nixredo/nixredo-gc

#!/bin/sh
[ "${S+x}" = x ] || { printf "Set S to the root location of your source tree\n"; exit 127; }
[ "${NIXREDO_ROOT+x}" = x ] || { printf "$0 only runs for private a nix store. Set NIXREDO_ROOT to a non-empty value\n"; exit 127; }

# Work around broken GCROOT support in local stores
# Add a fake gcroot which points to /nix/store/... instead of <local/store>/nix/store
# Remove fake roots after gc
roots=
mkdir -p "${NIXREDO_ROOT}/nix/var/nix/gcroots/auto"
for f in $(@find@ "$S" -path "${NIXREDO_ROOT}" -prune -o -type l -print) ; do
    p=$(realpath "$f")
    if [ "${p#${NIXREDO_ROOT}}" != "$p" ]; then
        gcroot=$(mktemp -u -p "${NIXREDO_ROOT}/nix/var/nix/gcroots/auto")
        ln -s "${p#${NIXREDO_ROOT}}" "$gcroot"
        roots="${roots} ${gcroot}"
    fi
done

nix-store --store "${NIXREDO_ROOT}" --gc
rm -rf -- "${NIXREDO_ROOT}/tmp"

for f in $roots; do
    rm -- "$f"
done