If you install some libs with sip with python 3.6 - PyQt5 for example - sip doesn't honor the default sip dir.
But files (for example QtXmlmod.sip) are installed in:
for example /usr/local/share/py-sip/PyQt5/QtXml/QtXmlmod.sip
https://reviews.freebsd.org/D8714 i prepared a versioned sip directory in that review a while ago. Maybe you can pick the proper parts from it if you have time :)
*** This bug has been marked as a duplicate of bug 219641 ***
With the new versions of Qt, there is always an error (see qgis bug 233726#c9)
(In reply to lbartoletti from comment #3)
The issue here is an error in pyqt.mk: in sip there is no _PYQT_VERSION defined, and therefore the sip-file locations line _SIPDIR_REL are broken.
Created attachment 201000 [details]
py-sip fix with PyQt5 as default
This is your patch. I only add a line for reinplace PyQt5 as default (post-install section)
(In reply to lbartoletti from comment #5)
I think something like this should work -- but it will require an exp-run, and some more thinking :)