Re: improved diff tool

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Aug 30, 2018, 11:33 UTC
Message-ID: <nycvar.QRO.7.76.6.1808301324120.71@tvgsbejvaqbjf.bet>
In-Reply-To: <CAJmvCd1BwPNgZM+g7c6An-EESMHDOSGQe7RjkAAz36eNY3fvGA@mail.gmail.com>

Hi Piers,

On Thu, 30 Aug 2018, Piers Titus van der Torren wrote:

> I've created a diff algorithm that focuses on creating readable diffs,
> see https://github.com/pierstitus/klondiff

Looks intriguing.

> The git integration as an external diff command works quite well,
> though it would be nice to integrate it deeper in git, and also in
> git-gui and gitk. Any way to use ext-diff from the gui tools?

Git GUI and gitk are both Tcl/Tk programs, and will need quite a bit of work to accommodate for your diff mode.

To put things into perspective: the `--color-words` mode is not integrated into Git GUI nor gitk, and it has been around for a while...

> Is there interest to incorporate this algorithm in the main git
> codebase? And if so, any hints on how to proceed?

The best advice I have is to look at the `--color-words` mode. It comes with its own "consume" function that accumulates lines from the diff, then outputs them in a different way than the regular colored diff. Your mode would want to do it very similarly.

This is the accumulating part:

	https://github.com/git/git/blob/v2.19.0-rc1/diff.c#L1886

and this is the display part:

	https://github.com/git/git/blob/v2.19.0-rc1/diff.c#L2013

Basically, I would suggest to do a `git grep color.words` to find the places where the `--color-words` mode is special-cased, and add new special-casing for your mode. Which, BTW, I would suggest to find a catchier name for ;-)

I have not looked closely at your implementation, but I could imagine that you might want to have at least part of your algorithm step in at a much lower level: If you can use the patience diff algorithm itself for pre-processing and initial diff generation, that's great, just force XDF_PATIENCE_DIFF; Otherwise you will have to implement an alternative, similar to https://github.com/git/git/blob/v2.19.0-rc1/xdiff/xpatience.c.

Ciao, Johannes