handling this differently in the future for a release ... I don't think this will resolve correctly for what we need.

But since this is still experimental we can leave it for now. But we will need to address it. It probably means that in the long run, oscars would need to be moved into boa OR the boa_string definitions will need to be added to boa_string