feat: support xdg foreign parenting

compositor/src/handlers/mod.rs

@@ -27,6 +27,7 @@ use smithay::{
                 PrimarySelectionHandler, PrimarySelectionState, set_primary_focus,
             },
         },
+        xdg_foreign::{XdgForeignHandler, XdgForeignState},
     },
 };
 
@@ -150,6 +151,12 @@ impl PrimarySelectionHandler for Ferese {
     }
 }
 
+impl XdgForeignHandler for Ferese {
+    fn xdg_foreign_state(&mut self) -> &mut XdgForeignState {
+        &mut self.xdg_foreign_state
+    }
+}
+
 smithay::delegate_compositor!(Ferese);
 smithay::delegate_data_device!(Ferese);
 smithay::delegate_fractional_scale!(Ferese);
@@ -165,4 +172,5 @@ smithay::delegate_single_pixel_buffer!(Ferese);
 smithay::delegate_viewporter!(Ferese);
 smithay::delegate_xdg_activation!(Ferese);
 smithay::delegate_xdg_decoration!(Ferese);
+smithay::delegate_xdg_foreign!(Ferese);
 smithay::delegate_xdg_shell!(Ferese);

compositor/src/handlers/xdg_shell.rs

@@ -51,6 +51,31 @@ impl XdgShellHandler for Ferese {
         }
     }
 
+    fn parent_changed(&mut self, surface: ToplevelSurface) {
+        let Some(parent) = surface.parent() else {
+            return;
+        };
+        let parent = self.window_ids.iter().find_map(|(window, id)| {
+            window
+                .toplevel()
+                .is_some_and(|toplevel| toplevel.wl_surface() == &parent)
+                .then_some(*id)
+        });
+        let child = self
+            .space
+            .elements()
+            .find(|window| {
+                window
+                    .toplevel()
+                    .is_some_and(|toplevel| toplevel.wl_surface() == surface.wl_surface())
+            })
+            .cloned();
+
+        if let (Some(parent), Some(child)) = (parent, child) {
+            self.make_window_transient(&child, parent);
+        }
+    }
+
     fn toplevel_destroyed(&mut self, surface: ToplevelSurface) {
         let Some(window) = self
             .space