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Adding support for languages#

Registering server#

Here it is the minimal configuration that is needed for new language server registration. Refer to the documentation of lsp-mode.el for the additional settings supported on registration time. lsp-language-id-configuration must be updated to contain the corresponding mode -> language id - in this case (python-mode . "python")

(defvar lsp-language-id-configuration
    (python-mode . "python")
;; if you are adding the support for your language server in separate repo use
;; (add-to-list 'lsp-language-id-configuration '(python-mode . "python"))

 (make-lsp-client :new-connection (lsp-stdio-connection "pyls")
                  :activation-fn (lsp-activate-on "python")
                  :server-id 'pyls))

lsp-mode is using lsp-language-id-configuration to determine what is the buffer language. When the major-mode is not sufficient to determine the language (e.g. web-mode is used for javascript, html, and css) you can put regex.

Note: In the above example, when a new client is created using make-lsp-client, a new connection to the language server is created using lsp-stdio-connection. Please carefully check its documentation, as the function checks for various things (e.g. testing for the executable in PATH) and handles respective errors. Often while adding a server, the LSP client author might do these checks themselves, but without handling the errors correctly. This leads to features like lsp-install-server breaking for other users; e.g. see this issue. This is a common mistake that keeps reoccurring.

Here's an example of how to set up a custom language server in your init.el file:

;; Use shopify-cli / theme-check-language-server for Shopify's liquid syntax
(with-eval-after-load 'lsp-mode
  (add-to-list 'lsp-language-id-configuration
    '(shopify-mode . "shopify"))

    (make-lsp-client :new-connection (lsp-stdio-connection "theme-check-language-server")
                     :activation-fn (lsp-activate-on "shopify")
                     :server-id 'theme-check)))

Note: This example assumes that you've already set up a major mode of your own either by deriving it from web-mode or perhaps by writing it yourself.

If the language server supports environment variables to control additional behavior, you can register that by using the :environment-fn function, like the Bash language client does:

 (make-lsp-client :new-connection (lsp-stdio-connection '("bash-language-server" "start"))
                  :activation-fn (lsp-activate-on "shellscript")
                  :priority -1
                  :environment-fn (lambda ()
                                    '(("EXPLAINSHELL_ENDPOINT" . lsp-bash-explainshell-endpoint)
                                      ("HIGHLIGHT_PARSING_ERRORS" . lsp-bash-highlight-parsing-errors)))
                  :server-id 'bash-ls))

lsp-bash-explainshell-endpoint and lsp-bash-highlight-parsing-errors are language client defcustom that expose supported server environment settings in a type-safe way. If you change any of those variables, restart the language server with lsp-restart-workspace for the changes to be applied.

Also, if new client support customizing language server path. It's recommended to make a wrapper function so the user can customize the value even after the client has been loaded.

(defcustom lsp-tex-executable "digestif"
  "Command to start the Digestif language server."
  :group 'lsp-tex
  :risky t
  :type 'file)

  ;; instead of `:new-connection (lsp-stdio-connection lsp-tex-executable)` use
  :new-connection (lsp-stdio-connection (lambda () lsp-tex-executable))
  :activation-fn (lsp-activate-on "plaintex" "latex")
  :priority -1
  :server-id 'digestif))


lsp-mode provides tools to bridge emacs defcustom as a language configuration sections properties(see specification workspace/configuration). In addition you may use lsp-generate-settings from Generate Settings script to generate lsp-defcustom from package.json VScode plugin manifest. Example:

(lsp-defcustom lsp-foo-language-server-property "bar"
  "Demo property."
  :group 'foo-ls
  :lsp-path "")

(lsp-configuration-section "foo")
;; =>  (("foo" ("settings" ("property" . "bar"))))


  • Add the new language server to the lsp-clients.json file sorted by the full-name key alphabetically.
  • Create a new navigation entry in mkdocs.yml file.

Last update: February 27, 2024