vim-patch:9.0.0061: ml_get error with nested autocommand

Problem:    ml_get error with nested autocommand.
Solution:   Also check line numbers for a nested autocommand. (closes vim/vim#10761)
https://github.com/vim/vim/commit/5fa9f23a63651a8abdb074b4fc2ec9b1adc6b089

3 files changed, 47 insertions, 10 deletions

diff --git a/src/nvim/autocmd.c b/src/nvim/autocmd.c
index 73c2cda92b..2b4c9c5b9c 100644
--- a/src/nvim/autocmd.c
+++ b/src/nvim/autocmd.c
@@ -1837,9 +1837,13 @@ bool apply_autocmds_group(event_T event, char *fname, char *fname_io, bool force
     }
     ap->last = true;
 
+    // Make sure cursor and topline are valid.  The first time the current
+    // values are saved, restored by reset_lnums().  When nested only the
+    // values are corrected when needed.
     if (nesting == 1) {
-      // make sure cursor and topline are valid
       check_lnums(true);
+    } else {
+      check_lnums_nested(true);
     }
 
     // Execute the autocmd. The `getnextac` callback handles iteration.
diff --git a/src/nvim/testdir/test_autocmd.vim b/src/nvim/testdir/test_autocmd.vim
index 438851a0ad..ed439ff6ec 100644
--- a/src/nvim/testdir/test_autocmd.vim
+++ b/src/nvim/testdir/test_autocmd.vim
@@ -2170,6 +2170,25 @@ func Test_autocmd_nested()
   call assert_fails('au WinNew * nested nested echo bad', 'E983:')
 endfunc
 
+func Test_autocmd_nested_cursor_invalid()
+  set laststatus=0
+  copen
+  cclose
+  call setline(1, ['foo', 'bar', 'baz'])
+  3
+  augroup nested_inv
+    autocmd User foo ++nested copen
+    autocmd BufAdd * let &laststatus = 2 - &laststatus
+  augroup END
+  doautocmd User foo
+
+  augroup nested_inv
+    au!
+  augroup END
+  set laststatus&
+  bwipe!
+endfunc
+
 func Test_autocmd_once()
   " Without ++once WinNew triggers twice
   let g:did_split = 0
diff --git a/src/nvim/window.c b/src/nvim/window.c
index 97ca45662e..f00d98ca60 100644
--- a/src/nvim/window.c
+++ b/src/nvim/window.c
@@ -6858,17 +6858,16 @@ bool only_one_window(void) FUNC_ATTR_PURE FUNC_ATTR_WARN_UNUSED_RESULT
   return count <= 1;
 }
 
-/// Correct the cursor line number in other windows.  Used after changing the
-/// current buffer, and before applying autocommands.
-///
-/// @param do_curwin  when true, also check current window.
-void check_lnums(bool do_curwin)
+/// Implementation of check_lnums() and check_lnums_nested().
+static void check_lnums_both(bool do_curwin, bool nested)
 {
   FOR_ALL_TAB_WINDOWS(tp, wp) {
     if ((do_curwin || wp != curwin) && wp->w_buffer == curbuf) {
-      // save the original cursor position and topline
-      wp->w_save_cursor.w_cursor_save = wp->w_cursor;
-      wp->w_save_cursor.w_topline_save = wp->w_topline;
+      if (!nested) {
+        // save the original cursor position and topline
+        wp->w_save_cursor.w_cursor_save = wp->w_cursor;
+        wp->w_save_cursor.w_topline_save = wp->w_topline;
+      }
 
       if (wp->w_cursor.lnum > curbuf->b_ml.ml_line_count) {
         wp->w_cursor.lnum = curbuf->b_ml.ml_line_count;
@@ -6877,13 +6876,28 @@ void check_lnums(bool do_curwin)
         wp->w_topline = curbuf->b_ml.ml_line_count;
       }
 
-      // save the corrected cursor position and topline
+      // save the (corrected) cursor position and topline
       wp->w_save_cursor.w_cursor_corr = wp->w_cursor;
       wp->w_save_cursor.w_topline_corr = wp->w_topline;
     }
   }
 }
 
+/// Correct the cursor line number in other windows.  Used after changing the
+/// current buffer, and before applying autocommands.
+///
+/// @param do_curwin  when true, also check current window.
+void check_lnums(bool do_curwin)
+{
+  check_lnums_both(do_curwin, false);
+}
+
+/// Like check_lnums() but for when check_lnums() was already called.
+void check_lnums_nested(bool do_curwin)
+{
+  check_lnums_both(do_curwin, true);
+}
+
 /// Reset cursor and topline to its stored values from check_lnums().
 /// check_lnums() must have been called first!
 void reset_lnums(void)