zeta: Show deletions when inline completion is shown in menu (#22186)

If an inline completion isn't shown in a menu, we highlight text in the
editor as deleted.

But if it's shown in the menu, we didn't even show deleted text, which
makes it hard to understand what's going on.

This fixes it.
![screenshot-2024-12-18-14 34
55@2x](https://github.com/user-attachments/assets/579639e4-5ed9-4fe6-8e21-65166d192432)


Release Notes:

- N/A

crates/editor/src/editor.rs

@@ -4864,7 +4864,7 @@ impl Editor {
 
             let text = match &self.active_inline_completion.as_ref()?.completion {
                 InlineCompletion::Edit(edits) => {
-                    inline_completion_edit_text(&editor_snapshot, edits, cx)
+                    inline_completion_edit_text(&editor_snapshot, edits, true, cx)
                 }
                 InlineCompletion::Move(target) => {
                     let target_point =
@@ -14630,6 +14630,7 @@ pub fn diagnostic_block_renderer(
 fn inline_completion_edit_text(
     editor_snapshot: &EditorSnapshot,
     edits: &Vec<(Range<Anchor>, String)>,
+    include_deletions: bool,
     cx: &WindowContext,
 ) -> InlineCompletionText {
     let edit_start = edits
@@ -14653,12 +14654,24 @@ fn inline_completion_edit_text(
         offset = old_offset_range.end;
 
         let start = text.len();
-        text.push_str(new_text);
+        let color = if include_deletions && new_text.is_empty() {
+            text.extend(
+                editor_snapshot
+                    .buffer_snapshot
+                    .chunks(old_offset_range.start..offset, false)
+                    .map(|chunk| chunk.text),
+            );
+            cx.theme().status().deleted_background
+        } else {
+            text.push_str(new_text);
+            cx.theme().status().created_background
+        };
         let end = text.len();
+
         highlights.push((
             start..end,
             HighlightStyle {
-                background_color: Some(cx.theme().status().created_background),
+                background_color: Some(color),
                 ..Default::default()
             },
         ));