WIP/experiment: use as-any instead of downcast-rs

wayland-backend/Cargo.toml

@@ -14,10 +14,10 @@ readme = "README.md"
 build = "build.rs"
 
 [dependencies]
+as-any = "0.3"
 wayland-sys = { version = "0.31.0", path = "../wayland-sys", features = [] }
 log = { version = "0.4", optional = true }
 scoped-tls = "1.0"
-downcast-rs = "1.2"
 raw-window-handle = { version = "0.5.0", optional = true }
 
 [dependencies.smallvec]

wayland-backend/src/client_api.rs

@@ -12,14 +12,16 @@ use super::client_impl;
 
 pub use crate::types::client::{InvalidId, NoWaylandLib, WaylandError};
 
+use as_any::AsAny;
+
 /// A trait representing your data associated to an object
 ///
 /// You will only be given access to it as a `&` reference, so you
 /// need to handle interior mutability by yourself.
 ///
 /// The methods of this trait will be invoked internally every time a
 /// new object is created to initialize its data.
-pub trait ObjectData: downcast_rs::DowncastSync {
+pub trait ObjectData: Send + Sync + AsAny {
     /// Dispatch an event for the associated object
     ///
     /// If the event has a `NewId` argument, the callback must return the object data
@@ -58,8 +60,6 @@ impl std::fmt::Debug for dyn ObjectData {
     }
 }
 
-downcast_rs::impl_downcast!(sync ObjectData);
-
 /// An ID representing a Wayland object
 ///
 /// The backend internally tracks which IDs are still valid, invalidates them when the protocol object they

wayland-backend/src/rs/server_impl/handle.rs

@@ -18,6 +18,8 @@ use super::{
     InnerClientId, InnerGlobalId, InnerObjectId, ObjectData, ObjectId,
 };
 
+use as_any::Downcast;
+
 pub(crate) type PendingDestructor<D> = (Arc<dyn ObjectData<D>>, InnerClientId, InnerObjectId);
 
 #[derive(Debug)]
@@ -269,7 +271,7 @@ impl InnerHandle {
     }
 }
 
-pub(crate) trait ErasedState: downcast_rs::Downcast {
+pub(crate) trait ErasedState: as_any::AsAny {
     fn object_info(&self, id: InnerObjectId) -> Result<ObjectInfo, InvalidId>;
     fn insert_client(
         &mut self,
@@ -302,8 +304,6 @@ pub(crate) trait ErasedState: downcast_rs::Downcast {
     fn flush(&mut self, client: Option<ClientId>) -> std::io::Result<()>;
 }
 
-downcast_rs::impl_downcast!(ErasedState);
-
 impl<D> ErasedState for State<D> {
     fn object_info(&self, id: InnerObjectId) -> Result<ObjectInfo, InvalidId> {
         self.clients.get_client(id.client_id.clone())?.object_info(id)

wayland-backend/src/server_api.rs

@@ -11,14 +11,29 @@ pub use crate::types::server::{Credentials, DisconnectReason, GlobalInfo, InitEr
 
 use super::server_impl;
 
+use as_any::AsAny;
+
+/// Extends `AsAny` to support `Sync` traits that thus support `Arc` downcasting as well.
+pub trait IntoAnyArc: Send + Sync + AsAny {
+    /// Convert `Arc<Trait>` (where `Trait: Downcast`) to `Arc<Any>`. `Arc<Any>` can then be
+    /// further `downcast` into `Arc<ConcreteType>` where `ConcreteType` implements `Trait`.
+    fn into_any_arc(self: Arc<Self>) -> Arc<dyn std::any::Any + Send + Sync>;
+}
+
+impl<T: Send + Sync + AsAny> IntoAnyArc for T {
+    fn into_any_arc(self: Arc<Self>) -> Arc<dyn std::any::Any + Send + Sync> {
+        self
+    }
+}
+
 /// A trait representing your data associated to an object
 ///
 /// You will only be given access to it as a `&` reference, so you
 /// need to handle interior mutability by yourself.
 ///
 /// The methods of this trait will be invoked internally every time a
 /// new object is created to initialize its data.
-pub trait ObjectData<D>: downcast_rs::DowncastSync {
+pub trait ObjectData<D>: IntoAnyArc {
     /// Dispatch a request for the associated object
     ///
     /// If the request has a `NewId` argument, the callback must return the object data
@@ -47,8 +62,6 @@ pub trait ObjectData<D>: downcast_rs::DowncastSync {
     }
 }
 
-downcast_rs::impl_downcast!(sync ObjectData<D>);
-
 impl<D: 'static> std::fmt::Debug for dyn ObjectData<D> {
     #[cfg_attr(coverage, coverage(off))]
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
@@ -57,7 +70,7 @@ impl<D: 'static> std::fmt::Debug for dyn ObjectData<D> {
 }
 
 /// A trait representing the handling of new bound globals
-pub trait GlobalHandler<D>: downcast_rs::DowncastSync {
+pub trait GlobalHandler<D>: Send + Sync + AsAny {
     /// Check if given client is allowed to interact with given global
     ///
     /// If this function returns false, the client will not be notified of the existence
@@ -102,10 +115,8 @@ impl<D: 'static> std::fmt::Debug for dyn GlobalHandler<D> {
     }
 }
 
-downcast_rs::impl_downcast!(sync GlobalHandler<D>);
-
 /// A trait representing your data associated to a client
-pub trait ClientData: downcast_rs::DowncastSync {
+pub trait ClientData: Send + Sync + AsAny {
     /// Notification that the client was initialized
     fn initialized(&self, _client_id: ClientId) {}
     /// Notification that the client is disconnected
@@ -128,8 +139,6 @@ impl std::fmt::Debug for dyn ClientData {
 
 impl ClientData for () {}
 
-downcast_rs::impl_downcast!(sync ClientData);
-
 /// An ID representing a Wayland object
 ///
 /// The backend internally tracks which IDs are still valid, invalidates them when the protocol object they

wayland-backend/src/sys/server_impl/mod.rs

@@ -18,6 +18,7 @@ use crate::protocol::{
     check_for_signature, same_interface, AllowNull, Argument, ArgumentType, Interface, Message,
     ObjectInfo, ANONYMOUS_INTERFACE,
 };
+use as_any::Downcast;
 use scoped_tls::scoped_thread_local;
 use smallvec::SmallVec;
 
@@ -822,7 +823,7 @@ impl InnerHandle {
     }
 }
 
-pub(crate) trait ErasedState: downcast_rs::Downcast {
+pub(crate) trait ErasedState: as_any::AsAny {
     fn object_info(&self, id: InnerObjectId) -> Result<ObjectInfo, InvalidId>;
     fn insert_client(
         &self,
@@ -857,8 +858,6 @@ pub(crate) trait ErasedState: downcast_rs::Downcast {
     fn display_ptr(&self) -> *mut wl_display;
 }
 
-downcast_rs::impl_downcast!(ErasedState);
-
 impl<D: 'static> ErasedState for State<D> {
     fn object_info(&self, id: InnerObjectId) -> Result<ObjectInfo, InvalidId> {
         if !id.alive.load(Ordering::Acquire) {

wayland-backend/tests/rs_sys_impls.rs

@@ -107,17 +107,17 @@ mod server {
     fn test_impls() {
         // ObjectData
         assert_impl!(
-            dyn server::ObjectData<()>: std::fmt::Debug, downcast_rs::DowncastSync
+            dyn server::ObjectData<()>: std::fmt::Debug, Send, Sync, as_any::AsAny
         );
 
         // GlobalHandler
         assert_impl!(
-            dyn server::GlobalHandler<()>: std::fmt::Debug, downcast_rs::DowncastSync
+            dyn server::GlobalHandler<()>: std::fmt::Debug, Send, Sync, as_any::AsAny
         );
 
         // ClientData
         assert_impl!(
-            dyn server::ClientData: std::fmt::Debug, downcast_rs::DowncastSync
+            dyn server::ClientData: std::fmt::Debug, Send, Sync, as_any::AsAny
         );
 
         // ObjectId
@@ -150,7 +150,7 @@ mod client {
     fn test_impls() {
         // ObjectData
         assert_impl!(
-            dyn client::ObjectData: std::fmt::Debug, downcast_rs::DowncastSync
+            dyn client::ObjectData: std::fmt::Debug, Send, Sync, as_any::AsAny
         );
 
         // ObjectId

wayland-server/Cargo.toml

@@ -15,10 +15,10 @@ readme = "README.md"
 [dependencies]
 wayland-backend = { version = "0.3.0", path = "../wayland-backend" }
 wayland-scanner = { version = "0.31.0", path = "../wayland-scanner" }
+as-any = "0.3"
 bitflags = "2"
 log = { version = "0.4", optional = true }
 nix = { version = "0.26.0", default-features = false }
-downcast-rs = "1.2"
 io-lifetimes = "2"
 
 [package.metadata.docs.rs]

wayland-server/src/client.rs

@@ -29,6 +29,7 @@ impl Client {
     ///
     /// Returns [`None`] if the provided `Data` type parameter is not the correct one.
     pub fn get_data<Data: ClientData + 'static>(&self) -> Option<&Data> {
+        use as_any::Downcast;
         (*self.data).downcast_ref()
     }