wayland/layer: In arrange(), handle exclusive zone surfaces first

Iterate over surfaces that have an exclusive zone first, then other
surfaces. This allows a surface that doesn't have an exclusive zone to
be moved or resized for a later surface that does have an exclusive
zone. As is probably desired.

Author: ids1024

src/desktop/wayland/layer.rs

@@ -272,7 +272,15 @@ impl LayerMap {
             );
             trace!("Arranging layers into {:?}", output_rect.size);
 
-            for layer in self.layers.iter() {
+            let exclusive_surfaces = self
+                .layers
+                .iter()
+                .filter(|l| matches!(l.exclusive_zone(), ExclusiveZone::Exclusive(_)));
+            let non_exclusive_surfaces = self
+                .layers
+                .iter()
+                .filter(|l| !matches!(l.exclusive_zone(), ExclusiveZone::Exclusive(_)));
+            for layer in exclusive_surfaces.chain(non_exclusive_surfaces) {
                 let surface = layer.wl_surface();
 
                 with_surface_tree_downward(
@@ -718,6 +726,16 @@ impl LayerSurface {
     pub fn user_data(&self) -> &UserDataMap {
         &self.0.userdata
     }
+
+    fn exclusive_zone(&self) -> ExclusiveZone {
+        with_states(self.wl_surface(), |states| {
+            states
+                .cached_state
+                .get::<LayerSurfaceCachedState>()
+                .current()
+                .exclusive_zone
+        })
+    }
 }
 
 impl WaylandFocus for LayerSurface {