Function get_message_interface_version 

pub unsafe fn get_message_interface_version(
    callback: retro_environment_t,
) -> u32

The returned value is the API version number of the message interface supported by the frontend. If the underlying callback failed, API version is assumed to be 0.

In legacy code, messages may be displayed in an implementation-specific manner by passing a struct of type retro_message to set_message. This may be still be done regardless of the message interface version.

If version is >= 1 however, messages may instead be displayed by calling set_message_ext. This allows the core to specify message logging level, priority and destination (OSD, logging interface or both).