It requires media-libs/mutagen to be installed. Installing =media-libs/mutagen-1.41.1 made this bug go away, without needing to recompile nicotine+.
The bug has been closed via the following commit(s): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=064a0f547b24e106202481e5d08796a7b0e53868 commit 064a0f547b24e106202481e5d08796a7b0e53868 Author: Pacho Ramos <pacho@gentoo.org> AuthorDate: 2019-01-12 10:30:51 +0000 Commit: Pacho Ramos <pacho@gentoo.org> CommitDate: 2019-01-12 10:30:51 +0000 net-p2p/nicotine+: Fix deps Closes: https://bugs.gentoo.org/673916 Package-Manager: Portage-2.3.53, Repoman-2.3.12 Signed-off-by: Pacho Ramos <pacho@gentoo.org> net-p2p/nicotine+/nicotine+-1.4.1-r1.ebuild | 32 +++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+)