TIL:

with import <nixpkgs> { }; someNewTool.overrideDerivation (drv: { src = ./myUrl; })

o/ this lets you use a local copy myUrl of the code for a project (someNewTool could be systrayhelper). the shell can then be used to built it and run tests while keeping the setup nix expressions in the nixpkgs repo.

reading more of node2nix readme, espc Wrapping or patching the code or any of its dependencies was also very educational.

https://nixos.wiki/wiki/Configuration_Collection is another good place for a deepdive into different positbilites of system configuration.