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Re: [Taler] Coding style clang-format

From: Christian Grothoff
Subject: Re: [Taler] Coding style clang-format
Date: Thu, 18 Apr 2019 14:16:19 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

Dear Taler hackers,

There has been a (long-ish) discussion about using clang-format for
source formatting among the GNUnet developers.  WDYT about applying the
same rules to GNU Taler and also enforcing them via Git hooks on commit?

See in particular the following e-mails from the GNUnet discussion:

On 4/15/19 10:02 AM, Schanzenbach, Martin wrote on [GNUnet-developers]:
> Hi,
> FYI I added a clang-format at "contrib/conf/editors/clang-format".
> Clang-format is usable with most editors (vim, emacs, vscode) with respective 
> plugins.
> This way, we can have a unified coding style.
> Clang-format has a nice documentation and allows fine-grained setting which 
> are also human readable: 
> https://clang.llvm.org/docs/ClangFormatStyleOptions.html
> Let's use it and put it as a note into our coding guidelines?

Martin also wrote:

> Most editors have plugins:
> emacs: 
> https://llvm.org/svn/llvm-project/cfe/trunk/tools/clang-format/clang-format.el
> (n)vim: https://github.com/rhysd/vim-clang-format
> vscode: native
> sublime: https://packagecontrol.io/packages/Clang%20Format

And most recently I wrote (latest point of the discussion):

> 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
> "soon")
> ((c-mode
>   (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" . "https://melpa.org/packages/";))
> ;; initialize package system
> (package-initialize)
> ;; 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
> https://clang.llvm.org/docs/ClangFormatStyleOptions.html
> 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,
>                      -1);
>  /* 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!
> Christian

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