Re: A case where diff.colorMoved=plain is more sensible than diff.colorMoved=zebra & others

From: Stefan Beller <sbeller@google.com>
Date: Dec 6, 2018, 18:11 UTC
Message-ID: <CAGZ79kZVfMNELXuir+t9U8bSg2PVF=oX8aya-OqmRaP0gHRgFw@mail.gmail.com>
In-Reply-To: <b23422fa-8a1d-e508-a008-a2fe27b7b49f@talktalk.net>

On Thu, Dec 6, 2018 at 6:58 AM Phillip Wood <phillip.wood@talktalk.net> wrote:

Show 7 quoted lines

> > So is there some "must be at least two consecutive lines" condition for
> > not-plain, or is something else going on here?
>
> To be considered a block has to have 20 alphanumeric characters - see
> commit f0b8fb6e59 ("diff: define block by number of alphanumeric chars",
> 2017-08-15). This stops things like random '}' lines being marked as
> moved on their own.

This is spot on.

All but the "plain" mode use the concept of "blocks" of code (there is even one mode called "blocks", which adds to the confusion).

> It might be better to use some kind of frequency
> information (a bit like python's difflib junk parameter) instead so that
> (fairly) unique short lines also get marked properly.

Yes that is what I was initially thinking about. However to have good information, you'd need to index a whole lot (the whole repository, i.e. all text blobs in existence?) to get an accurate picture of frequency information, which I'd prefer to call entropy as I come from a background familiar with https://en.wikipedia.org/wiki/Information_theory, I am not sure where 'frequency information' comes from -- it sounds like the same concept.

Of course it is too expensive to run an operation O(repository size) just for this diff, so maybe we could get away with some smaller corpus to build up this information on what is sufficient for coloring.

When only looking at the given diff, I would imagine that each line would not carry a whole lot of information as its characters occur rather frequently compared to the rest of the diff.

Best, Stefan