Another excellent code font is [Hack](https://sourcefoundry.org/hack/) (GitHub: [source-foundry/Hack](https://github.com/source-foundry/Hack)), which has its roots in DejaVu Sans Mono / Bitstream Vera Sans Mono.
Hack has a higher underscore position and so may not be affected by this geany bug.
I have released [HackSlash](https://github.com/ashjoubert/HackSlash), a variant of the Hack typeface with forward slashed zero alternate glyphs from the [alt-hack](https://github.com/source-foundry/alt-hack) library of alternative glyphs for Hack.