Re: [PATCH v4] Allow update hooks to update refs on their own.

> The rebase would be "rebase --onto W' X Z", so it is not strictly
> necessary to keep the fact that X corresponds to X', but somehow I
> thought it was necessary, and Steven's message was hinting about that:
> 
>   > If we want that status in principle, I'd argue that sending down the
>   > updated commit SHA1 is actually the right way to indicate it, because
>   > it gives the client all the information it needs to make an
>   > intelligent choice about what to do next. If you don't transmit the
>   > modified SHA1, the client will have to do another fetch to find out
>   > what rewriting was done by the server, and if another push happened in
>   > the meantime, the client will have to basically guess about which
>   > commits correspond to the ones it pushed.
> 
> (notice the last part).
> 
> So if we want to transmit minimum amount of information, we can just
> send a bit ("the ref was rewritten") back to send-pack without telling
> it what X' is (but it would not hurt to send it back either).  With that
> one bit of information, send-pack can refrain from updating tracking ref
> from Y to X.