[Unison-hackers] Extending the "rename" detection

[Nathan Thern]

Hello -
Longtime unison user. I have known for some time that renaming a file on 
one replica will result in a simple "copy-and-delete" operation at the 
target mirror replica when the two replicas are sync'd.

Recently, I encountered a situation where several directories which 
contained large files were renamed on a replica. It happens to be a kind 
of "dropbox" folder for my family to put media content for me to 
download while I am traveling. I unison sync the folder rather than 
rsync it because I delete the content on my end as I consume it. My wife 
recently "helpfully" re-organized some of the directories in that folder 
and I found my unison process re-downloading big content that I actually 
already had because the directories had been "renamed". As unison saw 
it, some directories had been deleted and others added.

So, I thought, "This could be a good addition to unison. Add a 
capability to compare newly deleted files to newly added files and 
detect that they are actually renames or moves across directories." I 
figured it would probably best be added as a new command-line option.

I downloaded the source and started looking at it. I do not know ocaml, 
but was immediately impressed with the expressive power I could see. 
Unfortunately, I soon got lost in the code.

Any hints on where to get started in the source to implement this? I'm 
currently working on learning ocaml, but I also want to get rolling on 
this project as soon as I can.

regards,
NT