What is a "code paper"?
One way to get non-traditional research outputs counted in the promotion and tenure process is to create a more conventional output alongside it, such as a data paper describing your dataset. This is not widespread for research code, but the option does exist, and may be valuable for researchers who spend considerable amounts of time and effort contributing to packages and tools that help others conduct research but may not result in publications otherwise.
The Journal of Open Source Software (JOSS) is one option that allows you to submit a short paper alongside a code repository for peer review and publication, which gives you an opportunity to get feedback and suggestions for improvement of your software from reviewers, makes your code more discoverable, and also helps it to be counted towards your research outputs.