M-x Eglot

Emacs Polyglot: an Emacs LSP client that stays out of your way:

• 📽 Scroll down this README for some pretty gifs
• 📚 Read the manual
• 📣 Read the NEWS file
• 🏆 Folks over at Google seem to like it. Thanks!

1-2-3

Install from GNU ELPA or MELPA. Just type M-x package-install RET eglot RET into Emacs 26.1+.

Now find some source file, any source file, and type M-x eglot.

That's it. If you're lucky, this guesses the LSP program to start for the language you're using. Otherwise, it prompts you to enter one.

1-2-3-pitfall!

By design, Eglot doesn't depend on anything but Emacs. But there are ELPA dependencies to newer versions of so-called "core packages" developed in the Emacs mainline. So unless you're using a bleeding-edge Emacs, where loading eglot.el is all you'd need to do, make sure your package system pulls in and loads the newest project.el, xref.el, eldoc.el, etc... In case of trouble M-x find-library can help you tell if that happened.

Connecting to a server

M-x eglot can guess and work out-of-the-box with these servers:

• Ada's ada_language_server
• Bash's bash-language-server
• C/C++'s clangd or ccls
• C#'s omnisharp
• Clojure's clojure-lsp
• CMake's cmake-language-server
• CSS's css-languageserver
• Dart's analysis_server
• Dockerfile's docker-langserver
• Elixir's elixir-ls
• Elm's elm-language-server
• Erlang's erlang_ls
• Fortran's fortls
• Futhark's futhark lsp
• Go's gopls
• Godot Engine's built-in LSP
• HTML html-languageserver
• Haskell's haskell-language-server
• JSON's vscode-json-languageserver
• Java's Eclipse JDT Language Server
• Javascript's TS & JS Language Server
• Kotlin's kotlin-language-server
• Lua's lua-lsp
• Markdown's marksman
• Mint's mint-ls
• Nix's rnix-lsp
• Ocaml's ocaml-lsp
• Perl's Perl::LanguageServer
• PHP's php-language-server
• PureScript's purescript-language-server
• Python's pylsp, pyls pyright, or jedi-language-server
• R's languageserver
• Racket's racket-langserver
• Ruby's solargraph
• Rust's rust-analyzer
• Scala's metals
• TeX/LaTeX's Digestif
• VimScript's vim-language-server
• YAML's yaml-language-server
• Zig's zls

I'll add to this list as I test more servers.

Obligatory animated gif section

Completion

The animation shows company-mode presenting the completion candidates to the user, but Eglot works with the built-in completion-at-point function as well, which is usually bound to C-M-i.

Snippet completion

Eglot provides template based completion if the server supports snippet completion and yasnippet is enabled before Eglot connects to the server. The animation shows company-mode, but completion-at-point also works with snippets.

Diagnostics

Eglot relays the diagnostics information received from the LSP server to Emacs's Flymake, which annotates/underlines the problematic parts of the buffer. The information is shared with the ElDoc system, meaning that the commands eldoc and eldoc-doc-buffer (the latter bound to C-h-. for convenience) show diagnostics along with other documentation under point.

Flymake provides other convenient ways to view and manage diagnostic errors. These are described in its manual.

When Eglot manages a buffer, it disables pre-existing Flymake backends. See variable eglot-stay-out-of to change that.

Code Actions

The LSP server may provide code actions, for example, to fix a diagnostic error or to suggest refactoring edits. The commands are frequently associating with Flymake diagnostic annotations, so that left-clicking them shows a menu. Additionally, the command eglot-code-actions asks the server for any code spanning a given region.

Sometimes, these code actions are initiated by the server. See eglot-confirm-server-initiated-edits to control that behaviour.

Hover on symbol /function signature

Here, too, the LSP server's view of a given symbol or function signature is relayed to the ElDoc system. The commands eldoc and eldoc-doc-buffer commands access that information.

There are customization variables to help adjust ElDoc's liberal use of the lower "echo area", among other options. If you still find the solicitous nature of this LSP feature too distracing, you can use eglot-ignored-server-capabilities to turn it off.

Rename

Type M-x eglot-rename RET to rename the symbol at point.

Find definition

To jump to the definition of a symbol, use the built-in xref-find-definitions command, which is bound to M-..

Find references

Eglot here relies on Emacs' built-in functionality as well. xref-find-references is bound to M-?. Additionally, Eglot provides the following similar commands: eglot-find-declaration, eglot-find-implementation, eglot-find-typeDefinition.

Historical differences to lsp-mode.el

Around May 2018, I wrote a comparison of Eglot to lsp-mode.el, and was discussed with its then-maintainer. That mode has since been refactored/rewritten and now purports to support a lot of features that differentiated Eglot from it. It may now be very different or very similar to Eglot, or even sing with the birds in the trees, so go check it out. That said, here's the original comparison, which I will not be updating any more.

"Eglot is considerably less code and hassle than lsp-mode.el. In most cases, there's nothing to configure. It's a minimalist approach focused on user experience and performance.

User-visible differences:

• The single most visible difference is the friendly entry point M-x eglot, not M-x eglot-<language>. Also, there are no eglot-<language> extra packages.

• There's no "whitelisting" or "blacklisting" directories to languages. M-x eglot starts servers to handle file of a major mode inside a specific project, using Emacs's built-in project.el library to discover projects. Then it automatically detects current and future opened files under that project and syncs with server;

• Easy way to quit/restart a server, just middle/right click on the connection name;

• Pretty interactive mode-line section for live tracking of server communication;

• Automatically restarts frequently crashing servers;

• Slow-to-start servers start asynchronously in the background;

• Server-initiated edits are confirmed with the user;

• Diagnostics work out-of-the-box (no flycheck.el needed);

• Smoother/more responsive (read below).

Under the hood:

• Message parser is much simpler.
• Defers signature requests like textDocument/hover until server is ready.
• Sends textDocument/didChange for groups of edits, not one per each tiny change.
• Easier to read and maintain elisp. Yeah I know, very subjective, so judge for yourself.
• Doesn't require anything other than Emacs, but will automatically upgrade to work with stuff outside Emacs, like company, markdown-mode, if you happen to have these installed.
• Has automated tests that check against actual LSP servers."

Copyright Assignment

Eglot is subject to the same copyright assignment policy as GNU Emacs.

Any legally significant contributions can only be merged after the author has completed their paperwork. Please ask for the request form, and we'll send it to you.