I see. The "problem" comes from this link :
/usr/share/webapps/dokuwiki/lib/plugins -> ../../../../../../var/lib/dokuwiki/plugins
I think this is not how DokuWiki is supposed to be installed. I've never seen that before. Plugins should really be in /usr/share/webapps/dokuwiki/lib/plugins with the rest of DokuWiki.
For most plugins, this not a problem, because dokuwiki is already loaded and DOKU_INC is already defined as /usr/share/webapps/dokuwiki. When needed, theses plugins use DOKU_INC/lib/plugins/foo/bar (which in this case is/usr/share/webapps/dokuwiki/plugins/foo/bar), the symlink does its job, and everything is ok.
What's the better way? Is there a global variable set somewhere that defines docuwiki's root dir?
godiag/fetch.php is called directly, (
<img class="godiagimg" src="/lib/plugins/godiag/fetch.php?f=fcdb5d6c5589e00fbd979ba137d958a7&t=png" alt="go diagram">
), without DW beeing loaded (and DOKU_INC set). So it has to guess. Because of the symlink however, its guess is wrong and it ends up wirh /var/lib instead of /usr/share/webapps/dokuwiki.
So, no variable defined that can be used. I'm afraid you have no choice but manually modify godiag/fetch.php and do what you already have done, define DOKU_INC as /usr/share/webapps/dokuwiki
Of course, this is a bug a should be reported. I think it is a pacman bug. If @andi (DW lead dev) happens to read this thread, he would probably confirm that this not to be considered a godiag bug.