fix: don't leak GC roots in Table::copy

crates/wasmtime/src/runtime/externals/table.rs

@@ -430,22 +430,26 @@ impl Table {
                  destination table's element type",
             )?;
 
+        let mut copy_elem = |src: u64, dst: u64| -> Result<()> {
+            let scope = store.enter_gc_lifo_scope();
+            let result = match src_table.get(&mut *store, src) {
+                Some(val) => dst_table.set(&mut *store, dst, val),
+                None => Err(Trap::TableOutOfBounds.into()),
+            };
+            store.exit_gc_lifo_scope(scope);
+            result
+        };
+
         // Do a forwards or backwards copy depending on the indices involved to
         // ensure that elements that are part of the copy aren't accidentally
         // clobbered.
         if dst_index < src_index {
             for (src, dst) in src_range.zip(dst_range) {
-                let val = src_table
-                    .get(&mut *store, src)
-                    .ok_or(Trap::TableOutOfBounds)?;
-                dst_table.set(&mut *store, dst, val)?;
+                copy_elem(src, dst)?;
             }
         } else {
             for (src, dst) in src_range.rev().zip(dst_range.rev()) {
-                let val = src_table
-                    .get(&mut *store, src)
-                    .ok_or(Trap::TableOutOfBounds)?;
-                dst_table.set(&mut *store, dst, val)?;
+                copy_elem(src, dst)?;
             }
         }
         Ok(())

tests/all/gc.rs

@@ -883,6 +883,34 @@ fn table_copy_doesnt_leak() -> Result<()> {
     Ok(())
 }
 
+#[test]
+#[cfg_attr(miri, ignore)]
+fn table_copy_without_root_scope_doesnt_leak() -> Result<()> {
+    let _ = env_logger::try_init();
+
+    let mut store = Store::<()>::default();
+    let flag = Arc::new(AtomicBool::new(false));
+
+    let table = Table::new(
+        &mut store,
+        TableType::new(RefType::EXTERNREF, 10, Some(10))?,
+        Ref::Extern(None),
+    )?;
+
+    {
+        let mut scope = RootScope::new(&mut store);
+        let x = ExternRef::new(&mut scope, SetFlagOnDrop(flag.clone()))?;
+        table.fill(&mut scope, 2, x.into(), 3)?;
+    }
+
+    Table::copy(&mut store, &table, 5, &table, 2, 3)?;
+    table.fill(&mut store, 0, Ref::Extern(None), 10)?;
+
+    store.gc(None)?;
+    assert!(flag.load(SeqCst));
+    Ok(())
+}
+
 #[test]
 #[cfg_attr(miri, ignore)]
 fn table_set_doesnt_leak() -> Result<()> {