currently the notmuch ebuild has a DEPEND like: <dev-libs/xapian-1.3 because with earlier versions of xapian 1.3 notmuch did not work. But $Summary Please change the dependency to xapian so that xapian can be upgraded. Background: the new KDE PIM suiste pased on KF5 uses xapian, too but requires a version >=1.3 so currently notmuch and new KDE PIM cannot be installed at the same time. Blocker. Not tested, but || ( <dev-libs/xapian-1.3 >=dev-libs/xapian-1.3.4 should work.
ping?
At some point I was testing it with xapian-1.3 and it failed tests. But that was correlated with some other dep problem. I'll try again soon. Anyway you could try build it yourself with +test and +debug flags enabled.
I have checked that it fails on 2 tests. It will probably be fixed in next release. I will remove blocker in 0.22. 0.21 doesn't work with xapian 1.3, so closing it as won't fix.
Thanks for you feedback. But I am using it every day for some months now and I did not have a single problem. I did not run any tests though.