Fix two crashes when a display connection is lost

This fixes errors caused by invalid error traps being left on
the error handler stack if an IO error causes a non-local exit
out of the protected code, and another crash caused by
delete_frame trying to read async input.

* src/eval.c (unwind_to_catch, push_handler_nosignal): Save and
restore the X error handler stack.
* src/lisp.h (struct handler): [HAVE_X_WINDOWS]: New field
`x_error_handler_depth'.

* src/xterm.c (struct x_error_message_stack): Make string a
regular string.
(x_unwind_errors_to): New function.
(x_error_catcher, x_catch_errors_with_handler)
(x_uncatch_errors_after_check, x_uncatch_errors): Update the
stack depth.
(x_check_errors): Stop manually unwinding since unwind_to_catch
now does that for us.
(x_had_errors_p, x_clear_errors): Update for new type of
`string'.
(x_connection_closed): Block input between just before
delete_frame to when the terminal is unlinked.

* src/xterm.h: Update prototypes.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/eval.c b/src/eval.c
index c3be1dc12c8..d4d4a6cfdd8 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1251,6 +1251,13 @@ unwind_to_catch (struct handler *catch, enum nonlocal_exit type,
   set_poll_suppress_count (catch->poll_suppress_count);
   unblock_input_to (catch->interrupt_input_blocked);
 
+#ifdef HAVE_X_WINDOWS
+  /* Restore the X error handler stack.  This is important because
+     otherwise a display disconnect won't unwind the stack of error
+     traps to the right depth.  */
+  x_unwind_errors_to (catch->x_error_handler_depth);
+#endif
+
   do
     {
       /* Unwind the specpdl stack, and then restore the proper set of
@@ -1625,6 +1632,9 @@ push_handler_nosignal (Lisp_Object tag_ch_val, enum handlertype handlertype)
   c->act_rec = get_act_rec (current_thread);
   c->poll_suppress_count = poll_suppress_count;
   c->interrupt_input_blocked = interrupt_input_blocked;
+#ifdef HAVE_X_WINDOWS
+  c->x_error_handler_depth = x_error_message_count;
+#endif
   handlerlist = c;
   return c;
 }