Neovim for Beginners — LSP (Part 1)

Configure the built-in LSP (Language Server Protocol) client.

Neovim supports the Language Server Protocol (LSP), which means it acts as a client to LSP servers and includes a Lua framework vim.lsp (:h vim.lsp) for building enhanced LSP tools. The language servers are provided by third parties.

In this article, we are going to

• Configure the nvim-lspconfigplugin that provides common configuration for various language servers.
• Configure a language server installer to make it easy to install any language server.
• Configure key mappings for the LSP features.
• Configure the vim.lsp.omnifunc function (:h vim.lsp.omnifunc) as the omnifunc(:h omnifunc) handler. The omnifuncoption specifies a function to be used for insert mode omni completion with CTRL-X CTRL-O.
• Configure the vim.lsp.formatexpr function as the handler for formatexpr(:h formatexpr). The formatexpr option specifies an expression that is evaluated to format a range of lines for the gqoperator or automatic formatting (:h formatoptions).
• Configure LSP completion using coq.nvim and nvim-cmp. Previously, we talked about these two completion plugins in this article.

This article is part of the Neovim for Beginners series.

The Neovim configuration files can be found in this repository.

Unlike treesitter or ctags, LSP facilitates features like go-to-definition, find-references, hover, completion, rename, format, refactor, etc., using semantic whole-project analysis. We will get started by installing and configuring nvim-lspconfig.

nvim-lspconfig

nvim-lspconfig is a collection of common configurations for Neovim’s built-in language server client.

Installation

In thelua/plugins.lua file, add the following lines.

We also install nvim-lsp-installer which is a companion plugin for nvim-lspconfig that allows us to install LSP servers locally.

Language Servers

Create a new file lua/config/lsp/init.lua with the following content.

• We install the language servers for Go (gopls), HTML (html), JSON (jsonls), Python (pyright), Rust (rust_analyzer), Lua (sumeko_lua), Javascript/Typescript (tsserver), and Vimscript (vimls).
• Check out the list of supported language servers here.
• Currently, we do not configure any specific settings for all the language servers so the Lua tables are empty. We will see how to fine-tune a particular language server later.
• The on_attach function is called when a language server is attached to a buffer. In this function, we attach the LSP handlers to omnifunc and formatexpr. We also call the function to configure the key mappings.
• Check out the documentation (:h vim.lsp.start_client) on the LSP configuration. The debounce_text_changes flag debounces didChange notifications to the server by the given number in milliseconds. No debounce occurs if nil.

LSP Installer

Create a new file lua/config/lsp/installer.lua with the following content.

• We use the nvim-lsp-installer plugin to install the language servers.
• The language servers are installed automatically.

Note: We leverage the utils module which uses vim-notify to show a popup notification.

Key Mappings

Create a new file lua/config/lsp/keymaps.lua with the following content.

• We configure key mappings for some of the LSP functions in normal mode. E.g. [d, ]d to navigate the diagnostic messages, K to show the hover documentation.
• We also use whichkey to map the prefix <Leader>l and g to several LSP functions. E.g. gd to show the definition, gt to show the type definition.

Tip: For a newer version of Neovim (0.7 and above), try using the new keymap APIs (:h vim.keymap.set()). E.g. we can define the key for hover action like below. Buffer 0 or true means the current buffer.

-- For normal mode
vim.keymap.set("n", "K", vim.lsp.buf.hover, { buffer = 0 })

-- For normal and visual mode
vim.keymap.set({"n", "v"}, "K", vim.lsp.buf.hover, { buffer = 0 })

Screenshots

Run the :PackerInstall command to install the plugins now.

The language servers are installed automatically.

Omni completion (CTRL-X CTRL-O) should work now.

The LSP key mappings should also work if the capability is supported. E.g. gd to go to the definition, and gs to show the signature help.

Type :LspInfo and we can see the language server details for the current buffer.

Tip: We press K to show the documentation. To go into the hover documentation, press K again. To exit, press q.

Tips:

• We press gd, gt, gI to navigate to the definition, type definition, or implementation. To go back, we can press Ctrl-t (:h Ctrl-t). Ctrl-t jumps to an older entry in the tag stack.
• Type :tags and we can see that the older entries are saved into the tag list. Ctrl-o and Ctrl-i are used for the jump list (:h jumplist).
• E.g. in the below screenshot, we press gd to go the definition of the joblib module. We jump to different locations within the file. To go back to the joblib location, instead of pressing Ctrl-o multiple times, we just need to press Ctrl-t.

nvim-cmp

The built-in omni completion is not so helpful. Let’s proceed to configure a completion plugin.

In the lua/plugins.lua file, for nvim-cmp add the lines to install cmp-nvim-lsp(line 16).

We also install lsp_signature.nvim (line 12) to show the function signature as we type.

In the lua/config/lsp/init.lua file, we configure lsp_signature.nvim and update the capability for cmp-nvim-lsp.

In the lua/config/cmp.lua file, we add the completion source for cmp-nvim-lsp.

Screenshots

Run the :PackerInstall command to install the plugins now.

Completion should work now for the configured language servers, and we can also see the function signature as we type.

coq.nvim

Let’s try out coq.nvim.

First, we need to disable nvim-cmp. In the lua/plugins.lua file, set the disable option to true. For coq_nvim we set it to false.

use {
  "hrsh7th/nvim-cmp",
  disable = true
}

use {
  "ms-jpq/coq_nvim",
  disable = false,
}

For the nvim-lspconfig plugin, instead of cmp-nvim-lsp, we want to use coq_nvim.

In the lua/config/lsp/init.lua file, comment out the lines for nvim-cmp.

Now in the lua/config/lsp/installer.lua file, add the lines for coq.nvim.

Screenshots

Run the :PackerInstall command to install the plugins now.

Completion should work now for the configured language servers, and we can also see the function signature as we type.

In the next article, we will fine-tune the configuration to further improve the coding experience.

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