Handle invalid frame_or_window slots in tty input events (Bug#78966)

* src/frame.c (make_terminal_frame): Initialize terminal's
top_frame slot if it has not been set up yet (Bug#78966).
* src/keyboard.c (kbd_buffer_get_event): Do not assume that the
event's frame_or_window slot always produces a valid frame
(Bug#78966).
(tty_read_avail_input): Try to make sure that the input event we
create has a valid frame_or_window slot (Bug#78966).  Add assertion
to that purpose.

2 files changed, 34 insertions, 10 deletions

diff --git a/src/frame.c b/src/frame.c
index 95fcb9ca7ff..70e200d9219 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -1449,6 +1449,15 @@ make_terminal_frame (struct terminal *terminal, Lisp_Object parent,
   FRAME_BACKGROUND_PIXEL (f) = FACE_TTY_DEFAULT_BG_COLOR;
 #endif /* not MSDOS */
 
+  struct tty_display_info *tty = terminal->display_info.tty;
+
+  if (NILP (tty->top_frame))
+    /* If this frame's terminal's top frame has not been set up yet,
+       make the new frame its top frame so the top frame has been set up
+       before the first do_switch_frame on this terminal happens.  See
+       Bug#78966.  */
+    tty->top_frame = frame;
+
 #ifdef HAVE_WINDOW_SYSTEM
   f->vertical_scroll_bar_type = vertical_scroll_bar_none;
   f->horizontal_scroll_bars = false;
diff --git a/src/keyboard.c b/src/keyboard.c
index fcb66f4c58a..b389d98feaa 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -4281,22 +4281,29 @@ kbd_buffer_get_event (KBOARD **kbp,
         break;
       default:
         {
-          /* If this event is on a different frame, return a
-             switch-frame this time, and leave the event in the queue
-             for next time.  */
           Lisp_Object frame;
           Lisp_Object focus;
 
+          /* It's not safe to assume that the following will always
+             produce a valid, live frame (Bug#78966).  */
           frame = event->ie.frame_or_window;
           if (CONSP (frame))
             frame = XCAR (frame);
           else if (WINDOWP (frame))
             frame = WINDOW_FRAME (XWINDOW (frame));
 
-          focus = FRAME_FOCUS_FRAME (XFRAME (frame));
-          if (! NILP (focus))
-            frame = focus;
+          /* If the input focus of this frame is on another frame,
+             continue with that frame.  */
+          if (FRAMEP (frame))
+            {
+              focus = FRAME_FOCUS_FRAME (XFRAME (frame));
+              if (! NILP (focus))
+                frame = focus;
+            }
 
+          /* If this event is on a different frame, return a
+             switch-frame this time, and leave the event in the queue
+             for next time.  */
           if (!EQ (frame, internal_last_event_frame)
               && !EQ (frame, selected_frame))
             obj = make_lispy_switch_frame (frame);
@@ -8245,13 +8252,21 @@ tty_read_avail_input (struct terminal *terminal,
          value of selected_frame is not reliable here, redisplay tends
          to temporarily change it.  However, if the selected frame is a
          child frame, don't do that since it will cause switch frame
-         events to switch to the root frame instead.  */
-      if (FRAME_PARENT_FRAME (XFRAME (selected_frame))
-          && (root_frame (XFRAME (selected_frame))
-              == XFRAME (tty->top_frame)))
+         events to switch to the root frame instead.  If the tty's top
+         frame has not been set up yet, always use the selected frame
+         (Bug#78966).  */
+      if (!FRAMEP (tty->top_frame)
+          || (FRAME_PARENT_FRAME (XFRAME (selected_frame))
+              && (root_frame (XFRAME (selected_frame))
+                  == XFRAME (tty->top_frame))))
         buf.frame_or_window = selected_frame;
       else
         buf.frame_or_window = tty->top_frame;
+
+      /* If neither the selected frame nor the top frame were set,
+         something must have gone really wrong.  */
+      eassert (FRAMEP (buf.frame_or_window));
+
       buf.arg = Qnil;
 
       kbd_buffer_store_event (&buf);