feat: show relative line numbers around primary cursor

src/tui.rs

@@ -246,7 +246,12 @@ fn draw(frame: &mut Frame, editor: &Editor, top: &mut usize, left: &mut usize) {
                     } else {
                         Style::default().fg(Color::DarkGray)
                     };
-                    Line::styled(format!("{:>digits$} ", row + 1), style)
+                    let number = if row == cursor.row {
+                        row + 1
+                    } else {
+                        row.abs_diff(cursor.row)
+                    };
+                    Line::styled(format!("{number:>digits$} "), style)
                 })
                 .collect();
             frame.render_widget(Paragraph::new(numbers), gutter);
@@ -509,7 +514,7 @@ mod tests {
             .unwrap();
         assert_eq!((top, left), (8, 8));
         let buffer = terminal.backend().buffer();
-        for (y, expected) in [(2, " 9 "), (3, "10 "), (4, "11 ")] {
+        for (y, expected) in [(2, " 2 "), (3, " 1 "), (4, "11 ")] {
             let number: String = (3..6).map(|x| buffer[(x, y)].symbol()).collect();
             assert_eq!(number, expected);
             assert_eq!(buffer[(6, y)].symbol(), "8");
@@ -533,6 +538,26 @@ mod tests {
             terminal.get_cursor_position().unwrap(),
             ratatui::layout::Position::new(6, 4)
         );
+        editor.handle(Input::Up);
+        editor.handle(Input::Up);
+        terminal
+            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
+            .unwrap();
+        let buffer = terminal.backend().buffer();
+        for (y, expected) in [(2, "10 "), (3, " 1 "), (4, " 2 ")] {
+            let number: String = (3..6).map(|x| buffer[(x, y)].symbol()).collect();
+            assert_eq!(number, expected);
+        }
+        editor.handle(Input::Ctrl('e'));
+        assert_eq!(editor.selection_count(), 2);
+        terminal
+            .draw(|frame| draw(frame, &editor, &mut top, &mut left))
+            .unwrap();
+        let buffer = terminal.backend().buffer();
+        for (y, expected) in [(2, " 1 "), (3, "11 "), (4, " 1 ")] {
+            let number: String = (3..6).map(|x| buffer[(x, y)].symbol()).collect();
+            assert_eq!(number, expected);
+        }
     }
 
     #[test]