Re: [PATCH v2 3/5] diffcore-rename: enable limiting rename detection to relevant destinations

[Derrick Stolee <stolee@gmail.com>]

On 6/1/2021 10:58 AM, Elijah Newren via GitGitGadget wrote:
> From: Elijah Newren <newren@gmail.com>
> 
> Our former optimizations focused on limiting rename detection to a
> pre-specified set of relevant sources.  This was because the merge logic
> only had a way of knowing which sources were relevant.  However, other
> callers of rename detection might benefit from being able to limit
> rename detection to a known set of relevant destinations.  In
> particular, a properly implemented `git log --follow` might benefit from
> such an ability.

I would be interested in seeing such an improvement. It could also
help the batch-download of missing blobs in a partial clone situation
because it would only need the "deletes" portion of the diff, since we
only care about one "add" (we'd need that blob, too, of course).
 
> Since the code to implement such limiting is very similar to what we've
> already done, just implement it now even though we do not yet have any
> callers making use of this ability.

However, I'm not sure that this change is warranted without such an
integration. Perhaps keep this patch here on the list as a reference
for anyone who wants to do the `git log --follow` speedup? This person
can include "you in the future".

I'm just worried that without a consumer, this code has no automated
validation and can either be buggy now or become buggy in the future
before someone starts trying to use the logic.

Thanks,
-Stolee