[PATCH 1/1] Cygwin: console: Maintain EXTENDED_FLAGS state

[Mitchell Hentges <mhentges@mozilla.com>]

As well-described over in this post [1], it's possible for
the active console mode to be impossible to correctly determine.
Specifically, if ENABLE_EXTENDED_FLAGS is at any point unset,
then the flags it's associated with (ENABLE_INSERT_MODE,
ENABLE_QUICK_EDIT_MODE) will no longer be discoverable - they'll
always show up as unset, regardless of real console state.

It's not possible to work around this by setting
ENABLE_EXTENDED_FLAGS once then re-querying, because setting
ENABLE_EXTENDED_FLAGS on it's own will *disable* its related
flags.

Anyways, to avoid this case, all programs doing SetConsoleMode()
must be good community citizens and carefully maintain its state.
Unfortunately, we're accidentally stepping on this in
fhandler_console::set_input_mode().

This patch solves this by carrying forward ENABLED_EXTENDED_FLAGS
and friends in the only place where it had been ignoring it.
Since the previous behaviour of leaving all three flags unset would
essentially maintain their existing state (except for the footgun
being worked around here), *adding* the carry-over of the flags now
should not alter console behaviour.
---
 winsup/cygwin/fhandler_console.cc | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/winsup/cygwin/fhandler_console.cc b/winsup/cygwin/fhandler_console.cc
index 7a1a45bc1..b2554c3ba 100644
--- a/winsup/cygwin/fhandler_console.cc
+++ b/winsup/cygwin/fhandler_console.cc
@@ -458,16 +458,18 @@ void
 fhandler_console::set_input_mode (tty::cons_mode m, const termios *t,
 				  const handle_set_t *p)
 {
-  DWORD flags = 0, oflags;
+  DWORD oflags;
   WaitForSingleObject (p->input_mutex, mutex_timeout);
   GetConsoleMode (p->input_handle, &oflags);
+  DWORD flags = oflags
+      & (ENABLE_EXTENDED_FLAGS | ENABLE_INSERT_MODE | ENABLE_QUICK_EDIT_MODE);
   switch (m)
     {
     case tty::restore:
-      flags = ENABLE_ECHO_INPUT | ENABLE_LINE_INPUT | ENABLE_PROCESSED_INPUT;
+      flags |= ENABLE_ECHO_INPUT | ENABLE_LINE_INPUT | ENABLE_PROCESSED_INPUT;
       break;
     case tty::cygwin:
-      flags = ENABLE_WINDOW_INPUT;
+      flags |= ENABLE_WINDOW_INPUT;
       if (wincap.has_con_24bit_colors () && !con_is_legacy)
 	flags |= ENABLE_VIRTUAL_TERMINAL_INPUT;
       else
-- 
2.35.1