Re: [PATCH] Document the textconv filter.

From: Matthieu Moy <matthieu.moy@imag.fr>
Date: Sep 28, 2008, 12:29 UTC
Message-ID: <vpq7i8wzc5b.fsf@bauges.imag.fr>
In-Reply-To: <200809281307.21409.johannes.sixt@telecom.at>

Johannes Sixt <johannes.sixt@telecom.at> writes:

Show 15 quoted lines

> On Sonntag, 28. September 2008, Matthieu Moy wrote:
>> +Converting files to text before a diff
>> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> +
>> +The attribute `textconv` affects 'git diff' in a way similar to the
>> +`diff` attribute, but with `textconv`, the user provides only a way to
>> +convert the file into text, and git takes care of doing the diff as
>> +usual (i.e. other options of 'git diff' such as '--color' remain
>> +available).
>> +
>> +The value of `textconv` must be a string, which is the textconv
>> +driver.
>
> Wouldn't it be much more useful to have git parse stdout of the custom diff 
> tool in order to colorize it?

That would do it for --color, but not --color-words for example. The problem with the GIT_EXTERNAL_DIFF is that the diff tool has to re-implement everything that "git diff" already do.

Take my opendocument diff script :

http://www-verimag.imag.fr/~moy/opendocument/git-oodiff

That's 77 lines of code as a wrapper to odt2txt and diff. With the "textconv" attribute, it's one line in .gitattributes, and two in ~/.gitconfig.

Show 13 quoted lines

> Of course, this would mean that external diff tools are more
> complicated and their stdout has to conform mostly to the git diff
> syntax. But:
>
>> +To tell git to use the `exif` filter for jpeg images, use:
>> +
>> +----------------------------------------------------------------
>> +*.jpg   textconv=exif
>> +----------------------------------------------------------------
>
> In this very example it would be possible that the external diff driver shows 
> the differences in the image in a window and also produces EXIF information 
> on stdout.

Yes, but that's really a specific example. Having git colorize the diff would be a little extra, but that wouldn't reduce the effort to write the external diff tool itself, and doesn't give you _all_ of git-diff, just --color.

-- 
Matthieu