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Re: [GNUnet-developers] clang formatting discussion

From: Christian Grothoff
Subject: Re: [GNUnet-developers] clang formatting discussion
Date: Thu, 18 Apr 2019 14:00:04 +0200
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On 4/17/19 11:25 PM, Schanzenbach, Martin wrote:
>> There is still a few things we need to figure out (others on
>> gnunet-developers might weigh in here). First of all, how compatible is
>> this actually going to be with editing in Emacs and other editors?
> I thought I said that in the beginning? Most editors have plugins:
> emacs: 
> (n)vim:
> vscode: native
> sublime:

Yes, the question is this: are there any developers here where their
editor cannot be reasonably integrated with clang-format? If so, please
do shout out now!

I've so far heard only positive feedback for Martin's overall initiative
to get indentation under control, so for now I'll proceed with the
assumption that there are no blockers. But if you do have an issue with
this, please do let me know (on or off list) as soon as possible. If
there are no (sound) objections soon, I will give ng0/schanzen the
go-ahead to enable enforcement of clang formatting for all Git commits
in the future!

Anyway, aside from the general policy debate, please read on for more
specific related issues.

//// Deployment experience

I had to install clang-format-9 from Debian experimental, as our
configuration includes options that are only in v9.

For Emacs user's reference: Without v9, the Emacs integration silently
failed. I also had to create a symlink from clang-format to
clang-format-9, as the Emacs integration only looks for the clang-format
binary (and otherwise also fails silently).

Other than that, Emacs integration was straightforward:

I added to gnunet/.dir-locals.el a hook on save (this may end up in Git

  (eval add-hook 'before-save-hook #'clang-format-buffer nil t)))

and to .emacs the logic to find the clang-format package

(require 'package)
(add-to-list 'package-archives '("melpa" . "";))
;; initialize package system
;; actually load the package
(require 'clang-format)

And of course also installed the clang-format package (interactively,
M-x install-package) as per documentation from Martin's first link above.

Finally, the clang-format style symlink must be set:

# Install clang format symlink
ln -s contrib/conf/editors/clang-format .clang-format

(this I will at to the bootstrap script).

//// Formatting gripes

My remaining main issue with
is that it cannot currently be forced to put a break after each argument
and each parameter, and it also cannot detect the exception that a
function has key-value pairs and thus should keep the arguments paired.

However, the latter case is solvable! If we have key-value pairs, we can do:

/* clang-format off */
fun (generalargs,
     key1, value1,
     key2, value2,
     key3, value3);
/* clang-format on */

Real-world example from gnunet-gtk/src/namestore/gnunet-namestore-gtk.c:

 /* clang-format off */
 gtk_tree_model_get (tm, &iter,
                     GNS_TREESTORE_COL_RECORD_TYPE, &n_type,
                     GNS_TREESTORE_COL_IS_PUBLIC, &n_public,
                     GNS_TREESTORE_COL_EXP_TIME, &n_exp_time,
                     GNS_TREESTORE_COL_EXP_TIME_IS_REL, &n_is_relative,
                     GNS_TREESTORE_COL_IS_SHADOW, &n_is_shadow,
                     GNS_TREESTORE_COL_VAL_AS_STR, &n_value,
 /* clang-format on */

That way, clang-format won't touch the *nice* formatting. So if there is
a very strong reason, I would definitively approve turning off clang for
parts of the source.

For this reason, please do NOT simply apply clang-format globally to
GNUnet.  Instead, when editing a file, do a quick check to see if
clang-format would destroy something that's just done "right", and *turn
it off* for those regions.  After that, a single commit with just the
clang-forward should be OK.

Happy hacking!


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