fix: preserve terminal live follow through resize

1 files changed, 49 insertions, 1 deletions

diff --git a/src/pane/terminal.rs b/src/pane/terminal.rs
index 8e33b1b3..2c83f8f2 100644
--- a/src/pane/terminal.rs
+++ b/src/pane/terminal.rs
@@ -2390,7 +2390,12 @@ fn ghostty_set_scroll_offset_from_bottom(
         return;
     };
     let max_offset = scrollbar.total.saturating_sub(scrollbar.len);
-    terminal.scroll_viewport_row(max_offset.saturating_sub(offset_from_bottom));
+    let offset_from_bottom = offset_from_bottom.min(max_offset);
+    if offset_from_bottom == 0 {
+        terminal.scroll_viewport_bottom();
+    } else {
+        terminal.scroll_viewport_row(max_offset - offset_from_bottom);
+    }
 }
 
 fn ghostty_extract_selection(
@@ -4193,6 +4198,49 @@ mod tests {
     }
 
     #[test]
+    fn empty_or_short_resize_keeps_following_bottom_when_output_creates_scrollback() {
+        for initial in [b"".as_slice(), b"seed\r\n".as_slice()] {
+            let (tx, _rx) = mpsc::channel(4);
+            let mut terminal = crate::ghostty::Terminal::new(10, 3, 100).unwrap();
+            terminal.write(initial);
+            let pane = GhosttyPaneTerminal::new(terminal, tx.clone()).unwrap();
+            let pane_id = PaneId::from_raw(1);
+
+            pane.resize(3, 10, 0, 0);
+            pane.process_pty_bytes(
+                pane_id,
+                0,
+                b"000000\r\n000001\r\n000002\r\n000003\r\n000004",
+                &tx,
+            );
+
+            let metrics = pane.scroll_metrics().expect("scroll metrics after output");
+            assert_eq!(metrics.offset_from_bottom, 0);
+            assert!(pane.visible_text().contains("000004"));
+        }
+    }
+
+    #[test]
+    fn resize_that_removes_scrollback_restores_live_follow() {
+        let (tx, _rx) = mpsc::channel(4);
+        let mut terminal = crate::ghostty::Terminal::new(10, 3, 100).unwrap();
+        terminal.write(b"000000\r\n000001\r\n000002\r\n000003\r\n000004");
+        let pane = GhosttyPaneTerminal::new(terminal, tx.clone()).unwrap();
+        let pane_id = PaneId::from_raw(1);
+
+        pane.set_scroll_offset_from_bottom(1);
+        pane.resize(5, 10, 0, 0);
+        let resized = pane.scroll_metrics().expect("scroll metrics after resize");
+        assert_eq!(resized.max_offset_from_bottom, 0);
+
+        pane.process_pty_bytes(pane_id, 0, b"\r\n000005\r\n000006", &tx);
+
+        let metrics = pane.scroll_metrics().expect("scroll metrics after output");
+        assert_eq!(metrics.offset_from_bottom, 0);
+        assert!(pane.visible_text().contains("000006"));
+    }
+
+    #[test]
     fn detection_text_stays_at_bottom_when_viewport_is_scrolled() {
         let (tx, _rx) = mpsc::channel(4);
         let mut terminal = crate::ghostty::Terminal::new(80, 3, 100).unwrap();