Highlighting word diffs

Highlighting word diffs

[Suvayu Ali]

Hi,

I wanted to use word diffs for text-modes (i.e. Org, TeX, plain text,
etc).  So I change diff-switches in text-mode-hook, and the output looks
as expected.  However the highlighting in diff-mode does not seem to
work.  I guess there is probably a switch, or maybe I need to change a
regex; I can't seem to find it though.

Any pointers?

Cheers,

-- 
Suvayu

Open source is the future. It sets us free.

Re: Highlighting word diffs

[Stefan Monnier]

> I wanted to use word diffs for text-modes (i.e. Org, TeX, plain text,
> etc).  So I change diff-switches in text-mode-hook, and the output looks
> as expected.

I don't know how you changed diff-switches, and I don't know what this
expected output looks like, nor which command you used to get it.

> However the highlighting in diff-mode does not seem to work.

I don't know how it fails to work either.


        Stefan

Re: Highlighting word diffs

[Suvayu Ali]

Hi Stefan,

On Sat, Apr 18, 2015 at 09:25:51AM -0400, Stefan Monnier wrote:
> > I wanted to use word diffs for text-modes (i.e. Org, TeX, plain text,
> > etc).  So I change diff-switches in text-mode-hook, and the output looks
> > as expected.
> 
> I don't know how you changed diff-switches, and I don't know what this
> expected output looks like, nor which command you used to get it.
>

This is how I set it:

  (setq vc-git-diff-switches (list "--word-diff"))

And I use vc-diff to generate the diff.  Here is a sample of how it
looks:

  diff --git a/time-acceptance.org b/time-acceptance.org
  index 361a6ee..33fac7c 100644
  --- a/time-acceptance.org
  +++ b/time-acceptance.org
  @@ -1,35 +1,43 @@
  #+title: [-Decay time-]{+Decay-time+} dependent acceptance
  
  #+include: options.org
  #+include: macros.org
  
  * WInP [-Decay time-]{+Decay-time+} dependent acceptance
    :PROPERTIES:
    :CUSTOM_ID: ch:tacc
    :END:
  An ideal event selection would accept all events that are true signal
  events, and reject the rest.  Reality is different however.  Since the
  flight distance and [-decay time-]{+decay-time+} are directly related{{{todo(Cite eqn
  from introduction)}}}, some selection requirements related to the
  flight distance of the B_{s} meson could bias the sample of accepted
  events in [-decay time.-]{+decay-time[fn:: One might even think of this as a selection+}
  {+efficiency function.].+}  The {+most effective+} selection [-requirement responsible could be any-]{+requirements are+}
  {+often designed to reject displaced vertices not associated with a+}
  {+B_{s} meson.  Which is inevitably at odds with an unbiased decay-time.+}
  
... and so on.

> > However the highlighting in diff-mode does not seem to work.
> 
> I don't know how it fails to work either.

I would expect the [-text-] bits to be coloured red, and {+text+} bits
to be coloured green.  That's what I get in the terminal with:

  $ git diff --word-diff

Does that help?  Is there support for this?  If not, would it be a valid
feature request?

Thanks for any comments.

-- 
Suvayu

Open source is the future. It sets us free.

Re: Highlighting word diffs

[Stefan Monnier]

> I would expect the [-text-] bits to be coloured red, and {+text+} bits
> to be coloured green.  That's what I get in the terminal with:

>   $ git diff --word-diff

> Does that help?

Yes, thank you.

> Is there support for this?

No, there isn't so far.

> If not, would it be a valid feature request?

Of course.

Looking at your sample output I can't see any indication that diff-mode
could use to detect that "word-diff" was used.  Also "diff --word-diff
a b" tells me that this option is not supported, so either it's a new
feature in recent diffutils or (more likely) it's specific to Git.
Also "git diff --help" tells me:

           plain
               Show words as [-removed-] and {+added+}.  Makes no attempts to
               escape the delimiters if they appear in the input, so the
               output may be ambiguous.

so making diff-mode highlight [-<foo>-] specially might lead to
completely broken highlighting if the file contains "[-" or "-]".

So, the best options to get reliable highlighting in diff-mode would be
either --word-diff=color (and then process the output to turn the color
escape sequence into faces) or --word-diff=porcelain and then
post-process the output to hide the extra stuff.
For example, applying

   (while (re-search-forward "\n\\(?:[-+ ]\\|\\(~\\)\n\\)" nil t)
     (let ((m (if (match-end 1) 1 0)))
       (put-text-property (match-beginning 0) (match-end m) 'invisible t)))

to the body of each hunk (in porcelain format) results in acceptable
display (basically equivalent to word-diff=color).  But of course,
there's a lot more work to be done for actual support (e.g. for
diff-goto-source, diff-apply-hunk, diff-reverse-direction, ...).


        Stefan

Re: Highlighting word diffs

[Marcin Borkowski]

On 2015-04-18, at 18:46, Stefan Monnier <monnier@iro.umontreal.ca> wrote:

>> I would expect the [-text-] bits to be coloured red, and {+text+} bits
>> to be coloured green.  That's what I get in the terminal with:
>
>>   $ git diff --word-diff
>
>> Does that help?
>
> Yes, thank you.
>
>> Is there support for this?
>
> No, there isn't so far.

I'm pretty sure that something like this works in Magit.

>         Stefan

Best,

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University

Re: Highlighting word diffs

[Stefan Monnier]

> I'm pretty sure that something like this works in Magit.

Oh, that's likely.  I was only talking about diff-mode.


        Stefan