Re: [PATCH 2/5] add object-cache infrastructure

On Tue, Jul 12, 2011 at 05:36:07PM -0400, Jeff King wrote:

In the normal case of applying patch B on top of patch A, it doesn't
matter if we use per-hunk patch-ids or normal patch-ids. Because even if
we decide to actually go through with the merge of B on top of A, any
hunks that _would have_ had their per-hunk patch-ids match will merge
cleanly.

But in the real world, it is about applying patch Z on top of patches
A..Y, where Z has similar hunks to patch N. And then it _does_ make a
difference, because it is about skipping hunks from Z that are already
in N, but will end up applied on top of Y. And what's in Y and what's in
N may be quite different.

Does that sound right?

Yes, exactly.

And one possible solution would be to drop all hunks from Z which
are already somewhere in A..Y. But that undermines the whole
changeset idea.

If we detect the similarities between Z and N, then we could rebase
Z to N, make the user resolve any conflicts, which should make more
sense than what we would have between Z and Y. Then we have Z' on
top of N:

  Z      Z'     Z"
 /      /      /
A--..--N--..--Y

Subsequently we rebase Z' to Y, at which point only changes remain
that we disagreed with. For those we may have to do conflict
resolution again. So, in some cases this approach could result in
more work.

Clemens