Pre-computed similarity indexes

[Philip <philip.c.peterson@gmail.com>]

Hello all,

I noticed that Git LFS-tracked files cannot correctly detect renames,
probably because Git is not doing a similarity check on the content.
Doing so would require having the content (instead of just the LFS
pointer), and that would require running the smudge filter, which
could take a very long time due to network requests, very expensive if
done on every file in the repo. When doing a `git log` for example, it
would need to run the smudge filter on all LFS files in all revisions,
potentially pulling down all the content from the LFS server, just to
decide if there were any renames.

I wonder if there has been any thought given to whether a similarity
index can be pre-computed somewhere? (Maybe upon commit with each of
the commit's ancestors.) Or if this limitation has been discussed
before here.

Thank you,
Philip Peterson