Script to sync the locked revisions your nix flake inputs to those of the system flake (or any other flake)

gnx-syslock.bash

#!/usr/bin/env bash
set -e

# argument handling based on:
# https://stackoverflow.com/a/14203146

POSITIONAL_ARGS=()
# default system flake (adjust according to your needs)
SYSFLAKE="/home/username/sysflake"                                  # <-- adjust here
# default target flake is current directory
TARGET=.

while [[ $# -gt 0 ]]; do
    case $1 in
        -i|--ignore-mismatch)
            IGNORE_MISMATCH=YES
            shift # past argument
            ;;
        -t|--target)
            if [[ -z "$2" ]]; then echo "Target path must be provided after -t"; exit 1; fi
            TARGET="$2"
            shift # past argument
            shift # past value
            ;;
        -s|--sysflake)
            if [[ -z "$2" ]]; then echo "Sysflake path must be provided after -s"; exit 1; fi
            SYSFLAKE="$2"
            shift # past argument
            shift # past value
            ;;
        -*|--*)
            echo "Unknown option $1"
            exit 1
            ;;
        *)
            POSITIONAL_ARGS+=("$1") # save positional arg
            shift # past argument
            ;;
    esac
done

# if no mapping was passed, we default to setting "nixpkgs" to the latest one in my system flake
if [[ -z $POSITIONAL_ARGS ]]; then
    POSITIONAL_ARGS+=("nixpkgs=desktop-linux-nixpkgs-2605")                     # <-- adjust here
fi

set -- "${POSITIONAL_ARGS[@]}" # restore positional parameters

echo "IGNORE_MISMATCH  = ${IGNORE_MISMATCH}"
echo "SYSFLAKE         = ${SYSFLAKE}"
echo "TARGET           = ${TARGET}"

# go through each mapping on the arg list
for MAPPING; do
    SRC="${MAPPING#*=}" # after =
    DST="${MAPPING%=*}" # before =
    # both must be non-emoty
    if [[ (-z $SRC) || (-z $DST) ]]; then
        echo "Invalid mapping syntax, expected dst=src"
        exit 1
    fi
    
    # using § to indicate inputs (similar to the standard # for outputs)
    ORIGINALS_EQUAL=$(jq -n \
        --slurpfile sysflake <(nix flake metadata $SYSFLAKE --json) \
        --slurpfile target <(nix flake metadata $TARGET --json) \
        --arg src $SRC \
        --arg dst $DST \
        '$target[0].locks.nodes[$dst].original == $sysflake[0].locks.nodes[$src].original'
    )
    
    if [[ ($ORIGINALS_EQUAL == false) && (! $IGNORE_MISMATCH) ]]; then
        echo "Input definition of '$TARGET§$DST' doesn't match that of '$SYSFLAKE§$SRC'. This might not be intended and may not work. Ignore this warning using the -i flag."
        exit 1
    fi

    echo "Locking '$TARGET§$DST' to '$SYSFLAKE§$SRC'"
    
    # replace "locked" section in target flake input with that of the sysflake
    # while updating lastModified
    OLD_SYS_METADATA=$(nix flake metadata $TARGET --json)
    echo $OLD_SYS_METADATA | jq \
        --slurpfile sysflake <(nix flake metadata $SYSFLAKE --json) \
        --arg src $SRC \
        --arg dst $DST \
        --argjson timestamp $(date +%s) \
        '.locks.nodes[$dst].locked = $sysflake[0].locks.nodes[$src].locked | .locks.nodes[$dst].locked.lastModified = $timestamp | .locks' \
    > "$TARGET/flake.lock"
done

See https://elektron.work/posts/nix-flake-syslock/ for explanation