Subject: Re: bug#31312: Segmentation fault with doom-emacs, NeoTree and Zoom

From: Noam Postavsky <[email-masked]>
Date: Wed, 02 May 2018 08:21:15 -0400

martin rudalics <[email-masked]> writes:

> and the only ways this could cause w != XWINDOW(selected_window)
> before the last call is either !WINDOWP (selected_window) or that
> clear_garbaged_frames or prepare_menu_bars change selected_window.
> Can you find the responsible?

Yes, found it, seems to be a combination of zoom
window-size-change-functions called via prepare_menu_bars and doom
advice on balance-windows.  I got 12 changes of selected_window.  First
hit summarized inline, the rest of the backtraces are attached below.

#0  select_window_1 (window=XIL(0x1601c35), inhibit_point_swap=false) at ../../src/window.c:562
#1  0x00000000004aff15 in select_window (window=XIL(0x1601c35), norecord=XIL(0xc090), inhibit_point_swap=false) at ../../src/window.c:520
#2  0x00000000004b0183 in Fselect_window (window=XIL(0x1601c35), norecord=XIL(0xc090)) at ../../src/window.c:590
#3  0x00000000004beaa7 in Fdelete_window_internal (window=XIL(0x1696c35)) at ../../src/window.c:4667

#79 0x0000000000441b1a in safe_call1 (fn=XIL(0x4a9e6d0), arg=XIL(0x1600c35)) at ../../src/xdisp.c:2644
#80 0x00000000004bb27a in run_window_size_change_functions (frame=XIL(0x1600c35)) at ../../src/window.c:3457
#81 0x0000000000460409 in prepare_menu_bars () at ../../src/xdisp.c:12065
#82 0x0000000000465141 in redisplay_internal () at ../../src/xdisp.c:13937
#83 0x0000000000463c16 in redisplay () at ../../src/xdisp.c:13518

Lisp Backtrace:
[...]
"delete-window" (0xffff9ab0)
[...]
"doom/popup-close" (0xffffa068)
[...]
"doom*popups-save" (0xffffaa00)
[...]
"ad-Advice-balance-windows" (0xffffb530)
"apply" (0xffffb528)
"balance-windows" (0xffffb960)
"let" (0xffffbcc0)
"zoom--update" (0xffffbe10)
[...]
"zoom--handler" (0xffffc928)
"redisplay_internal (C function)" (0x0)

(defun zoom--on ()
  [...]
  (add-hook 'window-size-change-functions #'zoom--handler)

(defun zoom--handler (&optional window-or-frame norecord)
  [...]
    (with-selected-window
      [...]
      (zoom--update))))

(defun zoom--update ()
  "Update the window layout in the current frame."
  (let (;; temporarily disables this mode during resize to avoid infinite
        ;; recursion (probably not needed thanks to the following)
        (zoom-mode nil)
        ;; temporarily disable all (even external) hooks about window
        ;; configuration changes to try to avoid potential flickering since
        ;; `balance-windows' calls them
        (window-configuration-change-hook nil)
        ;; make sure that other windows are resized nicely after resizing the
        ;; selected one
        (window-combination-resize t)
        ;; make sure that the exact same amount of pixels is assigned to all the
        ;; siblings
        (window-resize-pixelwise t))
    ;; start from a balanced layout anyway
    (balance-windows)
    ;; check if the selected window is not ignored
    (unless (zoom--window-ignored-p)
      (zoom--resize)
      (zoom--fix-scroll))))

;; doom/core/core-popups.el:
  (advice-add #'balance-windows :around #'doom*popups-save)

(defun doom*popups-save (orig-fn &rest args)
  "Sets aside all popups before executing the original function, usually to
prevent the popup(s) from messing up the UI (or vice versa)."
  (save-popups! (apply orig-fn args)))

(defmacro save-popups! (&rest body)
  "Sets aside all popups before executing the original function, usually to
prevent the popup(s) from messing up the UI (or vice versa)."
  `(let ((in-popup-p (doom-popup-p))
         (popups (doom-popup-windows))
         (doom-popup-remember-history t)
         (doom-popup-inhibit-autokill t))
     (when popups
       (mapc #'doom/popup-close popups))
     (unwind-protect
         (progn ,@body)
       (when popups
         (let ((origin (selected-window)))
           (doom/popup-restore)
           (unless in-popup-p
             (select-window origin)))))))

diff --git i/src/.gdbinit w/src/.gdbinit
index cc06b2e11c..0ebf07f0f7 100644
--- i/src/.gdbinit
+++ w/src/.gdbinit
@@ -1264,6 +1264,35 @@ commands
 end

+watch selected_window
+set $selwindow_watch = $bpnum
+commands $selwindow_watch
+  bt
+end
+disable $selwindow_watch
+
+# this one never happens, I think
+break xdisp.c:13929 if !WINDOWP(selected_window)
+
+break xdisp.c:13929 if WINDOWP(selected_window)
+commands
+  silent
+  enable $selwindow_watch
+  continue
+end
+set $enable_selwindow_watch = $bpnum
+disable $enable_selwindow_watch
+printf "selected window watch enabler = %d\n", $enable_selwindow_watch
+
+break xdisp.c:13939 if !NILP(w->contents)
+commands
+  silent
+  disable $selwindow_watch
+  continue
+end
+
+break xdisp.c:13939 if NILP(w->contents)
+
 # Put the Python code at the end of .gdbinit so that if GDB does not
 # support Python, GDB will do all the above initializations before
 # reporting an error.