edit predictions: Handle no keybind for preview (#25015)

If the user removes all modified keybinds in `edit_prediction_conflict`,
the preview bar above the completions menu would disappear. This PR
handles that case slightly better by still showing the 1-line preview
(which they might accept via an unmodified keybind) and hides the `|
Preview ⌥` section since it's impossible to invoke in this case.

Release Notes:

- Handle `edit_prediction_conflict` context without modified keybinds
for `AcceptEditPrediction`

crates/editor/src/editor.rs

@@ -5762,7 +5762,7 @@ impl Editor {
         max_width: Pixels,
         cursor_point: Point,
         style: &EditorStyle,
-        accept_keystroke: &gpui::Keystroke,
+        accept_keystroke: Option<&gpui::Keystroke>,
         _window: &Window,
         cx: &mut Context<Editor>,
     ) -> Option<AnyElement> {
@@ -5841,7 +5841,7 @@ impl Editor {
                             )
                             .child(Label::new("Hold").size(LabelSize::Small))
                             .child(h_flex().children(ui::render_modifiers(
-                                &accept_keystroke.modifiers,
+                                &accept_keystroke?.modifiers,
                                 PlatformStyle::platform(),
                                 Some(Color::Default),
                                 Some(IconSize::Small.rems().into()),
@@ -5906,7 +5906,12 @@ impl Editor {
                         .overflow_hidden()
                         .child(completion),
                 )
-                .child(
+                .when_some(accept_keystroke, |el, accept_keystroke| {
+                    if !accept_keystroke.modifiers.modified() {
+                        return el;
+                    }
+
+                    el.child(
                         h_flex()
                             .h_full()
                             .border_l_1()
@@ -5935,6 +5940,7 @@ impl Editor {
                             .child(Label::new("Preview").into_any_element())
                             .opacity(if has_completion { 1.0 } else { 0.4 }),
                     )
+                })
                 .into_any(),
         )
     }

crates/editor/src/element.rs

@@ -3255,7 +3255,7 @@ impl EditorElement {
                             max_width,
                             cursor_point,
                             style,
-                            accept_binding.keystroke()?,
+                            accept_binding.keystroke(),
                             window,
                             cx,
                         )?;