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wiki/notebook/tools.nix.flakes.org
Gabriel Arazas 732ef34ca8 Update notebook as of 2021-10-09 
Welp, I rarely take notes nowadays due to more specialized work and
stuff. Though, I should have more incentives for writing. In other
words, I'm just lazy. ;p

More free-thinking morning sessions should be done soon.
2021-10-09 18:14:46 +08:00

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Nix flakes

As of 2021-06-30, the version used for this note is at v2.3 so it needs to be invoked with the unstable version.

  • similar to Guix channels
  • a collection of packages and functions while making it easy to configure Nix declaratively
  • replaces the traditional Nix channels since fully reproducing an environment with Nix requires special care in practice; it isn't fully reproducible in practice such as the inclusion of Nix paths embedded in environment variables and access to arbitrary files; plus, there's no standard way of composing projects with Nix
  • as of 2021-06-30, this is on the unstable version of the Nix package manager and needs some additional configuration

why flakes?

  • provides a structure for discoverability
  • makes 100% reproducibility a little easier with Nix
  • in case you're using NixOS, it also provides an easier way to extend it with third-party custom modules

Here's an example to interact with a flake. It will show the entire outputs of a flake as well as the normalized version of the flake object.

#! nix-shell -i bash -p nixUnstable
nix --experimental-features 'nix-command flakes' flake show <<flake-sample-object()>> | sed -e "s/\x1b\[.\{1,5\}m//g"
github:edolstra/dwarffs/f691e2c991e75edb22836f1dbe632c40324215c5
├───checks
│   ├───aarch64-linux
│   │   ├───build: derivation 'dwarffs-0.1.20210121.f691e2c'
│   │   └───test: derivation 'vm-test-run-unnamed'
│   ├───i686-linux
│   │   ├───build: derivation 'dwarffs-0.1.20210121.f691e2c'
│   │   └───test: derivation 'vm-test-run-unnamed'
│   └───x86_64-linux
│       ├───build: derivation 'dwarffs-0.1.20210121.f691e2c'
│       └───test: derivation 'vm-test-run-unnamed'
├───defaultPackage
│   ├───aarch64-linux: package 'dwarffs-0.1.20210121.f691e2c'
│   ├───i686-linux: package 'dwarffs-0.1.20210121.f691e2c'
│   └───x86_64-linux: package 'dwarffs-0.1.20210121.f691e2c'
├───nixosModules
│   └───dwarffs: NixOS module
└───overlay: Nixpkgs overlay

Let's build from one of the outputs of call_flake-sample-object().

#! nix-shell -i bash -p nixUnstable
nix --experimental-features 'nix-command flakes' build 'github:edolstra/dwarffs#checks.aarch64-linux.build'

nix --experimental-features 'nix-command flakes' shell 'github:edolstra/dwarffs' --command dwarffs --version
fusermount version: 2.9.9

For full reproducibility, you can refer to specific point of a flake (e.g., commit).

To easily get a pinned URL, you can run flake metadata subcommand.

#! nix-shell -i bash -p nixUnstable
nix --experimental-features 'nix-command flakes' flake metadata 'github:edolstra/dwarffs' | sed -e "s/\x1b\[.\{1,5\}m//g"
Resolved URL:  github:edolstra/dwarffs
Locked URL:    github:edolstra/dwarffs/f691e2c991e75edb22836f1dbe632c40324215c5
Description:   A filesystem that fetches DWARF debug info from the Internet on demand
Path:          /nix/store/769s05vjydmc2lcf6b02az28wsa9ixh1-source
Revision:      f691e2c991e75edb22836f1dbe632c40324215c5
Last modified: 2021-01-21 22:41:26
Inputs:
├───nix: github:NixOS/nix/6254b1f5d298ff73127d7b0f0da48f142bdc753c
│   ├───lowdown-src: github:kristapsdz/lowdown/1705b4a26fbf065d9574dce47a94e8c7c79e052f
│   └───nixpkgs: github:NixOS/nixpkgs/ad0d20345219790533ebe06571f82ed6b034db31
└───nixpkgs follows input 'nix/nixpkgs'

#! nix-shell -i bash -p nixUnstable
nix --experimental-features 'nix-command flakes' shell github:edolstra/dwarffs/f691e2c991e75edb22836f1dbe632c40324215c5 --command dwarffs --version
fusermount version: 2.9.9