bug#31373: 26.1; frame-list-z-order segfaults on initial daemon frame

[Noam Postavsky]

"Basil L. Contovounesios" <contovob@tcd.ie> writes:

> Ah, yes, thank you.  I forgot about --fg-daemon (which I now remembered
> is documented in '(emacs) Initial Options') because it is not mentioned
> in the emacs(1) man page; do you think this option should be added there?

Oh, yes it should be.

>> +        if (XFRAME (frame)->output_method == output_x_window

Also, I noticed that there is FRAME_X_P for this.  I can't find any more
obvious instances of missing this check, although it's hard to tell in
many cases if the frame is really guaranteed to have output_x_window has
the output_method.

>From 5ad7571a59eb744c65a23198729ea2b56155a2c2 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Sun, 6 May 2018 10:07:25 -0400
Subject: [PATCH v2] Don't check non-X frames for z order (Bug#31373)

* src/xfns.c (x_frame_list_z_order): Only use frames with
`output_method' set to `output_x_window'.
---
 src/xfns.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/xfns.c b/src/xfns.c
index 20fe61bffd..863fdefa5f 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -5303,8 +5303,9 @@ x_frame_list_z_order (Display* dpy, Window window)
            /* With a reparenting window manager the parent_desc field
               usually specifies the topmost windows of our frames.
               Otherwise FRAME_OUTER_WINDOW should do.  */
-           if (XFRAME (frame)->output_data.x->parent_desc == children[i]
-               || FRAME_OUTER_WINDOW (XFRAME (frame)) == children[i])
+            if (FRAME_X_P (frame)
+                && (XFRAME (frame)->output_data.x->parent_desc == children[i]
+                    || FRAME_OUTER_WINDOW (XFRAME (frame)) == children[i]))
              frames = Fcons (frame, frames);
        }
 
-- 
2.11.0