Add a mode indicator for vim (#2763)

Release Notes:

- vim: add a mode indicator
([#409](https://github.com/zed-industries/community/issues/409))

Now updated screenshots with @iamnbutler 
<img width="1043" alt="Screenshot 2023-07-25 at 11 11 57"
src="https://github.com/zed-industries/zed/assets/94272/8301479a-8b58-42d8-81a1-bc40e1e0a4df">
<img width="1043" alt="Screenshot 2023-07-25 at 11 12 00"
src="https://github.com/zed-industries/zed/assets/94272/89c3b8bd-9cbc-4fd7-ad10-dac5538ed3a3">
<img width="1043" alt="Screenshot 2023-07-25 at 11 12 12"
src="https://github.com/zed-industries/zed/assets/94272/adc87fe3-a720-4779-853b-df9443407046">

crates/vim/src/vim.rs

@@ -3,6 +3,7 @@ mod test;
 
 mod editor_events;
 mod insert;
+mod mode_indicator;
 mod motion;
 mod normal;
 mod object;
@@ -18,6 +19,7 @@ use gpui::{
     Subscription, ViewContext, ViewHandle, WeakViewHandle, WindowContext,
 };
 use language::CursorShape;
+pub use mode_indicator::ModeIndicator;
 use motion::Motion;
 use normal::normal_replace;
 use serde::Deserialize;
@@ -119,6 +121,7 @@ pub fn observe_keystrokes(cx: &mut WindowContext) {
 pub struct Vim {
     active_editor: Option<WeakViewHandle<Editor>>,
     editor_subscription: Option<Subscription>,
+    mode_indicator: Option<ViewHandle<ModeIndicator>>,
 
     enabled: bool,
     state: VimState,
@@ -178,6 +181,10 @@ impl Vim {
         self.state.mode = mode;
         self.state.operator_stack.clear();
 
+        if let Some(mode_indicator) = &self.mode_indicator {
+            mode_indicator.update(cx, |mode_indicator, cx| mode_indicator.set_mode(mode, cx))
+        }
+
         // Sync editor settings like clip mode
         self.sync_vim_settings(cx);
 
@@ -264,6 +271,44 @@ impl Vim {
         }
     }
 
+    fn sync_mode_indicator(cx: &mut WindowContext) {
+        let Some(workspace) = cx.root_view()
+            .downcast_ref::<Workspace>()
+            .map(|workspace| workspace.downgrade()) else {
+                return;
+            };
+
+        cx.spawn(|mut cx| async move {
+            workspace.update(&mut cx, |workspace, cx| {
+                Vim::update(cx, |vim, cx| {
+                    workspace.status_bar().update(cx, |status_bar, cx| {
+                        let current_position = status_bar.position_of_item::<ModeIndicator>();
+
+                        if vim.enabled && current_position.is_none() {
+                            if vim.mode_indicator.is_none() {
+                                vim.mode_indicator =
+                                    Some(cx.add_view(|_| ModeIndicator::new(vim.state.mode)));
+                            };
+                            let mode_indicator = vim.mode_indicator.as_ref().unwrap();
+                            let position = status_bar
+                                .position_of_item::<language_selector::ActiveBufferLanguage>();
+                            if let Some(position) = position {
+                                status_bar.insert_item_after(position, mode_indicator.clone(), cx)
+                            } else {
+                                status_bar.add_left_item(mode_indicator.clone(), cx)
+                            }
+                        } else if !vim.enabled {
+                            if let Some(position) = current_position {
+                                status_bar.remove_item_at(position, cx)
+                            }
+                        }
+                    })
+                })
+            })
+        })
+        .detach_and_log_err(cx);
+    }
+
     fn set_enabled(&mut self, enabled: bool, cx: &mut AppContext) {
         if self.enabled != enabled {
             self.enabled = enabled;
@@ -314,6 +359,8 @@ impl Vim {
                 self.unhook_vim_settings(editor, cx);
             }
         });
+
+        Vim::sync_mode_indicator(cx);
     }
 
     fn unhook_vim_settings(&self, editor: &mut Editor, cx: &mut ViewContext<Editor>) {