CodingStyle indentation and alignment

[Bernd Petrovitsch]

Hia ll!

On Mon, 2016-09-26 at 18:28 +0100, Laurence Rochfort wrote:
> [...]
> I've read Documentation/CodingStyle and it states to use 8 character
> tabs.

That means, that a <tab> uses up to eight columns and not that one
should replacre some 8 spaces somewhere with a <tab> or that spaces are
not allowed.

> 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.

Why should that be a problem.

> 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)

Which of the three versions is most readable/consistent?
IMHO the first (and it is the only consistent).
Consider more than 2 paramaters which I align as in
----  snip  ----
static int foobarfunc(struct usb_interface       *interface,
		      const struct usb_device_id *id,
		      int                         whatever,
		      const char                 *and_a_string) 
----  snip  ----
Would it be "better" as
----  snip  ----
static int foobarfunc(
	struct usb_interface       *interface,
	
const struct usb_device_id *id,
	int                        
whatever,
	const char                 *and_a_string
	)
----
 snip  ----
(which is also somewhat used somewhere)?
That wastes two
lines IMHO.
Same for
----  snip  ----
static int
foobarfunc(
	struct usb_interface       *interface,
	
const struct usb_device_id *id,
	int                        
whatever,
	const char                 *and_a_string
	) 
----
 snip  ----
which has the motivation "I can grep the function body with
^functionname" (but in the light of IDEs and `ctags` isn't that
important anymore).

And remember that we are here for 99% in the "what one is used to" department.

> Is a mixture of tabs and spaces acceptable if it enhances
> readability?

Only readability is really important - not some document (describing
the rough direction to go an gives some simple direct hints for the
undisputed details) or output of some simple script/tool which tries to
detect violations[0].
Both of them are just guidelines and do not justify a single patch
stupidly and blindly just "correcting" some checkpatch complaint.

Actually "checkpatch" needs some "do not warn in the next n lines"
mechanism (or similar, e.g. `indent` and probably all source code
formatters hava that too) so that known/intended violations for good
reason are silenced.

	Bernd

[0]: And "checkpatch" is a good tool but it is just a tool and one 
     needs to see the source to decide if it's better - not the simple 
     warning of eome reg-exp.
-- 
Bernd Petrovitsch                  Email : bernd at petrovitsch.priv.at
                     LUGA : http://www.luga.at