CURLOPT_SSLVERSION: C++20 deprecation warning when values of two enums are combined

[mkauf]

I did this

C++20 compilers emit a deprecation warning if values from two different enums are combined with a bitwise operation. This may happen when using CURLOPT_SSLVERSION.

Example program:

#include <curl/curl.h>

int main(void)
{
  CURL *curl = curl_easy_init();
  curl_easy_setopt(curl, CURLOPT_SSLVERSION, CURL_SSLVERSION_TLSv1_2 | CURL_SSLVERSION_MAX_TLSv1_2);
  return 0;
}

g++:

$ g++ -std=c++20 -Wall -Icurl-inst/include -Lcurl-inst/lib simplessl.cpp  -lcurl
In file included from simplessl.cpp:1:
simplessl.cpp: In function ‘int main()’:
simplessl.cpp:6:70: warning: bitwise operation between different enumeration types ‘<unnamed enum>’ and ‘<unnamed enum>’ is deprecated [-Wdeprecated-enum-enum-conversion]
    6 |   curl_easy_setopt(curl, CURLOPT_SSLVERSION, CURL_SSLVERSION_TLSv1_2 | CURL_SSLVERSION_MAX_TLSv1_2);
      |                                              ~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
curl-inst/include/curl/curl.h:3244:72: note: in definition of macro ‘curl_easy_setopt’
 3244 | #define curl_easy_setopt(handle,opt,param) curl_easy_setopt(handle,opt,param)
      |                                                                        ^~~~~

clang++:

$ clang++ -std=c++20 -Wall -Icurl-inst/include -Lcurl-inst/lib simplessl.cpp  -lcurl
simplessl.cpp:6:70: warning: bitwise operation between different enumeration types ('(unnamed enum at curl-inst/include/curl/curl.h:2321:1)' and '(unnamed enum at curl-inst/include/curl/curl.h:2334:1)') is deprecated [-Wdeprecated-anon-enum-enum-conversion]
    6 |   curl_easy_setopt(curl, CURLOPT_SSLVERSION, CURL_SSLVERSION_TLSv1_2 | CURL_SSLVERSION_MAX_TLSv1_2);
      |                                              ~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~
curl-inst/include/curl/curl.h:3244:72: note: expanded from macro 'curl_easy_setopt'
 3244 | #define curl_easy_setopt(handle,opt,param) curl_easy_setopt(handle,opt,param)
      |                                                                        ^~~~~
1 warning generated.

Possible solutions:

• define all values for CURLOPT_SSLVERSION in the same enum
• add example code to the documentation at https://curl.se/libcurl/c/CURLOPT_SSLVERSION.html that demonstrates how to avoid the compiler warning
• ... ?

I expected the following

No compiler warning.

curl/libcurl version

curl master

operating system

Fedora Linux 39

[mkauf]

I have updated the issue, the warning is also generated in C++20 mode (but not in C++17 mode).