From mboxrd@z Thu Jan  1 00:00:00 1970
From: me@tobin.cc (Tobin C. Harding)
Date: Mon, 13 Mar 2017 19:20:21 +1100
Subject: diff
In-Reply-To: <20170313074300.GA15170@osadl.at>
References: <20170313065714.GA654@eros>
 <20170313074300.GA15170@osadl.at>
Message-ID: <20170313082021.GA12083@eros>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

On Mon, Mar 13, 2017 at 07:43:00AM +0000, Nicholas Mc Guire wrote:
> On Mon, Mar 13, 2017 at 05:57:14PM +1100, Tobin C. Harding wrote:
> > On occasions diff output does not render the same as it does when
> > editing a file. For example, while removing checkpatch tab warning
> > the following diff was generated
> > 
> > -#define KS_WLAN_SET_WPS_ENABLE                 SIOCIWFIRSTPRIV + 4
> > -#define KS_WLAN_GET_WPS_ENABLE                 SIOCIWFIRSTPRIV + 5
> > +#define KS_WLAN_SET_WPS_ENABLE         SIOCIWFIRSTPRIV + 4
> > +#define KS_WLAN_GET_WPS_ENABLE         SIOCIWFIRSTPRIV + 5
> > 
> > However when editing the file the alignment was not changed, just tabs
> > were inserted instead of spaces.
> 
> if the removed lines were using tabs which they should then they are
> moved by the inserted "-" while the added lines were using spaces
> and thus did not "jump" to the next tabstop.
> 
> > 
> > I had the same thing happen a few days ago (reproduced here from
> > memory)
> > 
> > -static void foo(struct bar *barp, struct baz *bazp)
> > +static void foo(struct bar *barp,
> > +               struct baz *bazp)
> > {
> >         ...
> > 
> > When editing the file the two s's in struct were aligned but not in
> > the diff output. I reapplied this patch to a clean tree and it applied
> > correctly.
> 
> this is simply because the insertion is by tabs so when diff added the
> +/- output it moved the "static void foo..." but not the "struct baz"
> so this looks unaligned in the diff output while it actually is aligned
> properly.
> 
> > 
> > How do maintainers visually parse this if the output is not identical in the
> > diff and the file once applied?
> >
> checkpatch will warn if spaces were used and if its based on tabs
> I guess most can see if aligment is correct or not.

Nice explanation, thank you.

Regards,
Tobin.