Adjust InputBackend for libinput compatibility

- Make id be an `u64` to be able to populate it by a hash
- Add internal interface to get a mutable capabilities reference from a `Seat`.
- `InputConfig` type does not need to be `Sized` on `InputBackend`

src/backend/input.rs

@@ -12,19 +12,24 @@ use std::error::Error;
 /// separated users, all with their own focus, input and cursor available.
 ///
 /// Seats can be checked for equality and hashed for differentiation.
+// FIXME: Impl PartialEq, Eq and Hash only dependant on `id`.
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct Seat {
-    id: u32,
+    id: u64,
     capabilities: SeatCapabilities,
 }
 
 impl SeatInternal for Seat {
-    fn new(id: u32, capabilities: SeatCapabilities) -> Seat {
+    fn new(id: u64, capabilities: SeatCapabilities) -> Seat {
         Seat {
             id: id,
             capabilities: capabilities,
         }
     }
+
+    fn capabilities_mut(&mut self) -> &mut SeatCapabilities {
+        &mut self.capabilities
+    }
 }
 
 impl Seat {
@@ -182,7 +187,7 @@ pub enum TouchEvent {
 /// given events.
 pub trait InputBackend: Sized {
     /// Type of input device associated with the backend
-    type InputConfig;
+    type InputConfig: ?Sized;
 
     /// Type representing errors that may be returned when processing events
     type EventError: Error;

src/backend/mod.rs

@@ -28,7 +28,8 @@ pub use glium::*;
 /// Internal functions that need to be accessible by the different backend implementations
 
 trait SeatInternal {
-    fn new(id: u32, capabilities: input::SeatCapabilities) -> Self;
+    fn new(id: u64, capabilities: input::SeatCapabilities) -> Self;
+    fn capabilities_mut(&mut self) -> &mut input::SeatCapabilities;
 }
 
 trait TouchSlotInternal {