fix: diff_buffers clear-to-end when deleting wide graphemes

codex-rs/tui/src/custom_terminal.rs

@@ -418,14 +418,19 @@ fn diff_buffers<'a>(a: &'a Buffer, b: &'a Buffer) -> Vec<DrawCommand<'a>> {
         let row = &next_buffer[row_start..row_end];
         let bg = row.last().map(|cell| cell.bg).unwrap_or(Color::Reset);
 
-        let x = row
-            .iter()
-            .rposition(|cell| {
-                cell.symbol() != " " || cell.bg != bg || cell.modifier != Modifier::empty()
-            })
-            .unwrap_or(0);
+        let mut last_nonblank: Option<usize> = None;
+        let mut col = 0usize;
+        while col < row.len() {
+            let cell = &row[col];
+            let width = cell.symbol().width().max(1);
+            if cell.symbol() != " " || cell.bg != bg || cell.modifier != Modifier::empty() {
+                last_nonblank = Some(col + width.saturating_sub(1));
+            }
+            col += width;
+        }
+        let x = last_nonblank.unwrap_or(0);
         last_nonblank_column[y as usize] = x as u16;
-        if x < (a.area.width as usize).saturating_sub(1) {
+        if x + 1 < row.len() {
             let (x_abs, y_abs) = a.pos_of(row_start + x + 1);
             updates.push(DrawCommand::ClearToEnd {
                 x: x_abs,
@@ -592,6 +597,7 @@ mod tests {
     use super::*;
     use pretty_assertions::assert_eq;
     use ratatui::layout::Rect;
+    use ratatui::style::Style;
 
     #[test]
     fn diff_buffers_does_not_emit_clear_to_end_for_full_width_row() {
@@ -620,4 +626,22 @@ mod tests {
             "expected diff_buffers to update the final cell; commands: {commands:?}",
         );
     }
+
+    #[test]
+    fn diff_buffers_clear_to_end_starts_after_wide_char() {
+        let area = Rect::new(0, 0, 10, 1);
+        let mut previous = Buffer::empty(area);
+        let mut next = Buffer::empty(area);
+
+        previous.set_string(0, 0, "中文", Style::default());
+        next.set_string(0, 0, "中", Style::default());
+
+        let commands = diff_buffers(&previous, &next);
+        assert!(
+            commands
+                .iter()
+                .any(|command| matches!(command, DrawCommand::ClearToEnd { x: 2, y: 0, .. })),
+            "expected clear-to-end to start after the remaining wide char; commands: {commands:?}"
+        );
+    }
 }