Re: disallowing push to currently checked-out branch

From: Jeff King <peff@peff.net>
Date: Feb 17, 2009, 00:23 UTC
Message-ID: <20090217002352.GA23507@coredump.intra.peff.net>
In-Reply-To: <7vhc2uezl7.fsf@gitster.siamese.dyndns.org>

On Mon, Feb 16, 2009 at 03:23:00PM -0800, Junio C Hamano wrote:

Show 6 quoted lines

> >   1. How can we improve this situation?
> 
> The situation you described is all about "don't allow a push that is NOT
> CONTROLLED BY YOU and that can interfere with what you are doing into a
> live repository", and you are right, we have operations that deliberately
> detach the HEAD and expect nobody mucks with the branch.

I don't agree that it has to be a push not controlled by you. I have many times left a rebase-in-progress sitting in a repository, either accidentally because I meant to "--abort" it after a conflict but forgot, or because I got interrupted during an interactive edit and needed to come back to it.

So the problem is simply that the repository you're pushing into is not in the state you think it is (either because you forgot what state you left it in, didn't realize what state you left it in, or because it is somebody else's repo).

> But is this something even worth considering about in the same context as
> the denyCurrentBranch?  The same thing can happen even if you are not
> detaching HEAD.

I don't think it's the same, but I think it is a related problem. I don't think the solutions are related, though.

Show 17 quoted lines

> For example, I sometimes end up with an ugly series on a branch, whose
> endpoint is a good looking tree.  And a refactoring I would want to do
> would be too cumbersome for the interactive rebase (I could do it, but the
> machinery does not help as much as it would for a simpler case).  In such
> a case, often I would just say:
> 
> 	$ git branch -f goal
>         $ git reset --hard master
>         : repeat from here until "diff HEAD goal" becomes empty
>         ... cherry-pick $a_commit_in_goal_branch, or
>         ... edit "show $a_commit_in_goal_branch" output and apply, or
>         ... edit the files in place.
>         ... make a commit, perhaps using -c $a_commit_in_goal_branch
> 	: repeat up to here
> 
> I would not push into this repository to update the branch "goal" while I
> am doing this, as it will obviously screw up the whole process.  I think

OK, that is a good example of how this is basically impossible to protect from fully (and a good argument why pushing into a repo used for work is probably not a good idea in general). I think the rebase example is a little worse because:

  - It's subtle. with denyCurrentBranch, we generally protect the user
    from pushing into the current branch and messing things up. But
    during a rebase we don't, and the only way the user would realize
    that is if they understand that rebasing happens on a detached HEAD.

  - the error message is confusing, and there is no clear way out of the
    error case. You can "rebase --abort" which throws away your rebase
    work _and_ the push.  But what you probably want to do, I described
    earlier.

> It's just a common sense thing.  What denyCurrentBranch protects you from
> is a push from elsewhere *while* you are not there, and then next day,
> getting confused by what such a push did in the receiving repository.  In

See above for why I think this can happen while you are not there. It is about repo state for long-running workflows. I'm not too concerned with somebody pushing in the exact half second while you are making running "git commit".

> Obviously you can tell receive-pack to refuse pushing into a non-bare
> repository, with a "I know what I am doing" configuration, but I think at
> that point the whole "you could break things this way, so let's prevent a
> new user from making such mistake" goes into the realm of absurdity.

I think that is insane, too. This is not all that likely to happen compared to the possible benefits of pushing into a non-bare repo. And as you say, in most cases common sense rules: don't push into something you are actively working on.

I am really just proposing that the "ref was not what we expected" message to better indicate what is going on, and how the user might get out of it. Do you not agree with that?

-Peff