[rekado]

Guix has package transformations, which lets you use different commits or git URIs for a given package definition.

It also doesn't require the definition of a package if all you want is an environment to hack on the code in a git repo. People use `manifest.scm` or `guix.scm` for these purposes.

Guix System services are in fact all built together, but upgrading individual software or services does not require "roll[ing] back the complete Guix system ".

(I want to point out that describing Guix as "a NIH version of Nix" is a symptom of the attitudes that made me almost completely retreat from discussions of software online. It's so grating to deal with dismissive attitudes like that again and again. Sucks all the fun out of hacking.)