Output of awesome --version:

awesome v4.3 (Too long)
• Compiled against Lua 5.3.6 (running with Lua 5.3)
• D-Bus support: ✔
• execinfo support: ✔
• xcb-randr version: 1.6
• LGI version: 0.9.2

How to reproduce the issue:

Define a custom keyboard layout in /usr/share/X11/xkb/symbols/custom and add it as a variant in /usr/share/X11/rules/{base,evdev}.{lst,xml}. (This is on arch linux)
Then use that layout e.g. with setxkbmap -layout custom,de -variant mycustomlayoutname,nodeadkeys.

Also have the awful.widget.keyboardlayout() active.

Actual result:

When the custom layout is active, the widget shows de(nodeadkeys) and when that layout is actually active, the widget shows nothing.

Expected result:

The widget shows custom(mycustomlayoutname), when the custom layout is active and de(nodeadkeys) when the predefined layout is active.

I choose to create a variant in the custom xkb layout, because that already exists in the .xml and .lst of xkeyboard-config, just with no variants. Cf. https://gitlab.freedesktop.org/xkeyboard-config/xkeyboard-config/-/blob/master/rules/base.xml#L6867-6874

Adding ["custom"] = true, in keyboardlayout.xkeyboard_country_code is enough to solve this problem for me, but I think when a layout can not be found, there should at least be some kind of placeholder text and the order of the layouts should not be affected as described above.