mongoc_collection_create_index_with_opts takes a mongoc_index_opt_t parameter. This has the unfortunately consequence that it must be updated as the server changes adds or deprecates index options. It also makes it harder for wrapper drivers to do anything other than implement a similar API.

We'd like a API to just provide a bson_t* for index options and pass it through to the server and make construction of a correct index options document a user responsibility.