Re: [WIP PATCH] Manual rename correction

On Wed, Aug 1, 2012 at 2:23 AM, Jeff King [off-list ref] wrote:

quoted

It is a good direction to go in, I would think, to give users a way
to explicitly tell that "in comparison between these two trees, I
know path B in the postimage corresponds to path A in the preimage".

I do not think that is the right direction. Let's imagine that I have a
commit "A" and I annotate it (via notes or whatever) to say "between
A^^{tree} and A^{tree}, foo.c became bar.c". That will help me when
doing "git show" or "git log". But it will not help me when I later try
to merge "A" (or its descendent). In that case, I will compute the diff
between "A" and the merge-base (or worse, some descendent of "A" and the
merge-base), and I will miss this hint entirely.

A much better hint is to annotate pairs of sha1s, to say "do not bother
doing inexact rename correlation on this pair; I promise that they have
value N".

I haven't had time to think it through yet but I throw my thoughts in
any way. I actually went with your approach first. But it's more
difficult to control the renaming. Assume we want to tell git to
rename SHA-1 "A" to SHA-1 "B". What happens if we have two As in the
source tree and two Bs in the target tree? What happens if two As and
one B, or one A and two Bs? What if a user defines A -> B and A -> C,
and we happen to have two As in source tree and B and C in target
tree?

There's also the problem with transferring this information. With
git-notes I think I can transfer it (though not automatically). How do
we transfer sha1 map (that you mentioned in the commit generation mail
in this thread)?

Then it will find that pair no matter which trees or commits
are being diffed, and it will do so relatively inexpensively[1].

But does that happen often in practice? I mean diff-ing two arbitrary
trees and expect rename correction. I disregarded it as "git log" is
my main case, but I'm just a single user..
-- 
Duy