void assertCanExtractShardKeyFromDocs(OperationContext* opCtx,
                                      const NamespaceString& nss,
                                      std::vector<InsertStatement>::const_iterator begin,
                                      std::vector<InsertStatement>::const_iterator end) {
    const auto metadata = CollectionShardingRuntime::get(opCtx, nss)->getCurrentMetadataIfKnown();
    // A user can manually create a 'db.system.resharding.' collection that isn't guaranteed to be
    // sharded outside of running reshardCollection.
    uassert(ErrorCodes::NamespaceNotSharded,
            str::stream() << "Temporary resharding collection " << nss.toString()
                          << " is not sharded",
            metadata && metadata->isSharded());

    ...
}