elm-language-server

This is the language server implementation for the Elm programming language.

Table of Contents

• Installation
  • Alternative: Compile and install from source
  • Alternative: Install with Nix
• Requirements
• Configuration
• Features
• Server Settings
• Editor Support
  • VSCode
  • Vim
    • coc.nvim
    • ALE
    • LanguageClient
  • Kakoune
    • kak-lsp
  • Emacs
    • Emacs Doom
  • Sublime
• Awesome libraries this is based on
• Contributing

Installation

Note for VSCode users: The plugin contains the language-server. No installation necessary.

The server can be installed via npm (or from source).

npm install -g @elm-tooling/elm-language-server

Then, you should be able to run the language server with the following command:

elm-language-server

You might need to use this, if your using powershell:

elm-language-server.cmd

Follow the instructions below to integrate the language server into your editor.

Alternative: Compile and install from source

First, clone this repo and compile it. npm link will add elm-language-server to the PATH.

git clone [email protected]:elm-tooling/elm-language-server.git
cd elm-language-server
npm install
npm run compile
npm link

Alternative: Install with Nix

elm-languager-server and its dependencies are available in nixpkgs.

nix-env -i -A nixpkgs.elmPackages.elm-language-server

Requirements

You will need to install elm and elm-test to get all diagnostics and elm-format for formatting. Alternatively you can also just install these to your local npm package.json.

npm install -g elm elm-test elm-format

Or use local versions from your node_modules directory, if you want to do that you need to set the paths, via the settings (e.g. set elmPath to ./node_modules/.bin/elm).

Configuration

Create an elm-tooling.json file next to your elm.json to configure the language server.

Currently there’s just one thing that you can configure: entrypoints. The language server runs elm make to get type errors. By default elm make is run on the current file only. To get errors for the entire project you can specify your entrypoint files – basically, those with main = in them. Then the language server will run elm make on those instead.

Example elm-tooling.json:

{
  "entrypoints": ["./src/Main.elm"]
}

The entrypoints are relative to the directory where your elm.json and elm-tooling.json is and must start with ./.

Check out the elm-tooling CLI for creating and validating your elm-tooling.json! You can run it without installing:

npx elm-tooling init

Features

Supports Elm 0.19 and up

Server Settings

This server contributes the following settings:

• elmLS.trace.server: Enable/disable trace logging of client and server communication
• elmLS.elmPath: The path to your elm executable. Should be empty by default, in that case it will assume the name and try to first get it from a local npm installation or a global one. If you set it manually it will not try to load from the npm folder.
• elmLS.elmFormatPath: The path to your elm-format executable. Should be empty by default, in that case it will assume the name and try to first get it from a local npm installation or a global one. If you set it manually it will not try to load from the npm folder.
• elmLS.elmTestPath: The path to your elm-test executable. Should be empty by default, in that case it will assume the name and try to first get it from a local npm installation or a global one. If you set it manually it will not try to load from the npm folder.
• elmLS.disableElmLSDiagnostics: Enable/Disable linting diagnostics from the language server.
• elmLS.skipInstallPackageConfirmation: Skip confirmation for the Install Package code action.
• elmLS.onlyUpdateDiagnosticsOnSave: Only update compiler diagnostics on save, not on document change.

Settings may need a restart to be applied.

Editor Support

VSCode

Just install the elm-tooling/elm-language-client-vscode plugin from the VSCode MarketPlace

To enable linked editing in VSCode, use the setting "editor.linkedEditing": true.

Vim

There are general setup instructions and FAQ for Vim.

It's recommended to install syntax highlighting, which also adds the required detection of elm as filetype. An example vim configuration can be found in elm-vim/vim-config-example.

coc.nvim

To enable support with coc.nvim, run :CocConfig and add the language server config below.

If needed, you can set the paths to elm, elm-test and elm-format with the elmPath, elmTestPath and elmFormatPath variables.

{
  "languageserver": {
    "elmLS": {
      "command": "elm-language-server",
      "filetypes": ["elm"],
      "rootPatterns": ["elm.json"]
    }
  },
  // If you use neovim you can enable codelenses with this
  "codeLens.enable": true
}

Much of this is covered in the Example vim configuration section in Coc's readme.

ALE

ALE contains the elm_ls linter.

let g:ale_linters = { 'elm': ['elm_ls'] }

If needed, you can set the paths to elm, elm-test and elm-format. The configuration can be found here

let g:ale_elm_ls_use_global = 1
let g:ale_elm_ls_executable = "/path/to/elm-language-server"
let g:ale_elm_ls_elm_path = "/path/to/elm"
let g:ale_elm_ls_elm_format_path = "/path/to/elm-format"
let g:ale_elm_ls_elm_test_path = "/path/to/elm-test"

LanguageClient

To use this language server with LanguageClient add the following configuration to you neovim/vim.

let g:LanguageClient_serverCommands = {
  \ 'elm': ['elm-language-server'],
  \ }

let g:LanguageClient_rootMarkers = {
  \ 'elm': ['elm.json'],
  \ }

Kakoune

kak-lsp

First install kak-lsp, and enable it in the kakrc. One way would be to add these lines to your .config/kak/kakrc file:

eval %sh{kak-lsp --kakoune -s $kak_session}
lsp-enable

Then, assuming installation of elm-language-server, elm-format, and elm-test, add this section to your .config/kak-lsp/kak-lsp.toml file:

[language.elm]
filetypes = ["elm"]
roots = ["elm.json"]
command = "elm-language-server"

Emacs

The language client is included in lsp-mode, specifically here. See specifically this section for a minimal use-package configuration for lsp-mode.

Emacs Doom

• Uncomment lsp and elm in your configuration file .doom.d/init.el and add the +lsp feature flag to the elm layer:

lsp
(elm +lsp)

• Optional configuration for lsp-mode and lsp-ui-mode. Add this to your .doom.d/config.el:

(after! lsp
  (setq lsp-enable-symbol-highlighting nil)
  )
(after! lsp-ui
  (setq lsp-ui-doc-max-width 100)
  (setq lsp-ui-doc-max-height 30)
  (setq company-lsp-cache-candidates nil)
  )

• Run ~/.emacs.d/bin/doom sync

Sublime

1. Install Elm Syntax Highlighting, LSP and LSP-elm from Package Control.
2. Restart Sublime.

You should now be able to use the integrations from Sublime. You might want to read about the features offered

Awesome libraries this is based on

• elm-format
• elm-test
• tree-sitter-elm

Contributing

Please do :) As the best thing about a language server is that multiple clients will improve that way.