Re: Fwd: possible Improving diff algoritm

From: Junio C Hamano <gitster@pobox.com>
Date: Dec 12, 2012, 20:29 UTC
Message-ID: <7vtxrr2evm.fsf@alter.siamese.dyndns.org>
In-Reply-To: <7vvcc73yzh.fsf@alter.siamese.dyndns.org>

Junio C Hamano <gitster@pobox.com> writes:

Show 24 quoted lines

> Kevin <ikke@ikke.info> writes:
>
>> Regularly I notice that the diffs that are provided (through diff, or
>> add -p) tend to disconnect changes that belong to each other and
>> report lines being changed that are not changed.
>>
>> An example for this is:
>>
>>      /**
>> +     * Default parent
>> +     *
>> +     * @var int
>> +     * @access protected
>> +     * @index
>> +     */
>> +    protected $defaultParent;
>> +
>> +    /**
>>
>> I understand this is a valid view of what is changed, but not a very
>> logical view from the point of the user.
>>
>> I wondered if there is a way to improve this, or would that have other
>> consequences.

I forgot to mention consequences. Changing it obviously changes the shape of the diff, hence changes the patch id. Anything that caches output from "git cherry" to match up "identical patches" will need to discard and repopulate its cache. Your "rerere" database will go stale.

Also "kup" tool used at k.org allows an uploader to pretend to upload an incremental diff between two known commits by only sending the GPG signature of the diff the uploader generates. The actual diff is generated on the k.org machine locally and deposited next to the GPG signature file, with the expectation that the signture matches the diff. Changing the output from diff between two versions will break the optimization and force the uploader to upload the diff over the wire.