nixredo/nixredo

#!/bin/sh
exec >&2
[ "${S+x}" = x ] || { printf "Set S to the root location of your source tree\n"; exit 127; }
[ "${NIXREDO_ROOT-x}" != x ] || { printf "Set NIXREDO_ROOT. Set empty to use global nix store\n"; exit 127; }
if [ $# -eq 0 ]; then set -- all; fi

S=$(realpath -s "$S")

if [ "${NIXREDO_ROOT#$S}" != "${NIXREDO_ROOT}" ]; then
    filter=$(realpath -s "${NIXREDO_ROOT}")
else
    filter=
fi

set -e
set -- "$1" "$1" "$1.redo.tmp"
f=$(realpath -s "$1")
out=$(nix -vL --show-trace build ${NIXREDO_ROOT:+--store "$NIXREDO_ROOT"} \
          --option auto-optimise-store true --option substituters daemon \
          --impure --json --no-link \
          --expr " import @buildernix@ { lib = import @libnix@ {}; root =\"$S\"; filter = [ \"$filter\" ]; } \"$f\"" |
          @jq@ -r '.[0].outputs.out')
[ -n "$out" ] || exit 127
rm -rf "$3"
ln -s "${NIXREDO_ROOT+$NIXREDO_ROOT}$out" "$3"
# ln "${NIXREDO_ROOT+$NIXREDO_ROOT/}$out" "$3"
# chmod +w "$3"
# touch "$3"
mv "$3" "$1"