Language Server Protocol Support for Emacs

Table of Contents

• Language Server Protocol Support for Emacs
  • Why?
  • Overview
  • Installation
    • Install via melpa
  • Configuration
    • Install language server
    • Configure lsp-mode
      • Vanilla Emacs
      • Spacemacs
      • use-package
    • How it works?
  • Supported languages
  • Commands
  • Settings
  • Screenshots
  • Extensions
    • TRAMP (Experimental)
      • How does it work?
      • Sample configuration
  • Troubleshooting
  • Adding support for languages
  • FAQ
  • See also

Why?

• ❤️ Community Driven
• 💎 Fully featured - supports LSP core and Language Server non-standard extensions
• 🚀 Easy to configure - works out of the box and automatically upgrades if additional packages are present
• 🌟 Flexible - could be configured as full-blown IDE with flashy UI or minimal distraction free

Overview

Client for Language Server Protocol (v3.14). lsp-mode aims to provide IDE-like experience by providing optional integration with the most popular Emacs packages like company, flycheck and projectile.

• Non-blocking asynchronous calls
• Real-time Diagnostics/linting (via builtin flymake when Emacs > 26 or flycheck/lsp-ui)
• Code completion - using company-lsp or builtin completion-at-point
• Hovers - using lsp-ui
• Code actions - using lsp-execute-code-action or lsp-ui
• Code outline - using builtin imenu or helm-imenu
• Code navigation - using builtin xref
• Code lens (references/implementations) - using builtin xref
• Highlights
• Formatting
• Debugger - dap-mode
• Helm integration - helm-lsp

Installation

Install via melpa

The recommended way to install lsp-mode is via package.el - the built-in package manager in Emacs. lsp-mode is available on the two major package.el community maintained repos - MELPA Stable and MELPA.

M-x package-install [RET] lsp-mode [RET]

Configuration

Install language server

Check the table bellow with the list of supported servers and the corresponding instructions on how to install the server.

Configure lsp-mode

Vanilla Emacs

You could go minimal and use lsp-mode as it is without external packages with the built-in flymake and completion-at-point or you could install the following extensions for better experience:

• install lsp-ui for flycheck integration and higher level UI modules.
• install company-lsp if you want to use company-mode for completion.

(require 'lsp-mode)
(add-hook 'XXX-mode-hook #'lsp)

where XXX could be major mode like python, java, c++. Alternatively, if you want to minimize you configuration you may use prog-mode-hook. In case you do that, lsp will try to start for each programming mode and echo a message when there is no client registered for the current mode or if the corresponding server is not present. In addition, lsp-mode will automatically detect and configure lsp-ui and company-lsp. To turn off that behavior you could set lsp-auto-configure to nil.

Spacemacs

lsp-mode is included in spacemacs develop branch. Add lsp to dotspacemacs-configuration-layers and configure the language that you want to use to be backed by lsp backend.

use-package

Replace (require 'lsp-mode) with the following if you use use-package.

(use-package lsp-mode
  :commands lsp
  :init
  (setq ...))

(use-package lsp-ui :commands lsp-ui-mode)
(use-package company-lsp :commands company-lsp)

How it works?

lsp-mode has predefined list of server configurations (located in lsp-clients.el) containing a mapping from major-mode to the server configuration. In addition to the default server configuration located in lsp-clients.el there are few languages servers which require separate package(check Supported languages). When you open a file from a particular project lsp-mode and call lsp command lsp-mode will look for server registrations able to handle current major-mode. If there is such client lsp-mode will look for the project root. If you open a file from the project for the first time you will be prompted the project. Once the project is imported project root is saved in lsp-session file and it will be loaded the next time you start Emacs so you no longer will be asked for a project root when you open a file from that project. Later if you want to change the project root you may use lsp-workspace-folder-remove to remove the project and call lsp-workspace-folder-add to add the root. If you want to force starting a particular language server in a file you may use C-u M-x lsp which will prompt you to select language server to start.

Supported languages

Some of the servers are directly supported by lsp-mode by requiring lsp-clients.el while other require installing additional package which provide server specific functionality.

Language	Language Server	Built-in	Installation command	Debugger
Bash	bash-language-server	Yes	npm i -g bash-language-server
C++	ccls	emacs-ccls	ccls	Yes (via llvm debug adapter)
C++	clangd	Yes	clangd	Yes (via llvm debug adapter)
C++	cquery	emacs-cquery	cquery	Yes (via llvm debug adapter)
CSS/LessCSS/SASS/SCSS	css	Yes	npm install -g vscode-css-languageserver-bin
Dart	dart_language_server	Yes	pub global activate dart_language_server
Elixir	elixir-ls	Yes	elixir-ls	Yes
Fortran	fortran-language-server	Yes	pip install fortran-language-server
Go	bingo	Yes	bingo
Groovy	groovy-language-server	Yes	groovy-language-server
HTML	html	Yes	npm install -g vscode-html-languageserver-bin
Haskell	IDE engine	lsp-haskell	IDE engine
Java	Eclipse JDT LS	lsp-java	Automatic by lsp-java	Yes
JavaScript/TypeScript	typescript-language-server (recommended)	Yes	npm i -g typescript-language-server; npm i -g typescript
JavaScript/TypeScript	javascript-typescript-stdio	Yes	npm i -g javascript-typescript-langserver
JavaScript Flow	flow (add-on if working on a Flow file)	Yes	flow
Ocaml	ocaml-language-server	Yes	ocaml-language-server
PHP	php-language-server	Yes	php-language-server	Yes
Python	pyls	Yes	pip install ‘python-language-server[all]’	Yes
Python(Microsoft)	Microsoft Python Language Server	lsp-python-ms	lsp-python-ms	Yes
Ruby	solargraph	Yes	gem install solargraph	Yes
Rust	rls	Yes	rls	Yes (via llvm debug adapter)
Scala	lsp-scala	lsp-scala	lsp-scala
Swift	sourcekit-LSP	lsp-sourcekit	sourcekit-LSP	Yes (via llvm debug adapter)
Vue	vue-language-server	Yes	npm install -g vue-language-server

Commands

• lsp-describe-session - Display session folders and running servers.
• lsp-describe-thing-at-point - Display help for the thing at point.
• lsp-execute-code-action - Execute code action.
• lsp-format-buffer - Format current buffer
• lsp-goto-implementation - Go to implementation
• lsp-goto-type-definition - Go to type definition
• lsp-rename - Rename symbol at point
• lsp-restart-workspace - Restart project
• lsp-symbol-highlight - Highlight all relevant references to the symbol under point.
• lsp-workspace-folders-add - Add workspace folder
• lsp-workspace-folders-remove - Remove workspace folder
• lsp-workspace-folders-switch - Switch workspace folder
• imenu or helm-imenu - display document structure.
• completion-at-point - display completion using built-in emacs completion-at-point framework.
• lsp-find-definition - to find the definition for the symbol under point.
• lsp-find-references - Find references for the symbol under point.
• lsp-lens-show - Show lenses in the current file
• lsp-lens-hide - Hide lenses in the current file
• lsp-lens-mode (experimental) - Turn on/off lenses in the current file.
• lsp-save-logs - Save a trace of all messages to and from the language server to a given file. Only works when lsp-save-logs is non-nil.

Settings

• lsp-print-io - If non-nil, print all messages to and from the language server to *lsp-log*.
• lsp-trace - If non-nil, keep a trace of all messages to and from the language server, which can be saved to a file with lsp-save-logs.
• lsp-print-performance - If non-nil, print performance info. to *lsp-log*.
• lsp-inhibit-message - If non-nil, inhibit the message echo via inhibit-message.
• lsp-report-if-no-buffer - If non nil the errors will be reported even when the file is not open.
• lsp-keep-workspace-alive - If non nil keep workspace alive when the last workspace buffer is closed.
• lsp-enable-snippet - Enable/disable snippet completion support.
• lsp-auto-guess-root - Automatically guess the project root using projectile/project.
• lsp-restart - Defines how server exited event must be handled.
• lsp-session-file - Automatically guess the project root using projectile/project.
• lsp-auto-configure - Auto configure lsp-mode. When set to t lsp-mode will auto-configure lsp-ui and company-lsp.
• lsp-document-sync-method - How to sync the document with the language server.
• lsp-auto-execute-action - Auto-execute single action.
• lsp-eldoc-render-all - Define whether all of the returned by document/onHover will be displayed. If lsp-markup-display-all is set to nil eldoc will show only the symbol information.
• lsp-enable-completion-at-point - Enable completion-at-point integration.
• lsp-enable-xref - Enable xref integration.
• lsp-prefer-flymake - If you prefer flycheck and lsp-ui-flycheck is available, (setq lsp-prefer-flymake nil). If set to :none neither of two will be enabled.
• lsp-enable-indentation - Indent regions using the file formatting functionality provided by the language server.
• lsp-enable-on-type-formatting - Enable textDocument/onTypeFormatting integration.
• lsp-before-save-edits - If non-nil, lsp-mode will apply edits suggested by the language server before saving a document.
• lsp-imenu-show-container-name - Display the symbol’s container name in an imenu entry.
• lsp-imenu-container-name-separator - Separator string to use to separate the container name from the symbol while displaying imenu entries.
• lsp-imenu-sort-methods - How to sort the imenu items. The value is a list of kind, name or position. Priorities are determined by the index of the element.
• lsp-response-timeout - Number of seconds to wait for a response from the language server before timing out.

Screenshots

• RUST Completion with company-lsp
• Typescript references using lsp-ui
• Debugging Python using dap-mode
• Call hierarchy via ccls

Extensions

TRAMP (Experimental)

LSP mode has support for tramp buffers with the following requirements.

• The language server have to be present on the remote server since it is running on the remote machine.
• Having multi folder language server (like Eclipse JDT LS) cannot have local and remote servers.

How does it work?

lsp-mode detects whether a particular file is located on remote machine and looks for a client which can handle the current major mode and it is marked as :remote? t. Then lsp-mode starts the client through tramp.

Sample configuration

Here it is example how you can configure python language server to work when using TRAMP.

(lsp-register-client
 (make-lsp-client :new-connection (lsp-tramp-connection "pyls")
                  :major-modes '(python-mode)
                  :remote? t
                  :server-id 'pyls))

Troubleshooting

• set lsp-print-io to t to inspect communication between client and the server.
• lsp-describe-session will show the current projects roots + the started severs and allows inspecting the server capabilities.

Adding support for languages

Here it is the minimal configuration that is needed for new language server registration. Refer to the documentation of lsp-client.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")

(lsp-register-client
 (make-lsp-client :new-connection (lsp-stdio-connection "pyls")
                  :major-modes '(python-mode)
                  :server-id 'pyls))

FAQ

• How to configure a server with local variables? Add lsp server call to hack-local-variables-hook which runs right after the local variables are loaded.

  (add-hook 'hack-local-variables-hook
            (lambda () (when (derived-mode-p 'XXX-mode) (lsp))))
      

• I have multiple language servers registered for language FOO. Which one will be used when opening a project? The one with highest priority wins. lsp-clients.el predefined servers have priority -1, lower than external packages (priority 0 if unspecified). If a server is registered with :add-on? flag set to t it will be started in parallel to the other servers that are registered for the current mode.

See also

• dap-mode - Debugger integration for lsp-mode.
• eglot - An alternative minimal LSP implementation.