Implement "join pane into next" (#16077)

Closes #12409

Release Notes:

- Added "join pane into next" action ([#12409](https://github.com/zed-industries/zed/issues/12409))


https://github.com/zed-industries/zed/assets/727422/00cc8599-e5d6-4fb8-9f0d-9b232d2210ef

---------

Co-authored-by: Kirill Bulatov <kirill@zed.dev>

crates/assistant/src/assistant_panel.rs

@@ -492,7 +492,7 @@ impl AssistantPanel {
         cx: &mut ViewContext<Self>,
     ) {
         let update_model_summary = match event {
-            pane::Event::Remove => {
+            pane::Event::Remove { .. } => {
                 cx.emit(PanelEvent::Close);
                 false
             }

crates/tab_switcher/src/tab_switcher.rs

@@ -173,16 +173,16 @@ impl TabSwitcherDelegate {
         };
         cx.subscribe(&pane, |tab_switcher, _, event, cx| {
             match event {
-                PaneEvent::AddItem { .. } | PaneEvent::RemovedItem { .. } | PaneEvent::Remove => {
-                    tab_switcher.picker.update(cx, |picker, cx| {
-                        let selected_item_id = picker.delegate.selected_item_id();
-                        picker.delegate.update_matches(cx);
-                        if let Some(item_id) = selected_item_id {
-                            picker.delegate.select_item(item_id, cx);
-                        }
-                        cx.notify();
-                    })
-                }
+                PaneEvent::AddItem { .. }
+                | PaneEvent::RemovedItem { .. }
+                | PaneEvent::Remove { .. } => tab_switcher.picker.update(cx, |picker, cx| {
+                    let selected_item_id = picker.delegate.selected_item_id();
+                    picker.delegate.update_matches(cx);
+                    if let Some(item_id) = selected_item_id {
+                        picker.delegate.select_item(item_id, cx);
+                    }
+                    cx.notify();
+                }),
                 _ => {}
             };
         })

crates/terminal_view/src/terminal_panel.rs

@@ -347,7 +347,7 @@ impl TerminalPanel {
         match event {
             pane::Event::ActivateItem { .. } => self.serialize(cx),
             pane::Event::RemovedItem { .. } => self.serialize(cx),
-            pane::Event::Remove => cx.emit(PanelEvent::Close),
+            pane::Event::Remove { .. } => cx.emit(PanelEvent::Close),
             pane::Event::ZoomIn => cx.emit(PanelEvent::ZoomIn),
             pane::Event::ZoomOut => cx.emit(PanelEvent::ZoomOut),
 

crates/workspace/src/pane.rs

@@ -147,6 +147,7 @@ actions!(
         CloseItemsToTheRight,
         GoBack,
         GoForward,
+        JoinIntoNext,
         ReopenClosedItem,
         SplitLeft,
         SplitUp,
@@ -175,7 +176,9 @@ pub enum Event {
     ActivateItem {
         local: bool,
     },
-    Remove,
+    Remove {
+        focus_on_pane: Option<View<Pane>>,
+    },
     RemoveItem {
         idx: usize,
     },
@@ -183,6 +186,7 @@ pub enum Event {
         item_id: EntityId,
     },
     Split(SplitDirection),
+    JoinIntoNext,
     ChangeItemTitle,
     Focus,
     ZoomIn,
@@ -204,7 +208,7 @@ impl fmt::Debug for Event {
                 .debug_struct("ActivateItem")
                 .field("local", local)
                 .finish(),
-            Event::Remove => f.write_str("Remove"),
+            Event::Remove { .. } => f.write_str("Remove"),
             Event::RemoveItem { idx } => f.debug_struct("RemoveItem").field("idx", idx).finish(),
             Event::RemovedItem { item_id } => f
                 .debug_struct("RemovedItem")
@@ -214,6 +218,7 @@ impl fmt::Debug for Event {
                 .debug_struct("Split")
                 .field("direction", direction)
                 .finish(),
+            Event::JoinIntoNext => f.write_str("JoinIntoNext"),
             Event::ChangeItemTitle => f.write_str("ChangeItemTitle"),
             Event::Focus => f.write_str("Focus"),
             Event::ZoomIn => f.write_str("ZoomIn"),
@@ -668,6 +673,10 @@ impl Pane {
         }
     }
 
+    fn join_into_next(&mut self, cx: &mut ViewContext<Self>) {
+        cx.emit(Event::JoinIntoNext);
+    }
+
     fn history_updated(&mut self, cx: &mut ViewContext<Self>) {
         self.toolbar.update(cx, |_, cx| cx.notify());
     }
@@ -1318,6 +1327,33 @@ impl Pane {
         activate_pane: bool,
         close_pane_if_empty: bool,
         cx: &mut ViewContext<Self>,
+    ) {
+        self._remove_item(item_index, activate_pane, close_pane_if_empty, None, cx)
+    }
+
+    pub fn remove_item_and_focus_on_pane(
+        &mut self,
+        item_index: usize,
+        activate_pane: bool,
+        focus_on_pane_if_closed: View<Pane>,
+        cx: &mut ViewContext<Self>,
+    ) {
+        self._remove_item(
+            item_index,
+            activate_pane,
+            true,
+            Some(focus_on_pane_if_closed),
+            cx,
+        )
+    }
+
+    fn _remove_item(
+        &mut self,
+        item_index: usize,
+        activate_pane: bool,
+        close_pane_if_empty: bool,
+        focus_on_pane_if_closed: Option<View<Pane>>,
+        cx: &mut ViewContext<Self>,
     ) {
         self.activation_history
             .retain(|entry| entry.entity_id != self.items[item_index].item_id());
@@ -1354,7 +1390,9 @@ impl Pane {
             item.deactivated(cx);
             if close_pane_if_empty {
                 self.update_toolbar(cx);
-                cx.emit(Event::Remove);
+                cx.emit(Event::Remove {
+                    focus_on_pane: focus_on_pane_if_closed,
+                });
             }
         }
 
@@ -2259,6 +2297,7 @@ impl Render for Pane {
             .on_action(cx.listener(|pane, _: &SplitDown, cx| pane.split(SplitDirection::Down, cx)))
             .on_action(cx.listener(|pane, _: &GoBack, cx| pane.navigate_backward(cx)))
             .on_action(cx.listener(|pane, _: &GoForward, cx| pane.navigate_forward(cx)))
+            .on_action(cx.listener(|pane, _: &JoinIntoNext, cx| pane.join_into_next(cx)))
             .on_action(cx.listener(Pane::toggle_zoom))
             .on_action(cx.listener(|pane: &mut Pane, action: &ActivateItem, cx| {
                 pane.activate_item(action.0, true, true, cx);

crates/workspace/src/persistence/model.rs

@@ -360,7 +360,9 @@ impl SerializedPaneGroup {
                 } else {
                     let pane = pane.upgrade()?;
                     workspace
-                        .update(cx, |workspace, cx| workspace.force_remove_pane(&pane, cx))
+                        .update(cx, |workspace, cx| {
+                            workspace.force_remove_pane(&pane, &None, cx)
+                        })
                         .log_err()?;
                     None
                 }

crates/workspace/src/workspace.rs

@@ -2955,7 +2955,10 @@ impl Workspace {
             pane::Event::Split(direction) => {
                 self.split_and_clone(pane, *direction, cx);
             }
-            pane::Event::Remove => self.remove_pane(pane, cx),
+            pane::Event::JoinIntoNext => self.join_pane_into_next(pane, cx),
+            pane::Event::Remove { focus_on_pane } => {
+                self.remove_pane(pane, focus_on_pane.clone(), cx)
+            }
             pane::Event::ActivateItem { local } => {
                 pane.model.update(cx, |pane, _| {
                     pane.track_alternate_file_items();
@@ -3103,6 +3106,23 @@ impl Workspace {
         }))
     }
 
+    pub fn join_pane_into_next(&mut self, pane: View<Pane>, cx: &mut ViewContext<Self>) {
+        let next_pane = self
+            .find_pane_in_direction(SplitDirection::Right, cx)
+            .or_else(|| self.find_pane_in_direction(SplitDirection::Down, cx))
+            .or_else(|| self.find_pane_in_direction(SplitDirection::Left, cx))
+            .or_else(|| self.find_pane_in_direction(SplitDirection::Up, cx));
+        let Some(next_pane) = next_pane else {
+            return;
+        };
+
+        let item_ids: Vec<EntityId> = pane.read(cx).items().map(|item| item.item_id()).collect();
+        for item_id in item_ids {
+            self.move_item(pane.clone(), next_pane.clone(), item_id, 0, cx);
+        }
+        cx.notify();
+    }
+
     pub fn move_item(
         &mut self,
         source: View<Pane>,
@@ -3126,7 +3146,7 @@ impl Workspace {
         if source != destination {
             // Close item from previous pane
             source.update(cx, |source, cx| {
-                source.remove_item(item_ix, false, true, cx);
+                source.remove_item_and_focus_on_pane(item_ix, false, destination.clone(), cx);
             });
         }
 
@@ -3137,9 +3157,14 @@ impl Workspace {
         });
     }
 
-    fn remove_pane(&mut self, pane: View<Pane>, cx: &mut ViewContext<Self>) {
+    fn remove_pane(
+        &mut self,
+        pane: View<Pane>,
+        focus_on: Option<View<Pane>>,
+        cx: &mut ViewContext<Self>,
+    ) {
         if self.center.remove(&pane).unwrap() {
-            self.force_remove_pane(&pane, cx);
+            self.force_remove_pane(&pane, &focus_on, cx);
             self.unfollow_in_pane(&pane, cx);
             self.last_leaders_by_pane.remove(&pane.downgrade());
             for removed_item in pane.read(cx).items() {
@@ -3932,7 +3957,7 @@ impl Workspace {
                 }
             }
             Member::Pane(pane) => {
-                self.force_remove_pane(&pane, cx);
+                self.force_remove_pane(&pane, &None, cx);
             }
         }
     }
@@ -3942,12 +3967,21 @@ impl Workspace {
         self.serialize_workspace_internal(cx)
     }
 
-    fn force_remove_pane(&mut self, pane: &View<Pane>, cx: &mut ViewContext<Workspace>) {
+    fn force_remove_pane(
+        &mut self,
+        pane: &View<Pane>,
+        focus_on: &Option<View<Pane>>,
+        cx: &mut ViewContext<Workspace>,
+    ) {
         self.panes.retain(|p| p != pane);
-        self.panes
-            .last()
-            .unwrap()
-            .update(cx, |pane, cx| pane.focus(cx));
+        if let Some(focus_on) = focus_on {
+            focus_on.update(cx, |pane, cx| pane.focus(cx));
+        } else {
+            self.panes
+                .last()
+                .unwrap()
+                .update(cx, |pane, cx| pane.focus(cx));
+        }
         if self.last_active_center_pane == Some(pane.downgrade()) {
             self.last_active_center_pane = None;
         }
@@ -6449,6 +6483,143 @@ mod tests {
         });
     }
 
+    #[gpui::test]
+    async fn test_join_pane_into_next(cx: &mut gpui::TestAppContext) {
+        init_test(cx);
+
+        let fs = FakeFs::new(cx.executor());
+
+        let project = Project::test(fs, None, cx).await;
+        let (workspace, cx) = cx.add_window_view(|cx| Workspace::test_new(project, cx));
+
+        // Let's arrange the panes like this:
+        //
+        // +-----------------------+
+        // |         top           |
+        // +------+--------+-------+
+        // | left | center | right |
+        // +------+--------+-------+
+        // |        bottom         |
+        // +-----------------------+
+
+        let top_item = cx.new_view(|cx| {
+            TestItem::new(cx).with_project_items(&[TestProjectItem::new(1, "top.txt", cx)])
+        });
+        let bottom_item = cx.new_view(|cx| {
+            TestItem::new(cx).with_project_items(&[TestProjectItem::new(2, "bottom.txt", cx)])
+        });
+        let left_item = cx.new_view(|cx| {
+            TestItem::new(cx).with_project_items(&[TestProjectItem::new(3, "left.txt", cx)])
+        });
+        let right_item = cx.new_view(|cx| {
+            TestItem::new(cx).with_project_items(&[TestProjectItem::new(4, "right.txt", cx)])
+        });
+        let center_item = cx.new_view(|cx| {
+            TestItem::new(cx).with_project_items(&[TestProjectItem::new(5, "center.txt", cx)])
+        });
+
+        let top_pane_id = workspace.update(cx, |workspace, cx| {
+            let top_pane_id = workspace.active_pane().entity_id();
+            workspace.add_item_to_active_pane(Box::new(top_item.clone()), None, false, cx);
+            workspace.split_pane(workspace.active_pane().clone(), SplitDirection::Down, cx);
+            top_pane_id
+        });
+        let bottom_pane_id = workspace.update(cx, |workspace, cx| {
+            let bottom_pane_id = workspace.active_pane().entity_id();
+            workspace.add_item_to_active_pane(Box::new(bottom_item.clone()), None, false, cx);
+            workspace.split_pane(workspace.active_pane().clone(), SplitDirection::Up, cx);
+            bottom_pane_id
+        });
+        let left_pane_id = workspace.update(cx, |workspace, cx| {
+            let left_pane_id = workspace.active_pane().entity_id();
+            workspace.add_item_to_active_pane(Box::new(left_item.clone()), None, false, cx);
+            workspace.split_pane(workspace.active_pane().clone(), SplitDirection::Right, cx);
+            left_pane_id
+        });
+        let right_pane_id = workspace.update(cx, |workspace, cx| {
+            let right_pane_id = workspace.active_pane().entity_id();
+            workspace.add_item_to_active_pane(Box::new(right_item.clone()), None, false, cx);
+            workspace.split_pane(workspace.active_pane().clone(), SplitDirection::Left, cx);
+            right_pane_id
+        });
+        let center_pane_id = workspace.update(cx, |workspace, cx| {
+            let center_pane_id = workspace.active_pane().entity_id();
+            workspace.add_item_to_active_pane(Box::new(center_item.clone()), None, false, cx);
+            center_pane_id
+        });
+        cx.executor().run_until_parked();
+
+        workspace.update(cx, |workspace, cx| {
+            assert_eq!(center_pane_id, workspace.active_pane().entity_id());
+
+            // Join into next from center pane into right
+            workspace.join_pane_into_next(workspace.active_pane().clone(), cx);
+        });
+
+        workspace.update(cx, |workspace, cx| {
+            let active_pane = workspace.active_pane();
+            assert_eq!(right_pane_id, active_pane.entity_id());
+            assert_eq!(2, active_pane.read(cx).items_len());
+            let item_ids_in_pane =
+                HashSet::from_iter(active_pane.read(cx).items().map(|item| item.item_id()));
+            assert!(item_ids_in_pane.contains(&center_item.item_id()));
+            assert!(item_ids_in_pane.contains(&right_item.item_id()));
+
+            // Join into next from right pane into bottom
+            workspace.join_pane_into_next(workspace.active_pane().clone(), cx);
+        });
+
+        workspace.update(cx, |workspace, cx| {
+            let active_pane = workspace.active_pane();
+            assert_eq!(bottom_pane_id, active_pane.entity_id());
+            assert_eq!(3, active_pane.read(cx).items_len());
+            let item_ids_in_pane =
+                HashSet::from_iter(active_pane.read(cx).items().map(|item| item.item_id()));
+            assert!(item_ids_in_pane.contains(&center_item.item_id()));
+            assert!(item_ids_in_pane.contains(&right_item.item_id()));
+            assert!(item_ids_in_pane.contains(&bottom_item.item_id()));
+
+            // Join into next from bottom pane into left
+            workspace.join_pane_into_next(workspace.active_pane().clone(), cx);
+        });
+
+        workspace.update(cx, |workspace, cx| {
+            let active_pane = workspace.active_pane();
+            assert_eq!(left_pane_id, active_pane.entity_id());
+            assert_eq!(4, active_pane.read(cx).items_len());
+            let item_ids_in_pane =
+                HashSet::from_iter(active_pane.read(cx).items().map(|item| item.item_id()));
+            assert!(item_ids_in_pane.contains(&center_item.item_id()));
+            assert!(item_ids_in_pane.contains(&right_item.item_id()));
+            assert!(item_ids_in_pane.contains(&bottom_item.item_id()));
+            assert!(item_ids_in_pane.contains(&left_item.item_id()));
+
+            // Join into next from left pane into top
+            workspace.join_pane_into_next(workspace.active_pane().clone(), cx);
+        });
+
+        workspace.update(cx, |workspace, cx| {
+            let active_pane = workspace.active_pane();
+            assert_eq!(top_pane_id, active_pane.entity_id());
+            assert_eq!(5, active_pane.read(cx).items_len());
+            let item_ids_in_pane =
+                HashSet::from_iter(active_pane.read(cx).items().map(|item| item.item_id()));
+            assert!(item_ids_in_pane.contains(&center_item.item_id()));
+            assert!(item_ids_in_pane.contains(&right_item.item_id()));
+            assert!(item_ids_in_pane.contains(&bottom_item.item_id()));
+            assert!(item_ids_in_pane.contains(&left_item.item_id()));
+            assert!(item_ids_in_pane.contains(&top_item.item_id()));
+
+            // Single pane left: no-op
+            workspace.join_pane_into_next(workspace.active_pane().clone(), cx)
+        });
+
+        workspace.update(cx, |workspace, _cx| {
+            let active_pane = workspace.active_pane();
+            assert_eq!(top_pane_id, active_pane.entity_id());
+        });
+    }
+
     struct TestModal(FocusHandle);
 
     impl TestModal {