Add a new experimental API as a possible alternative.

Author: sunfishcode

text/0000-io-safety.md

@@ -347,14 +347,6 @@ I/O safety approach will require changes to Rust code in crates such as
 [`RawFd`], though the changes can be made gradually across the ecosystem rather
 than all at once.
 
-## New types for `RawFd`/`RawHandle`/`RawSocket`
-
-Some comments on [rust-lang/rust#76969] suggest introducing new wrappers
-around the raw handles. Completely closing the safety loophole would also
-require designing new traits, since `AsRaw*` doesn't have a way to limit the
-lifetime of its return value. This RFC doesn't rule this out, but it would be a
-bigger change.
-
 ## I/O safety but not `IoSafe`
 
 The I/O safety concept doesn't depend on `IoSafe` being in `std`. Crates could
@@ -374,6 +366,35 @@ it returns raw types, arguably it would be better to make it work more like
 connected to reference lifetimes. If the concept of borrowing is desired, new
 types could be introduced, with better ergonomics, in a separate proposal.
 
+## New types and traits
+
+New types and traits could provide a much cleaner API, along the lines of:
+
+```rust
+pub struct BorrowedFd<'owned> { ... }
+pub struct OwnedFd { ... }
+pub struct OptionFd { ... }
+
+pub trait AsBorrowedFd { ... }
+pub trait IntoOwnedFd { ... }
+pub trait FromOwnedFd { ... }
+```
+
+An initial prototype of this here:
+
+<https://github.com/sunfishcode/io-experiment>
+
+The details are mostly obvious, though one notable aspect of this design is
+the use of `repr(transparent)` to define types that can participate in FFI
+directly, leading to FFI usage patterns that don't interact with raw types
+at all. An example of this is here:
+
+<https://github.com/sunfishcode/io-experiment/blob/main/examples/hello.rs>
+
+This provides a cleaner API than `*Raw*` + `IoSafe`. The main obvious downside
+is that a lot of code will likely need to continue to support `*Raw*` for a
+long time, so this would increase the amount of code they have to maintain.
+
 # Prior art
 [prior-art]: #prior-art