assistant2: Wire up basic @-mention interaction for context (#22197)

This PR adds an initial version of using `@` in the message editor to
add context to the thread.

We don't yet insert any sort of reference to it in the message body
itself.

Release Notes:

- N/A

crates/assistant2/src/message_editor.rs

@@ -1,20 +1,24 @@
 use std::sync::Arc;
 
-use editor::{Editor, EditorElement, EditorStyle};
+use editor::{Editor, EditorElement, EditorEvent, EditorStyle};
 use fs::Fs;
-use gpui::{AppContext, FocusableView, Model, TextStyle, View, WeakModel, WeakView};
+use gpui::{
+    AppContext, DismissEvent, FocusableView, Model, Subscription, TextStyle, View, WeakModel,
+    WeakView,
+};
 use language_model::{LanguageModelRegistry, LanguageModelRequestTool};
 use language_model_selector::{LanguageModelSelector, LanguageModelSelectorPopoverMenu};
+use rope::Point;
 use settings::{update_settings_file, Settings};
 use theme::ThemeSettings;
 use ui::{
-    prelude::*, ButtonLike, CheckboxWithLabel, ElevationIndex, KeyBinding, PopoverMenuHandle,
-    Tooltip,
+    prelude::*, ButtonLike, CheckboxWithLabel, ElevationIndex, KeyBinding, PopoverMenu,
+    PopoverMenuHandle, Tooltip,
 };
 use workspace::Workspace;
 
 use crate::assistant_settings::AssistantSettings;
-use crate::context_picker::ContextPicker;
+use crate::context_picker::{ConfirmBehavior, ContextPicker};
 use crate::context_store::ContextStore;
 use crate::context_strip::ContextStrip;
 use crate::thread::{RequestKind, Thread};
@@ -27,9 +31,12 @@ pub struct MessageEditor {
     context_store: Model<ContextStore>,
     context_strip: View<ContextStrip>,
     context_picker_menu_handle: PopoverMenuHandle<ContextPicker>,
+    inline_context_picker: View<ContextPicker>,
+    inline_context_picker_menu_handle: PopoverMenuHandle<ContextPicker>,
     language_model_selector: View<LanguageModelSelector>,
     language_model_selector_menu_handle: PopoverMenuHandle<LanguageModelSelector>,
     use_tools: bool,
+    _subscriptions: Vec<Subscription>,
 }
 
 impl MessageEditor {
@@ -42,6 +49,7 @@ impl MessageEditor {
     ) -> Self {
         let context_store = cx.new_model(|_cx| ContextStore::new());
         let context_picker_menu_handle = PopoverMenuHandle::default();
+        let inline_context_picker_menu_handle = PopoverMenuHandle::default();
 
         let editor = cx.new_view(|cx| {
             let mut editor = Editor::auto_height(80, cx);
@@ -50,6 +58,22 @@ impl MessageEditor {
 
             editor
         });
+        let inline_context_picker = cx.new_view(|cx| {
+            ContextPicker::new(
+                workspace.clone(),
+                Some(thread_store.clone()),
+                context_store.downgrade(),
+                ConfirmBehavior::Close,
+                cx,
+            )
+        });
+        let subscriptions = vec![
+            cx.subscribe(&editor, Self::handle_editor_event),
+            cx.subscribe(
+                &inline_context_picker,
+                Self::handle_inline_context_picker_event,
+            ),
+        ];
 
         Self {
             thread,
@@ -66,6 +90,8 @@ impl MessageEditor {
                 )
             }),
             context_picker_menu_handle,
+            inline_context_picker,
+            inline_context_picker_menu_handle,
             language_model_selector: cx.new_view(|cx| {
                 let fs = fs.clone();
                 LanguageModelSelector::new(
@@ -81,6 +107,7 @@ impl MessageEditor {
             }),
             language_model_selector_menu_handle: PopoverMenuHandle::default(),
             use_tools: false,
+            _subscriptions: subscriptions,
         }
     }
 
@@ -143,6 +170,40 @@ impl MessageEditor {
         None
     }
 
+    fn handle_editor_event(
+        &mut self,
+        editor: View<Editor>,
+        event: &EditorEvent,
+        cx: &mut ViewContext<Self>,
+    ) {
+        match event {
+            EditorEvent::SelectionsChanged { .. } => {
+                editor.update(cx, |editor, cx| {
+                    let snapshot = editor.buffer().read(cx).snapshot(cx);
+                    let newest_cursor = editor.selections.newest::<Point>(cx).head();
+                    if newest_cursor.column > 0 {
+                        let behind_cursor = Point::new(newest_cursor.row, newest_cursor.column - 1);
+                        let char_behind_cursor = snapshot.chars_at(behind_cursor).next();
+                        if char_behind_cursor == Some('@') {
+                            self.inline_context_picker_menu_handle.show(cx);
+                        }
+                    }
+                });
+            }
+            _ => {}
+        }
+    }
+
+    fn handle_inline_context_picker_event(
+        &mut self,
+        _inline_context_picker: View<ContextPicker>,
+        _event: &DismissEvent,
+        cx: &mut ViewContext<Self>,
+    ) {
+        let editor_focus_handle = self.editor.focus_handle(cx);
+        cx.focus(&editor_focus_handle);
+    }
+
     fn render_language_model_selector(&self, cx: &mut ViewContext<Self>) -> impl IntoElement {
         let active_model = LanguageModelRegistry::read_global(cx).active_model();
         let focus_handle = self.language_model_selector.focus_handle(cx).clone();
@@ -199,6 +260,7 @@ impl Render for MessageEditor {
         let font_size = TextSize::Default.rems(cx);
         let line_height = font_size.to_pixels(cx.rem_size()) * 1.5;
         let focus_handle = self.editor.focus_handle(cx);
+        let inline_context_picker = self.inline_context_picker.clone();
         let bg_color = cx.theme().colors().editor_background;
 
         v_flex()
@@ -211,7 +273,7 @@ impl Render for MessageEditor {
             .p_2()
             .bg(bg_color)
             .child(self.context_strip.clone())
-            .child(div().id("thread_editor").overflow_y_scroll().h_12().child({
+            .child({
                 let settings = ThemeSettings::get_global(cx);
                 let text_style = TextStyle {
                     color: cx.theme().colors().editor_foreground,
@@ -232,7 +294,18 @@ impl Render for MessageEditor {
                         ..Default::default()
                     },
                 )
-            }))
+            })
+            .child(
+                PopoverMenu::new("inline-context-picker")
+                    .menu(move |_cx| Some(inline_context_picker.clone()))
+                    .attach(gpui::Corner::TopLeft)
+                    .anchor(gpui::Corner::BottomLeft)
+                    .offset(gpui::Point {
+                        x: px(0.0),
+                        y: px(-16.0),
+                    })
+                    .with_handle(self.inline_context_picker_menu_handle.clone()),
+            )
             .child(
                 h_flex()
                     .justify_between()