tiles: Fix active_panel method to returns actually Panel view, avoid return TabPanel. (#665)

- Limit `add_item` only allows TabPanel type.
- Export `items` method in DockArea.

crates/ui/src/dock/mod.rs

@@ -442,6 +442,11 @@ impl DockArea {
         self.bounds
     }
 
+    /// Return the items of the dock area.
+    pub fn items(&self) -> &DockItem {
+        &self.items
+    }
+
     /// Subscribe to the tiles item drag item drop event
     fn subscribe_tiles_item_drop(
         &mut self,

crates/ui/src/dock/panel.rs

@@ -2,7 +2,7 @@ use std::{collections::HashMap, sync::Arc};
 
 use crate::{button::Button, popup_menu::PopupMenu};
 use gpui::{
-    AnyElement, AnyView, App, Entity, EventEmitter, FocusHandle, Focusable, Global, Hsla,
+    AnyElement, AnyView, App, Entity, EntityId, EventEmitter, FocusHandle, Focusable, Global, Hsla,
     IntoElement, Render, SharedString, WeakEntity, Window,
 };
 
@@ -129,6 +129,7 @@ pub trait Panel: EventEmitter<PanelEvent> + Render + Focusable {
 #[allow(unused_variables)]
 pub trait PanelView: 'static + Send + Sync {
     fn panel_name(&self, cx: &App) -> &'static str;
+    fn panel_id(&self, cx: &App) -> EntityId;
     fn title(&self, window: &Window, cx: &App) -> AnyElement;
     fn title_style(&self, cx: &App) -> Option<TitleStyle>;
     fn closable(&self, cx: &App) -> bool;
@@ -149,6 +150,10 @@ impl<T: Panel> PanelView for Entity<T> {
         self.read(cx).panel_name()
     }
 
+    fn panel_id(&self, _: &App) -> EntityId {
+        self.entity_id()
+    }
+
     fn title(&self, window: &Window, cx: &App) -> AnyElement {
         self.read(cx).title(window, cx)
     }

crates/ui/src/dock/tiles.rs

@@ -13,7 +13,9 @@ use crate::{
     v_flex, ActiveTheme, Icon, IconName,
 };
 
-use super::{DockArea, Panel, PanelEvent, PanelInfo, PanelState, PanelView, TabPanel, TileMeta};
+use super::{
+    DockArea, Panel, PanelEvent, PanelInfo, PanelState, PanelView, StackPanel, TabPanel, TileMeta,
+};
 use gpui::{
     actions, canvas, div, point, px, size, AnyElement, App, AppContext, Bounds, Context,
     DismissEvent, DragMoveEvent, Empty, EntityId, EventEmitter, FocusHandle, Focusable, Half,
@@ -359,6 +361,11 @@ impl Tiles {
         window: &mut Window,
         cx: &mut Context<Self>,
     ) {
+        assert!(
+            item.panel.view().downcast::<TabPanel>().is_ok(),
+            "only allows to add TabPanel type"
+        );
+
         self.panels.push(item.clone());
         window.defer(cx, {
             let panel = item.panel.clone();
@@ -487,12 +494,20 @@ impl Tiles {
     }
 
     /// Returns the active panel, if any.
-    pub fn active_panel(&self) -> Option<Arc<dyn PanelView>> {
+    pub fn active_panel(&self, cx: &App) -> Option<Arc<dyn PanelView>> {
         let Some(active_index) = self.active_index else {
             return None;
         };
 
-        self.panels.get(active_index).map(|item| item.panel.clone())
+        self.panels.get(active_index).and_then(|item| {
+            if let Ok(tab_panel) = item.panel.view().downcast::<TabPanel>() {
+                tab_panel.read(cx).active_panel(cx)
+            } else if let Ok(_) = item.panel.view().downcast::<StackPanel>() {
+                None
+            } else {
+                Some(item.panel.clone())
+            }
+        })
     }
 
     fn set_active_index(&mut self, index: Option<usize>, cx: &mut Context<Self>) {