While implementing support for let in CDRIVER-4198, I realized that there are various differences to how _mongoc_collection_update_or_replace and _mongoc_delete_one_or_many are implemented. Both of those functions are the common helpers for their respective CRUD methods.

A few, but not all, inconsistencies are as follows:

• _mongoc_delete_one_or_many is missing the "collection" prefix found on the update/replace helper.
• The delete_one and delete_many methods pass an initialized bson_t as a limit parameter, which is the used to append individual options for the delete statement and later passed as the opts parameter _mongoc_write_command_init_delete_idl. That document is later destroyed in the corresponding public CRUD method. In _mongoc_collection_update_or_replace, the equivalent structure exists entirely within the helper method.
• _mongoc_delete_one_or_many asserts that the incoming bson_t *reply is empty or null. No such assertion is made in the update helper.
• _mongoc_collection_update_or_replace checks that an explicit write concern is not being used within a transaction, while _mongoc_delete_one_or_many has no such check.
• _mongoc_delete_one_or_many receives extra opts (from mongoc_delete_one_opts_t and mongoc_delete_many_opts_t) and passes those as the cmd_opts parameter to _mongoc_write_command_init_delete_idl. In _mongoc_collection_update_or_replace, the extra opts are used to append options for the update statement and later passed as the opts parameter to _mongoc_write_command_init_update_idl (akin to how the limit document in the delete methods is used).

Of these inconsistencies, I believe only the transaction error checking is relevant to users. The other issues seem mostly internal, but could improve maintainability if addressed.