#+TITLE:   tools/direnv
#+DATE:    July 10, 2019
#+SINCE:   v2.1.0
#+STARTUP: inlineimages

* Table of Contents :TOC_3:noexport:
- [[#description][Description]]
  - [[#module-flags][Module Flags]]
  - [[#plugins][Plugins]]
  - [[#hacks][Hacks]]
- [[#prerequisites][Prerequisites]]
  - [[#macos][MacOS]]
  - [[#arch-linux][Arch Linux]]
  - [[#nixos][NixOS]]
- [[#troubleshooting][Troubleshooting]]
  - [[#direnv--nix-is-slow][direnv + nix is slow]]

* Description
This module integrates direnv into Emacs.

#+begin_quote
direnv is an environment switcher for the shell. It knows how to hook into bash,
zsh, tcsh, fish shell and elvish to load or unload environment variables
depending on the current directory. This allows project-specific environment
variables without cluttering the ~/.profile file.

Before each prompt, direnv checks for the existence of a ".envrc" file in the
current and parent directories. If the file exists (and is authorized), it is
loaded into a bash sub-shell and all exported variables are then captured by
direnv and then made available to the current shell.
#+end_quote

** Module Flags
This module provides no flags.

** Plugins
+ [[https://github.com/purcell/envrc][envrc]]

** Hacks
+ Normally, the direnv environment is updated on ~post-command-hook~. We've
  changed it to update on ~doom-switch-buffer-hook~, ~doom-switch-window-hook~
  and ~doom-switch-frame-hook~ instead.
+ Special direnv keywords/commands are highlighted in direnv-envrc-mode.
+ A fix has been applied to ensure flycheck searches for executables from within
  the direnv environment, if any.

* Prerequisites
This module requires the ~direnv~ utility.

** MacOS
#+BEGIN_SRC bash
brew install direnv
#+END_SRC

** Arch Linux
#+BEGIN_SRC bash
sudo pacman -S direnv
#+END_SRC

** NixOS
#+BEGIN_SRC nix
environment.systemPackages = [ pkgs.direnv ];
#+END_SRC

Or ~nix-env -i direnv~

* Troubleshooting
** direnv + nix is slow
Consider augmenting direnv with [[https://github.com/target/lorri][lorri]], which will cache nix builds and speed up
direnv tremendously:

#+BEGIN_SRC nix
services.lorri.enable = true;
#+END_SRC
