The method appendWriteConcernErrorToCmdResponse() is currently only linked into mongos, but is used by a command that is moving to the config server.

It is the only (standalone) function in the file it exists in (sharded_command_processing.

{h,cpp}), and can instead be moved to cluster_commands_common.{h,cpp}

.

If this ticket is done after SERVER-29566, this will make appendWriteConcernErrorToCmdResponse automatically linked into both mongos and mongod.