Remove meaningless UnsafeCell

The shared memory is behind a raw pointer, which reference visibility
semantics don't see through. See
bevyengine/bevy#2172 for discussion.

src/archetype.rs

@@ -9,7 +9,6 @@ use crate::alloc::alloc::{alloc, dealloc, Layout};
 use crate::alloc::boxed::Box;
 use crate::alloc::{vec, vec::Vec};
 use core::any::{type_name, TypeId};
-use core::cell::UnsafeCell;
 use core::hash::{BuildHasher, BuildHasherDefault, Hasher};
 use core::ops::Deref;
 use core::ptr::{self, NonNull};
@@ -30,9 +29,7 @@ pub struct Archetype {
  state: OrderedTypeIdMap<TypeState>,
  len: u32,
  entities: Box<[u32]>,
- // UnsafeCell allows unique references into `data` to be constructed while shared references
- // containing the `Archetype` exist
- data: UnsafeCell<NonNull<u8>>,
+ data: NonNull<u8>,
  data_size: usize,
  /// Maps static bundle types to the archetype that an entity from this archetype is moved to
  /// after removing the components from that bundle.
@@ -66,7 +63,7 @@ impl Archetype {
  types,
  entities: Box::new([]),
  len: 0,
- data: UnsafeCell::new(NonNull::new(max_align as *mut u8).unwrap()),
+ data: NonNull::new(max_align as *mut u8).unwrap(),
  data_size: 0,
  remove_edges: HashMap::default(),
  }
@@ -108,9 +105,7 @@ impl Archetype {
  assert_eq!(id, &TypeId::of::<T>());
 
  unsafe {
- NonNull::new_unchecked(
- (*self.data.get()).as_ptr().add(state.offset).cast::<T>() as *mut T
- )
+ NonNull::new_unchecked(self.data.as_ptr().add(state.offset).cast::<T>() as *mut T)
  }
  }
 
@@ -217,7 +212,7 @@ impl Archetype {
  ) -> Option<NonNull<u8>> {
  debug_assert!(index <= self.len);
  Some(NonNull::new_unchecked(
- (*self.data.get())
+ self.data
  .as_ptr()
  .add(self.state.get(&ty)?.offset + size * index as usize)
  .cast::<u8>(),
@@ -280,21 +275,21 @@ impl Archetype {
  let old_off = self.state.get(&ty.id).unwrap().offset;
  let new_off = new_state.get(&ty.id).unwrap().offset;
  ptr::copy_nonoverlapping(
- (*self.data.get()).as_ptr().add(old_off),
+ self.data.as_ptr().add(old_off),
  new_data.as_ptr().add(new_off),
  ty.layout.size() * old_count,
  );
  }
  dealloc(
- (*self.data.get()).as_ptr().cast(),
+ self.data.as_ptr().cast(),
  Layout::from_size_align_unchecked(
  old_data_size,
  self.types.first().map_or(1, |x| x.layout.align()),
  ),
  );
  }
 
- self.data = UnsafeCell::new(new_data);
+ self.data = new_data;
  self.state = new_state;
  }
  }
@@ -390,9 +385,10 @@ impl Archetype {
  self.reserve(other.len);
  for info in &self.types {
  let src_off = other.state.get(&info.id()).unwrap().offset;
- let src = (*other.data.get()).as_ptr().add(src_off);
+ let src = other.data.as_ptr().add(src_off);
  let dst_off = self.state.get(&info.id()).unwrap().offset;
- let dst = (*self.data.get())
+ let dst = self
+ .data
  .as_ptr()
  .add(dst_off + self.len as usize * info.layout.size());
  dst.copy_from_nonoverlapping(src, other.len as usize * info.layout.size())
@@ -418,7 +414,7 @@ impl Drop for Archetype {
  if self.data_size != 0 {
  unsafe {
  dealloc(
- (*self.data.get()).as_ptr().cast(),
+ self.data.as_ptr().cast(),
  Layout::from_size_align_unchecked(
  self.data_size,
  self.types.first().map_or(1, |x| x.layout.align()),