Re: RFE: support change-id generation natively

[Junio C Hamano <gitster@pobox.com>]

Johannes Sixt <j.sixt@viscovery.net> writes:

> Am 10/24/2013 7:25, schrieb Duy Nguyen:
>> On Thu, Oct 24, 2013 at 11:11 AM, Nasser Grainawi <nasser@codeaurora.org> wrote:
>>>>> It is not clear to me how you envision to make it work.
>>>>
>>>> I don't have the source code.
>>>
>>> Now you do: https://gerrit.googlesource.com/gerrit/+/master/gerrit-server/src/main/resources/com/google/gerrit/server/tools/root/hooks/commit-msg
>> 
>> Thanks. So you do have tree sha-1 by running "git write-tree". But at
>> that point I'm not sure if cache-tree is written down to disk yet, so
>> write-tree could be more expensive than necessary (one good point for
>> building --change-id in).
>
> Consider that I make a commit with a change-id. Then I rewrite the commit,
> but keep the change-id. Then I push the rewritten commit to Gerrit. Gerrit
> does not have the objects that the change-id is based on; the change-id is
> just a random number and has no other significance. Right?
>
> Why do you go all the length in computing a change-id instead of just
> pulling 20 bytes from /dev/random?

Very good point.

The quoted script does not necessarily give the right commit object
name at least under three scenarios:

 - when we would need to add encoding header, etc.;

 - when we are recording merges (perhaps merges will not get rebased
   in Gerrit workflow and it does not matter what random garbage
   this script added to them).

 - when we record the commit after 1-sec boundary since _gen_ChangeIdInput
   in the script was called.

I wouldn't call the script "buggy", but I tend to agree with you
that it is an unnecessarily more complex way to spell "grab 20
random bytes" ;-)

> That said, I don't think that --change-id option that the user must not
> forget to use is any better than a hook that the user must not forget to
> install.

That is why I said this in my first response to this thread:

>> ...  We may even want to
>> introduce commit.changeId boolean configuration variable if we did
>> so.