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 #10761)

src/autocmd.c

@@ -2209,9 +2209,13 @@ apply_autocmds_group(
 	    ap->last = FALSE;
 	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);
 
 	save_did_emsg = did_emsg;
 

src/proto/window.pro

@@ -77,6 +77,7 @@ int tabline_height(void);
 int min_rows(void);
 int only_one_window(void);
 void check_lnums(int do_curwin);
+void check_lnums_nested(int do_curwin);
 void reset_lnums(void);
 void make_snapshot(int idx);
 void restore_snapshot(int idx, int close_curwin);

src/testdir/test_autocmd.vim

@@ -2301,6 +2301,25 @@ 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

src/version.c

@@ -735,6 +735,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    61,
 /**/
     60,
 /**/

src/window.c

@@ -6770,34 +6770,55 @@ only_one_window(void)
 }
 
 /*
- * Correct the cursor line number in other windows.  Used after changing the
- * current buffer, and before applying autocommands.
- * When "do_curwin" is TRUE, also check current window.
+ * Implementation of check_lnums() and check_lnums_nested().
  */
-    void
-check_lnums(int do_curwin)
+    static void
+check_lnums_both(int do_curwin, int nested)
 {
     win_T	*wp;
     tabpage_T	*tp;
 
     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;
 	    if (wp->w_topline > curbuf->b_ml.ml_line_count)
 		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.
+ * When "do_curwin" is TRUE, also check current window.
+ */
+    void
+check_lnums(int do_curwin)
+{
+    check_lnums_both(do_curwin, FALSE);
+}
+
+/*
+ * Like check_lnums() but for when check_lnums() was already called.
+ */
+    void
+check_lnums_nested(int 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!