feat: handle global removals, recalc output scale (#367)

All `GlobalRemove` events sent from the server are now handled by
recording them in a new clientside `vec` and passing the identifier
returned by `create_global` (now stored by a map in the state) to
`disable_global`. `handle_globals` (the top-level function) and
`handle_new_globals` (the `InnerServerState` member function) have
swapped names to better represent their new purposes.

This enables action to be taken when globals are removed. In this case,
the desired action is to forward output removal, so that the scaling
calculation does not account for disconnected monitors in its logic.

Resolves #351.

src/server/mod.rs

@@ -65,6 +65,7 @@ use wayland_protocols::{
 use wayland_server::protocol::wl_seat::WlSeat;
 use wayland_server::{
     Client, DisplayHandle, Resource, WEnum,
+    backend::GlobalId,
     protocol::{
         wl_callback::WlCallback, wl_compositor::WlCompositor, wl_output::WlOutput, wl_shm::WlShm,
         wl_surface::WlSurface,
@@ -342,7 +343,8 @@ enum ObjectEvent {
 }
 }
 
-fn handle_globals<'a, S: X11Selection + 'static>(
+fn handle_new_globals<'a, S: X11Selection + 'static>(
+    globals_map: &mut HashMap<GlobalName, (Global, GlobalId)>,
     dh: &DisplayHandle,
     globals: impl IntoIterator<Item = &'a Global>,
 ) {
@@ -353,7 +355,8 @@ fn handle_globals<'a, S: X11Selection + 'static>(
                     $(
                         ref x if x == <$global>::interface().name => {
                             let version = u32::min(global.version, <$global>::interface().version);
-                            dh.create_global::<InnerServerState<S>, $global, Global>(version, global.clone());
+                            let global_id = dh.create_global::<InnerServerState<S>, $global, Global>(version, global.clone());
+                            globals_map.insert(GlobalName(global.name), (global.clone(), global_id));
                         }
                     )+
                     _ => {}
@@ -377,6 +380,9 @@ fn handle_globals<'a, S: X11Selection + 'static>(
     }
 }
 
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub(super) struct GlobalName(pub u32);
+
 struct FocusData {
     window: x::Window,
     output_name: Option<String>,
@@ -446,6 +452,7 @@ pub struct InnerServerState<S: X11Selection> {
     world: MyWorld,
     queue: EventQueue<MyWorld>,
     qh: QueueHandle<MyWorld>,
+    globals_map: HashMap<GlobalName, (Global, GlobalId)>,
     client: Client,
     to_focus: Option<FocusData>,
     unfocus: bool,
@@ -532,9 +539,10 @@ impl<S: X11Selection> ServerState<NoConnection<S>> {
 
         dh.create_global::<InnerServerState<S>, XwaylandShellV1, _>(1, ());
 
+        let mut globals_map = HashMap::new();
         global_list
             .contents()
-            .with_list(|globals| handle_globals::<S>(&dh, globals));
+            .with_list(|globals| handle_new_globals::<S>(&mut globals_map, &dh, globals));
 
         let world = MyWorld::new(global_list);
         let client = dh.insert_client(client, std::sync::Arc::new(())).unwrap();
@@ -545,6 +553,7 @@ impl<S: X11Selection> ServerState<NoConnection<S>> {
             client,
             queue,
             qh,
+            globals_map,
             dh,
             to_focus: None,
             unfocus: false,
@@ -613,7 +622,7 @@ impl<C: XConnection> ServerState<C> {
     }
 
     pub fn handle_clientside_events(&mut self) {
-        self.handle_new_globals();
+        self.handle_globals();
 
         for (target, event) in self.world.read_events() {
             if !self.world.contains(target) {
@@ -659,8 +668,10 @@ impl<C: XConnection> ServerState<C> {
         }
 
         if !self.updated_outputs.is_empty() {
-            for output in self.updated_outputs.iter() {
-                let output_scale = self.world.get::<&OutputScaleFactor>(*output).unwrap();
+            for output in std::mem::take(&mut self.updated_outputs).iter() {
+                let Ok(output_scale) = self.world.get::<&OutputScaleFactor>(*output) else {
+                    continue;
+                };
                 if matches!(*output_scale, OutputScaleFactor::Output(..)) {
                     let mut surface_query = self
                         .world
@@ -684,7 +695,6 @@ impl<C: XConnection> ServerState<C> {
                     }
                 }
             }
-            self.updated_outputs.clear();
 
             let mut mixed_scale = false;
             let mut scale;
@@ -780,9 +790,33 @@ impl<S: X11Selection + 'static> InnerServerState<S> {
         self.queue.as_fd()
     }
 
-    fn handle_new_globals(&mut self) {
+    fn handle_globals(&mut self) {
         let globals = std::mem::take(&mut self.world.new_globals);
-        handle_globals::<S>(&self.dh, globals.iter());
+        handle_new_globals::<S>(&mut self.globals_map, &self.dh, &globals);
+
+        let globals = std::mem::take(&mut self.world.removed_globals);
+        if globals.is_empty() {
+            return;
+        }
+        let query = self
+            .world
+            .query_mut::<(&WlOutput, &GlobalName)>()
+            .into_iter()
+            .map(|(e, (_, name))| (e, *name))
+            .collect::<Vec<_>>();
+        for global in globals {
+            let (global_struct, global_id) = self.globals_map.remove(&global).unwrap();
+            self.dh.disable_global::<InnerServerState<S>>(global_id);
+            if global_struct.interface == <WlOutput>::interface().name {
+                for (entity, name) in query.iter() {
+                    if *name == global {
+                        self.updated_outputs.push(*entity);
+                        self.world.despawn(*entity).unwrap();
+                        break;
+                    }
+                }
+            }
+        }
     }
 
     pub fn new_window(