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Re: Tools that do an automatic fetch defeat "git push --force-with-lease"




On Mon, Apr 10, 2017 at 2:58 AM, Ævar Arnfjörð Bjarmason
<avarab@xxxxxxxxx> wrote:
> On Mon, Apr 10, 2017 at 10:08 AM, Jacob Keller <jacob.keller@xxxxxxxxx> wrote:
>> On Sun, Apr 9, 2017 at 4:00 AM, Stefan Haller <haller@xxxxxxxxxxx> wrote:
>>> Jacob Keller <jacob.keller@xxxxxxxxx> wrote:
>>>
>>>> Agreed. You "take" a lease whenever you push to the remote or when you
>>>> pull from the remote and when you pull into the branch. It should
>>>> store something that tracks both the branch and remote branch together
>>>> so that you can generalize it to multiple remotes.
>>>
>>> I don't see why it has to support multiple remotes (but then I don't
>>> have much experience with workflows involving multiple remotes, so I may
>>> well be missing something). A local branch can only have one remote
>>> tracking branch on one remote, and in my view --force-with-lease without
>>> arguments works with that remote tracking branch only. Is this view too
>>> simple?
>>>
>>
>> I think that's fine. Thinking in terms of only one remote at a time is easier.
>>
>>>> It doesn't necessarily track perfectly with a branch that contains
>>>> extra work such as when doing pull --rebase, but maybe you have an
>>>> idea about that?
>>>
>>> Maybe I wasn't clear enough about that in my proposal, but I propose to
>>> always store the commit hash of the remote tracking branch as a new
>>> lease after push and pull, not the local branch. This way it works
>>> nicely with pull --rebase and a branch that has extra local commits.
>>>
>>>
>>
>> Oh right. The main thing it doesn't give is that this doesn't enforce
>> that your local branch *has* to have at one point prior to the push
>> matched the remote branch that you're overwriting, which would be even
>> more evidence that your changes are what you expect and aren't
>> deleting anything unexpectedly. However, I think that's not strictly
>> necessary to require that since it would also break pull-rebase
>> workflow anyways.
>>
>> So something like:
>>
>> For a branch, also store its last known "lease" sha1 value, which
>> updates once every time that we push that branch to the remote
>> tracking branch or any time that we pull into the branch using the
>> remote tracking branch.
>>
>> This value is what we would default to, and we only need to store the
>> latest one, since that's the last known good value. If the value is
>> wrong then we will error and avoid deleting work, and if it's correct,
>> then we know that the remote branch is correct for this specific push
>> and is safe.
>>
>> I think this is straight forward and reasonable approach to solve the
>> problem, and makes using force-with-lease much nicer.
>
> Does this proposal require that all the things that can update a ref
> be hooked to maintain these lease values?
>
> In lieu of patches it would be nice for us trying to follow along to
> at least get some partial list of things that would need to be hooked
> up, how the command workflow would look like, what things wouldn't
> work that do now, or work that don't now etc.
>
> E.g. now if I:
>
>      git fetch
>      git show origin/master # manually note the sha1
>      git checkout -b blah <that-sha1>
>      git commit --amend
>      git branch --set-upstream-to origin/master
>      git push --force-with-lease
>
> It'll work unless origin/master was updated in the meantime, but
> there's no hint in any log that the branch was created from
> origin/master to begin with, just from the sha it happened to point
> to.
>
> I think this is a really important property of git, you don't have to
> go through some chosen UI that'll record things because you told it
> "I'd like to checkout stuff from that branch", you can just copy/paste
> the sha1.
>
> How will this work in this proposed "lease" workflow? Will some lease
> metadata not get created and I'll need to manually retcon that with
> some new command?
>
> I'm not just trying to come up with contrived scenarios, I've had to
> do several force pushes (on repos used by many people) and it's
> usually due to some giant commit being pushed. At that point the
> machine I'm investigating the situation on might not be the machine
> where I do the push from, so often I'm just copy/pasting a sha1 across
> machines.
>
> To me the *main* feature of --force-with-lease is that it's less
> shitty than --force, without imposing too much UI overhead. We have to
> be really careful not to make --force-with-lease so complex by default
> that people just give u and go back to using --force, which would be
> worse than either whatever current problems there are with the
> current --force-with-lease behavior, or anything we replace it with.

If you're already copying sha1s around you could use those as the
--force-with-lease=branch:<commit>, no?

That's better guarantee than just using --force-with-lease alone.

Thanks,
Jake