Break ground on assistant2 (#21109)

This PR breaks ground on a new `assistant2` crate.

In order to see this new version of the assistant, both of the following
must be true:
1. The `assistant2` feature flag is enabled for your user
   - It is **not** currently enabled for all staff.
2. You are running a development build of Zed

The intent here is to enable the folks working on `assistant2` to
incrementally land work onto `main` without breaking use of the current
Assistant for anyone.

<img width="1136" alt="Screenshot 2024-11-23 at 10 46 08 AM"
src="https://github.com/user-attachments/assets/5723a13f-5be1-4486-9460-ead7329ba78e">

Release Notes:

- N/A

crates/assistant2/src/assistant_panel.rs

@@ -0,0 +1,123 @@
+use anyhow::Result;
+use gpui::{
+    prelude::*, px, Action, AppContext, AsyncWindowContext, EventEmitter, FocusHandle,
+    FocusableView, Pixels, Task, View, ViewContext, WeakView, WindowContext,
+};
+use ui::prelude::*;
+use workspace::dock::{DockPosition, Panel, PanelEvent};
+use workspace::{Pane, Workspace};
+
+use crate::{NewChat, ToggleFocus};
+
+pub fn init(cx: &mut AppContext) {
+    cx.observe_new_views(
+        |workspace: &mut Workspace, _cx: &mut ViewContext<Workspace>| {
+            workspace.register_action(|workspace, _: &ToggleFocus, cx| {
+                workspace.toggle_panel_focus::<AssistantPanel>(cx);
+            });
+        },
+    )
+    .detach();
+}
+
+pub struct AssistantPanel {
+    pane: View<Pane>,
+}
+
+impl AssistantPanel {
+    pub fn load(
+        workspace: WeakView<Workspace>,
+        cx: AsyncWindowContext,
+    ) -> Task<Result<View<Self>>> {
+        cx.spawn(|mut cx| async move {
+            workspace.update(&mut cx, |workspace, cx| {
+                cx.new_view(|cx| Self::new(workspace, cx))
+            })
+        })
+    }
+
+    fn new(workspace: &Workspace, cx: &mut ViewContext<Self>) -> Self {
+        let pane = cx.new_view(|cx| {
+            let mut pane = Pane::new(
+                workspace.weak_handle(),
+                workspace.project().clone(),
+                Default::default(),
+                None,
+                NewChat.boxed_clone(),
+                cx,
+            );
+            pane.set_can_split(false, cx);
+            pane.set_can_navigate(true, cx);
+
+            pane
+        });
+
+        Self { pane }
+    }
+}
+
+impl FocusableView for AssistantPanel {
+    fn focus_handle(&self, cx: &AppContext) -> FocusHandle {
+        self.pane.focus_handle(cx)
+    }
+}
+
+impl EventEmitter<PanelEvent> for AssistantPanel {}
+
+impl Panel for AssistantPanel {
+    fn persistent_name() -> &'static str {
+        "AssistantPanel2"
+    }
+
+    fn position(&self, _cx: &WindowContext) -> DockPosition {
+        DockPosition::Right
+    }
+
+    fn position_is_valid(&self, _: DockPosition) -> bool {
+        true
+    }
+
+    fn set_position(&mut self, _position: DockPosition, _cx: &mut ViewContext<Self>) {}
+
+    fn size(&self, _cx: &WindowContext) -> Pixels {
+        px(640.)
+    }
+
+    fn set_size(&mut self, _size: Option<Pixels>, _cx: &mut ViewContext<Self>) {}
+
+    fn is_zoomed(&self, cx: &WindowContext) -> bool {
+        self.pane.read(cx).is_zoomed()
+    }
+
+    fn set_zoomed(&mut self, zoomed: bool, cx: &mut ViewContext<Self>) {
+        self.pane.update(cx, |pane, cx| pane.set_zoomed(zoomed, cx));
+    }
+
+    fn set_active(&mut self, _active: bool, _cx: &mut ViewContext<Self>) {}
+
+    fn pane(&self) -> Option<View<Pane>> {
+        Some(self.pane.clone())
+    }
+
+    fn remote_id() -> Option<proto::PanelId> {
+        Some(proto::PanelId::AssistantPanel)
+    }
+
+    fn icon(&self, _cx: &WindowContext) -> Option<IconName> {
+        Some(IconName::ZedAssistant)
+    }
+
+    fn icon_tooltip(&self, _cx: &WindowContext) -> Option<&'static str> {
+        Some("Assistant Panel")
+    }
+
+    fn toggle_action(&self) -> Box<dyn Action> {
+        Box::new(ToggleFocus)
+    }
+}
+
+impl Render for AssistantPanel {
+    fn render(&mut self, _cx: &mut ViewContext<Self>) -> impl IntoElement {
+        div().child(Label::new("Assistant II"))
+    }
+}