Integrate with mason.nvim

We can use mason.nvim and mason-lspconfig.nvim to help us manage the installation of language servers. And then we can use lspconfig to setup the servers only when they are installed.

Here is a basic example.

require('mason').setup({})
require('mason-lspconfig').setup({
  -- Replace the language servers listed here 
  -- with the ones you want to install
  ensure_installed = {'lua_ls', 'rust_analyzer'},
  handlers = {
    function(server_name)
      require('lspconfig')[server_name].setup({})
    end,
  },
})

This config will tell mason-lspconfig to install lua_ls and rust_analyzer automatically if they are missing. And lspconfig will handle the configuration of those servers.

The servers listed in the ensure_installed option must be on this list.

Note that after you install a language server you will need to restart Neovim so the language server can be configured properly.

Configure a language server

If we need to add a custom configuration for a server, you'll need to add a property to handlers. This new property must have the same name as the language server you want to configure, and you need to assign a function to it.

Lets use an imaginary language server called example_server as an example.

--- in your own config you should replace 
--- `example_server` with the name of a language server

require('mason-lspconfig').setup({
  handlers = {
    -- this first function is the "default handler"
    -- it applies to every language server without a "custom handler"
    function(server_name)
      require('lspconfig')[server_name].setup({})
    end,

    -- this is the "custom handler" for `example_server`
    example_server = function()
      require('lspconfig').example_server.setup({
        ---
        -- in here you can add your own
        -- custom configuration
        ---
      })
    end,
  },
})

Here we use the module lspconfig to setup the language server and we add our custom config in the first argument of .example_server.setup().

Exclude a language server from the automatic setup

If we want to ignore a language server we can use an empty function as a handler. This will make mason-lspconfig ignore the setup for the language server.

--- in your own config you should replace 
--- `example_server` with the name of a language server

local noop = function() end

require('mason-lspconfig').setup({
  handlers = {
    -- this first function is the "default handler"
    -- it applies to every language server without a "custom handler"
    function(server_name)
      require('lspconfig')[server_name].setup({})
    end,

    -- this is the "custom handler" for `example_server`
    example_server = noop,
  },
})

So example_server = noop is the same thing as this.

example_server = function() end

When the time comes for mason-lspconfig to setup example_server it will execute an empty function.