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366 lines
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<title>NixCon 2023 slides</title>
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<div class="reveal">
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<div class="slides">
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<section class="title-slide">
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<h1>Finding things in nixpkgs and NixOS source</h1>
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<div class="meta">
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<p>
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Jade Lovelace <jade at jade dot fyi>
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</p>
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<p>
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Get the slides at <a href="https://jade.fyi/nixcon2023/slides">https://jade.fyi/nixcon2023/slides</a>
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</div>
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</section>
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<section data-markdown><textarea data-template>
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# whoami
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* Author of nix-doc (not to be confused with nixdoc)
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* Most involved in Nix for Haskell and Rust packaging
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* I use NixOS as a dev workstation and server
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# the sources are for everyone
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* We do need to improve our documentation
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* Nix is uniquely participatory: a *lot* of us write modules and packages, which means reading sources
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* Navigating the source is a bit of witchcraft, and there's a lot of it
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* With good tooling, the sources of the docs sometimes are faster than the docs
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# motivation (2.94 million lines of it)
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<pre><code class="text"><script type="text/template">
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dev/nixpkgs » tokei -t nix .
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=======================================
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Language Files Lines
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=======================================
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Nix 30400 2941526
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=======================================
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Total 30400 2941526
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=======================================
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</script></code></pre>
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</textarea></section>
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<section data-markdown><textarea data-template>
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# roadmap
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* nix
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* static analysis
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* nixd
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* ctags
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* dynamic analysis
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* using the repl
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* using nix-doc
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* nixos
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* ctags
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* repl usage
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# Static analysis
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* Any method that takes 15 seconds or less and doesn't involve running any code
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* I am showing the fancy ways of doing it
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* ripgrep is static analysis too; it's a good fallback
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# nixd
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Newish language server, using Nix as a library. In nixpkgs as `nixd`.
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Good for:
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* need go-to-definition
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* interactive help writing nix code
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Limitations:
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* does not eval everything
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* needs some setup per-project
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* completions are imperfect but they exist
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* not sure how to get goto definition to go past args for some things
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# nixd setup
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Install from nixpkgs and configure in your editor. Then:
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`.nixd.json`:
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<pre><code class="json"><script type="text/template">
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{
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"eval": {
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"target": {
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"args": [
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"--expr",
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"with import ./. {}; nix-doc"
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]
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}
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}
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}
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</script></code></pre>
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# demo (nixd)
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FIXME
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# ctags
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* Very old and simple source code index format
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* Usually gets through abstraction by being too naive to get broken
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* Typically generated by simple parse-tree traversal
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* Wide editor support ([VSCode extension](https://marketplace.visualstudio.com/items?itemName=jaydenlin.ctags-support), built into vim/emacs)
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Sample:
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```
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boot.initrd.luks.reusePassphrases nixos/modules/system/boot/luksroot.nix 533
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```
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# ctags on nix
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* `nix-doc tags .` in nixpkgs, then in vim you can `:tj fixedPoints`, `C-]`, etc.
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* [WIP ctags for NixOS options](https://github.com/NixOS/nixpkgs/pull/249243)
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# demo (ctags on nix)
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FIXME
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# summary (static analysis)
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# dynamic analysis
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* Static analysis often doesn't cut it, power tools time!
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* `nix repl` is your friend
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# using the repl (nix)
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* `nix repl -f .`, `nix repl -f '<nixpkgs>`
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* `:lf flake-ref` (more on this later)
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* `:e derivation-or-function` to open in editor
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# getting docs in the repl
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<pre><code class="text"><script type="text/template">
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nix-repl> :doc builtins.head
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Synopsis: builtins.head list
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Return the first element of a list; abort evaluation if the argument isn’t a list or is
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an empty list. You can test whether a list is empty by comparing it with [].
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</script></code></pre>
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# getting docs in the repl (ii)
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<pre><code class="text"><script type="text/template">
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nix-repl> :doc haskell.lib.overrideSrc
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error: value does not have documentation
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</script></code></pre>
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Oops.
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Related:
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* [RFC 0145](https://github.com/NixOS/rfcs/pull/145)
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* [nix#3904](https://github.com/NixOS/nix/issues/3904)
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# nix-doc?
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<pre><code class="nix"><script type="text/template">
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{ pkgs, ... }: {
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nix.extraOptions = ''
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plugin-files = ${pkgs.nix-doc}/lib/libnix_doc_plugin.so
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'';
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}
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</script></code></pre>
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# using nix-doc with the repl
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<pre><code class="text"><script type="text/template">
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nix-repl> builtins.doc haskell.lib.overrideSrc
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Override the sources for the package and optionally the version.
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This also takes of removing editedCabalFile.
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func = drv: src: ...
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# /nix/store/wl5m5xfayd69ycyspzyd4rilfgl6wmh0-source/pkgs/development/haskell-modules/lib/default.n
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ix:285
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null
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</script></code></pre>
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# `builtins.unsafeGetAttrPos`
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Probably the biggest dynamic analysis hammer.
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<pre><code class="text"><script type="text/template">
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nix-repl> builtins.doc pkgs.fetchFromGitHub
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error: value is a set while a lambda was expected
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nix-repl> :e pkgs.fetchFromGitHub
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error: package 'fetchFromGitHub' has no source location information
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nix-repl> builtins.unsafeGetAttrPos "fetchFromGitHub" pkgs
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{ column = 3; file = "/nix/store/wl5m5xfayd69ycyspzyd4rilfgl6wmh0-source/pkgs/top-level/all-package
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s.nix"; line = 1193; }
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</script></code></pre>
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# summary (dynamic analysis)
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* `:e function/package`
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* \+ works pretty well
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* \+ built-in
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* \- issues with wrappers (e.g. `fetchFromGitHub`: `lib.makeOverridable`)
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* \- doesn't help for attr sets
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* `builtins.doc` (nix-doc)
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* \+ concise output on functions
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* \- issues with wrappers
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* `builtins.unsafeGetAttrPos`
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* \+ can get you close to the source if other things fail due to abstraction
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* \- unergonomic args and return value for interactive use
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# NixOS ctags ([PR](https://github.com/NixOS/nixpkgs/pull/249243))
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With the PR checked out:
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<pre><code class="text"><script type="text/template">
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$ nix build -f nixos/release.nix optionsCtags -o opts-tags
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</script></code></pre>
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</textarea>
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Then add `opts-tags` to ctags search path (`:set tags+=opts-tags` in vim).
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</section>
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<section data-markdown><textarea data-template>
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# NixOS ctags (demo)
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FIXME
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# NixOS in the repl
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Getting the configuration into the repl:
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* Non-flakes: `nix repl -I nixos-config=/path/to/configuration.nix -f <nixpkgs/nixos>`
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* Flakes: `nix repl`, `:lf .`, `nixosConfigurations.xx.{....}`
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</textarea>
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</section>
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<section data-markdown><textarea data-template>
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# NixOS in the repl (demo)
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FIXME
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<!--
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nix-repl> config.documentation.man.generateCaches
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true
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nix-repl> options.documentation.man.generateCaches
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{ __toString = «lambda @ /nix/store/wl5m5xfayd69ycyspzyd4rilfgl6wmh0-source/lib/modules.nix:807:22»
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; _type = "option"; declarations = [ ... ]; default = false; definitions = [ ... ]; definitionsWith
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Locations = [ ... ]; description = "Whether to generate the manual page index caches.\nThis allows
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searching for a page or\nkeyword using utilities like {manpage}`apropos(1)`\nand the `-k` option of
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\n{manpage}`man(1)`.\n"; files = [ ... ]; highestPrio = 1000; isDefined = true; loc = [ ... ]; opti
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ons = [ ... ]; type = { ... }; value = true; }
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nix-repl> options.documentation.man.generateCaches.definitions
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[ true ]
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nix-repl> options.documentation.man.generateCaches.definitionsWithLocations
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[ { ... } ]
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nix-repl> :p options.documentation.man.generateCaches.definitionsWithLocations
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[ { file = "/nix/store/wl5m5xfayd69ycyspzyd4rilfgl6wmh0-source/nixos/modules/programs/fish.nix"; va
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lue = true; } ]
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-->
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</textarea>
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</section>
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