nix-doc

A Nix developer tool leveraging the rnix Nix parser for intelligent documentation search and tags generation.

Features

• Nix plugin that adds a builtin that can display the signature and documentation for a lambda object in a friendly format
• Command line tool that searches Nix files in a directory for functions and shows documentation for matching ones
• Tags generator similar to ctags that can generate a vim compatible tags file for Nix source
• High performance, threaded implementation in Rust

Setup

# nix-doc is in nixpkgs
$ nix-env -i nix-doc

# you can alternatively get it from git
$ nix-env -i -f https://github.com/lf-/nix-doc/archive/main.tar.gz

# or if you don't want to use nix (only includes the command line tool for
# search and tags)
$ cargo install --locked nix-doc

Nix Plugin

To install the Nix plugin on a single-user installation of Nix, add this to your Nix config at ~/.config/nix/nix.conf after installing nix-doc with nix-env:

plugin-files = /home/YOURUSERNAMEHERE/.nix-profile/lib/libnix_doc_plugin.so

For a multi-user installation, you will need to do something like this:

$ sudo ln -s $(nix-build '<nixpkgs>' -A nix-doc) /opt/nix-doc

and then put this into your /etc/nix/nix.conf:

plugin-files = /opt/nix-doc/lib/libnix_doc_plugin.so

NixOS Installation

Link the plugin file using nix.extraOptions:

{ pkgs, ... }:

{
  nix.extraOptions = ''
    plugin-files = ${pkgs.nix-doc}/lib/libnix_doc_plugin.so
  '';

  environment.systemPackages = with pkgs; [
    nix-doc
  ];
}

Usage

CLI

nix-doc <command>

nix-doc tags [dir]

Generates a vim-compatible tags file in the current directory, for all nix script files below the directory dir.

Example:

nixpkgs$ nix-doc tags

nixpkgs$ file tags
tags: Exuberant Ctags tag file, ASCII text, with very long lines (502)

# opens vim to the function callCabal2nix
nixpkgs$ vim -t callCabal2nix

nix-doc search <regex> [dir]

Example output:

nixpkgs$ nix-doc search callPackage
   Call the package function in the file `fn' with the required
   arguments automatically.  The function is called with the
   arguments `args', but any missing arguments are obtained from
   `autoArgs'.  This function is intended to be partially
   parameterised, e.g.,

   callPackage = callPackageWith pkgs;
   pkgs = {
   libfoo = callPackage ./foo.nix { };
   libbar = callPackage ./bar.nix { };
   };

   If the `libbar' function expects an argument named `libfoo', it is
   automatically passed as an argument.  Overrides or missing
   arguments can be supplied in `args', e.g.

   libbar = callPackage ./bar.nix {
   libfoo = null;
   enableX11 = true;
   };
callPackageWith = autoArgs: fn: args: ...
# ./lib/customisation.nix:117
─────────────────────────────────────────────
   Like callPackage, but for a function that returns an attribute
   set of derivations. The override function is added to the
   individual attributes.
callPackagesWith = autoArgs: fn: args: ...
# ./lib/customisation.nix:127
─────────────────────────────────────────────
   Similar to callPackageWith/callPackage, but without makeOverridable
callPackageWith = autoArgs: fn: args: ...
# ./pkgs/development/beam-modules/lib.nix:7

Nix plugin

The Nix plugin provides three builtins:

builtins.doc f

Prints the documentation of the function f to the screen. Returns null.

builtins.getDoc f

Returns the documentation message for the function f as a string (exactly the same output as builtins.doc, just as a string).

builtins.unsafeGetLambdaPos

A backport of NixOS/Nix#3912. Returns the position of a lambda, in a similar fashion to unsafeGetAttrPos for attributes.

Sample usage:

» nix repl
Welcome to Nix version 2.3.7. Type :? for help.

nix-repl> n=import <nixpkgs> {}

nix-repl> builtins.doc n.lib.callPackageWith
   Call the package function in the file `fn' with the required
   arguments automatically.  The function is called with the
   arguments `args', but any missing arguments are obtained from
   `autoArgs'.  This function is intended to be partially
   parameterised, e.g.,

     callPackage = callPackageWith pkgs;
     pkgs = {
       libfoo = callPackage ./foo.nix { };
       libbar = callPackage ./bar.nix { };
     };

   If the `libbar' function expects an argument named `libfoo', it is
   automatically passed as an argument.  Overrides or missing
   arguments can be supplied in `args', e.g.

     libbar = callPackage ./bar.nix {
       libfoo = null;
       enableX11 = true;
     };
func = autoArgs: fn: args: ...
# /nix/store/frpij1x0ihnyc4r5f7v0zxwpslkq6s27-nixpkgs-20.09pre237807.0dc87c6e54f/nixpkgs/lib/customisation.nix:117
null

Development

This repository is set up as a Cargo workspace with the plugin and the command line tool/library as parts.

It is not really possible to build the plugin outside a Nix shell since Nix does not provide libraries outside the shell environment. As such, it is suggested to use a nix shell while developing the plugin as follows:

$ nix-shell
[nix-shell]$ cargo build
[nix-shell]$ cargo check
[nix-shell]$ cargo test
# etc

TODO

• Tech: should update rnix to the latest major.

Related work

• NixOS/nix#1652: A PR implementing basically the same thing as this tool's plugin in Nix itself, which has been deferred indefinitely due to disagreements about what syntax to use in documentation comments.
• https://github.com/tazjin/nixdoc: A Rust tool producing DocBook documentation for Nix library functions.
• https://github.com/mlvzk/manix: An early fork of this tool with a stronger focus on CLI usage, with support for indexing and faster search. By comparison, their CLI is better, but they don't do tags or a Nix plugin.

Project information

Everyone is expected to follow the code of conduct while participating in this project.