CodingStyle indentation and alignment

[Laurence Rochfort]

Thanks very much for the comprehensive answer.

Using spaces and tabs for alignment does make the code more readable
to my mind.

The reason behind my question originally was that the CodingStyle doc
states:

"Outside of comments, documentation and except in Kconfig, spaces are never
used for indentation, and the above example is deliberately broken."

however most code I have seen is not compliant with that.

Should the docs be updated?

Cheers,
Laurence.

On Mon, Sep 26, 2016 at 10:32:06PM +0300, Andrey Utkin wrote:
> On Mon, Sep 26, 2016 at 06:28:58PM +0100, Laurence Rochfort wrote:
> > Hi all,
> >
> > I've read Documentation/CodingStyle and it states to use 8 character
tabs.
> >
> > Reading several USB driver files including drivers/usb/usb-skeleton.c,
I see that multi-line lists of argument and operands are often aligned on
top of each other using a mixture of tabs and spaces. checkpatch doesn't
complain about the mixture.
> >
> > For instance from usb-skeleton.c:
> >
> > static int skel_probe(struct usb_interface *interface,
> >                       const struct usb_device_id *id)
> >
> > uses two tabs and 6 spaces, not just tabs like:
> >
> > static int skel_probe(struct usb_interface *interface,
> >                const struct usb_device_id *id)
> >
> > or
> >
> > static int skel_probe(struct usb_interface *interface,
> >                                  const struct usb_device_id *id)
> >
> >
> > Is a mixture of tabs and spaces acceptable if it enhances readability?
If not, which of the tabs-only forms is correct?
> >
> > Similarly, what about assignment alignment in structs?
>
> By my observations, conventional alignment in kernel contributions
> nowadays is N*tab followed by M*space, where M < 8. For details, consult
> "checkpatch --strict" output. It's not a paramount to make all existing
> codebase to pass that check cleanly, but if you are polishing your new
> patch, you can use that as guidance.
>
> If you use Vim, see https://github.com/vivien/vim-linux-coding-style -
> it will indent your code more or less in accordance with coding style,
> also making checkpatch happy.
>
> checkpatch in --strict mode actually prefers trailing lines to be
> aligned on opening brace. Tabs and spaces are allowed for such alignment
> (and you _need_ spaces to be able to align like that).
>
> So what above vim plugin makes, and what is widely used in kernel
> codebase, is something like this ("|tab--->" or a smaller part
> represents tab character, "." represents space):
>
> static int blah_blah_blah(struct usb_interface *interface,
> |tab--->|tab--->|tab--->..const struct usb_device_id *id)
> {
> |tab--->if (1) {
> |tab--->|tab--->int var = blah_blah(interface->foo_bar->baz_fuzz,
> |tab--->|tab--->|tab--->|tab--->....11111111111111 + 111111111111111);
>
> Also
>
> |tab--->|tab--->|tab--->|tab--->|tab--->|tab--->|tab---> (shown for
reference)
> #define DRIVERNAME_REGISTER1_NAMEXXX--->|tab--->0xdead
> #define DRIVERNAME_REGISTER2_NAME_WHICH_IS_LONG>0xdeaf
>
> Which looks this way with actual tab characters:
>
> #define DRIVERNAME_REGISTER1_NAMEXXX          0xdead
> #define DRIVERNAME_REGISTER2_NAME_WHICH_IS_LONG       0xdeaf
>
> This is supposed to be displayed ALWAYS with 8-char tab (this is carved
> in slate of CodingStyle), thus arguments about breaking viewing with
> different tab sizes are to be ignored.
>
> To my taste this is not best possible approach, and I would like all
> readers of this thread to check this article:
> http://dmitryfrank.com/articles/indent_with_tabs_align_with_spaces
> But, unfortunately, checkpatch is explicitly not happy with that
> approach, giving notices of ERROR and WARNING levels for first example,
> however accepting #define case to be aligned with spaces IIRC.
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