Emacs Polyglot: an Emacs LSP client that stays out of your way:
📽Scroll down this README for some pretty gifs 📚Read about servers, commands and keybindings, and customization 📣Read the NEWS file
Now find some source file, any source file, and type
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.
Connecting to a server
M-x eglot can guess and work out-of-the-box with these servers:
- Rust's rls
- Python's pyls
- Ruby's solargraph
- Java's Eclipse JDT Language Server
- Bash's bash-language-server
- PHP's php-language-server
- C/C++'s ccls (cquery and clangd also work)
- Haskell's IDE engine
- Elm's elm-language-server
- Kotlin's kotlin-language-server
- Go's gopls
- Ocaml's ocaml-language-server
- R's languageserver
- Dart's dart_language_server
- Elixir's elixir-ls
- Erlang's erlang_ls
- Ada's ada_language_server
- Scala's metals
- TeX/LaTeX's Digestif
- Godot Engine's built-in LSP
I'll add to this list as I test more servers. In the meantime you can
(add-to-list 'eglot-server-programs '(foo-mode . ("foo-language-server" "--args")))
Let me know how well it works and we can add it to the list.
To skip the guess and always be prompted use
C-u M-x eglot.
You can also do:
(add-hook 'foo-mode-hook 'eglot-ensure)
, to attempt to start an eglot session automatically everytime a
foo-mode buffer is visited.
Connecting via TCP
The examples above use a "pipe" to talk to the server, which works fine on Linux and OSX but in some cases may not work on Windows.
To circumvent this limitation, or if the server doesn't like pipes,
you can use
C-u M-x eglot and give it
server:port pattern to
connect to a previously started TCP server serving LSP information.
If you don't want to start it manually every time, you can configure Eglot to start it and immediately connect to it. Ruby's solargraph server already works this way out-of-the-box.
For another example, suppose you also wanted start Python's
(add-to-list 'eglot-server-programs `(python-mode . ("pyls" "-v" "--tcp" "--host" "localhost" "--port" :autoport)))
You can see that the element associated with
python-mode is now a
more complicated invocation of the
pyls program, which requests that
it be started as a server. Notice the
:autoport symbol in there: it
is replaced dynamically by a local port believed to be vacant, so that
the ensuing TCP connection finds a listening server.
Per-project server configuration
Most servers can guess good defaults and will operate nicely out-of-the-box, but some need to be configured specially via LSP interfaces. Additionally, in some situations, you may also want a particular server to operate differently across different projects.
Per-project settings are realized with Emacs's directory variables
and the Elisp variable
eglot-workspace-configuration. To make a
particular Python project always enable Pyls's snippet support, put a
.dir-locals.el in the project's root:
((python-mode . ((eglot-workspace-configuration . ((:pyls . (:plugins (:jedi_completion (:include_params t)))))))))
This tells Emacs that any
python-mode buffers in that directory
should have a particular buffer-local value of
eglot-workspace-configuration. That variable's value should be
association list of parameter sections which are presumably
understood by the server. In this example, we associate section
pyls with the parameters object
(:plugins (:jedi_completion (:include_params t))).
Now, supposing that you also had some Go code in the very same
project, you can configure the Gopls server in the same file. Adding
a section for
go-mode, the file's contents become:
((python-mode . ((eglot-workspace-configuration . ((:pyls . (:plugins (:jedi_completion (:include_params t)))))))) (go-mode . ((eglot-workspace-configuration . ((:gopls . (:usePlaceholders t)))))))
If you can't afford an actual
.dir-locals.el file, or if managing
these files becomes cumbersome, the Emacs manual teaches you
programmatic ways to leverage per-directory local variables.
Handling quirky servers
Some servers need even more special hand-holding to operate correctly. If your server has some quirk or non-conformity, it's possible to extend Eglot via Elisp to adapt to it. Here's an example on how to get cquery working:
(add-to-list 'eglot-server-programs '((c++ mode c-mode) . (eglot-cquery "cquery"))) (defclass eglot-cquery (eglot-lsp-server) () :documentation "A custom class for cquery's C/C++ langserver.") (cl-defmethod eglot-initialization-options ((server eglot-cquery)) "Passes through required cquery initialization options" (let* ((root (car (project-roots (eglot--project server)))) (cache (expand-file-name ".cquery_cached_index/" root))) (list :cacheDirectory (file-name-as-directory cache) :progressReportFrequencyMs -1)))
eglot.el's section on Java's JDT server for an even more
Having trouble connecting to a server? Expected to have a certain capability supported by it (e.g. completion) but nothing happens? Or do you get spurious and annoying errors in an otherwise smooth operation? We may have help, so open a new issue and try to be as precise and objective about the problem as you can:
Include the invaluable events transcript. You can display that buffer with
M-x eglot-events-buffer. It contains the JSONRPC messages exchanged between client and server, as well as the messages the server prints to stderr.
If Emacs errored (you saw -- and possibly heard -- an error message), make sure you repeat the process using
M-x toggle-debug-on-errorso you get a backtrace of the error that you should also attach to the bug report.
Try to replicate the problem with as clean an Emacs run as possible. This means an empty
.emacsinit file or close to it (just loading
yasnippet.elfor example, and you don't even need
use-package.elto do that).
Some more notes: it is often the case the you will have to report the problem to the LSP server's developers, too, though it's understandable that you report it Eglot first, since it is the user-facing frontend first. If the problem is indeed on Eglot's side, we do want to fix it, but because Eglot's developers have limited resources and no way to test all the possible server combinations, you'll sometimes have to do most of the testing.
Commands and keybindings
Here's a summary of available commands:
M-x eglot, as described above;
M-x eglot-reconnectreconnects to the server;
M-x eglot-shutdownsays bye-bye to the server;
M-x eglot-renameask the server to rename the symbol at point;
M-x eglot-formatasks the server to format buffer or the active region;
M-x eglot-code-actionsasks the server for any code actions at point. These may tipically be simple fixes, like deleting an unused variable, or fixing an import. Left click on diagnostics to check if there are any there;
M-x eglot-help-at-pointasks the server for help for symbol at point.
M-x eglot-events-bufferjumps to the events buffer for debugging communication with the server.
M-x eglot-stderr-bufferif the LSP server is printing useful debug information in stderr, jumps to a buffer with these contents.
M-x eglot-signal-didChangeConfigurationupdates the LSP server configuration according to the value of the variable
eglot-workspace-configuration, which you may be set in a
.dir-localsfile, for example.
There are no keybindings specific to Eglot, but you can bind stuff
eglot-mode-map, which is active as long as Eglot is managing a
file in your project. The commands don't need to be Eglot-specific,
(define-key eglot-mode-map (kbd "C-c h") 'eglot-help-at-point) (define-key eglot-mode-map (kbd "<f6>") 'xref-find-definitions)
Here's a quick summary of the customization options. In Eglot's
customization group (
M-x customize-group) there is more
documentation on what these do.
eglot-autoreconnect: Control ability to reconnect automatically to the LSP server;
eglot-connect-timeout: Number of seconds before timing out LSP connection attempts;
eglot-sync-connect: Control blocking of LSP connection attempts;
eglot-events-buffer-size: Control the size of the Eglot events buffer;
eglot-ignored-server-capabilites: LSP server capabilities that Eglot could use, but won't;
eglot-confirm-server-initiated-edits: If non-nil, ask for confirmation before allowing server to edit the source buffer's text;
There are a couple more variables that you can customize via Emacs lisp:
eglot-server-programs: as described above;
eglot-strict-mode: Set to
nilby default, meaning Eglot is generally lenient about non-conforming servers. Set this to
(disallow-non-standard-keys enforce-required-keys)when debugging servers.
eglot-server-initialized-hook: Hook run after server is successfully initialized;
eglot-managed-mode-hook: Hook run after Eglot started or stopped managing a buffer. Use
eglot-managed-pto tell if current buffer is still being managed.
How does Eglot work?
M-x eglot starts a server via a shell-command guessed from
eglot-server-programs, using the current major-mode (for whatever
language you're programming in) as a hint.
If the connection is successful, you see an
indicator pop up in your mode-line. More importantly, this means
current and future file buffers of that major mode inside your
current project automatically become "managed" by the LSP server,
This means that information about these file's contents is exchanged
periodically to provide enhanced coding assistance. Eglot works
primarily with Emacs' built-in libraries and not with third-party
replacements for those facilities.
- definitions can be found via
- on-the-fly diagnostics are given by
- function signature hints are given by
- completion can be summoned with
- projects are discovered via
Some extra features are provided if certain libraries are installed and enabled, such as:
- completion dropdowns via company;
- snippet completions via yasnippet;
- marked-up documentation via markdown.
Eglot doesn't require these libraries to work effectively, but will use them automatically if they are found to be active.
To "unmanage" a project's buffers, shutdown the server with
Supported Protocol features
- client/registerCapability (but only
workspace/didChangeWatchedFiles, like RLS asks)
- client/unregisterCapability (ditto)
- workspace/workspaceFolders (3.6.0)
- workspace/didChangeWorkspaceFolders (3.6.0)
- workspace/configuration (3.6.0)
- textDocument/didChange (incremental or full)
- completionItem/resolve (works quite well with company-mode)
- textDocument/signatureHelp (fancy stuff with Python's pyls)
- textDocument/typeDefinition (3.6.0)
- textDocument/implementation (3.6.0)
- textDocument/declaration (3.14)
- textDocument/colorPresentation (3.6.0)
Obligatory animated gif section
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
Eglot provides template based completion if the server supports
snippet completion and yasnippet is enabled before
Eglot connects to the server. The animation shows
completion-at-point also works with
Eglot relays the diagnostics information received from the server to
display-local-help (bound to
shows the diagnostic message under point, but flymake provides other
convenient ways to handle diagnostic errors.
When Eglot manages a buffer, it disables other flymake backends. See
eglot-stay-out-of to change that.
The server may provide code actions, for example, to fix a diagnostic
error or to suggest refactoring edits. Command
queries the server for possible code actions at point. See variable
eglot-confirm-server-initiated-edits to customize its behavior.
Hover on symbol
M-x eglot-rename RET to rename the symbol at point.
To jump to the definition of a symbol, use the built-in
xref-find-definitions command, which is bound to
Eglot here relies on emacs' built-in functionality as well.
xref-find-references is bound to
M-?. Additionally, Eglot
provides the following similar commands:
Historical differences to lsp-mode.el
Around May 2018, I wrote a comparison of Eglot to
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.
The single most visible difference is the friendly entry point
M-x eglot, not
M-x eglot-<language>. Also, there are no
There's no "whitelisting" or "blacklisting" directories to languages.
M-x eglotstarts servers to handle file of a major mode inside a specific project, using Emacs's built-in
project.ellibrary 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 (like RLS);
Slow-to-start servers start asynchronously in the background;
Server-initiated edits are confirmed with the user;
Diagnostics work out-of-the-box (no
Smoother/more responsive (read below).
Under the hood:
- Message parser is much simpler.
- Defers signature requests like
textDocument/hoveruntil server is ready.
textDocument/didChangefor 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
markdown-mode, if you happen to have these installed.
- Has automated tests that check against actual LSP servers."