CDRIVER-4010 document let option for aggregate command

Author: rcsanchez97

build/generate-opts.py

@@ -321,7 +321,7 @@ def __init__(self, items, **defaults):
         collation_option,
         server_option,
         ('batchSize', {'type': 'int32_t', 'help': 'An ``int32`` representing number of documents requested to be returned on each call to :symbol:`mongoc_cursor_next`', 'check_set': True}),
-        ('let', {'type': 'bson_t', 'help': 'A BSON document consisting of any number of parameter names, each followed by definitions of constants in the MQL Aggregate Expression language'})
+        ('let', {'type': 'document', 'help': 'A BSON document consisting of any number of parameter names, each followed by definitions of constants in the MQL Aggregate Expression language'})
     ])),
 
     ('mongoc_find_and_modify_appended_opts_t', Struct([

src/libmongoc/src/mongoc/mongoc-opts.c

@@ -1885,7 +1885,7 @@ _mongoc_aggregate_opts_parse (
    mongoc_aggregate_opts->serverId = 0;
    mongoc_aggregate_opts->batchSize = 0;
    mongoc_aggregate_opts->batchSize_is_set = false;
-   mongoc_aggregate_opts->let = NULL;
+   bson_init (&mongoc_aggregate_opts->let);
    bson_init (&mongoc_aggregate_opts->extra);
 
    if (!opts) {
@@ -1969,7 +1969,7 @@ _mongoc_aggregate_opts_parse (
          mongoc_aggregate_opts->batchSize_is_set = true;
       }
       else if (!strcmp (bson_iter_key (&iter), "let")) {
-         if (!_mongoc_convert_bson_t (
+         if (!_mongoc_convert_document (
                client,
                &iter,
                &mongoc_aggregate_opts->let,
@@ -2003,6 +2003,7 @@ _mongoc_aggregate_opts_cleanup (mongoc_aggregate_opts_t *mongoc_aggregate_opts)
       mongoc_write_concern_destroy (mongoc_aggregate_opts->writeConcern);
    }
    bson_destroy (&mongoc_aggregate_opts->collation);
+   bson_destroy (&mongoc_aggregate_opts->let);
    bson_destroy (&mongoc_aggregate_opts->extra);
 }