editor: Show hints for using AI features on empty lines (#20824)

Co-Authored-by: Thorsten <thorsten@zed.dev>
Co-Authored-by: Antonio <antonio@zed.dev>

Screenshot:

![screenshot-2024-11-18-17 11
08@2x](https://github.com/user-attachments/assets/610fd7db-7476-4b9b-9465-a3d55df12340)

TODO:
- [x] docs

Release Notes:

- Added inline hints that guide users on how to invoke the inline
assistant and open the assistant panel. (These hints can be disabled by
setting `{"assistant": {"show_hints": false}}`.)

---------

Co-authored-by: Thorsten <thorsten@zed.dev>
Co-authored-by: Antonio <antonio@zed.dev>
Co-authored-by: Thorsten Ball <mrnugget@gmail.com>

crates/zed/src/main.rs

@@ -66,7 +66,7 @@ use zed::{
     OpenRequest,
 };
 
-use crate::zed::inline_completion_registry;
+use crate::zed::{assistant_hints, inline_completion_registry};
 
 #[cfg(feature = "mimalloc")]
 #[global_allocator]
@@ -401,6 +401,7 @@ fn main() {
             stdout_is_a_pty(),
             cx,
         );
+        assistant_hints::init(cx);
         repl::init(
             app_state.fs.clone(),
             app_state.client.telemetry().clone(),

crates/zed/src/zed.rs

@@ -1,4 +1,5 @@
 mod app_menus;
+pub mod assistant_hints;
 pub mod inline_completion_registry;
 #[cfg(any(target_os = "linux", target_os = "freebsd"))]
 pub(crate) mod linux_prompts;

crates/zed/src/zed/assistant_hints.rs

@@ -0,0 +1,115 @@
+use assistant::assistant_settings::AssistantSettings;
+use collections::HashMap;
+use editor::{ActiveLineTrailerProvider, Editor, EditorMode};
+use gpui::{AnyWindowHandle, AppContext, ViewContext, WeakView, WindowContext};
+use settings::{Settings, SettingsStore};
+use std::{cell::RefCell, rc::Rc};
+use theme::ActiveTheme;
+use ui::prelude::*;
+use workspace::Workspace;
+
+pub fn init(cx: &mut AppContext) {
+    let editors: Rc<RefCell<HashMap<WeakView<Editor>, AnyWindowHandle>>> = Rc::default();
+
+    cx.observe_new_views({
+        let editors = editors.clone();
+        move |_: &mut Workspace, cx: &mut ViewContext<Workspace>| {
+            let workspace_handle = cx.view().clone();
+            cx.subscribe(&workspace_handle, {
+                let editors = editors.clone();
+                move |_, _, event, cx| match event {
+                    workspace::Event::ItemAdded { item } => {
+                        if let Some(editor) = item.act_as::<Editor>(cx) {
+                            if editor.read(cx).mode() != EditorMode::Full {
+                                return;
+                            }
+
+                            cx.on_release({
+                                let editor_handle = editor.downgrade();
+                                let editors = editors.clone();
+                                move |_, _, _| {
+                                    editors.borrow_mut().remove(&editor_handle);
+                                }
+                            })
+                            .detach();
+                            editors
+                                .borrow_mut()
+                                .insert(editor.downgrade(), cx.window_handle());
+
+                            let show_hints = should_show_hints(cx);
+                            editor.update(cx, |editor, cx| {
+                                assign_active_line_trailer_provider(editor, show_hints, cx)
+                            })
+                        }
+                    }
+                    _ => {}
+                }
+            })
+            .detach();
+        }
+    })
+    .detach();
+
+    let mut show_hints = AssistantSettings::get_global(cx).show_hints;
+    cx.observe_global::<SettingsStore>(move |cx| {
+        let new_show_hints = should_show_hints(cx);
+        if new_show_hints != show_hints {
+            show_hints = new_show_hints;
+            for (editor, window) in editors.borrow().iter() {
+                _ = window.update(cx, |_window, cx| {
+                    _ = editor.update(cx, |editor, cx| {
+                        assign_active_line_trailer_provider(editor, show_hints, cx);
+                    })
+                });
+            }
+        }
+    })
+    .detach();
+}
+
+struct AssistantHintsProvider;
+
+impl ActiveLineTrailerProvider for AssistantHintsProvider {
+    fn render_active_line_trailer(
+        &mut self,
+        style: &editor::EditorStyle,
+        focus_handle: &gpui::FocusHandle,
+        cx: &mut WindowContext,
+    ) -> Option<gpui::AnyElement> {
+        if !focus_handle.is_focused(cx) {
+            return None;
+        }
+
+        let chat_keybinding =
+            cx.keystroke_text_for_action_in(&assistant::ToggleFocus, focus_handle);
+        let generate_keybinding =
+            cx.keystroke_text_for_action_in(&zed_actions::InlineAssist::default(), focus_handle);
+
+        Some(
+            h_flex()
+                .id("inline-assistant-instructions")
+                .w_full()
+                .font_family(style.text.font().family)
+                .text_color(cx.theme().status().hint)
+                .line_height(style.text.line_height)
+                .child(format!(
+                    "{chat_keybinding} to chat, {generate_keybinding} to generate"
+                ))
+                .into_any(),
+        )
+    }
+}
+
+fn assign_active_line_trailer_provider(
+    editor: &mut Editor,
+    show_hints: bool,
+    cx: &mut ViewContext<Editor>,
+) {
+    let provider = show_hints.then_some(AssistantHintsProvider);
+    editor.set_active_line_trailer_provider(provider, cx);
+}
+
+fn should_show_hints(cx: &AppContext) -> bool {
+    let assistant_settings = AssistantSettings::get_global(cx);
+    assistant_settings.enabled && assistant_settings.show_hints
+}