Add TODO to simplify Borrow<T> to &T.

To be done once linear handles are the default.

sdk/rust/oak/src/io/mod.rs

@@ -120,6 +120,7 @@ fn send_init<Init, Command, InitSender>(
 where
     Init: Encodable + Decodable,
     Command: Encodable + Decodable,
+    // TODO(#1854): Only accept references once handles are always linear types
     InitSender: Borrow<Sender<oak_io::InitWrapper<Init, Command>>>,
 {
     let (command_sender, command_receiver) =

sdk/rust/oak/src/lib.rs

@@ -68,6 +68,7 @@ pub mod proto {
 
 // Build a chunk of memory that is suitable for passing to oak_abi::wait_on_channels,
 // holding the given collection of channel handles.
+// TODO(#1854): Only accept &[&ReadHandle] once handles are always linear types
 fn new_handle_space<R: Borrow<ReadHandle>>(handles: &[R]) -> Vec<u8> {
     let mut space = Vec::with_capacity(oak_abi::SPACE_BYTES_PER_HANDLE * handles.len());
     for handle in handles {
@@ -95,6 +96,7 @@ fn prep_handle_space(space: &mut [u8]) {
 /// This is a convenience wrapper around the [`oak_abi::wait_on_channels`] host
 /// function. This version is easier to use in Rust but is less efficient
 /// (because the notification space is re-created on each invocation).
+// TODO(#1854): Only accept &[&ReadHandle] once handles are always linear types
 pub fn wait_on_channels<R: Borrow<ReadHandle>>(
     handles: &[R],
 ) -> Result<Vec<ChannelReadStatus>, OakStatus> {
@@ -125,6 +127,7 @@ pub fn wait_on_channels<R: Borrow<ReadHandle>>(
 /// The provided vectors for received data and associated handles will be
 /// resized to accommodate the information in the message; any data already
 /// held in the vectors will be overwritten.
+// TODO(#1854): Only accept &ReadHandle once handles are always linear types
 pub fn channel_read<R: Borrow<ReadHandle>>(
     half: R,
     buf: &mut Vec<u8>,
@@ -213,6 +216,7 @@ pub fn channel_read<R: Borrow<ReadHandle>>(
 }
 
 /// Write a message to a channel.
+// TODO(#1854): Only accept &WriteHandle once handles are always linear types
 pub fn channel_write<W: Borrow<WriteHandle>>(
     half: W,
     buf: &[u8],
@@ -233,6 +237,7 @@ pub fn channel_write<W: Borrow<WriteHandle>>(
 
 /// The same as [`channel_write`](#method.channel_write), but also applies the current Node's
 /// downgrade privilege when checking IFC restrictions.
+// TODO(#1854): Only accept &WriteHandle once handles are always linear types
 pub fn channel_write_with_downgrade<W: Borrow<WriteHandle>>(
     half: W,
     buf: &[u8],