patch 9.0.2168: Moving tabpages on :drop may cause an endless loop

Problem:  Moving tabpages on :drop may cause an endless loop
Solution: Disallow moving tabpages on :drop when cleaning up the arglist
          first

Moving tabpages during drop command may cause an endless loop

When executing a :tab drop command, Vim will close all windows not in
the argument list. This triggers various autocommands. If a user has
created an 'au Tabenter * :tabmove -' autocommand, this can cause Vim to
end up in an endless loop, when trying to iterate over all tabs (which
would trigger the tabmove autocommand, which will change the tpnext
pointer, etc).

So instead of blocking all autocommands before we actually try to edit
the given file, lets simply disallow to move tabpages around. Otherwise,
we may change the expected number of events triggered during a :drop
command, which users may rely on (there is actually a test, that expects
various TabLeave/TabEnter autocommands) and would therefore be a
backwards incompatible change.

Don't make this an error, as this could trigger several times during the
drop command, but silently ignore the :tabmove command in this case (and
it should in fact finally trigger successfully when loading the given
file in a new tab). So let's just be quiet here instead.

fixes:  #13676
closes: #13686

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/arglist.c

@@ -983,6 +983,9 @@ arg_all_close_unused_windows(arg_all_state_T *aall)
 
     if (aall->had_tab > 0)
 	goto_tabpage_tp(first_tabpage, TRUE, TRUE);
+
+    // moving tabpages around in an autocommand may cause an endless loop
+    tabpage_move_disallowed++;
     for (;;)
     {
 	tpnext = curtab->tp_next;
@@ -1093,6 +1096,7 @@ arg_all_close_unused_windows(arg_all_state_T *aall)
 
 	goto_tabpage_tp(tpnext, TRUE, TRUE);
     }
+    tabpage_move_disallowed--;
 }
 
 /*

src/globals.h

@@ -792,8 +792,9 @@ EXTERN int	is_mac_terminal INIT(= FALSE);  // recognized Terminal.app
 #endif
 
 EXTERN int	autocmd_busy INIT(= FALSE);	// Is apply_autocmds() busy?
-EXTERN int	autocmd_no_enter INIT(= FALSE); // *Enter autocmds disabled
-EXTERN int	autocmd_no_leave INIT(= FALSE); // *Leave autocmds disabled
+EXTERN int	autocmd_no_enter INIT(= FALSE); // Buf/WinEnter autocmds disabled
+EXTERN int	autocmd_no_leave INIT(= FALSE); // Buf/WinLeave autocmds disabled
+EXTERN int	tabpage_move_disallowed INIT(= FALSE);  // moving tabpages around disallowed
 
 EXTERN int	modified_was_set;		// did ":set modified"
 EXTERN int	did_filetype INIT(= FALSE);	// FileType event found

src/testdir/test_tabpage.vim

@@ -903,4 +903,23 @@ func Test_tabpage_last_line()
   bwipe!
 endfunc
 
+" this was causing an endless loop
+func Test_tabpage_drop_tabmove()
+  augroup TestTabpageTabmove
+    au!
+    autocmd! TabEnter * :if tabpagenr() > 1 | tabmove - | endif
+  augroup end
+  $tab drop XTab_99.log
+  $tab drop XTab_98.log
+  $tab drop XTab_97.log
+
+  autocmd! TestTabpageTabmove
+  augroup! TestTabpageTabmove
+
+  " clean up
+  bwipe!
+  bwipe!
+  bwipe!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2168,
 /**/
     2167,
 /**/

src/window.c

@@ -4970,6 +4970,9 @@ tabpage_move(int nr)
     if (first_tabpage->tp_next == NULL)
 	return;
 
+    if (tabpage_move_disallowed)
+	return;
+
     for (tp = first_tabpage; tp->tp_next != NULL && n < nr; tp = tp->tp_next)
 	++n;