perf(redraw): reduce redraw with undo and extmarks or 'spell' (#27442)

vim-patch:9.1.0100: Redrawing can be improved with undo and 'spell'

Problem:  When undoing with 'spell', redrawWinline() is called after
          changed_lines(), while later win_update() sets redraw type to
          UPD_NOT_VALID, even though w_redraw_top and w_redraw_bot are
          still valid.
Solution: Only set redraw type to UPD_NOT_VALID when inserting/deleting
          lines after parts of window has pending redraw, i.e., when
          changed_lines() is called after redrawWinline().
          (zeertzjq)

closes: vim/vim#14019

https://github.com/vim/vim/commit/f2d90a351159fd6843f450850f52004f42e00183

1 files changed, 7 insertions, 0 deletions

diff --git a/src/nvim/change.c b/src/nvim/change.c
index a7c885bf4d..1c7724f010 100644
--- a/src/nvim/change.c
+++ b/src/nvim/change.c
@@ -326,6 +326,13 @@ static void changed_common(buf_T *buf, linenr_T lnum, colnr_T col, linenr_T lnum
         wp->w_redr_type = UPD_VALID;
       }
 
+      // When inserting/deleting lines and the window has specific lines
+      // to be redrawn, w_redraw_top and w_redraw_bot may now be invalid,
+      // so just redraw everything.
+      if (xtra != 0 && wp->w_redraw_top != 0) {
+        redraw_later(wp, UPD_NOT_VALID);
+      }
+
       linenr_T last = lnume + xtra - 1;  // last line after the change
 
       // Reset "w_skipcol" if the topline length has become smaller to