---
title: Use Language Servers for Development in the FreeBSD Src Tree
authors:
  - author: Ka Ho Ng
    email: khng@FreeBSD.org
copyright: 2021 The FreeBSD Foundation
description: Use Language Servers for development in the FreeBSD src tree to get precise go-to-definition and completion results.
trademarks: ["freebsd"]
tags: ["FreeBSD", "Language Server", "LSP"]

---

= Use Language Servers for Development in the FreeBSD Src Tree
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[[intro]]
== Introduction

This guide is about setting up a FreeBSD src tree with language servers performing source code indexing.

[[ports-required]]
== Required Ports

Some ports are required throughout the guide.
Choose a favorite combination of tools from each category below:

* Language server implementations
** package:devel/ccls[]
** package:devel/llvm12[] (Other versions are okay, but newer is better. Replace `clangd12` with clangdN in case other versions are used.)
* Editors
** package:editors/vim[]
** package:editors/neovim[]
** package:editors/vscode[]
* Compilation database generator
** package:devel/python[] (For llvm's scan-build-py implementation)
** package:devel/py-pip[] (For rizsotto's scan-build implementation)
** package:devel/bear[]

[[editor-settings]]
== Editor settings

[[settings-vim]]
=== Vim/Neovim

==== LSP client plugins

The built-in plugin manager is used for both editors in this example.
The LSP client plugin used is link:https://github.com/prabirshrestha/vim-lsp[prabirshrestha/vim-lsp].

To set up the LSP client plugin for Neovim:

[source,shell]
....
# mkdir -p ~/.config/nvim/pack/lsp/start
# git clone https://github.com/prabirshrestha/vim-lsp ~/.config/nvim/pack/lsp/start/vim-lsp
....

and for Vim:

[source,shell]
....
# mkdir -p ~/.vim/pack/lsp/start
# git clone https://github.com/prabirshrestha/vim-lsp ~/.vim/pack/lsp/start/vim-lsp
....

To enable the LSP client plugin in the editor, add the following snippet into [.filepath]#~/.config/nvim/init.vim# when using Neovim, or [.filepath]#~/.vim/vimrc# when using Vim:

.For ccls
[source,vim]
....
au User lsp_setup call lsp#register_server({
    \ 'name': 'ccls',
    \ 'cmd': {server_info->['ccls']},
    \ 'allowlist': ['c', 'cpp', 'objc'],
    \ 'initialization_options': {
    \     'cache': {
    \         'hierarchicalPath': v:true
    \     }
    \ }})
....

.For clangd
[source,vim]
....
au User lsp_setup call lsp#register_server({
    \ 'name': 'clangd',
    \ 'cmd': {server_info->['clangd12', '--background-index', '--header-insertion=never']},
    \ 'allowlist': ['c', 'cpp', 'objc'],
    \ 'initialization_options': {},
    \ })
....

Please refer to link:https://github.com/prabirshrestha/vim-lsp/blob/master/README.md#registering-servers[] to learn about setting up key bindings and code completion.
The official site of clangd is link:https://clangd.llvm.org[], and the repository link of ccls is link:https://github.com/MaskRay/ccls/[].

Below are the reference settings of keybindings and code completions.
Put the following snippet into [.filepath]#~/.config/nvim/init.vim#, or [.filepath]#~/.vim/vimrc# for Vim users to use it:

[source,vim]
....
function! s:on_lsp_buffer_enabled() abort
    setlocal omnifunc=lsp#complete
    setlocal completeopt-=preview
    setlocal keywordprg=:LspHover

    nmap <buffer> <C-]> <plug>(lsp-definition)
    nmap <buffer> <C-W>] <plug>(lsp-peek-definition)
    nmap <buffer> <C-W><C-]> <plug>(lsp-peek-definition)
    nmap <buffer> gr <plug>(lsp-references)
    nmap <buffer> <C-n> <plug>(lsp-next-reference)
    nmap <buffer> <C-p> <plug>(lsp-previous-reference)
    nmap <buffer> gI <plug>(lsp-implementation)
    nmap <buffer> go <plug>(lsp-document-symbol)
    nmap <buffer> gS <plug>(lsp-workspace-symbol)
    nmap <buffer> ga <plug>(lsp-code-action)
    nmap <buffer> gR <plug>(lsp-rename)
    nmap <buffer> gm <plug>(lsp-signature-help)
endfunction

augroup lsp_install
    au!
    autocmd User lsp_buffer_enabled call s:on_lsp_buffer_enabled()
augroup END
....

[[settings-vscode]]
=== VSCode

==== LSP client plugins

LSP client plugins are required to launch the language server daemon.
Press `Ctrl+Shift+X` to show the extension online search panel.
Enter `llvm-vs-code-extensions.vscode-clangd` when running clangd, or `ccls-project.ccls` when running ccls.

Then, press `Ctrl+Shift+P` to show the editor commands palette.
Enter `Preferences: Open Settings (JSON)` into the palette and hit `Enter` to open [.filepath]#settings.json#.
Depending on the language server implementations, put one of the following JSON key/value pairs in [.filepath]#settings.json#:

.For clangd
[source,json]
....
[
    /* Begin of your existing configurations */
    ...
    /* End of your existing configurations */
    "clangd.arguments": [
        "--background-index",
        "--header-insertion=never"
    ],
    "clangd.path": "clangd12"
]
....

.For ccls
[source,json]
....
[
    /* Begin of your existing configurations */
    ...
    /* End of your existing configurations */
    "ccls.cache.hierarchicalPath": true
]
....

[[cdb]]
== Compilation database

A Compilation database contains an array of compile command objects.
Each object specifies a way of compiling a source file.
The compilation database file is usually [.filename]#compiler_commands.json#.
The database is used by language server implementations for indexing purpose.

Please refer to link:https://clang.llvm.org/docs/JSONCompilationDatabase.html#format[] for details on the format of the compilation database file.

[[cdb-generators]]
=== Generators

[[generators-scan-build-py]]
==== Using scan-build-py

===== Installation

`intercept-build` tool from scan-build-py is used to generate compilation
database.

Install package:devel/python[] to get python interpreter first. To get
`intercept-build` from LLVM:

[source,shell]
....
# git clone https://github.com/llvm/llvm-project /path/to/llvm-project
....

where [.filename]#/path/to/llvm-project/# is your desired path for the repository. Make an alias in the shell configuration file for convenience:

[source,shell]
....
alias intercept-build='/path/to/llvm-project/clang/tools/scan-build-py/bin/intercept-build'
....

link:https://github.com/rizsotto/scan-build[rizsotto/scan-build] can be used instead of LLVM's scan-build-py.
The LLVM's scan-build-py was rizsotto/scan-build merged into the LLVM tree.
This implementation can be installed by `pip install --user scan-build`.
The `intercept-build` script is in [.filename]#~/.local/bin# by default.

===== Usage

In the top-level directory of the FreeBSD src tree, generate the compilation database with `intercept-build`:

[source,shell]
....
# intercept-build --append make buildworld buildkernel -j`sysctl -n hw.ncpu`
....

The `--append` flag tells the `intercept-build` to read an existing compilation database (if a compilation database exists) and append the results to the database.
Entries with duplicated command keys are merged.
The generated compilation database by default is saved in the current working directory as [.filename]#compiler_commands.json#.

[[generators-bear]]
==== Using devel/bear

===== Usage

In the top-level directory of the FreeBSD src tree, to generate compilation database with `bear`:

[source,shell]
....
# bear --append make buildworld buildkernel -j`sysctl -n hw.ncpu`
....

The `--append` flag tells `bear` to read an existing compilation database if it is present, and append the results to the database.
Entries with duplicated command key are merged.
The generated compilation database by default is saved in the current working directory as [.filename]#compiler_commands.json#.

[[final]]
== Final

Once the compilation database is generated, open any source files in the FreeBSD src tree and LSP server daemon will be launched as well in background.
Opening source files in the src tree for the first time takes significantly longer time before the LSP server is able to give a complete result, due to initial background indexing by the LSP server compiling all the listed entries in the compilation database.
The language server daemon however does not index the source files not appearing in the compilation database, thus no complete results are shown on source files not being compiled during the `make`.
