Re: Invalid dates in git log

From: Andreas Ericsson <ae@op5.se>
Date: Dec 12, 2007, 15:51 UTC
Message-ID: <47600392.5050809@op5.se>
In-Reply-To: <34660cca0712120619r708ee7a8ta20a5458ca11a5ac@mail.gmail.com>

Eirik Bjørsnøs wrote:

Show 10 quoted lines

>> Your best guess is probably the committer information. Try this:
> 
> Thanks Jeff, Junio,
> 
> I'll just use the committer date instead.
> 
> Being a Git newbie (only started looking at it yesterday) I'm not sure
> my understanding of "author" and "committer" and how they releate to
> dates is correct:
>

They're often the same. They will end up being different if
* you cherry-pick a commit made by someone else.
   ("someone else" is author, you are the committer)
* you rebase a series of commit containing changes from others
   ("others" are the authors, you are the committer)
* you apply a patch using "git am" from someone
   ("someone" is the author, you are the committer)
* you "git commit --amend" a commit from someone else
   ("someone else" is author, you are the committer)

There are probably other cases, but those were the ones I could think of right now.

In short, whenever a commit is modified in some way, it gets a new committer. It might help if you think of author as "contributor" and "committer" as "integrator", where various integrators merge between each other. A merge obviously doesn't fiddle with commits, so once a commit has entered an integrators repository, both author and committer stays intact (that's not strictly true, but for the sake of this argument, which concerns the linux kernel, it will suffice and be mostly correct insofar as I understand the kernel workflow).

> * author: Original source of the change. This person may typically
> have sent a committer an email with a patch. It's the commiter's
> responsibility to supply this information.

No, it's the author's responsibility to supply this information. Author is hardly ever changed.

> * author date: The commiter is free to specify a date for the contribution.
>

No, the author does that too :)

> * committer: First committer to actually add this change to a repository

No, committer is the person who added the commit to the repository by some other means than merging from another repository.

> * committer date: Date of the actual commit, added by the git client
> during the commit. Typically the system clock at the time of the
> commit.
>

Sort of, yes, although commits can be created by other means than just running "git commit". The operations listed in bullets at the top of this mail all create new commits, in the sense that they can't have the same SHA1 as their original ones. Hence, committer and commitdate must be updated.

> * A transfer of a commit across repositories (pull, push) will not
> change the author, commit or date information
>

True. Since neither ancestry nor content is allowed to change, the commit will be exactly the same in the new repository as it was in the old one.

> If I got some of this wrong, I'd be happy if someone would correct me.
>

I think I just did. Perhaps I missed something, but I'm sure someone will correct me if that's the case.

-- 
Andreas Ericsson                   andreas.ericsson@op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231