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elm-language-server

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

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Table of Contents

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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 git@github.com: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

FeatureDescription
diagnosticsProvided via elm, elm-test and our own type inference and linter
formattingProvided via elm-format and post-processed to only return a diff of changes. This way it should not be as intrusive as running elm-format normal
codeLensesCurrently only shows if a type alias, custom type or function is exposed from that module
completionsShow completions for the current file and snippets
definitionsEnables you to jump to the definition of a type alias, module, custom type or function
documentSymbolsIdentifies all symbols in a document.
foldingLet's you fold the code on certain Elm constructs
hoverShows type annotations and documentation for a type alias, module, custom type or function
linkedEditingEnables auto renaming a function name when the type annotation name is edited, or vice versa
referencesLists all references to a type alias, module, custom type or function
renameEnables you to rename a type alias, module, custom type or function
workspaceSymbolsIdentifies all symbols in the current workspace
selectionRangeEnables navigation by selectionRange (extend selection for e.g.)

Server Settings

This server contributes the following settings:

Settings may need a restart to be applied.

Editor Support

EditorDiagnosticsFormattingCode LensesCompletionsDefinitionsDocument SymbolsFoldingHoverLinked EditingReferencesRenameWorkspace Symbols
VSCode:heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark:
VIM CoC:heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::x::heavy_check_mark::heavy_check_mark::heavy_check_mark:
VIM LanguageClient:heavy_check_mark::heavy_check_mark::grey_question::heavy_check_mark::grey_question::grey_question::grey_question::grey_question::x::grey_question::grey_question::grey_question:
VIM ALE:heavy_check_mark::x::x::grey_question::heavy_check_mark::x::x::heavy_check_mark::x::heavy_check_mark::x::heavy_check_mark:
Kakoune:heavy_check_mark::heavy_check_mark::grey_question::heavy_check_mark::heavy_check_mark::heavy_check_mark::grey_question::heavy_check_mark::x::heavy_check_mark::heavy_check_mark::grey_question:
Emacs:heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::grey_question::heavy_check_mark::x::heavy_check_mark::heavy_check_mark::heavy_check_mark:
Sublime:heavy_check_mark::heavy_check_mark::x::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::heavy_check_mark::x::heavy_check_mark::heavy_check_mark::heavy_check_mark:

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.

FeatureHow to use it
Diagnostics:CocList diagnostics<br />Configure refresh with "diagnostic.refreshAfterSave": false
Formatting:call CocAction('format')
CodeLensesRequires Neovim. Add "coc.preferences.codeLens.enable": true to your coc-settings.json through :CocConfig
CompletionsOn by default, see Completion with sources for customizations
DefinitionsProvided as <Plug> mapping so that you can set it yourself, e.g. <br /> nmap <silent> gd <Plug>(coc-definition) <br/> nmap <silent> gy <Plug>(coc-type-definition)
DocumentSymbols:CocList outline
FoldingYou must set foldmethod=manual in your vimrc, one set Coc will handle folding with the usual commands, zc, zo, etc
Hover:call CocAction('doHover')
ReferencesProvided as a <Plug> mapping, e.g. nmap <silent> gr <Plug>(coc-references)
RenameProvided as a <Plug> mapping, e.g. nmap <leader>rn <Plug>(coc-rename)
Workspace Symbols:CocList symbols

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"
FeatureHow to use it
Diagnostics:ALENext/:ALEPrevious<br />Configure refresh with let g:ale_lint_on_text_changed = 0<br />let g:ale_lint_on_insert_leave = 1 <br /> let g:ale_lint_on_save = 1
FormattingALE doesn't currently support this through the language server integration, but elm-format is a supported ALE Fixer
CodeLensesNot currently supported
CompletionsOn by default, see :h ale-completion for more info
Definitions:ALEGoToDefinition, :ALEGoToTypeDefinition, see :h ale-go-to-definition and :h ale-go-to-type-definition
DocumentSymbolsOnly workspace symbols are currently supported
FoldingNot currently supported
Hover:ALEHover
References:ALEFindReferences
RenameNot currently supported
Workspace Symbols:ALESymbolSearch <query>

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

lsp
(elm +lsp)
(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

FeatureHow to use it
DiagnosticsOn by default
FormattingOn save
CodeLenseslsp-lens-mode, lsp-show-lens
CompletionsOn by default
Definitionslsp-find-definition, lsp-ui-peek-find-definitions
DocumentSymbolslsp-ui-imenu
Folding+fold/open, +fold/close
Hoverlsp-ui-sideline-mode, lsp-ui-doc-mode, lsp-ui-show-doc
Referenceslsp-ui-peek-find-references, lsp-find-references
Renamelsp-rename
SelectionRangelsp-extend-selection

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

Contributing

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