Comment 3 for bug 1766938

Ah, that assert is in mutter.

$ mkdir ~/xsrc
$ cd ~/xsrc
$ apt-get source libmutter-2-0
$ cd ~
$ apport-retrace -g _usr_bin_gnome-shell.1000.crash
(gdb) bt
...
(gdb) frame 7
#7 0x00007f75c6bb5fbe in standard_pict_format_for_depth (depth=<optimized out>) at x11/iconcache.c:303
303 x11/iconcache.c: No such file or directory.
(gdb) directory xsrc/mutter-3.28.1/src
(gdb) list 291
291 static int
292 standard_pict_format_for_depth (int depth)
293 {
294 switch (depth)
295 {
296 case 1:
297 return PictStandardA1;
298 case 24:
299 return PictStandardRGB24;
300 case 32:
301 return PictStandardARGB32;
302 default:
303 g_assert_not_reached ();
304 }

FWIW, that code was added in https://gitlab.gnome.org/GNOME/mutter/commit/9b903e93e3cd0601b436c55b7cea1fbecf29895f

So... uh... maybe some icon on my system is making it unhappy?

I gather gtk-update-icon-cache is involved?

buildbot@rbb-ubu1804-3:~$ ls -l /usr/share/icons/*/*.cache
-rw-r--r-- 1 root root 35776 Apr 24 14:57 /usr/share/icons/Adwaita/icon-theme.cache
-rw-r--r-- 1 root root 20312 Apr 25 09:40 /usr/share/icons/hicolor/icon-theme.cache
-rw-r--r-- 1 root root 49808 Apr 24 14:39 /usr/share/icons/HighContrast/icon-theme.cache
-rw-r--r-- 1 root root 26816 Apr 24 14:57 /usr/share/icons/Humanity-Dark/icon-theme.cache
-rw-r--r-- 1 root root 327184 Apr 24 14:57 /usr/share/icons/Humanity/icon-theme.cache
-rw-r--r-- 1 root root 628 Apr 24 14:57 /usr/share/icons/LoginIcons/icon-theme.cache
-rw-r--r-- 1 root root 54104 Apr 24 14:57 /usr/share/icons/ubuntu-mono-dark/icon-theme.cache
-rw-r--r-- 1 root root 55040 Apr 24 14:57 /usr/share/icons/ubuntu-mono-light/icon-theme.cache

But now I can't get it to crash anymore.
so maybe I accidentally fixed it by installing some package that updated the icon caches...?

$ grep hicolor /var/log/dpkg.log
...
2018-04-24 14:42:29 status installed hicolor-icon-theme:all 0.17-2
...
2018-04-24 15:33:00 status installed hicolor-icon-theme:all 0.17-2
...
2018-04-25 09:40:43 status installed hicolor-icon-theme:all 0.17-2

Hrmf. My uneducated theory is that an icon cache was corrupt, but is fine now.
Who knows?