nixos/xserver: keyboard compilation relies on the presence of `/bin/sh`

Nixpkgs version

• Unstable (25.11)

Describe the bug

Preface: I was experimenting with impermanence-like setup and mounted /bin, /etc, /lib*, /srv and /usr to tmpfs. Since /etc and /usr are always set as neededForBoot (and therefore were intact), /lib* are used purely for warnings, and /srv is empty, i only blame /bin (and, by extension, /bin/sh).

Bug itself: X server failed to launch. According to the logs (sadly, lost), it failed to compile keyboard layouts with xkbcomp. I don't know exactly, whether Xorg or xkbcomp failed (judging by the command, it was fed from stdin).

Steps to reproduce

1. Remove /bin/sh
2. Run sx dwm

Expected behaviour

Programs should not rely on /bin/sh

Screenshots

No response

Relevant log output

sadly, none

Additional context

Loosely related issue I've found on Arch forums (but you can see there what kinda errors I've seen): https://bbs.archlinux.org/viewtopic.php?id=54015

System metadata

Typing from phone, sry

Notify maintainers

Prolly random, but @quantenzitrone @K900 @trofi

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Start by reproducing the failure with /bin/sh removed and sx dwm, then trace the X server's xkbcomp invocation and determine which command path requires the shell. The issue provides no source file or test location, so the relevant X server or keyboard-compilation entry point must be located first. Done means keyboard compilation and X server startup work without /bin/sh.