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Elixir Development with Vim

I love Vim (more specifically, the NeoVim fork). Modal editing as part of my Unix IDE brings an immense amount of productivity and enjoyment to my day-to-day development activities. As such, whenever I take up a new language or framework, I enjoy experimenting with how best to integrate it into my existing workflow.

Having started programming in Elixir, I've started the customization journey for the language. Much as with Maslow's Hierarchy of Needs, there's a hierarchy of editor support required for an fulfilling programming experience. Let's get there with Elixir!

1. Indentation & Syntax Highlighting

Both smart indentation and syntax highlighting make editing less painful - the former reduces keystrokes (and occurrences of fighting the editor), while the latter makes it easier to scan and parse the code displayed. Vim ships with some presets, but they're either missing, incomplete, or outdated for newer, less-used languages. The good news is, one can author and share their language-specific rules. To save myself from this song and dance whenever I open source code for a bespoke programming language, I use the vim-polyglot plugin. It bundles the vim-elixir plugin (which is currently searching for new maintainers).

All I need to do is drop an Plug 'sheerun/vim-polyglot' into my init.vim's vim-plug section, and I'm off to the races.

2. Linting

I've experimented with different levels of linting intrusiveness - from the blocking, quickfix-window-popping-up-on-save, to manually-invoked lint checks whenever I want to validate things. As Vim (especially with the advent of NeoVim) became more async-y, I grew to like near-realtime linting of my code. Linter integration is challenging - most linters are standalone scripts, which are in turn wrapped by the editor plugins. They not only have to manage the script lifecycle, but also parse the output and map it to the code in a Vim buffer. This can lead to all sorts of fun and exciting failure states.

Previously, I've accomplished that with Syntastic and ALE. However, since then (and with credit to VS Code) we've entered a language server renaissance. They not only enable things like smart code completion (a la Intellisence), but also runtime linting. Despite being "standardized", however, much like the web, most language servers are coded to the quirks and functionality of a specific client - VS Code.

Enter coc.nvim. This plugin runs VS Code extensions in NeoVim, and offers advanced levels of integration into the editor. Not only does it provide gutter icons and highlights for linting errors, but it can also display the feedback as virtual text (vs. in a quickfix window). Additionally, if language-based autocompletion is your thing, it's got your back.

Installing is as straightforward as adding Plug 'neoclide/coc.nvim', {'branch': 'release'} to my init.vim, and then adding a global settings file in ~/.config/nvim/coc-settings.json. This can be conveniently opened by entering the :CocConfig command. Then, I install the Elixir plugin: :CocInstall coc-elixir

However, that wasn't quite enough on my system. I quickly discovered that the language server wasn't working. I dug through the backlog to discover that I was using a version of Elixir different from what the language server was compiled with. Thankfully, coc-elixir can be aimed at a different LSP.

  1. Clone the elixir-ls repository: git clone https://github.com/elixir-lsp/elixir-ls.git ~/.elixir-ls
  2. Enter the local repository: cd ~/.elixir-ls
  3. Download all dependencies: mix deps.get
  4. Build the package: mix compile
  5. Create a release distribution: mix elixir_ls.release -o release

Once built, I updated coc.nvim's global config to point to it:

// ~/.config/nvim/coc-settings.json
{
    "elixir.pathToElixirLS": "~/.elixir-ls/release/language_server.sh"
}

Honorable Mention: There's also the coc-diagnostic plugin, which can be configured to use credo.

3. Formatting

Code formatters are useful because they provide a default set of opinions for code layout. For newcomers to a language, or larger community projects, this is a boon. When developing in Python I use Black. While I disagree with some of its opinions, having well-formed code be an invocation away is pretty rad. Elixir ships with one - it can be invoked with mix format.

Vim itself supports external formatter integration through use of the formatprg setting. Once set, the formatter can be invoked by using the gq motion over a text object.

Tying these two things together is dead simple. In my init.vim:

autocmd FileType elixir setlocal formatprg=mix\ format\ -

This instructs NeoVim to set the formatprg for all Elixir files to mix format -. The hyphen indicates that the buffer should be supplied via stdin. With this setting, I can now run gggqG to format an entire file: gg to go to the first line, gq to start the formatter range selection, and G to set the range to the last line.

With the above needs met, I now have an enjoyable Elixir-authoring experience. What Vim customizations do you consider essential for your Elixir life?