nvim-config/lua/kickstart/plugins/autoformat.lua

-- Uses installed LSP servers to automatically format code on save.

return {
	'neovim/nvim-lspconfig',
	config = function()
		-- Switch for controlling whether you want autoformatting.
		local format_is_enabled = true
		vim.api.nvim_create_user_command('KickstartFormatToggle', function()
			format_is_enabled = not format_is_enabled
			print('Setting autoformatting to: ' .. tostring(format_is_enabled))
		end, {})

		-- Create an augroup that is used for managing our formatting autocmds.
		local _augroups = {}
		local get_augroup = function(client)
			if not _augroups[client.id] then
				local group_name = 'kickstart-lsp-format-' .. client.name
				local id = vim.api.nvim_create_augroup(group_name, { clear = true })
				_augroups[client.id] = id
			end

			return _augroups[client.id]
		end

		-- Whenever an LSP attaches to a buffer, we will run this function.
		vim.api.nvim_create_autocmd('LspAttach', {
			group = vim.api.nvim_create_augroup('kickstart-lsp-attach-format', { clear = true }),
			-- This is where we attach the autoformatting for reasonable clients
			callback = function(args)
				local client_id = args.data.client_id
				local client = vim.lsp.get_client_by_id(client_id)
				local bufnr = args.buf

				-- Only attach to clients that support document formatting
				if not client.server_capabilities.documentFormattingProvider then
					return
				end

				-- Create an autocmd that will run *before* we save the buffer.
				vim.api.nvim_create_autocmd('BufWritePre', {
					group = get_augroup(client),
					buffer = bufnr,
					callback = function()
						if not format_is_enabled then
							return
						end

						vim.lsp.buf.format {
							async = false,
							filter = function(c)
								return c.id == client.id
							end,
						}
					end,
				})
			end,
		})
	end,
}