Quickfix is all you need

In July 2023, the author of null-ls.nvim, jose-elias-alvarez, submitted a critical issue to the repository titled "IMPORTANT: Archiving null-ls". Within this thread, he asserted his intent to archive the repository, officially halting further maintenance and development of it. In effect, this meant the repository would be archived.

null-ls.nvim is a versatile plugin that empowers users to leverage external programs for code actions, diagnostics, and formatting. Essentially, it forms an integrated bridge connecting Neovim's built-in LSP client and these external programs.

Being a user of null-ls.nvim myself, primarily for displaying diagnostics for non-LSP languages, this news prompted my decision to create a replacement for the null-ls.nvim tool. Earlier projects related to this endeavor include but are not limited to, ALE, syntastic, and nvim-lint. Though these plugins are indeed valuable. However, I just simply want to display diagnostics for non-LSP languages on-the-fly. Nothing more, nothing less.

Presently, my coding work involves the use of Zig with Vim. Conveniently, zig.vim offers a LSP-free diagnostic feature for Zig. Fascinated by this, I am motivated to replicate this functionality for other languages.

Delving deeper, zig.vim owes its efficiency to Vim's quickfix feature. The workflow is structured below:

1. Run external program defind as 'makeprg' option in Vim.
2. Parse the output of the external program and convert it to a quickfix list.
3. Display the quickfix list by :copen command.

This is a very simple and easy-to-understand flow. We just to need the parsing logic for the output of the external program. No plugin is required because it uses the built-in quickfix feature of Vim.

The following is an example of the output of the external program.

    /path/to/file:line:col: error: message
    /path/to/file:line:col: warning: message

Then, we can parse the output as follows:

    setlocal errorformat=%f:%l:%c: %trror: %m,%f:%l:%c: %tarning: %m

The 'errorformat' option is used to parse the output of the external program. %f is the file name, %l is the line number, %c is the column number, %t is the type of the error, which is either e or w, and %m is the error message.

Then, we set the 'makeprg' option to the external program and run the :make. The output of the external program is parsed and converted to a quickfix list. Finally, we display the quickfix list by :copen command.

The following is the example settings to check on-the-fly for POD. This configuration triggers the 'make' command when the file is saved.

   local function run_make()
     vim.cmd[[silent make]]
     if #(vim.fn.getqflist()) > 0 then
       vim.cmd.copen()
     else
       vim.cmd.cclose()
     end
   end

   vim.api.nvim_create_autocmd("FileType", {
     pattern = "pod",
     callback = function()
       vim.opt_local.makeprg = "podchecker %"
       vim.opt_local.errorformat = {
         "*** %tRROR: %m at line %l in file %f",
         "*** %tARNING: %m at line %l in file %f",
         "%-G%.%#",
       }
       vim.api.nvim_create_autocmd("BufWritePost", {
         group = "Vimrc",
         buffer = 0,
         callback = run_make,
       })
     end
   })

This is a very simple and easy-to-understand flow. This is stable and has been used for a long time. I think this is the best way to display diagnostics for non-LSP languages. Shall we go back to the basics? Quickfix is all you need.

Cheers.