How to Update Single Inputs Within Nix Flakes Without Repinning nixpkgs

Nix utilizes a system of flax files, where inputs and their dependencies are declared. When you need an update for one specific input in your flake without affecting others—especially when avoiding re-pining large repositories like nixpkgs —you can use Nix’s built-in commands to target individual updates selectively.

The Problem: Updating Selective Inputs Without Unnecessary Repositories Refresh

Normally, running the command

nix flake update

will cause all inputs within your flake.lock file—and their transitive dependencies likewise—to be updated to align with what’s in those remote git repositories. While comprehensive updates are generally a good practice for maintaining an up-to-date environment, they can sometimes prove excessive when you need more surgical precision over your flake configuration changes.

The Solution: Targeted Input Updates Using nix flake lock

To perform only the select update necessary without touching all other inputs or triggering a complete repository refresh for heavyweights like Nixpkgs, execute this command to pinpoint just that specific input needing an upgrade:

nix flake lock --update-input <name_of_input>

By doing so you apply changes directly at the point of interest. If multiple inputs require updates in a cascading manner—each dependent on one another like cogs within machinery – chain these commands together as such:

nix flake lock --update-input nixpkgs --update-input <other_dependency> # and so forth...

This method ensures a focused update while maintaining the integrity of your entire setup. It’s an effective way to keep just one component in sync without affecting others or having them all recheck their remote sources unnecessarily, thereby saving time and resources during maintenance operations on Nix flakes.