Re: Sample pre-push hook can crash

> Stephen Morton <stephen.c.morton@gmail.com> writes:
>
>> That is interesting, so in the case of a non-ff push, there is no way
>> for a pre-push hook to know what is being pushed in order to run?
>
> If you were up-to-date from the other side once:
>
>     ---A---B---C
>
> and built one new commit on top:
>
>     ---A---B---C---D
>
> when you attempt to push it out, there are various possibilities.
>
> An ff situation is simple.  They didn't do anything, so the hook
> gets "we'd be updating their ref from C to D", and "rev-list C..D"
> would tell you that you would need to make sure D is sane.
>
> If your push does not fast-forward, that would mean something has
> happened on the other side while you were working on D.  Perhaps
> they accepted another commit that you haven't seen:
>
>     ---A---B---C---E
>
> and because you haven't fetched from them, even though the hook may
> say "we'd be updating their ref from E to D", you haven't heard of
> E, you do not know where it would be relative to the history you
> have:
>
>                   E???
>
>     ---A---B---C---D
>
> Or perhaps they themselves rewound their history and they now have
> this E at the tip:
>
>     ---A---B---C
>             \
>              E
>
> But again, because you do not yet know where E is relative to your
> history, you cannot say C is where you can stop checking your side
> of the history.
>
> Or perhaps they somehow obtained your D without you pushing into
> them (e.g. you pushed to the "next" tree and they fixed your commit
> and the result was merged there) and have something like this:
>
>     ---A---B---C---D---E
>
> In this case, D is not even a new commit from their point of view,
> and updating their tip E with your old D would lose the fixup E they
> made for D, but again, you do not know what E is yet, you cannot say
> "they have this already, so there is no check I need to do".
>
> In summary, you cannot even say which ones you have need to be
> checked.
>
> If you _are_ using @{u} tracking, then you would know at least they
> used to have up to C in their repository to limit your check, but
> you cannot unconditionally say ref@{u}.. without making sure ref@{u}
> makes sense in the first place.
>
> An obvious alternative for the sample script would be to instead let
> the non-ff push pass the pre-push check (as you may have other
> arrangements to forbid non-ff pushes) without actually checking
> anything.  As this sample script is to serve as a sample, I think
> such an advanced consideration of loosening checks depending on the
> situation should be left to the end users.
>