resolve_sync_destinations() {
    # destinations_ref is a nameref output filled by resolve_config_array.
    # shellcheck disable=SC2034
    local -n destinations_ref="$1"; shift
    local sync_decl

    # A list of rsync destinations is inherently a list, and the only
    # unambiguous spelling is a Bash array: SYNC_DESTINATIONS=( '/path/with
    # spaces/' ) preserves embedded spaces, whereas a scalar string would be
    # word-split (e.g. "/path/with spaces/" -> two broken destinations passed
    # to rsync). So we reject scalar declarations outright instead of silently
    # word-splitting them. (TAR_OPTS deliberately keeps scalar word-splitting:
    # turning "-c -v" into separate options is the desired behaviour there.)
    #
    # declare -p fails only when SYNC_DESTINATIONS was never set; that is a
    # legitimate "unset" case handled by the || true below, so we skip the
    # array-vs-scalar check entirely when the variable does not exist.
    if sync_decl=$(declare -p SYNC_DESTINATIONS 2>/dev/null); then
        case "$sync_decl" in
            declare\ -a*) ;;
            *)
                config_error \
                    'SYNC_DESTINATIONS must be an array, e.g. SYNC_DESTINATIONS=( '\''dest1'\'' '\''dest2'\'' )'
                return 1
                ;;
        esac
    fi

    # Parse SYNC_DESTINATIONS (always an array at this point) via the shared
    # config-array helper. Unlike TAR_OPTS there is no default: an unset or
    # empty value simply yields an empty destinations array for callers to
    # validate. The helper returns non-zero when SYNC_DESTINATIONS was never
    # declared; we ignore that (|| true) since the already-empty array is
    # exactly the desired result, and the bare non-zero return would otherwise
    # trip set -e.
    resolve_config_array SYNC_DESTINATIONS destinations_ref || true
}

sync_dist() {
    local destination
    local -a rsync_args=(-av)
    local -a sync_destinations=()

    resolve_sync_destinations sync_destinations

    if [ "$SYNC_DELETE" = yes ]; then
        rsync_args+=(--delete)
    fi

    for destination in "${sync_destinations[@]}"; do
        log_info "Syncing $DIST_DIR/ to $destination"
        rsync "${rsync_args[@]}" "$DIST_DIR/" "$destination"
    done
}