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diff --git a/users/wpcarro/website/blog/content/english/lets-learn-nix-dotfiles.md b/users/wpcarro/website/blog/content/english/lets-learn-nix-dotfiles.md new file mode 100644 index 000000000000..084fb19e4406 --- /dev/null +++ b/users/wpcarro/website/blog/content/english/lets-learn-nix-dotfiles.md @@ -0,0 +1,401 @@ +--- +title: "Let's Learn Nix: Dotfiles" +date: 2020-03-13T22:23:02Z +draft: true +--- + +## Let's Learn Nix: Dotfiles + +### Dependencies + +Speaking of dependencies, here's what you should know before reading this tutorial. + +- Basic Nix syntax: Nix 1p + +What version of Nix are we using? What version of `<nixpkgs>` are we using? What +operating system are we using? So many variables... + +Cartesian product of all possibilities... + +TODO(wpcarro): Create a graphic of the options. + +### The problems of dotfiles + +How do you manage your dependencies? + +You can use `stow` to install the dotfiles. + +### home-manager + +What we are going to write is most likely less preferable to the following +alternatives: +- using Nix home-manager +- committing your `.gitconfig` into your + +In the next tutorial, we will use [home-manager][wtf-home-mgr] to replace the +functionality that we wrote. + +So why bother completing this? + +### Let's begin + +Welcome to the first tutorial in the [Let's Learn Nix][wtf-lln] series. Today we +are going to create a Nix derivation for one of your dotfiles. + +"Dotfiles" refers to a user's collection of configuration files. Typically these +files look like: +- `.vimrc` +- `.xsessionrc` +- `.bashrc` + +The leading "dot" at the beginning gives dotfiles their name. + +You probably have amassed a collection of dotfiles whether or not you are +aware. For example, if you use [git][wtf-git], the file `~/.gitconfig` should +exist on your machine. You can verify this with: + +```shell +$ stat ~/.gitconfig +``` + +When I was first learning `git`, I learned to configure it using commands I +found in books and tutorials that often looked like: + +```shell +$ git config user.email +``` + +The `~/.gitconfig` file on your machine may look something like this: + +```.gitconfig +[user] + name = John Cleese + email = john@flying-circus.com + username = jcleese +[core] + editor = emacs +[web] + browser = google-chrome +[rerere] + enabled = 1 + autoupdate = 1 +[push] + default = matching +[color] + ui = auto +[alias] + a = add --all + ai = add -i + b = branch + cl = clone + cp = cherry-pick + d = diff + fo = fetch origin + lg = log --oneline --graph --decorate + ps = push + pb = pull --rebase + s = status +``` + +As I ran increasingly more `git config` commands to configure my `git` +preferences, the size of my `.gitconfig` increased, and the less likely I was to +remember which options I set to which values. + +Thankfully a coworker at the time, Ryan ([@rschmukler][who-ryan]), told me that +he version-controlled his `.gitconfig` file along with his other configuration +files (e.g. `.vimrc`) in a repository he called "dotfiles". + +Version-controlling your dotfiles improves upon a workflow where you have a +variety of configuration files scattered around your machine. + +If you look at the above `.gitconfig`, can you spot the dependencies? + +We explicitly depend `emacs` and `google-chrome`. We also *implicitly* depend on +`git`: there is not much value of having a `.gitconfig` file if you also do not +have `git` installed on your machine. + +Dependencies: +- `emacs` +- `google-chrome` + +Let's use Nix to generate this `.gitconfig` file. Here is what I would like our +API to be: + +Let's create a file `gitconfig.nix` and build our function section-by-section: + +TODO(wpcarro): Link to sections here +- options.user +- options.core +- options.web +- options.rerere +- options.push +- options.color +- options.alias + +```shell +$ touch gitconfig.nix +``` + +### options.user + +```haskell +AttrSet -> String +``` + +```nix +user = { + name = "John Cleese"; + email = "john@flying-circus.com"; + username = "jcleese"; +}; +``` + +```.gitconfig +[user] + name = John Cleese + email = john@flying-circus.com + username = jcleese +``` + +### options.core + +```nix +core = { + editor = "${pkgs.emacs}/bin/emacs"; +}; +``` + +```.gitconfig +[core] + editor = /nix/store/<hash>-emacs-<version>/bin/emacs +``` + +### options.web + +```nix +web.browser = "${pkgs.google-chrome}/bin/google-chrome"; +``` + +```.gitconfig +[web] + browser = /nix/store/<hash>-google-chrome-<version>/bin/google-chrome +``` + +### options.rerere + +```nix +rerere = { + enabled = true; + autoupdate = true; +}; +``` + +```.gitconfig +[rerere] + enabled = 1 + autoupdate = 1 +``` + +### options.push + +```nix +push.default = "matching"; +``` + +```.gitconfig +[push] + default = matching +``` + +### options.color + +```nix +color.ui = "auto"; +``` + +```.gitconfig +[color] + ui = auto +``` + +We need to define a function named `gitconfig` that creates a Nix [derivation][wtf-derivation]: + +```nix +# file: gitconfig.nix +let + # Import the <nixpkgs> package repository. + pkgs = import <nixpkgs> {}; + + # Stringify the attribute set, `xs`, as a multilined string formatted as "<key> = <value>". + # See attrsets.nix for more functions that work with attribute sets. + encodeAttrSet = xs: lib.concatStringsSep "\n" (lib.mapAttrsToList (k: v: "${k} = ${v}") xs); + + # Define out function name `gitconfig` that accepts an `options` argument. + gitconfig = options: pkgs.stdenv.mkDerivation { + # The gitconfig file that Nix builds will be located /nix/store/some-hash-gitconfig. + name = "gitconfig"; + src = pkgs.writeTextFile ".gitconfig" '' + [user] + name = ${options.user.name} + email = ${options.user.email} + username = ${options.user.username} + [core] + editor = ${options.core.editor} + [web] + editor = ${options.web.browser} + [rerere] + enabled = ${if options.rerere.enabled "1" else "0"} + autoupdate = ${if options.rerere.autoupdate "1" else "0"} + [push] + default = ${options.push.default} + [color] + ui = ${options.color.ui} + [alias] + ${encodeAttrSet options.aliases} + ''; + buildPhase = '' + ${pkgs.coreutils}/bin/cp $src $out + ''; + installPhase = '' + ${pkgs.coreutils}/bin/ln -s $out ~/.gitconfig + ''; + }; +} in gitconfig { + user = { + name = "John Cleese"; + email = "john@flying-circus.com"; + username = "jcleese"; + }; + core = { + editor = "${pkgs.emacs}/bin/emacs"; + }; + web.browser = "${pkgs.google-chrome}/bin/google-chrome"; + rerere = { + enabled = true; + autoupdate = true; + }; + push.default = "matching"; + color.ui = "auto"; + aliases = { + a = "add --all"; + ai = "add -i"; + b = "branch"; + cl = "clone"; + cp = "cherry-pick"; + d = "diff"; + fo = "fetch origin"; + lg = "log --oneline --graph --decorate"; + ps = "push"; + pb = "pull --rebase"; + s = "status"; + }; +} +``` + +### options.alias + +We want to write a function that accepts an attribute set and returns a +string. While Nix is a dynamically typed programming language, thinking in types +helps me clarify what I'm trying to write. + +```haskell +encodeAttrSet :: AttrSet -> String +``` + +I prefer using a Haskell-inspired syntax for describing type signatures. Even if +you haven't written Haskell before, you may find the syntax intuitive. + +Here is a non comprehensive, but demonstrative list of example type signatures: +- `[String]`: A list of strings (i.e. `[ "cogito" "ergo" "sum" ]`) +- `AttrSet`: A nix attribute set (i.e. `{ name = "John Cleese"; age = 80; }`). +- `add :: Integer -> Integer -> Integer`: A function named `add` that accepts + two integers and returns an integer. + +Specifically, we want to make sure that when we call: + +```nix +encodeAttrSet { + a = "add --all"; + b = "branch"; +} +``` + +...it returns a string that looks like this: + +```.gitconfig +a = "add --all" +b = "branch" +``` + + +TODO(wpcarro): @tazjin's nix-1p mentions this. Link to it. +Nix has useful functions scattered all over the place: +- `lib.nix` +- `list.nix` +- `lib.attrSet` + +But I cannot recall exactly which functions we will need to write +`encodeAttrSet`. In these cases, I do the following: +1. Run `nix repl`. +2. Browse the Nix source code. + +Google "nix attribute sets" and find the Github link to `attrsets.nix`. + +You should consider repeating this search but instead of searching for +"attribute sets" search for "lists" and "strings". That is how I found the +functions needed to write `encodeAttrSet`. Let's return to our `nix repl`. + +Load the nixpkgs set: + +```nix +nix-repl> :l <nixpkgs> +Added 11484 variables. +``` + +Define a test input called `attrs`: + +```nix +nix-repl> attrs = { fname = "John"; lname = "Cleese"; } +``` + +Map the attribute set into `[String]` using `lib.mapAttrsToList`: + +```nix +nix-repl> lib.mapAttrsToList (k: v: "${k} = ${toString v}") attrs +[ "fname = John" "lname = Cleese" ] +``` + +Now join the `[String]` together using `lib.concatStringsSep`: + +```nix +nix-repl> lib.concatStringsSep "\n" (lib.mapAttrsToList (k: v: "${k} = ${v}") attrs) +"fname = John\nlname = Cleese" +``` + +Now let's use this to define our function `encodeAttrSet`: + +```nix +# file: gitconfig.nix +encodeAttrSet = xs: lib.concatStringsSep "\n" (lib.mapAttrsToList (k: v: "${k} = ${v}") xs); +``` + +### Using nixpkgs search + +[Nixpkgs search][wtf-nixpkgs-search]. + +### Conclusion + +We learned how to help ourselves. + +- Where does `emacs` exist? What about `google-chrome`? [nixpkgs search][wtf-nixpkgs-search] +- Verify that I have it? [nix REPL][using-nix-repl] + +We used Nix to create our first derivation. + +[wtf-lln]: /lets-learn-nix +[wtf-git]: https://git-scm.com/ +[wtf-derivation]: https://nixos.org/nixos/nix-pills/our-first-derivation.html +[wtf-nixpkgs-search]: https://nixos.org/nixos/packages.html?channel=nixos-19.09 +[using-nix-repl]: /using-the-nix-repl +[wtf-home-mgr]: https://github.com/rycee/home-manager +[who-ryan]: https://twitter.com/rschmukler |