agent: Show delete thread icon buttons on hover/focus (#30370)

This PR's main goal is to show the delete thread button when the list
item is either focused or hovered. In order to do that, we ended up
refactoring (i.e., merging) the `PastThread` and `PastContext` elements
into a single `HistoryElementEntry` that already matches to the entry
type (i.e., context or thread).

Release Notes:

- agent: Simplify the UI by showing the delete thread icon button only
on hover or focus.

---------

Co-authored-by: Agus Zubiaga <[email protected]>

Author: danilo-leal

crates/agent/src/agent_panel.rs

@@ -55,10 +55,10 @@ use zed_llm_client::UsageLimit;
 use crate::active_thread::{self, ActiveThread, ActiveThreadEvent};
 use crate::agent_configuration::{AgentConfiguration, AssistantConfigurationEvent};
 use crate::agent_diff::AgentDiff;
-use crate::history_store::{HistoryEntry, HistoryStore, RecentEntry};
+use crate::history_store::{HistoryStore, RecentEntry};
 use crate::message_editor::{MessageEditor, MessageEditorEvent};
 use crate::thread::{Thread, ThreadError, ThreadId, TokenUsageRatio};
-use crate::thread_history::{EntryTimeFormat, PastContext, PastThread, ThreadHistory};
+use crate::thread_history::{HistoryEntryElement, ThreadHistory};
 use crate::thread_store::ThreadStore;
 use crate::ui::AgentOnboardingModal;
 use crate::{
@@ -356,6 +356,7 @@ pub struct AgentPanel {
     previous_view: Option<ActiveView>,
     history_store: Entity<HistoryStore>,
     history: Entity<ThreadHistory>,
+    hovered_recent_history_item: Option<usize>,
     assistant_dropdown_menu_handle: PopoverMenuHandle<ContextMenu>,
     assistant_navigation_menu_handle: PopoverMenuHandle<ContextMenu>,
     assistant_navigation_menu: Option<Entity<ContextMenu>>,
@@ -696,6 +697,7 @@ impl AgentPanel {
             previous_view: None,
             history_store: history_store.clone(),
             history: cx.new(|cx| ThreadHistory::new(weak_self, history_store, window, cx)),
+            hovered_recent_history_item: None,
             assistant_dropdown_menu_handle: PopoverMenuHandle::default(),
             assistant_navigation_menu_handle: PopoverMenuHandle::default(),
             assistant_navigation_menu: None,
@@ -2212,7 +2214,7 @@ impl AgentPanel {
                             .border_b_1()
                             .border_color(cx.theme().colors().border_variant)
                             .child(
-                                Label::new("Past Interactions")
+                                Label::new("Recent")
                                     .size(LabelSize::Small)
                                     .color(Color::Muted),
                             )
@@ -2237,18 +2239,20 @@ impl AgentPanel {
                         v_flex()
                             .gap_1()
                             .children(
-                                recent_history.into_iter().map(|entry| {
+                                recent_history.into_iter().enumerate().map(|(index, entry)| {
                                     // TODO: Add keyboard navigation.
-                                    match entry {
-                                        HistoryEntry::Thread(thread) => {
-                                            PastThread::new(thread, cx.entity().downgrade(), false, vec![], EntryTimeFormat::DateAndTime)
-                                                .into_any_element()
-                                        }
-                                        HistoryEntry::Context(context) => {
-                                            PastContext::new(context, cx.entity().downgrade(), false, vec![], EntryTimeFormat::DateAndTime)
-                                                .into_any_element()
-                                        }
-                                    }
+                                    let is_hovered = self.hovered_recent_history_item == Some(index);
+                                    HistoryEntryElement::new(entry.clone(), cx.entity().downgrade())
+                                        .hovered(is_hovered)
+                                        .on_hover(cx.listener(move |this, is_hovered, _window, cx| {
+                                            if *is_hovered {
+                                                this.hovered_recent_history_item = Some(index);
+                                            } else if this.hovered_recent_history_item == Some(index) {
+                                                this.hovered_recent_history_item = None;
+                                            }
+                                            cx.notify();
+                                        }))
+                                        .into_any_element()
                                 }),
                             )
                     )