vim-patch:9.0.2134: ml_get error when scrolling (#26264)

Problem:  ml_get error when scrolling after delete
Solution: mark topline to be validated in main_loop
          if it is larger than current buffers line
          count

reset_lnums() is called after e.g. TextChanged autocommands and it may
accidentally cause curwin->w_topline to become invalid, e.g. if the
autocommand has deleted some lines.

So verify that curwin->w_topline points to a valid line and if not, mark
the window to have w_topline recalculated in main_loop() in
update_topline() after reset_lnums() returns.

fixes: vim/vim#13568
fixes: vim/vim#13578

https://github.com/vim/vim/commit/c4ffeddfe5bd1824650e9b911ed9245bf56c69e3

The error doesn't happen in Nvim because Nvim triggers TextChanged after
calling update_topline().

Co-authored-by: Christian Brabandt <cb@256bit.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/nvim/window.c b/src/nvim/window.c
index ce038d2723..bcf245ef93 100644
--- a/src/nvim/window.c
+++ b/src/nvim/window.c
@@ -7101,8 +7101,9 @@ void reset_lnums(void)
 {
   FOR_ALL_TAB_WINDOWS(tp, wp) {
     if (wp->w_buffer == curbuf) {
-      // Restore the value if the autocommand didn't change it and it was
-      // set.
+      // Restore the value if the autocommand didn't change it and it was set.
+      // Note: This triggers e.g. on BufReadPre, when the buffer is not yet
+      //       loaded, so cannot validate the buffer line
       if (equalpos(wp->w_save_cursor.w_cursor_corr, wp->w_cursor)
           && wp->w_save_cursor.w_cursor_save.lnum != 0) {
         wp->w_cursor = wp->w_save_cursor.w_cursor_save;
@@ -7111,6 +7112,9 @@ void reset_lnums(void)
           && wp->w_save_cursor.w_topline_save != 0) {
         wp->w_topline = wp->w_save_cursor.w_topline_save;
       }
+      if (wp->w_save_cursor.w_topline_save > wp->w_buffer->b_ml.ml_line_count) {
+        wp->w_valid &= ~VALID_TOPLINE;
+      }
     }
   }
 }