So I noticed something a bit funny about the MariaDB 10.2 install process, when it comes to header files. It seems there are kinda two competing install processes.
The source code includes a libmariadb/ subdirectory, which is actually (in the git repo) the mariadb-connector-c project as a submodule. This project has its own include/ subdirectory, which contains several header files and some install rules for them in a CMakeLists.txt file.
But the mariadb source also has its own include/ subdirectory, which similarly contains several header files and some install rules for them. In several cases, the install rules for both include/ subdirectories try to install a file with the same name to the same place: this includes at least mysql.h and errmsg.h . You can spot cases like this in the console output by looking for the string 'Up-to-date', which basically seems to be CMake indicating that a file listed for installation already exists and won't be replaced.
AFAICS, at least during our (Fedora's) builds, the libmariadb/include/ subdirectory gets to go first, and then when the include/ subdirectory runs, it doesn't overwrite any file that the libmariadb/include/ subdirectory already installed. But as there are more headers in the include/ subdirectory, you ultimately wind up with a mish-mash of headers installed, some from the libmariadb/ subproject and some from mariadb itself.
This is particularly significant in the case of mysql.h; what actually winds up installed is libmariadb/include/mysql.h , not include/mysql.h . There are some significant differences between the two; for instance, the one from libmariadb/include/ includes mariadb_version.h from the same directory , whereas the mysql.h from include/ includes mysql_version.h from the same directory. libmariadb's mariadb_version.h defines rather fewer things than mariadb's mysql_version.h does. So ultimately, for instance, if you install MariaDB 10.2, then write some code that just does #include mysql.h , then you will have no MYSQL_SERVER_VERSION defined.
This is definitely confusing and ambiguous, and I think it's a straight up bug. I would think that when installing MariaDB itself then we really want to install include/mysql.h , not libmariadb/include/mysql.h .