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Nixos/hm-modules/theme/theme-switch.sh
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2026-07-03 17:31:31 +02:00

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# shellcheck shell=bash
# theme-switch — activate a pre-built Home Manager specialisation.
#
# Expects two variables to be injected by the Nix wrapper:
# baseVariant the variant that is the generation itself (not a
# specialisation), activated via `$gen/activate`.
# availableVariants space-separated list of all variant names (help text).
#
# Standalone usage for testing:
# baseVariant=gruvbox-dark \
# availableVariants="gruvbox-dark gruvbox-light catppuccin-dark catppuccin-light" \
# bash theme-switch.sh <variant>
: "${baseVariant:?theme-switch: baseVariant not set}"
: "${availableVariants:?theme-switch: availableVariants not set}"
set -euo pipefail
variant="${1:-}"
if [ -z "$variant" ]; then
echo "Usage: theme-switch <variant>"
echo "Available: ${availableVariants}"
exit 1
fi
# Resolve the Home Manager *base* generation — the one built by NixOS that
# actually contains the `specialisation/` directory holding every variant's
# activation script.
#
# IMPORTANT: do NOT use `current-home` / the HM profile as the primary
# source. Activating a specialisation repoints those to the specialisation's
# *leaf* generation, which has no `specialisation/` of its own — so after
# switching once, every other variant (and the base) would become unfindable.
# The NixOS-managed `home-manager-«user».service` unit references the base
# generation and only changes on a rebuild.
user="${USER:-$(id -un)}"
gen=""
if unit="$(systemctl cat "home-manager-${user}.service" 2>/dev/null)"; then
gen="$(printf '%s\n' "$unit" | grep -oE '/nix/store/[0-9a-z]+-home-manager-generation' | head -n1)"
fi
# Fallbacks for standalone Home Manager, where the profile symlink / gcroot
# points at the base generation (not a specialisation leaf).
for candidate in \
"${HOME}/.local/state/home-manager/gcroots/current-home" \
"/nix/var/nix/profiles/per-user/${user}/home-manager" \
"${HOME}/.local/state/home-manager/home-manager-generation"
do
[ -n "$gen" ] && break
if [ -e "$candidate" ]; then
gen="$(readlink -e "$candidate")" || gen=""
fi
done
if [ -z "$gen" ]; then
echo "error: could not resolve Home Manager base generation" >&2
exit 1
fi
case "$variant" in
"${baseVariant}")
# Base variant is the generation itself, not a specialisation.
activate="$gen/activate"
;;
*)
activate="$gen/specialisation/$variant/activate"
;;
esac
if [ ! -x "$activate" ]; then
echo "error: variant '$variant' not found at $activate" >&2
echo "Available: ${availableVariants}"
exit 1
fi
echo "Switching theme to $variant..."
exec "$activate"