Indeed. This is due to libgit2 0.23 breaking some API geany-plugins
uses. Upstream added support for it in
http://git.geany.org/geany-plugins/commit/?id=37aa25a1a4508c3d7559c0a2d00663b9c8d322c6,
and it should be trivial and safe to cherry-pick.
I applied this patch in raspbian stretch-staging* and it fixed the build
for us. So I strongly suspect it will for Debian too. I have not tested
it beyond checking that it built in raspbian stretch-staging.
A debdiff should appear soon under
http://debdiffs.raspbian.org/main/g/geany-plugins/
No intent to NMU in Debian.
* Raspbian stretch-staging is a suite used to import packages (from
Debian stretch), build them and perform some dependency checks before
they move to raspbian stretch.
