[Freeipa-devel] C coding style guide update

[Jakub Hrozek]

On Thu, Jul 23, 2015 at 06:21:25PM +0200, Michal Židek wrote:
> Hi,
> 
> in SSSD we use the freeipa coding guidelines which are located here:
> http://www.freeipa.org/page/Coding_Style
> 
> However this coding style guide is already dated and there are
> some rules we follow in SSSD which are not mentioned in the guide
> and also there are some C language features that we would like to
> start using in certain way but their usage should be covered in the
> coding style guide. So, update is needed (at least for SSSD).
> 
> I would like to start discussion about what to add to the coding
> guide (and maybe what to remove), but before that, I would like
> propose to move the coding style guide to SSSD wiki and just add link
> to it to FreeIPA wiki. The reason is that unlike FreeIPA, most of the
> SSSD code is written in C and SSSD team will more likely update and
> modify the guide according to new practices used in upstream
> development, where FreeIPA is mostly Python project and C coding
> style probably does not need revision as often. So SSSD wiki
> seems like more appropriate place.
> 
> Another possibility would be to fork the FreeIPA style and
> maintain SSSD coding style guide separately. But I think linking
> the two is better option, because the two projects are closely
> related and it makes sense to share the coding style guidelines.
> 
> So, my first question is, Is someone against moving the C coding
> style guide to SSSD wiki and adding link to it on FreeIPA wiki?

I don't really mind where the coding style is located as long as it's
on one place (no forks please) and the existing link points to a new
version (if any).

As per updating the coding standards, I would like to propose to:
    - explicitly say that C99 is fine to use. It's 2015 and any compiler
      that doesn't support C99 at this point is probably dead and should
      be avoided (Hello, MSVC!). We use stdbool.h and variadic macros
      already anyway.
    - Line-comments (//, aka C++ comments) should be still avoided,
      though
    - Variable Length arrays are very helpful, but explicitly mention
      they should be used with caution, especially if array size might
      come from the user
    - Also, I would warn about interleaved variable declarations. I
      think it's fine to declare some helper variable inside a for loop
      for example, but generally it might be better to refactor the
      function if we find out there's so many variables that the code
      author ends up declaring them inside blocks.

Personally, I would even go as far as to allow the __cleanup__
attribute. I really like how the systemd codebase uses it to define
helper "destructors" like:
    int closep(int fd)
    {
        if (fd >= 0) {
            close(fd);
        }
    }

    #define _cleanup_close_ _cleanup_(closep)

Then safely declare a file descriptor as:
    _cleanup_close_ int fdf = -1;
..and stop worrying about closing the fd in all branches.

It's not portable, but seriously...are there any compilers except gcc
and clang that are used at all these days??