Re: [PATCH] diff: add a config option to control orderfile

Jeff King [off-list ref] writes:

I am mostly thinking of the problems we had with the "kup" tool, which
expected stability across diffs that would be signed by both kernel.org.
But as far as I know, they do not use patch-id. More details in case you
are curious (including me arguing that we should not care, and it is
kup's problem!) are here:

  http://thread.gmane.org/gmane.comp.version-control.git/192331/focus=192424

rerere is mentioned in that thread, but I believe that it does its own
hash, and does not rely on patch-id.

It does not.  The reason rerere is relevant in that thread but is
not directly relevant here is because the thread is about changing
the diff algorithm, hence changing the common-sequence matches
between preimage and postimage, resulting in a different shape of
the conflicted section.  The hash rerere does still depends on the
patch text, but it is restricted to the conflicted region, so
whatever we do in patch-id will not affect it.  Also the rerere
database is not keyed by pathname (a conflict in _any_ file as long
as they have the same ours/theirs conflicted text is recognised as
the same conflict we have already seen), so changing the orderfile
would not affect it at all.