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
  • Linting
• 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

If you want to use elm-review:

npm install -g elm-review

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

We used to have a file called elm-tooling.json where you could specifiy "entrypoints". That’s not needed anymore – the language server finds the entrypoints automatically.

If all you had in elm-tooling.json was "entrypoints", you can safely remove that file.

Currently, no configuration at all is needed.

Linting

The Elm Language Server has built-in support for linting. Check out the documentation for configuring the linter.

Features

Supports Elm 0.19 and up

Parameter hovers include a link to the inferred type's declaration when the client advertises Markdown hover support. This includes function, anonymous function, and case-pattern parameters. Resolution prefers a type alias over its underlying type; unnamed or unresolved types have no link. Links use document URIs with one-based #L line fragments, without editor-specific commands. Clients must support opening the document URI, and exact-line navigation depends on the client because LSP does not standardize these fragments.

Virtual Elm package files use the LSP 3.18 workspace/textDocumentContent request when the client advertises support. Implementations include vscode-languageclient 10, coc.nvim, and Sublime LSP 2.13. Elm clients that do not support the standard request can continue to use elm/provideFileContents during the migration.

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.elmReviewPath: The path to your elm-review 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.elmReviewDiagnostics: Configure linting diagnostics from elm-review. Possible values: off, warning, error.
• 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, elm-review and elm-format with the elmPath, elmTestPath, elmReviewPath 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, elm-review 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 your 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-ui
  (setq lsp-ui-doc-max-width 100)
  (setq lsp-ui-doc-max-height 30)
  (setq lsp-ui-sideline-show-code-actions nil)
  (setq lsp-ui-doc-enable nil)
  (setq lsp-ui-doc-show-with-cursor nil)
  (setq lsp-ui-doc-show-with-mouse nil)
  (setq lsp-lens-enable nil)
  (setq lsp-enable-symbol-highlighting nil)
  )

You can also enable or disable more features: https://emacs-lsp.github.io/lsp-mode/tutorials/how-to-turn-off

• 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
• elm-review

Contributing

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