Move the Rust `Arena` type which wraps a upb_Arena into the upb directory.
PiperOrigin-RevId: 625317910
diff --git a/rust/upb/opaque_pointee.rs b/rust/upb/opaque_pointee.rs
new file mode 100644
index 0000000..92bd4a2
--- /dev/null
+++ b/rust/upb/opaque_pointee.rs
@@ -0,0 +1,16 @@
+// Macro to create structs that will act as opaque pointees. These structs are
+// never intended to be dereferenced in Rust.
+// This is a workaround until stabilization of [`extern type`].
+// TODO: convert to extern type once stabilized.
+// [`extern type`]: https://github.com/rust-lang/rust/issues/43467
+macro_rules! opaque_pointee {
+ ($name: ident) => {
+ #[repr(C)]
+ pub struct $name {
+ _data: [u8; 0],
+ _marker: std::marker::PhantomData<(*mut u8, std::marker::PhantomPinned)>,
+ }
+ };
+}
+
+pub(crate) use opaque_pointee;
