Getting these compiler warnings on mingw-w64. It still works but would be nice to fix.
mingw-w64 4.9.3
c:/Rtools/mingw_64/bin/gcc -I"C:/PROGRA~1/R/R-34~1.3/include" -DNDEBUG -I../windows/openssl-1.0.2h/include -I. -Ijsonsl -Ibson -Imongoc -DBSON_COMPILATION -DMONGOC_COMPILATION -DMONGOC_HAVE_SASL_CLIENT_DONE -D__USE_MINGW_ANSI_STDIO -Wno-unused-value -Wno-unused-variable -Wno-unused-but-set-variable -Wno-implicit-function-declaration -Wno-format -O2 -Wall -std=gnu99 -mtune=generic -c mongoc/mongoc-sspi.c -o mongoc/mongoc-sspi.o mongoc/mongoc-sspi.c: In function '_mongoc_sspi_auth_sspi_client_unwrap': mongoc/mongoc-sspi.c:363:59: warning: passing argument 4 of 'DecryptMessage' from incompatible pointer type status = DecryptMessage (&state->ctx, &wrapBufDesc, 0, &state->qop); ^ In file included from mongoc/mongoc-sspi-private.h:34:0, from mongoc/mongoc-sspi.c:29: C:/Rtools/mingw_64/x86_64-w64-mingw32/include/sspi.h:721:26: note: expected 'long unsigned int *' but argument is of type 'int *' SECURITY_STATUS WINAPI DecryptMessage(PCtxtHandle phContext,PSecBufferDesc pMessage,unsigned __LONG32 MessageSeqNo,unsigned __LONG32 *pfQOP); ^ c:/Rtools/mingw_64/bin/gcc -I"C:/PROGRA~1/R/R-34~1.3/include" -DNDEBUG -I../windows/openssl-1.0.2h/include -I. -Ijsonsl -Ibson -Imongoc -DBSON_COMPILATION -DMONGOC_COMPILATION -DMONGOC_HAVE_SASL_CLIENT_DONE -D__USE_MINGW_ANSI_STDIO -Wno-unused-value -Wno-unused-variable -Wno-unused-but-set-variable -Wno-implicit-function-declaration -Wno-format -O2 -Wall -std=gnu99 -mtune=generic -c mongoc/mongoc-cluster-sspi.c -o mongoc/mongoc-cluster-sspi.o mongoc/mongoc-cluster-sspi.c: In function '_mongoc_cluster_auth_node_sspi': mongoc/mongoc-cluster-sspi.c:172:59: warning: pointer targets in passing argument 2 of '_mongoc_sspi_auth_sspi_client_step' differ in signedness [-Wpointer-sign] res = _mongoc_sspi_auth_sspi_client_step (state, buf); ^ In file included from mongoc/mongoc-cluster-sspi.c:24:0: mongoc/mongoc-sspi-private.h:70:1: note: expected 'SEC_CHAR *' but argument is of type 'uint8_t *' _mongoc_sspi_auth_sspi_client_step (mongoc_sspi_client_state_t *state, ^ mongoc/mongoc-cluster-sspi.c:178:61: warning: pointer targets in passing argument 2 of '_mongoc_sspi_auth_sspi_client_unwrap' differ in signedness [-Wpointer-sign] res = _mongoc_sspi_auth_sspi_client_unwrap (state, buf); ^ In file included from mongoc/mongoc-cluster-sspi.c:24:0: mongoc/mongoc-sspi-private.h:74:1: note: expected 'SEC_CHAR *' but argument is of type 'uint8_t *' _mongoc_sspi_auth_sspi_client_unwrap (mongoc_sspi_client_state_t *state, ^ mongoc/mongoc-cluster-sspi.c:181:30: warning: passing argument 3 of '_mongoc_sspi_auth_sspi_client_wrap' discards 'const' qualifier from pointer target type state, response, tmp_creds, tmp_creds_len, 0); ^ In file included from mongoc/mongoc-cluster-sspi.c:24:0: mongoc/mongoc-sspi-private.h:78:1: note: expected 'SEC_CHAR *' but argument is of type 'const char *' _mongoc_sspi_auth_sspi_client_wrap (mongoc_sspi_client_state_t *state, ^ mongoc/mongoc-cluster-sspi.c:250:14: warning: assignment discards 'const' qualifier from pointer target type tmpstr = bson_iter_utf8 (&iter, &buflen); ^