workspace: Make Item::clone_on_split async (#41211)

Split out from https://github.com/zed-industries/zed/pull/40774 to
reduce the size of the reland of that PR (once I figure out the cause of
the issue)

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/workspace/src/workspace.rs

@@ -3627,7 +3627,8 @@ impl Workspace {
         if let Some(pane) = panes.get(action.0).map(|p| (*p).clone()) {
             window.focus(&pane.focus_handle(cx));
         } else {
-            self.split_and_clone(self.active_pane.clone(), SplitDirection::Right, window, cx);
+            self.split_and_clone(self.active_pane.clone(), SplitDirection::Right, window, cx)
+                .detach();
         }
     }
 
@@ -3994,7 +3995,8 @@ impl Workspace {
                 clone_active_item,
             } => {
                 if *clone_active_item {
-                    self.split_and_clone(pane.clone(), *direction, window, cx);
+                    self.split_and_clone(pane.clone(), *direction, window, cx)
+                        .detach();
                 } else {
                     self.split_and_move(pane.clone(), *direction, window, cx);
                 }
@@ -4135,21 +4137,27 @@ impl Workspace {
         direction: SplitDirection,
         window: &mut Window,
         cx: &mut Context<Self>,
-    ) -> Option<Entity<Pane>> {
-        let item = pane.read(cx).active_item()?;
-        let maybe_pane_handle =
-            if let Some(clone) = item.clone_on_split(self.database_id(), window, cx) {
-                let new_pane = self.add_pane(window, cx);
-                new_pane.update(cx, |pane, cx| {
-                    pane.add_item(clone, true, true, None, window, cx)
-                });
-                self.center.split(&pane, &new_pane, direction).unwrap();
-                cx.notify();
-                Some(new_pane)
+    ) -> Task<Option<Entity<Pane>>> {
+        let Some(item) = pane.read(cx).active_item() else {
+            return Task::ready(None);
+        };
+        let task = item.clone_on_split(self.database_id(), window, cx);
+        cx.spawn_in(window, async move |this, cx| {
+            if let Some(clone) = task.await {
+                this.update_in(cx, |this, window, cx| {
+                    let new_pane = this.add_pane(window, cx);
+                    new_pane.update(cx, |pane, cx| {
+                        pane.add_item(clone, true, true, None, window, cx)
+                    });
+                    this.center.split(&pane, &new_pane, direction).unwrap();
+                    cx.notify();
+                    new_pane
+                })
+                .ok()
             } else {
                 None
-            };
-        maybe_pane_handle
+            }
+        })
     }
 
     pub fn join_all_panes(&mut self, window: &mut Window, cx: &mut Context<Self>) {
@@ -8217,19 +8225,27 @@ pub fn clone_active_item(
     let Some(active_item) = source.read(cx).active_item() else {
         return;
     };
-    destination.update(cx, |target_pane, cx| {
-        let Some(clone) = active_item.clone_on_split(workspace_id, window, cx) else {
-            return;
-        };
-        target_pane.add_item(
-            clone,
-            focus_destination,
-            focus_destination,
-            Some(target_pane.items_len()),
-            window,
-            cx,
-        );
-    });
+    let destination = destination.downgrade();
+    let task = active_item.clone_on_split(workspace_id, window, cx);
+    window
+        .spawn(cx, async move |cx| {
+            let Some(clone) = task.await else {
+                return;
+            };
+            destination
+                .update_in(cx, |target_pane, window, cx| {
+                    target_pane.add_item(
+                        clone,
+                        focus_destination,
+                        focus_destination,
+                        Some(target_pane.items_len()),
+                        window,
+                        cx,
+                    );
+                })
+                .log_err();
+        })
+        .detach();
 }
 
 #[derive(Debug)]
@@ -8736,25 +8752,24 @@ mod tests {
                 cx,
             );
 
-            let right_pane = workspace
-                .split_and_clone(left_pane.clone(), SplitDirection::Right, window, cx)
-                .unwrap();
+            let right_pane =
+                workspace.split_and_clone(left_pane.clone(), SplitDirection::Right, window, cx);
 
-            right_pane.update(cx, |pane, cx| {
-                pane.add_item(
-                    single_entry_items[1].boxed_clone(),
-                    true,
-                    true,
-                    None,
-                    window,
-                    cx,
-                );
-                pane.add_item(Box::new(item_3_4.clone()), true, true, None, window, cx);
+            let boxed_clone = single_entry_items[1].boxed_clone();
+            let right_pane = window.spawn(cx, async move |cx| {
+                right_pane.await.inspect(|right_pane| {
+                    right_pane
+                        .update_in(cx, |pane, window, cx| {
+                            pane.add_item(boxed_clone, true, true, None, window, cx);
+                            pane.add_item(Box::new(item_3_4.clone()), true, true, None, window, cx);
+                        })
+                        .unwrap();
+                })
             });
 
             (left_pane, right_pane)
         });
-
+        let right_pane = right_pane.await.unwrap();
         cx.focus(&right_pane);
 
         let mut close = right_pane.update_in(cx, |pane, window, cx| {
@@ -10571,7 +10586,10 @@ mod tests {
                 window,
                 cx,
             );
+        });
+        cx.run_until_parked();
 
+        workspace.update(cx, |workspace, cx| {
             assert_eq!(workspace.panes.len(), 3, "Two new panes were created");
             for pane in workspace.panes() {
                 assert_eq!(