The Nix Hour

Currently Playing: The Nix Hour #1 [nixcon, reviewing a PR, debugging and tracing Nix evaluation]

This was the first public Nix Hour, hosted by Silvan Mosberger on 2022-10-22 at Nixcon 2022 titled QA Nix Lecture: https://talks.nixcon.org/nixcon-2022/talk/G3DUDG/ The Nix Hour is a weekly beginner-oriented improvised 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. The Nix hour happens every week, is open to the public and is recorded and uploaded to the Tweag YouTube channel. For more info check out https://discourse.nixos.org/t/the-nix-hour-a-weekly-nix-qa-lecture-by-tweag/22767 This week the following topics were covered: 0:00 Initial look at PR 186314 2:35 Markdown documentation in NixOS options 3:05 Systemd unit types and index manpage 4:14 Another look at the PR 6:04 Pattern for handling enumerations 8:03 lib.partition for splitting a list of values into two 10:05 lib.groupBy for splitting a list of values into more subsets 12:30 Following lib.groupBy with a lib.mapAttrs 13:22 Trying to figure out the evaluation error without reading the error message 14:53 Adding tracing using lib.debug.traceSeq 16:49 nix-instantiate flags relating to lazy/strict evaluation 17:56 Realizing the problem, missing --strict with --json 18:20 nix eval strictness 19:09 Setup to demonstrate problem with nix eval strictness compared to nix-instantiate 20:24 nix repl derivation output 22:00 Demonstrating problem with nix eval strictness compared to nix-instantiate 24:12 Using the GitHub CLI to check out PR 186314 25:13 Trying to do a "quick" refactoring using lib.groupBy and the enum handling pattern from earlier 32:27 How to find documentation for nixpkgs library functions 33:49 Except for Nix builtin functions re-exported from the nixpkgs library 34:38 How to find documentation for Nix builtin functions 35:16 nix repl :doc command for Nix builtin function docs 35:51 Starting a failed attempt at trying to add documentation to re-exported builtin functions 36:56 Trying out the Nix debugger 38:55 Working around a problem in the Nix debugger relating to builtins.tryEval 40:11 Inspecting variables in the error 40:32 Changing to another trace in the stack 41:45 Resuming the failed attempt at trying to add documentation for re-exported builtin functions 43:02 Trying to use the doc Makefile for more incremental builds 46:59 Looking closer at lib.debug 50:45 Trying out lib.generators.toPretty 51:40 Looking at builtins.seq and builtins.deepSeq 53:53 Looking at the implementation of builtins.seq 55:26 The strictness of attribute keys and list sizes