Re: patch subtraction bug

["Eli Carter" <eli.carter@commprove.com>]

> On Mon, 2006-10-23 at 17:26 -0500, Eli Carter wrote:
>> I tried abusing patchutils in a new way today, and it didn't do what I
>> wanted.
>>
>> First, pull one change out of a larger patch:
>> filterdiff -p1 -i some/file.py --hunks=5 < diff > one-change.patch
>> Now, I want to remove that change from the larger patch, so I combine
>> the
>> larger patch with a reversed version of the the one-change.patch:
>> interdiff one-change.patch /dev/null | combinediff diff /dev/stdin >
>> rest.patch
>>
>> What I got was a patch with the hunk from one-change.patch in rest.patch
>> twice with different line numbers for the change.
>
> Hmm, I just tried this myself and got the expected results -- the entire
> original patch with the single change removed.
>
> Sounds like it depends on the input you give it.  One thing that *might*
> account for it is described in the 'BUGS' section of the interdiff man
> page:
>
>   There are some sets of patches in which there is just not enough
>   information to produce a proper interdiff. In this case, the strategy
>   employed is to revert the original patch and apply the new patch.
>   This, unfortunately, means that interdiffs are not guaranteed to be
>   reversible.
>
> Do you think it could be that?

Perhaps... but I don't think--wait...
The doubling of the patch at the end I thought was [apply change] [apply
change], but the second one was the reverse of the first, as you
described... I misread the patch.

Oops.

Hmm... I still think interdiff has enough information to cancel the
hunks... but I'll have to play with the sources before I really make that
claim.

Sorry for wasting your time,

Eli