assistant2: Refine editing of previous messages (#11233)

This PR refines the UX of editing a previous message, including the
following:

- Focus the prev message body editor on double-click
- Restore previous body text on cancel
- Cancel pending completion upon submission of previous message
- Drive-by: Remove min height on composer editor

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <marshall@zed.dev>

crates/assistant2/src/assistant2.rs

@@ -231,12 +231,18 @@ pub struct AssistantChat {
     user_store: Model<UserStore>,
     next_message_id: MessageId,
     collapsed_messages: HashMap<MessageId, bool>,
-    editing_message_id: Option<MessageId>,
+    editing_message: Option<EditingMessage>,
     pending_completion: Option<Task<()>>,
     tool_registry: Arc<ToolRegistry>,
     project_index: Option<Model<ProjectIndex>>,
 }
 
+struct EditingMessage {
+    id: MessageId,
+    old_body: Arc<str>,
+    body: View<Editor>,
+}
+
 impl AssistantChat {
     fn new(
         language_registry: Arc<LanguageRegistry>,
@@ -271,13 +277,17 @@ impl AssistantChat {
             language_registry,
             project_index,
             next_message_id: MessageId(0),
-            editing_message_id: None,
+            editing_message: None,
             collapsed_messages: HashMap::default(),
             pending_completion: None,
             tool_registry,
         }
     }
 
+    fn editing_message_id(&self) -> Option<MessageId> {
+        self.editing_message.as_ref().map(|message| message.id)
+    }
+
     fn focused_message_id(&self, cx: &WindowContext) -> Option<MessageId> {
         self.messages.iter().find_map(|message| match message {
             ChatMessage::User(message) => message
@@ -291,30 +301,40 @@ impl AssistantChat {
 
     fn cancel(&mut self, _: &Cancel, cx: &mut ViewContext<Self>) {
         // If we're currently editing a message, cancel the edit.
-        self.editing_message_id.take();
-
-        if self.pending_completion.take().is_none() {
-            cx.propagate();
+        if let Some(editing_message) = self.editing_message.take() {
+            editing_message
+                .body
+                .update(cx, |body, cx| body.set_text(editing_message.old_body, cx));
             return;
         }
 
-        if let Some(ChatMessage::Assistant(message)) = self.messages.last() {
-            if message.body.text.is_empty() {
-                self.pop_message(cx);
+        if self.pending_completion.take().is_some() {
+            if let Some(ChatMessage::Assistant(message)) = self.messages.last() {
+                if message.body.text.is_empty() {
+                    self.pop_message(cx);
+                }
             }
+            return;
         }
+
+        cx.propagate();
     }
 
     fn submit(&mut self, Submit(mode): &Submit, cx: &mut ViewContext<Self>) {
-        // Don't allow multiple concurrent completions.
-        if self.pending_completion.is_some() {
-            cx.propagate();
-            return;
-        }
-
         if let Some(focused_message_id) = self.focused_message_id(cx) {
             self.truncate_messages(focused_message_id, cx);
+            self.pending_completion.take();
+            self.composer_editor.focus_handle(cx).focus(cx);
+            if self.editing_message_id() == Some(focused_message_id) {
+                self.editing_message.take();
+            }
         } else if self.composer_editor.focus_handle(cx).is_focused(cx) {
+            // Don't allow multiple concurrent completions.
+            if self.pending_completion.is_some() {
+                cx.propagate();
+                return;
+            }
+
             let message = self.composer_editor.update(cx, |composer_editor, cx| {
                 let text = composer_editor.text(cx);
                 let id = self.next_message_id.post_inc();
@@ -344,9 +364,7 @@ impl AssistantChat {
             .await
             .log_err();
 
-            this.update(&mut cx, |this, cx| {
-                let composer_focus_handle = this.composer_editor.focus_handle(cx);
-                cx.focus(&composer_focus_handle);
+            this.update(&mut cx, |this, _cx| {
                 this.pending_completion = None;
             })
             .context("Failed to push new user message")
@@ -572,11 +590,11 @@ impl AssistantChat {
                 .id(SharedString::from(format!("message-{}-container", id.0)))
                 .when(!is_last, |element| element.mb_2())
                 .map(|element| {
-                    if self.editing_message_id.as_ref() == Some(id) {
+                    if self.editing_message_id() == Some(*id) {
                         element.child(Composer::new(
                             body.clone(),
                             self.user_store.read(cx).current_user(),
-                            self.can_submit(),
+                            true,
                             self.tool_registry.clone(),
                             crate::ui::ModelSelector::new(
                                 cx.view().downgrade(),
@@ -588,9 +606,15 @@ impl AssistantChat {
                         element
                             .on_click(cx.listener({
                                 let id = *id;
-                                move |assistant_chat, event: &ClickEvent, _cx| {
+                                let body = body.clone();
+                                move |assistant_chat, event: &ClickEvent, cx| {
                                     if event.up.click_count == 2 {
-                                        assistant_chat.editing_message_id = Some(id);
+                                        assistant_chat.editing_message = Some(EditingMessage {
+                                            id,
+                                            body: body.clone(),
+                                            old_body: body.read(cx).text(cx).into(),
+                                        });
+                                        body.focus_handle(cx).focus(cx);
                                     }
                                 }
                             }))

crates/assistant2/src/ui/composer.rs

@@ -69,8 +69,7 @@ impl RenderOnce for Composer {
                                 v_flex()
                                     .justify_between()
                                     .w_full()
-                                    .gap_1()
-                                    .min_h(line_height * 4 + px(74.0))
+                                    .gap_2()
                                     .child({
                                         let settings = ThemeSettings::get_global(cx);
                                         let text_style = TextStyle {