Elixir Language Server (ElixirLS)

The Elixir Language Server provides a server that runs in the background, providing IDEs, editors, and other tools with information about Elixir Mix projects. It adheres to the Language Server Protocol, a standard for frontend-independent IDE support. Debugger integration is accomplished through the similar VS Code Debug Protocol.

This is now the main elixir-ls repo

The elixir-lsp/elixir-ls repo began as a fork when the original repo at JakeBecker/elixir-ls became inactive for an extended period of time. So we decided to start an active fork to merge dormant PR's and fix issues where possible. We also believe in an open and shared governance model to share the work instead of relying on one person to shoulder the whole burden.

The original repository has now been deprecated in favor of this one. Any IDE extensions that use ElixirLS should switch to using this repository.

Features

• Debugger support
• Automatic, incremental Dialyzer analysis
• Automatic inline suggestion of @specs based on Dialyzer's inferred success typings
• Inline reporting of build warnings and errors
• Documentation lookup on hover
• Go-to-definition
• Code completion
• Code formatter
• Find references to functions and modules (Thanks to @mattbaker)
• Quick symbol lookup in file (Thanks to @mattbaker)
• Quick symbol lookup in workspace and stdlib (both Elixir and erlang) (@lukaszsamson)

Note: On first run Dialyzer will build a PLT cache which will take a considerable amount of CPU time (usually 10+ minutes). After that is complete the CPU usage will go back to normal. Alternatively instead of waiting you can disable Dialyzer in the settings.

Supported versions

Elixir:

• 1.7.0 minimum

Erlang:

• OTP 20 minimum

You may want to install Elixir and Erlang from source, using the kiex and kerl tools. This will let you go-to-definition for core Elixir and Erlang modules.

IDE plugins

IDE	Plugin	Support
VS Code	elixir-lsp/vscode-elixir-ls	Supports all ElixirLS features
Atom IDE	JakeBecker/ide-elixir	Does not support debugger or @spec suggestions
Vim	ALE	Does not support debugger or @spec suggestions
Neovim	ALE	Does not support debugger
Neovim	coc.nvim	Does not support debugger
Emacs	lsp-mode	Supports debugger via dap-mode
Emacs	eglot
Kate	built-in LSP Client plugin	Does not support debugger
Sublime Text	LSP-elixir	Does not support debugger

Feel free to create and publish your own client packages and add them to this list!

Debugger support

ElixirLS includes debugger support adhering to the VS Code debugger protocol which is closely related to the Language Server Protocol. At the moment, only line breakpoints are supported.

When debugging in Elixir or Erlang, only modules that have been "interpreted" (using :int.ni/1 or :int.i/1) will accept breakpoints or show up in stack traces. The debugger in ElixirLS automatically interprets all modules in the Mix project and dependencies prior to launching the Mix task, so you can set breakpoints anywhere in your project or dependency modules.

In order to debug modules in .exs files (such as tests), they must be specified under requireFiles in your launch configuration so they can be loaded and interpreted prior to running the task. For example, the default launch configuration for "mix test" in the VS Code plugin looks like this:

{
  "type": "mix_task",
  "name": "mix test",
  "request": "launch",
  "task": "test",
  "taskArgs": ["--trace"],
  "projectDir": "${workspaceRoot}",
  "requireFiles": [
    "test/**/test_helper.exs",
    "test/**/*_test.exs"
  ]
}

Automatic builds and error reporting

Builds are performed automatically when files are saved. If you want this to happen automatically when you type, you can turn on "autosave" in your IDE.

Starting in Elixir 1.6, Mix compilers adhere to the Mix.Task.Compiler behaviour and return their error and warning diagnostics in a standardized way. Errors and warnings will be shown inline in your code as well as in the "Problems" pane in the IDE. If you're using an earlier version of Elixir, you'll need to look at the text log from the extension to see the errors and warnings.

Dialyzer integration

ElixirLS will automatically analyze your project with Dialyzer after each successful build. It maintains a "manifest" file in .elixir_ls/dialyzer_manifest that stores the results of the analysis. The initial analysis for a project can take a few minutes, but after that's completed, modules are re-analyzed only if necessary, so subsequent analyses are typically very fast -- often less than a second. It also looks at your modules' abstract code to determine whether they reference any modules that haven't been analyzed and includes them automatically.

You can control which warnings are shown using the elixirLS.dialyzerWarnOpts setting in your project or IDE's settings.json. To disable it completely, set elixirLS.dialyzerEnabled to false.

ElixirLS's Dialyzer integration uses internal, undocumented Dialyzer APIs, and so it won't be robust against changes to these APIs in future Erlang versions.

Code completion

ElixirLS bundles an advanced code completion provider. The provider builds on Elixir Sense library and utilizes two main mechanisms. The first one is reflection - getting information about compiled modules from Erlang and Elixir APIs. The second one is AST analysis of the current text buffer. While reflection gives precise results, it is not well suited for on demand completion of symbols from the currently edited file. The compiled version is likely to be outdated or the file may not compile at all. AST analysis helps in that case but it has its limitations. Unfortunately it is infeasible to be 100% accurate, especially with Elixir being a metaprogramming heavy language.

The completions include:

• keywords
• special form snippets
• functions
• macros
• modules
• variables
• struct fields (only if the struct type is explicitly stated or can be inferred from the variable binding)
• atom map keys (if map keys can be infered from variable binding)
• attributes
• types (in typespecs)
• behaviour callbacks (inside the body of implementing module)
• protocol functions (inside the body of implementing module)
• keys in keyword functions arguments (if defined in spec)
• function returns (if defined in spec)

Workspace Symbols

With Dialyzer integration enabled ElixirLS will build an index of symbols (modules, functions, types and callbacks). The symbols are taken from the current workspace, all dependencies and stdlib (Elixir and erlang). This feature enables quick navigation to symbol definitions. However due to sheer number of different symbols and fuzzy search utilized by the provider, ElixirLS uses query prefixes to improve search results relevance.

Use the following rules when navigating to workspace symbols:

• no prefix - search for modules
  • :erl
  • Enu
• f prefix - search for functions
  • f inse
  • f :ets.inse
  • f Enum.cou
  • f count/0
• t prefix - search for types
  • t t/0
  • t :erlang.time_u
  • t DateTime.
• c prefix - search for callbacks
  • c handle_info
  • c GenServer.in
  • c :gen_statem

Troubleshooting

Basic troubleshooting steps:

• Restart your editor (which will restart ElixirLS)
• After stopping your editor, remove the entire .elixir_ls directory, then restart your editor
  • NOTE: This will cause you to have to re-run the entire dialyzer build

If your code doesn't compile in ElixirLS, it may be because ElixirLS compiles code with MIX_ENV=test (by default). So if you are missing some configuration in the test environment, your code may not compile.

If you get an error like the following immediately on startup:

[Warn  - 1:56:04 PM] ** (exit) exited in: GenServer.call(ElixirLS.LanguageServer.JsonRpc, {:packet, %{...snip...}}, 5000)
    ** (EXIT) no process: the process is not alive or there's no process currently associated with the given name, possibly because its application isn't started

and you installed Elixir and Erlang from the Erlang Solutions repository, you may not have a full installation of erlang. This can be solved with sudo apt-get install esl-erlang. Originally reported in #208.

Known Issues/Limitations

• .exs files don't return compilation errors
• "Fetching n dependencies" sometimes get stuck (remove the .elixir_ls directory to fix)
• Debugger doesn't work in Elixir 1.10.0 - 1.10.2 (but it should work in 1.10.3 when this fix is released)
• "Go to definition" does not work within the scope of a Phoenix router
• On-hover docs do not work with erlang modules or functions (better support of EEP-48 is needed)
• On first launch dialyzer will cause high CPU usage for a considerable time
  • Possible mitigation in #96

Building and running

Run mix compile, then mix elixir_ls.release -o <release_dir>. This builds the language server and debugger as a set of .ez archives and creates .sh and .bat scripts to launch them.

If you're packaging these archives in an IDE plugin, make sure to build using the minimum supported OTP version for the best backwards-compatibility. Alternatively, you can use a precompiled release.

Local setup

Because ElixirLS may get launched from an IDE that itself got launched from a graphical shell, the environment may not be complete enough to run or even find the correct Elixir/OTP version. The wrapper scripts try to configure asdf-vm if available, but that may not be what you want or need. Therefore, prior to executing Elixir, the script will source $XDG_CONFIG_HOME/elixir_ls/setup.sh (e.g. ~/.config/elixir_ls/setup.sh), if available. The environment variable ELS_MODE is set to either debugger or language_server to help you decide what to do inside the script, if needed.

Acknowledgements and related projects

ElixirLS isn't the first frontend-independent server for Elixir language support. The original was Alchemist Server, which powers the Alchemist plugin for Emacs. Another project, Elixir Sense, builds upon Alchemist and powers the Elixir plugin for Atom as well as another VS Code plugin, VSCode Elixir. ElixirLS uses Elixir Sense for several code insight features. Credit for those projects goes to their respective authors.

License

ElixirLS source code is released under Apache License 2.0.

See LICENSE for more information.