The Nix Hour

Currently Playing: The Nix Hour #32 [extending nixpkgs lib and Nix builtins, Nix plugins]

The Nix Hour is an open beginner-oriented Q&A-style lecture on Nix, where you can bring your questions and we’ll answer them with more context, examples, alternatives, tradeoffs and related topics. Files from this session: https://github.com/tweag/nix-hour/tree/master/32 Jitsi Meeting to ask questions directly: https://meet.jit.si/nix-hour Matrix room for questions, feedback and notifications: https://matrix.to/#/%23nix-hour:matrix.org Issue tracker for asynchronous questions: https://github.com/tweag/nix-hour/issues Previous sessions playlist: https://www.youtube.com/playlist?list=PLyzwHTVJlRc8yjlx4VR4LU5A5O44og9in For more information and updates, check out https://discourse.nixos.org/t/the-nix-hour-a-weekly-nix-qa-lecture-by-tweag/22767 00:00 Intro 00:47 Q: How to extend nixpkgs.lib or builtins 01:28 Simple example, adding new fetcher to nixpkgs lib 02:26 lib.extend: overlay system for lib 03:14 Aside: evaluating function with all default args from cli 03:54 Why we can't use //, injecting new lib into NixOS module 06:49 Extending builtins by redefining the name builtins 08:32 builtins.scopedImport 10:38 Dangers and usecases of scopedImport 13:33 Adding builtins using Nix plugins 16:25 Adding custom fetcher with nixpkgs overlays, pkgs.extend, pkgs.appendOverlays 17:58 When use self and super or final and prev in overlays 19:34 Self-refferential packages using makeOverridable 22:16 Recursion using overrides 24:53 Overriding self-refferential derivation, why use super only on top level of the overlay 27:43 Looking for Nix plugins 29:53 Trying Nix plugin from nix-doc project 32:54 Overriding nix as a dependency for a plugin 37:20 aside: Evaluating NixOS config 40:50 Debugging dependency override 49:27 Using user's nix.conf 53:20 Exposing a value from inside NixOS module system 56:10 Testing final nix-doc configuration 58:55 Out of time