On a CentOS 5.7 box, I'm having trouble installing the newest version of the mysql2 gem; it's not finding errmsg.h:
/usr/bin/ruby extconf.rb
checking for rb_thread_blocking_region()... yes
checking for rb_wait_for_single_fd()... no
checking for mysql_query() in -lmysqlclient... yes
checking for mysql.h... no
checking for mysql/mysql.h... yes
checking for errmsg.h... no
-----
errmsg.h is missing. please check your installation of mysql and try again.
-----
*** extconf.rb failed ***
The mysql header files exist at /usr/include/mysql. An older version of the gem exists on the server, so it must have been built successfully at one point.
Note that it fails on a check for mysql.h, but succeeds on mysql/mysql.h. However, it doesn't repeat this for errmsg.h. By this I'm guessing that it's not looking at /usr/include, but I'm not sure.
I've dug into the extconf.rb source code and discovered that it's using the have_header
method to locate the header files. I debugged the execution to find out that it's looking for a relative path of "mysql/errmsg.h". But I haven't found any documentation that explains how it expands that into an absolute path.
Where & how does have_header locate its header files?