Subject: Re: .clang-format: how useful, how often used, and how well maintained?

From: Collin Funk <[email-masked]>
Date: Thu, 19 Jun 2025 14:31:03 -0700

"brian m. carlson" <[email-masked]> writes:

> I agree most people probably do not use it, probably for the reasons I
> don't.  I don't know if clang-format produces stable output: that is,
> using a newer version of clang-format with the same config does not
> result in diff changes.  If it does, then we can simply pick a set of
> style configs and a minimum version and tell people to apply it.
>
> We can then check it in CI and if CI fails, we can output a
> base64-encoded diff (since it's going to have lots of whitespace, base64
> encoding will be practically useful) that the author can apply.  Then
> people using esoteric systems without clang-format can simply apply the
> diff from CI.
>
> If clang-format does not produce stable output, we're going to have a
> bunch of practical problems.  I use Debian unstable at home and I know
> Peff does as well, but I also use Ubuntu 24.04 at work.  Some
> contributors use Fedora or Cygwin, and we're all going to have a giant
> problem picking a consistent version of clang-format to use such that
> people don't have to compile their own or use external packages. Perhaps
> we can create a small script that does the tidying in a Linux
> Docker/Podman container in that case.

>From what I remember, clang-format is not at all stable between
releases. Newer versions will produce different output than old 
ones (usually better, but that does not matter).

For the reasons that you already mention, it ends up being a chore, in
my opinion. I don't think we should expect everyone to build/install a
clang-format version that is newer or older than what their distro ships
with, just to align the output with the project.

If you wanted to be help avoid badly formatted patches adding a .vimrc
and .dir-locals.el file would cover most people, I think. For Emacs, the
.dir-locals.el would be something simple like:

    (c-mode . ((c-file-style . "linux")
               (fill-column . 80)
               ((indent-tabs-mode . t))))

At least with Emacs it is easy to type things that break these rules. So
one can avoid diffs like this, which clang-format would produce:

> -		/* Warn on any additional signatures, as they will be ignored. */
> +		/* Warn on any additional signatures, as they will be ignored.
> +		 */

I assume this is similar for vim, but I do not use it enough.

Collin