Remove feature hash_set_entry

Summary: We can live without it.

Reviewed By: bobyangyf

Differential Revision: D40893481

fbshipit-source-id: 0e48ba2c567c39eb5ba3b31abb4e7a8d2fa33c88

Author: stepancheg

starlark/src/lib.rs

@@ -359,7 +359,6 @@
 #![feature(const_type_id)]
 #![feature(core_intrinsics)]
 #![feature(generic_associated_types)]
-#![feature(hash_set_entry)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_write_slice)]
 #![feature(ptr_metadata)]

starlark/src/values/layout/heap/heap_type.rs

@@ -237,7 +237,10 @@ impl FrozenHeap {
     /// is kept alive. Used if a [`FrozenValue`] in this heap points at values in another
     /// [`FrozenHeap`].
     pub fn add_reference(&self, heap: &FrozenHeapRef) {
-        self.refs.borrow_mut().get_or_insert_owned(heap);
+        let mut refs = self.refs.borrow_mut();
+        if !refs.contains(heap) {
+            refs.insert(heap.dupe());
+        }
     }
 
     fn alloc_raw(&self, x: impl AValue<'static, ExtraElem = ()> + Send + Sync) -> FrozenValue {