sidebar: Add scrollbar and max-height to the thread switcher (#54471)

Just a little refinement as I experienced the thread switcher modal
overflowing beyond the viewport if there were enough threads on it.
Additionally, took the opportunity to render a scrollbar inside of it,
too.

Release Notes:

- N/A

crates/sidebar/src/thread_switcher.rs

@@ -3,9 +3,9 @@ use agent_client_protocol as acp;
 use agent_ui::thread_metadata_store::ThreadMetadata;
 use gpui::{
     Action as _, DismissEvent, Entity, EventEmitter, FocusHandle, Focusable, Modifiers,
-    ModifiersChangedEvent, Render, SharedString, prelude::*,
+    ModifiersChangedEvent, Render, ScrollHandle, SharedString, prelude::*,
 };
-use ui::{AgentThreadStatus, ThreadItem, ThreadItemWorktreeInfo, prelude::*};
+use ui::{AgentThreadStatus, ThreadItem, ThreadItemWorktreeInfo, WithScrollbar, prelude::*};
 use workspace::{ModalView, Workspace};
 use zed_actions::agents_sidebar::ToggleThreadSwitcher;
 
@@ -42,6 +42,7 @@ pub(crate) struct ThreadSwitcher {
     entries: Vec<ThreadSwitcherEntry>,
     selected_index: usize,
     init_modifiers: Option<Modifiers>,
+    scroll_handle: ScrollHandle,
 }
 
 impl ThreadSwitcher {
@@ -74,11 +75,15 @@ impl ThreadSwitcher {
         })
         .detach();
 
+        let scroll_handle = ScrollHandle::new();
+        scroll_handle.scroll_to_item(selected_index);
+
         Self {
             focus_handle,
             entries,
             selected_index,
             init_modifiers,
+            scroll_handle,
         }
     }
 
@@ -117,6 +122,7 @@ impl ThreadSwitcher {
     }
 
     fn emit_preview(&mut self, cx: &mut Context<Self>) {
+        self.scroll_handle.scroll_to_item(self.selected_index);
         if let Some(entry) = self.entries.get(self.selected_index) {
             cx.emit(ThreadSwitcherEvent::Preview {
                 metadata: entry.metadata.clone(),
@@ -151,6 +157,7 @@ impl ThreadSwitcher {
             return;
         }
         self.selected_index = index;
+        self.scroll_handle.scroll_to_item(index);
         self.emit_preview(cx);
         cx.notify();
     }
@@ -205,57 +212,66 @@ impl Focusable for ThreadSwitcher {
 }
 
 impl Render for ThreadSwitcher {
-    fn render(&mut self, _window: &mut gpui::Window, cx: &mut Context<Self>) -> impl IntoElement {
+    fn render(&mut self, window: &mut gpui::Window, cx: &mut Context<Self>) -> impl IntoElement {
         let selected_index = self.selected_index;
 
         v_flex()
             .key_context("ThreadSwitcher")
             .track_focus(&self.focus_handle)
-            .w(rems_from_px(440.))
             .p_1p5()
-            .gap_0p5()
+            .w(rems_from_px(440.))
             .elevation_3(cx)
             .on_modifiers_changed(cx.listener(Self::handle_modifiers_changed))
             .on_action(cx.listener(Self::confirm))
             .on_action(cx.listener(Self::cancel))
             .on_action(cx.listener(Self::toggle))
-            .children(self.entries.iter().enumerate().map(|(ix, entry)| {
-                let id = SharedString::from(format!("thread-switcher-{}", entry.session_id));
+            .child(
+                v_flex()
+                    .id("thread-switcher-list")
+                    .gap_0p5()
+                    .max_h_128()
+                    .overflow_y_scroll()
+                    .track_scroll(&self.scroll_handle)
+                    .children(self.entries.iter().enumerate().map(|(ix, entry)| {
+                        let id =
+                            SharedString::from(format!("thread-switcher-{}", entry.session_id));
 
-                ThreadItem::new(id, entry.title.clone())
-                    .rounded(true)
-                    .icon(entry.icon)
-                    .status(entry.status)
-                    .when_some(entry.icon_from_external_svg.clone(), |this, svg| {
-                        this.custom_icon_from_external_svg(svg)
-                    })
-                    .when_some(entry.project_name.clone(), |this, name| {
-                        this.project_name(name)
-                    })
-                    .worktrees(entry.worktrees.clone())
-                    .timestamp(entry.timestamp.clone())
-                    .title_generating(entry.is_title_generating)
-                    .notified(entry.notified)
-                    .when(entry.diff_stats.lines_added > 0, |this| {
-                        this.added(entry.diff_stats.lines_added as usize)
-                    })
-                    .when(entry.diff_stats.lines_removed > 0, |this| {
-                        this.removed(entry.diff_stats.lines_removed as usize)
-                    })
-                    .selected(ix == selected_index)
-                    .base_bg(cx.theme().colors().elevated_surface_background)
-                    .on_hover(cx.listener(move |this, hovered: &bool, _window, cx| {
-                        if *hovered {
-                            this.select_index(ix, cx);
-                        }
-                    }))
-                    // TODO: This is not properly propagating to the tread item.
-                    .on_click(
-                        cx.listener(move |this, _event: &gpui::ClickEvent, _window, cx| {
-                            this.select_and_confirm(ix, cx);
-                        }),
-                    )
-                    .into_any_element()
-            }))
+                        ThreadItem::new(id, entry.title.clone())
+                            .rounded(true)
+                            .icon(entry.icon)
+                            .status(entry.status)
+                            .when_some(entry.icon_from_external_svg.clone(), |this, svg| {
+                                this.custom_icon_from_external_svg(svg)
+                            })
+                            .when_some(entry.project_name.clone(), |this, name| {
+                                this.project_name(name)
+                            })
+                            .worktrees(entry.worktrees.clone())
+                            .timestamp(entry.timestamp.clone())
+                            .title_generating(entry.is_title_generating)
+                            .notified(entry.notified)
+                            .when(entry.diff_stats.lines_added > 0, |this| {
+                                this.added(entry.diff_stats.lines_added as usize)
+                            })
+                            .when(entry.diff_stats.lines_removed > 0, |this| {
+                                this.removed(entry.diff_stats.lines_removed as usize)
+                            })
+                            .selected(ix == selected_index)
+                            .base_bg(cx.theme().colors().elevated_surface_background)
+                            .on_hover(cx.listener(move |this, hovered: &bool, _window, cx| {
+                                if *hovered {
+                                    this.select_index(ix, cx);
+                                }
+                            }))
+                            // TODO: This is not properly propagating to the tread item.
+                            .on_click(cx.listener(
+                                move |this, _event: &gpui::ClickEvent, _window, cx| {
+                                    this.select_and_confirm(ix, cx);
+                                },
+                            ))
+                            .into_any_element()
+                    })),
+            )
+            .vertical_scrollbar_for(&self.scroll_handle, window, cx)
     }
 }

crates/ui/src/components/ai/thread_item.rs

@@ -387,6 +387,7 @@ impl RenderOnce for ThreadItem {
             .cursor_pointer()
             .group("thread-item")
             .relative()
+            .flex_shrink_0()
             .overflow_hidden()
             .w_full()
             .py_1()