Emacs - Language Server Protocol
Table of Contents
Introduction
Language server protocol (LSP) offers a uniform specification between a client and a server1.
The Language Server protocol is used between a tool (the client) and a language smartness provider (the server) to integrate features like auto complete, go to definition, find all references and alike into the tool
With LSP, different clients and development tools, e.g., integrated development environment (IDE), can share a common server. Taking C/C++ for instance, various clients, e.g., Emacs, Vim, Eclipse, etc. can communicate with a common server with their own clients. For Emacs, its client is enbodied as a mode, lsp-mode2.
Maskray has provided a good summary of cquery for reference3. This post just records the installation and configuration of LSP for C/C++.
C++
cquery provides an complete LSP for C/C++/Object-C, including a LSP server and a LSP client (which depends on lsp-mode). cquery can be installed and configured following a procedure as below.
Installation
cquery
Prerequisite
pacman -S clang llvm
Install binary package
pacman -S cquery-git
Build from source codes
git clone https://github.com/jacobdufault/cquery --recursive cd cquery python waf configure --prefix /opt/cquery --use-system-clang python waf build python waf install ln -s /opt/cquery/bin/cquery /usr/local/bin mkdir ~/.emacs.d/cquery cp emacs/cquery.el ~/.emacs.d/cquery cp -r third_party /opt/cquery
lsp-mode
lsp-mode can be easily installed via ELPA.
company-lsp
For LSP, company-lsp is an optional package. It is essentially the company backend for lsp-mode, which can also be installed via ELPA.
Configuration
Add following entries into ~/.emacs.d/init.el.
(add-to-list 'load-path "~/.emacs.d/cquery") (require 'cquery) (add-hook 'c-mode-common-hook 'lsp-cquery-enable) (setq cquery-cache-dir "/tmp/cquery_cache")
With LSP, two company backends, company-semantic and company-clang can be removed if used before.
(setq company-backends (delete 'company-semantic company-backends)) (setq company-backends (delete 'company-clang company-backends))
If company-lsp is installed, it can be appended in variable company-backends by adding the following entry in ~/.emacs.d/init.el.
(push 'company-lsp company-backends)
Usage
compile_commands.json
In the normal utilization of LSP, a compilation database is required4, i.e., compile_commands.json. It can be generated by a variety of tools, e.g., cmake, build ear, ninja, waf, etc.
Taking build ear for instance, which can be installed by
pacman -S bear
a compile_commands.json can be generated by compiling the target project, e.g.
bear make -j
.cquery
If compile_commands.json cannot be generated, an alternative solution is to create a file .cquery in the root directory of each project with its content as follows.
# Driver /usr/bin/clang # Language -xc++ -std=c++14 # Includes -I/opt/cquery/third_party
Provision
By default, the LSP client uses company-capf for completion, which is a company backend. Therefore, function company-complete can list the candidates for completion offered by LSP.
| Key binding | Function |
|---|---|
M-. |
xref-find-definitions |
M-, |
xref-pop-marker-stack |
C-M-i |
complete-symbol |
C-M-. |
xref-find-apropos |