fix: resize state and correctness (#5656)

* fix: resize state and correctness

* rustfmt

* add pr

CHANGELOG.md

@@ -13,6 +13,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 * feat: nested sessions input-mode + keybindings reporting (https://github.com/zellij-org/zellij/issues/5561)
 * fix: control characters occasionally appearing in panes on startup (https://github.com/zellij-org/zellij/pull/5655)
 * fix: group bar-plugins on viewport edge for layout purposes (https://github.com/zellij-org/zellij/pull/5653)
+* fix: resize state and correctness (https://github.com/zellij-org/zellij/pull/5656)
 * fix: compress kitty images if the host terminal supports it (https://github.com/zellij-org/zellij/pull/5608)
 
 ## [0.45.1] - 2026-08-28

zellij-server/src/panes/grid.rs

@@ -1367,18 +1367,21 @@ impl Grid {
         self.active_charset = index;
     }
     fn cursor_canonical_line_index(&self) -> usize {
-        let mut cursor_canonical_line_index = 0;
+        self.canonical_line_index_of_row(self.cursor.y)
+    }
+    fn canonical_line_index_of_row(&self, y: usize) -> usize {
+        let mut canonical_line_index = 0;
         let mut canonical_lines_traversed = 0;
         for (i, line) in self.viewport.iter().enumerate() {
             if line.is_canonical {
-                cursor_canonical_line_index = canonical_lines_traversed;
+                canonical_line_index = canonical_lines_traversed;
                 canonical_lines_traversed += 1;
             }
-            if i == self.cursor.y {
+            if i == y {
                 break;
             }
         }
-        cursor_canonical_line_index
+        canonical_line_index
     }
     // TODO: merge these two functions
     fn cursor_index_in_canonical_line(&self) -> usize {
@@ -1430,6 +1433,16 @@ impl Grid {
         }
         y_coordinates
     }
+    fn last_row_of_line_starting_at(&self, first_y: usize) -> usize {
+        let mut last_y = first_y;
+        for (y, row) in self.viewport.iter().enumerate().skip(first_y + 1) {
+            if row.is_canonical {
+                break;
+            }
+            last_y = y;
+        }
+        last_y
+    }
     fn kitty_canonical_line_starts(&self) -> Vec<usize> {
         let mut starts = Vec::new();
         let mut wrapped_row = 0usize;
@@ -1630,24 +1643,12 @@ impl Grid {
         found_something
     }
     pub fn force_change_size(&mut self, new_rows: usize, new_columns: usize) {
-        // this is an ugly hack - it's here because sometimes we need to change_size to the
-        // existing size (eg. when resizing an alternative_grid to the current height/width) and
-        // the change_size method is a no-op in that case. Should be fixed by making the
-        // change_size method atomic
-        let intermediate_rows = if new_rows == self.height {
-            new_rows + 1
-        } else {
-            new_rows
-        };
-        let intermediate_columns = if new_columns == self.width {
-            new_columns + 1
-        } else {
-            new_columns
-        };
-        self.change_size(intermediate_rows, intermediate_columns);
-        self.change_size(new_rows, new_columns);
+        self.resize_and_reflow(new_rows, new_columns, true);
     }
     pub fn change_size(&mut self, new_rows: usize, new_columns: usize) {
+        self.resize_and_reflow(new_rows, new_columns, false);
+    }
+    fn resize_and_reflow(&mut self, new_rows: usize, new_columns: usize, force_rewrap: bool) {
         // Do nothing if this pane hasn't been given a proper size yet
         if new_columns == 0 || new_rows == 0 {
             return;
@@ -1665,11 +1666,15 @@ impl Grid {
         self.sixel_grid.character_cell_size_possibly_changed();
         self.kitty_grid.character_cell_size_possibly_changed();
         self.kitty_reanchor_all_from_pixels();
-        let cursors = if new_columns != self.width {
+        let cursors = if force_rewrap || new_columns != self.width {
             self.horizontal_tabstops = create_horizontal_tabstops(new_columns);
             let mut cursor_canonical_line_index = self.cursor_canonical_line_index();
             let cursor_index_in_canonical_line = self.cursor_index_in_canonical_line();
             let saved_cursor_index_in_canonical_line = self.saved_cursor_index_in_canonical_line();
+            let mut saved_cursor_canonical_line_index = self
+                .saved_cursor_position
+                .as_ref()
+                .map(|saved_cursor| self.canonical_line_index_of_row(saved_cursor.y));
             let mut viewport_canonical_lines = vec![];
             for mut row in self.viewport.drain(..) {
                 if !row.is_canonical
@@ -1680,6 +1685,9 @@ impl Grid {
                     first_line_above.append(&mut row);
                     viewport_canonical_lines.push(first_line_above);
                     cursor_canonical_line_index += 1;
+                    if let Some(index) = saved_cursor_canonical_line_index.as_mut() {
+                        *index += 1;
+                    }
                 } else if row.is_canonical {
                     viewport_canonical_lines.push(row);
                 } else {
@@ -1736,13 +1744,20 @@ impl Grid {
 
             self.viewport = VecDeque::from(new_viewport_rows);
 
-            let mut new_cursor_y = self.canonical_line_y_coordinates(cursor_canonical_line_index)
-                + (cursor_index_in_canonical_line / new_columns);
-            let mut saved_cursor_y_coordinates =
-                self.saved_cursor_position.as_ref().map(|saved_cursor| {
-                    self.canonical_line_y_coordinates(saved_cursor.y)
-                        + saved_cursor_index_in_canonical_line.as_ref().unwrap() / new_columns
-                });
+            let cursor_line_first_y =
+                self.canonical_line_y_coordinates(cursor_canonical_line_index);
+            let cursor_line_last_y = self.last_row_of_line_starting_at(cursor_line_first_y);
+            let mut new_cursor_y =
+                cursor_line_first_y + (cursor_index_in_canonical_line / new_columns);
+            let mut saved_cursor_y_coordinates = match (
+                saved_cursor_canonical_line_index,
+                saved_cursor_index_in_canonical_line,
+            ) {
+                (Some(line_index), Some(index_in_line)) => Some(
+                    self.canonical_line_y_coordinates(line_index) + index_in_line / new_columns,
+                ),
+                _ => None,
+            };
 
             // A cursor at EOL has two equivalent positions - end of this line or beginning of
             // next. If not already at the beginning of line, bias to EOL so add character logic
@@ -1752,6 +1767,12 @@ impl Grid {
                 new_cursor_y = new_cursor_y.saturating_sub(1);
                 new_cursor_x = new_columns
             }
+            if new_cursor_y > cursor_line_last_y {
+                let offset_in_last_row = cursor_index_in_canonical_line
+                    .saturating_sub((cursor_line_last_y - cursor_line_first_y) * new_columns);
+                new_cursor_y = cursor_line_last_y;
+                new_cursor_x = offset_in_last_row.min(new_columns.saturating_sub(1));
+            }
             let saved_cursor_x_coordinates = match (
                 saved_cursor_index_in_canonical_line.as_ref(),
                 self.saved_cursor_position.as_mut(),
@@ -1779,7 +1800,7 @@ impl Grid {
                 new_cursor_x,
                 saved_cursor_x_coordinates,
             ))
-        } else if new_rows != self.height {
+        } else if new_rows != self.height || self.viewport.len() != new_rows {
             let saved_cursor_y_coordinates = self
                 .saved_cursor_position
                 .as_ref()

zellij-server/src/panes/terminal_pane.rs

@@ -1479,7 +1479,7 @@ impl TerminalPane {
     fn reflow_lines(&mut self) {
         let rows = self.get_content_rows();
         let cols = self.get_content_columns();
-        self.grid.force_change_size(rows, cols);
+        self.grid.change_size(rows, cols);
         if self.banner.is_some() {
             self.grid.reset_terminal_state();
             self.render_first_run_banner();

zellij-server/src/panes/unit/grid_tests.rs

@@ -9399,3 +9399,104 @@ fn a_character_wider_than_two_columns_advances_the_cursor_by_its_full_width() {
     assert_eq!(row.width(), 4);
     assert_eq!(cursor_position(&grid), Some((4, 0)));
 }
+
+fn create_sized_grid_with_content(rows: usize, columns: usize, content: &str) -> Grid {
+    let mut vte_parser = vte::Parser::new();
+    let mut grid = Grid::new(
+        rows,
+        columns,
+        Rc::new(RefCell::new(Palette::default())),
+        Rc::new(RefCell::new(HashMap::new())),
+        Rc::new(RefCell::new(LinkHandler::new())),
+        Rc::new(RefCell::new(None)),
+        Rc::new(RefCell::new(SixelImageStore::default())),
+        Rc::new(RefCell::new(KittyImageStore::default())),
+        Style::default(),
+        false,
+        true,
+        true,
+        true,
+        false,
+    );
+    vte_parser.advance(&mut grid, content.as_bytes());
+    grid
+}
+
+fn feed(grid: &mut Grid, content: &str) {
+    let mut vte_parser = vte::Parser::new();
+    vte_parser.advance(grid, content.as_bytes());
+}
+
+#[test]
+fn same_size_forced_reflow_keeps_cursor_at_start_of_wrapped_row() {
+    let mut grid = create_sized_grid_with_content(5, 10, "0123456789a\u{8}");
+    assert_eq!(cursor_position(&grid), Some((0, 1)));
+
+    grid.force_change_size(5, 10);
+    assert_eq!(cursor_position(&grid), Some((0, 1)));
+
+    feed(&mut grid, "\rX");
+    assert_eq!(rendered_row(&grid, 0), "0123456789");
+    assert_eq!(rendered_row(&grid, 1), "X");
+}
+
+#[test]
+fn height_only_resize_keeps_cursor_at_start_of_wrapped_row() {
+    let mut grid = create_sized_grid_with_content(5, 10, "0123456789a\u{8}");
+
+    grid.force_change_size(6, 10);
+    assert_eq!(cursor_position(&grid), Some((0, 1)));
+
+    grid.change_size(7, 10);
+    assert_eq!(cursor_position(&grid), Some((0, 1)));
+
+    feed(&mut grid, "\rX");
+    assert_eq!(rendered_row(&grid, 0), "0123456789");
+    assert_eq!(rendered_row(&grid, 1), "X");
+}
+
+#[test]
+fn prompt_redraw_after_same_size_reflow_does_not_duplicate_wrapped_prompt() {
+    let prompt = "> ~/c/zellij-code-2 on main";
+    let mut grid = create_sized_grid_with_content(5, 20, prompt);
+    for _ in 0..3 {
+        feed(&mut grid, "\r");
+        grid.force_change_size(5, 20);
+        feed(&mut grid, "\u{1b}[1A\u{1b}[J");
+        feed(&mut grid, prompt);
+    }
+    assert_eq!(rendered_row(&grid, 0), "> ~/c/zellij-code-2 ");
+    assert_eq!(rendered_row(&grid, 1).trim_end(), "on main");
+    assert_eq!(grid.viewport.len(), 2);
+}
+
+#[test]
+fn saved_cursor_follows_its_own_line_when_wrapped_lines_are_above_it() {
+    let mut grid = create_sized_grid_with_content(
+        6,
+        10,
+        "0123456789abcdefghij\n\rXY\u{1b}7Z\n\rline3\n\rline4",
+    );
+
+    grid.change_size(6, 20);
+    feed(&mut grid, "\u{1b}8Q");
+
+    assert_eq!(rendered_row(&grid, 0), "0123456789abcdefghij");
+    assert_eq!(rendered_row(&grid, 1), "XYQ");
+    assert_eq!(rendered_row(&grid, 2), "line3");
+    assert_eq!(rendered_row(&grid, 3), "line4");
+}
+
+#[test]
+fn shrinking_keeps_cursor_on_its_own_line_when_it_sits_past_the_content() {
+    let mut grid = create_sized_grid_with_content(6, 31, "first\n\r> prompt text here okay \x1b[J");
+    assert_eq!(cursor_position(&grid), Some((24, 1)));
+
+    grid.change_size(6, 23);
+    assert_eq!(cursor_position(&grid), Some((22, 1)));
+
+    feed(&mut grid, "\rX");
+    assert_eq!(rendered_row(&grid, 0), "first");
+    assert_eq!(rendered_row(&grid, 1), "X prompt text here okay");
+    assert_eq!(grid.viewport.len(), 2);
+}

zellij-server/src/tab/mod.rs

@@ -1957,9 +1957,6 @@ impl Tab {
             .non_fatal();
         }
         self.set_force_render();
-        self.senders
-            .send_to_pty_writer(PtyWriteInstruction::ApplyCachedResizes)
-            .with_context(|| format!("failed to apply cached resizes"))?;
         Ok(())
     }
     fn relayout_tiled_panes(&mut self, search_backwards: bool) -> Result<()> {
@@ -2014,9 +2011,6 @@ impl Tab {
         // we do this so that the new swap layout has a chance to pass through the constraint system
         self.tiled_panes.resize(display_area);
         self.set_should_clear_display_before_rendering();
-        self.senders
-            .send_to_pty_writer(PtyWriteInstruction::ApplyCachedResizes)
-            .with_context(|| format!("failed to apply cached resizes"))?;
         Ok(())
     }
     fn settled_tiled_pane_count(&self) -> usize {
@@ -5211,9 +5205,6 @@ impl Tab {
             let _ = self.relayout_tiled_panes(false);
         }
         self.set_should_clear_display_before_rendering();
-        self.senders
-            .send_to_pty_writer(PtyWriteInstruction::ApplyCachedResizes)
-            .with_context(|| format!("failed to update plugins with mode info"))?;
         LayoutApplier::offset_viewport(
             self.viewport.clone(),
             self.display_area.clone(),

zellij-server/src/unit/snapshots/zellij_server__screen__screen_tests__send_cli_write_action_to_screen.snap

@@ -2,4 +2,4 @@
 source: zellij-server/src/./unit/screen_tests.rs
 expression: "format!(\"{:?}\", *received_pty_instructions.lock().unwrap())"
 ---
-[StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ApplyCachedResizes, ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ApplyCachedResizes, ApplyCachedResizes, ResizePty(0, 119, 18, None, None), ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, Write([102, 111, 111], 0, None), ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, Exit]
+[StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, Write([102, 111, 111], 0, None), ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, Exit]

zellij-server/src/unit/snapshots/zellij_server__screen__screen_tests__send_cli_write_chars_action_to_screen.snap

@@ -2,4 +2,4 @@
 source: zellij-server/src/./unit/screen_tests.rs
 expression: "format!(\"{:?}\", *received_pty_instructions.lock().unwrap())"
 ---
-[StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ApplyCachedResizes, ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ApplyCachedResizes, ApplyCachedResizes, ResizePty(0, 119, 18, None, None), ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, Write([105, 110, 112, 117, 116, 32, 102, 114, 111, 109, 32, 116, 104, 101, 32, 99, 108, 105], 0, None), ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, Exit]
+[StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ResizePty(0, 119, 18, None, None), ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, Write([105, 110, 112, 117, 116, 32, 102, 114, 111, 109, 32, 116, 104, 101, 32, 99, 108, 105], 0, None), ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, StartCachingResizes, ApplyCachedResizes, Exit]