assistant: Improve the language model selector (#25125)

This PR includes change such as:

- Ensures the popover width is fixed/not dancing around
- Ensures the popover is not obscuring the trigger in the buffer and
terminal inline assistant scenarios
- Removes ellipsis from the trigger button label
- Ensures the scrollbar doesn't hide the check icon

| Terminal | Prompt Editor | Buffer |
|--------|--------|--------|
| ![Screenshot 2025-02-18 at 8 43
46 PM](https://github.com/user-attachments/assets/9cdfbaf1-f27e-4f48-877e-9cf61767ecee)
| ![Screenshot 2025-02-18 at 8 43
49 PM](https://github.com/user-attachments/assets/7abf9be2-bd2a-43d7-9a5d-d665e7e9fda3)
| ![Screenshot 2025-02-18 at 8 43
52 PM](https://github.com/user-attachments/assets/017bbdb3-185a-4bf6-9005-018ecafef9dd)
|

Release Notes:

- N/A

crates/assistant/src/inline_assistant.rs

@@ -1610,6 +1610,7 @@ impl Render for PromptEditor {
                                 cx,
                             )
                         },
+                        gpui::Corner::TopRight,
                     ))
                     .map(|el| {
                         let CodegenStatus::Error(error) = self.codegen.read(cx).status(cx) else {

crates/assistant/src/terminal_inline_assistant.rs

@@ -662,6 +662,7 @@ impl Render for PromptEditor {
                                 cx,
                             )
                         },
+                        gpui::Corner::TopRight,
                     ))
                     .children(
                         if let CodegenStatus::Error(error) = &self.codegen.read(cx).status {

crates/assistant2/src/assistant_model_selector.rs

@@ -61,13 +61,9 @@ impl Render for AssistantModelSelector {
                     h_flex()
                         .gap_0p5()
                         .child(
-                            div().max_w_32().child(
+                            Label::new(model_name)
-                                Label::new(model_name)
+                                .size(LabelSize::Small)
-                                    .size(LabelSize::Small)
+                                .color(Color::Muted),
-                                    .color(Color::Muted)
-                                    .text_ellipsis()
-                                    .into_any_element(),
-                            ),
                         )
                         .child(
                             Icon::new(IconName::ChevronDown)
@@ -84,6 +80,7 @@ impl Render for AssistantModelSelector {
                     cx,
                 )
             },
+            gpui::Corner::BottomRight,
         )
         .with_handle(self.menu_handle.clone())
     }

crates/assistant_context_editor/src/context_editor.rs

@@ -2404,13 +2404,9 @@ impl ContextEditor {
                     h_flex()
                         .gap_0p5()
                         .child(
-                            div().max_w_32().child(
+                            Label::new(model_name)
-                                Label::new(model_name)
+                                .size(LabelSize::Small)
-                                    .size(LabelSize::Small)
+                                .color(Color::Muted),
-                                    .color(Color::Muted)
-                                    .text_ellipsis()
-                                    .into_any_element(),
-                            ),
                         )
                         .child(
                             Icon::new(IconName::ChevronDown)
@@ -2427,6 +2423,7 @@ impl ContextEditor {
                     cx,
                 )
             },
+            gpui::Corner::BottomLeft,
         )
         .with_handle(self.language_model_selector_menu_handle.clone())
     }

crates/language_model_selector/src/language_model_selector.rs

@@ -2,8 +2,8 @@ use std::sync::Arc;
 
 use feature_flags::ZedPro;
 use gpui::{
-    Action, AnyElement, AnyView, App, DismissEvent, Entity, EventEmitter, FocusHandle, Focusable,
+    Action, AnyElement, AnyView, App, Corner, DismissEvent, Entity, EventEmitter, FocusHandle,
-    Subscription, Task, WeakEntity,
+    Focusable, Subscription, Task, WeakEntity,
 };
 use language_model::{LanguageModel, LanguageModelAvailability, LanguageModelRegistry};
 use picker::{Picker, PickerDelegate};
@@ -37,12 +37,13 @@ impl LanguageModelSelector {
             on_model_changed: on_model_changed.clone(),
             all_models: all_models.clone(),
             filtered_models: all_models,
-            selected_index: 0,
+            selected_index: Self::get_active_model_index(cx),
         };
 
         let picker = cx.new(|cx| {
             Picker::uniform_list(delegate, window, cx)
                 .show_scrollbar(true)
+                .width(rems(20.))
                 .max_height(Some(rems(20.).into()))
         });
 
@@ -100,6 +101,16 @@ impl LanguageModelSelector {
             })
             .collect::<Vec<_>>()
     }
+
+    fn get_active_model_index(cx: &App) -> usize {
+        let active_model = LanguageModelRegistry::read_global(cx).active_model();
+        Self::all_models(cx)
+            .iter()
+            .position(|model_info| {
+                Some(model_info.model.id()) == active_model.as_ref().map(|model| model.id())
+            })
+            .unwrap_or(0)
+    }
 }
 
 impl EventEmitter<DismissEvent> for LanguageModelSelector {}
@@ -126,6 +137,7 @@ where
     trigger: T,
     tooltip: TT,
     handle: Option<PopoverMenuHandle<LanguageModelSelector>>,
+    anchor: Corner,
 }
 
 impl<T, TT> LanguageModelSelectorPopoverMenu<T, TT>
@@ -137,12 +149,14 @@ where
         language_model_selector: Entity<LanguageModelSelector>,
         trigger: T,
         tooltip: TT,
+        anchor: Corner,
     ) -> Self {
         Self {
             language_model_selector,
             trigger,
             tooltip,
             handle: None,
+            anchor,
         }
     }
 
@@ -163,7 +177,7 @@ where
         PopoverMenu::new("model-switcher")
             .menu(move |_window, _cx| Some(language_model_selector.clone()))
             .trigger_with_tooltip(self.trigger, self.tooltip)
-            .anchor(gpui::Corner::BottomRight)
+            .anchor(self.anchor)
             .when_some(self.handle.clone(), |menu, handle| menu.with_handle(handle))
             .offset(gpui::Point {
                 x: px(0.0),
@@ -360,7 +374,7 @@ impl PickerDelegate for LanguageModelPickerDelegate {
                         .items_center()
                         .gap_1p5()
                         .pl_0p5()
-                        .min_w(px(240.))
+                        .w(px(240.))
                         .child(
                             div().max_w_40().child(
                                 Label::new(model_info.model.name().0.clone()).text_ellipsis(),
@@ -387,7 +401,7 @@ impl PickerDelegate for LanguageModelPickerDelegate {
                                 }),
                         ),
                 )
-                .end_slot(div().when(is_selected, |this| {
+                .end_slot(div().pr_3().when(is_selected, |this| {
                     this.child(
                         Icon::new(IconName::Check)
                             .color(Color::Accent)