Asynchronous :make in Neovim with Lua

The :make command in Vim is quite useful, it runs whatever program is under the makeprg option and returns its output in the quickfix list, where you’ll be able to hop through the errors if they were parsed correctly by the errorformat option.

For example, if you want to lint a Python file with flake8, it would suffice to

setlocal makeprg=flake8\ %setlocal errorformat=%f:%l:%c:\ %t%n\ %m

Or, you could create a :h compiler plugin named flake8, that set these options when you run :compiler flake8, as I have in my config.

There are a bunch of compiler plugins built into Vim that you might be interested, for example, :compiler pyunit for test suites written with the unittest library.

It works great once you have these options set correctly (although the errorformat can be tricky).

The only “problem” is that it is synchronous. Which means that for some expensive programs, you will not be able to edit until it finishes. In this post we will solve this in Neovim with Lua.

In a previous revision of this post, I used libuv bindings for Lua, accessible under vim.loop, but this is kind of a low level approach. An alternative is to use the jobstart() function, which offers several conveniences.

I put the following Lua script under ~/.config/nvim/lua/ (if you use Neovim you can get yours with :echo stdpath("config")) for it to be available at runtime as Lua module, named async_make.

local M = {} function M.make()  local lines = {""}  local winnr = vim.fn.win_getid()  local bufnr = vim.api.nvim_win_get_buf(winnr)   local makeprg = vim.api.nvim_buf_get_option(bufnr, "makeprg")  if not makeprg then return end   local cmd = vim.fn.expandcmd(makeprg)   local function on_event(job_id, data, event)    if event == "stdout" or event == "stderr" then      if data then        vim.list_extend(lines, data)      end    end     if event == "exit" then      vim.fn.setqflist({}, " ", {        title = cmd,        lines = lines,        efm = vim.api.nvim_buf_get_option(bufnr, "errorformat")      })      vim.api.nvim_command("doautocmd QuickFixCmdPost")    end  end   local job_id =    vim.fn.jobstart(    cmd,    {      on_stderr = on_event,      on_stdout = on_event,      on_exit = on_event,      stdout_buffered = true,      stderr_buffered = true,    }  )end return M

This function first get the current window number and the buffer in it, which I will then use to get the local values of makeprg and errorformat.

Then I expand the makeprg with expandcmd(), which transforms something like make % to make ~/program.c, and store it in a variable to be used by jobstart().

Then I create the function on_event to be a catch-all handler for job events. The callbacks passed to on_stdout, on_stderr and on_exit will receive the following arguments: ({chan-id}, {data}, {name}). So we take advantage of the third parameter here (see :h channel-callback).

When we receive data from stdout and stderr, we extend the lines variable with it. Because of stdout_buffered and stderr_buffered, the callback will only be called when all of the output was gathered (see :h channel-buffered).

When the program exits, we populate the quickfix list. This is done with :h setqflist(). We give it a title (the expanded makeprg), the lines to be parsed and the errorformat to parse the lines with.

Finally we trigger whatever autocmd is under the QuickFixCmdPost event.

Then, I’m able to use it inside nvim like this:

command! Make silent lua require'async_make'.make()nnoremap <silent> <space>m :Make<CR>

Then, if you may wish to run it on save, use this:

augroup LintOnSave  autocmd! BufWritePost <buffer> Makeaugroup END

A command to disable it is convenient (you can re-enable it with :e<CR>):

command! DisableLintOnSave autocmd! LintOnSave BufWritePost <buffer>

Get the full code in this gist.