Auto merge of #20399 - Xanewok:remove-heap-handle-mut, r=jdm

Sanitize Heap::handle(_mut) functions

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Complementary to https://github.com/servo/rust-mozjs/pull/404.

Removing `Heap::handle_mut` didn't warrant any changes on Servo side, and so the changes here are only to fix compilation with `Heap::handle` being now marked as `unsafe`.

The main idea is that we can't hand out handles to heap values themselves, since they're not guaranteed to be rooted, but it's safe to do when we are - hence why the safe impl on `RootedTraceableBox<Heap<T>>` and why it's safe to use inside structs that hold a Heap and are `#[must_root]`.

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [X] These changes do not require tests because the compiler forces correctness here.

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1 files changed, 8 insertions, 1 deletions

diff --git a/components/script/timers.rs b/components/script/timers.rs
index 4bc4bf37fff..a5e7020095f 100644
--- a/components/script/timers.rs
+++ b/components/script/timers.rs
@@ -500,7 +500,7 @@ impl JsTimerTask {
                     code_str, rval.handle_mut());
             },
             InternalTimerCallback::FunctionTimerCallback(ref function, ref arguments) => {
-                let arguments = arguments.iter().map(|arg| arg.handle()).collect();
+                let arguments = self.collect_heap_args(arguments);
                 let _ = function.Call_(this, arguments, Report);
             },
         };
@@ -516,4 +516,11 @@ impl JsTimerTask {
             timers.initialize_and_schedule(&this.global(), self);
         }
     }
+
+    // Returning Handles directly from Heap values is inherently unsafe, but here it's
+    // always done via rooted JsTimers, which is safe.
+    #[allow(unsafe_code)]
+    fn collect_heap_args(&self, args: &[Heap<JSVal>]) -> Vec<HandleValue> {
+        args.iter().map(|arg| unsafe { arg.handle() }).collect()
+    }
 }