fix: prevent mason setup from being run twice (nvim-lua#1298)

* fix: prevent mason setup from being run twice

Addresses nvim-lua#1297

Currently, we're calling `require('mason').setup(...)` twice:
* once when setting it as a dependency of `nvim-lspconfig` (since we set
	`config = true`)
* once in the `config` function we define for `nvim-lspconfig`

Calling setup twice can cause issues with, e.g., setting the `PATH`
option: you might append Mason's bin dir in one setup call and prepend
it in the other.

We've kept the setup of `mason` in the `nvim-lspconfig` dependencies
table since leaving it to the `config` function caused some
plugin-loading-order related issues in the past. See:
* nvim-lua#210
* nvim-lua#554
* nvim-lua#555
* nvim-lua#865

* docs: tweak comments per review feedback

Author: tomasgareau

init.lua

@@ -458,7 +458,9 @@ require('lazy').setup({
     'neovim/nvim-lspconfig',
     dependencies = {
       -- Automatically install LSPs and related tools to stdpath for Neovim
-      { 'williamboman/mason.nvim', config = true }, -- NOTE: Must be loaded before dependants
+      -- Mason must be loaded before its dependents so we need to set it up here.
+      -- NOTE: `opts = {}` is the same as calling `require('mason').setup({})`
+      { 'williamboman/mason.nvim', opts = {} },
       'williamboman/mason-lspconfig.nvim',
       'WhoIsSethDaniel/mason-tool-installer.nvim',
 
@@ -647,13 +649,16 @@ require('lazy').setup({
       }
 
       -- Ensure the servers and tools above are installed
-      --  To check the current status of installed tools and/or manually install
-      --  other tools, you can run
+      --
+      -- To check the current status of installed tools and/or manually install
+      -- other tools, you can run
       --    :Mason
       --
-      --  You can press `g?` for help in this menu.
-      require('mason').setup()
-
+      -- You can press `g?` for help in this menu.
+      --
+      -- `mason` had to be setup earlier: to configure its options see the
+      -- `dependencies` table for `nvim-lspconfig` above.
+      --
       -- You can add other tools here that you want Mason to install
       -- for you, so that they are available from within Neovim.
       local ensure_installed = vim.tbl_keys(servers or {})