With Neovim and null-ls plugin we can make code formatting work like a charm, as I stated in My Neovim Revamp previously. While I was happily enjoying it, I did some tweaking for a little more convenience, such as:

  • Format on save.

  • Customize formatter.

  • Format conditionally in runtime.

Let’s get right into it.

Format on save

This is plain easy if you check out the wiki of null-ls. According to this part, all you need is copy&paste the code into your own config.

Customize ruff&stylua

Formatters supported by null-ls all have defaults, like arguments. Sometimes we want to add more options, and that’s when extra_args comes in handy.

For instance, I’m using ruff for Python formatting to replace isort, so customization becomes:

    extra_args = { "--select", "I" }

And for Lua, I want stylua to use spaces instead of tabs, so I did:

    extra_args = { "--indent-type", "Spaces" }

In addition, you can replace default arguments totally with args, by following the config instruction here.

BTW, I found a few tricks regarding tabs&spaces:

  • In Neovim:

    • Use :retab to replace tabs with spaces(number of spaces defined by tabstop).

    • Use :set list to show tabs marking as > and trailing spaces as -.

  • In Shell:

    • Use sed to convert tabs to spaces in a bunch of files at one time.

    • On Linux: sed -i "s/\t//g" /path/to/files.

    • On macOS: sed -i "" "s/\t//g" /path/to/files. Here -i stands for extension rather than in-place editing.

Format conditionally

Auto-formatting is sweet, but what if I don’t want it? When I’m reading some source code or working on a shared project, I want things kept as they were.

Toggling formatters on&off can be annoying, is there a smarter way?

Yes, there sure is. Turns out null-ls has a runtime_condition setting to force it to check whether a formatter should run for the current buffer.

Essentially, you just need to add a function to determine if formatting is needed:

    runtime_condition = function(params)
        return string.match(params.bufname, "source") == nil

I keep all source code projects in ~/projects/source. Based on the above config black will check if current file belongs under this particular path, and if it is, no auto-formatting will be performed.

Just like this, you can easily split things up with a suitable condition statement in Lua. For reference of how to better write it, see:

Hope these tips can be helpful :)