[darcs-users] Colin Walters blogs on Arch changesets vs Darcs

Anthony Towns aj at azure.humbug.org.au
Thu Nov 25 05:31:06 UTC 2004

Zooko O'Whielacronx wrote:
> On 2004, Nov 24, at 15:34, Kenneth Knowles wrote:
>> Or use "diff", and send conventional patches to darcs-using developers.
> you will eventually get two copies or two variants of a patch imported from 
> outside-darcs-world to inside-darcs-world.

> Any contributor can do it, but if more than one contributor does it then 
> you have the matter/antimatter problem.

Hrm, hope that's enough context. If not: problem is when a single patch 
(in diff -u format, eg) gets imported by two separate people into their 
darcs repositories, and then those people try to push/pull from each 
other. darcs can't tell that the patch is "the same", so creates a 
conflict, and everything goes to hell.

That ought to be fixable though. How hard would it really be to 
canonicalise a "diff -u" patch to darcs? The issues are:

   (a) you need a canonical patch name (and description)
   (b) you need a canonical time
   (c) you need a canonical email address for the author
   (d) you need to ensure the patch body is equivalent

(c) should be obvious, hopefully.
(d) should be straightforward too, at least if there's no fuzz

(b) is trickier, but diff -u includes some timestamps:

+++ foo Thu Nov 25 15:18:42 2004

so you should be able to just use the most recent timestamp from the 
patch, I think.

(a) otoh, probably needs a policy solution. So you might require that 
all patches come with a description, and that when folks check it into 
darcs, they use that description. Or maybe you could change darcs to 
treat patches as the same if they've got the same email and timestamp, 
even if their descriptions differ? Or maybe you could expect email & 
timestamp to be the same, and one of description/patch-contents to be 
"the same". :-/

But we could do three out of four right now with a 
darcs-record-from-diff script, which isn't bad.

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