Re: [PATCH] bisect: test merge base if good rev is not an ancestor of bad rev

[Christian Couder <chriscool@tuxfamily.org>]

Le vendredi 11 juillet 2008, Junio C Hamano a écrit :
>
> But in real life, things are more like "Today's master does not work, but
> I am sure it used to work at 1.5.6.2".  I happen to always merge all of
> 'maint' to 'master' before pushing them out, so a good topology is
> guaranteed, but not everybody does this (it takes careful planning what
> to apply to 'maint' and where to fork topics from, and maintainers are
> not perfect):
>
>               Good
>           ?---o (maint)
>          /
>      ---?---?---?---?---x (master)
>         MB              Bad
>
> People _will_ face such a topology.  If the users Know Better, they will
> test MB=$(merge-base master maint) first to see if it is broken, and then
> the world will have two possibilities:
>
>     (1)       Good
>           ?---o (maint)
>          /
>      ---o---?---?---?---x (master)
>         Good            Bad
>
>     (2)       Good
>           ?---o (maint)
>          /
>      ---x---?---?---?---x (master)
>         Bad             Bad
>
>
> If (1), you go ahead with the usual bisection.  If (2), you cannot even
> bisect.  Instead, you flip good and bad to find the "fix" in the side
> branch (the answer has to be either the tip of maint or one previous in
> the picture) to forward port to, either by merging 'maint' to 'master' or
> cherry-picking.
>
> The idea to check merge-base first is about automating this process (I
> admit I still haven't looked at Christian's patch text yet).

Well in case (2) my patch does:

-------
		cat >&2 <<EOF
The merge base $_badmb is bad.
This means the bug has been fixed between $_badmb and $_g.
EOF
		exit 3
-------

but this can be improved upon in some latter patches.

Thanks,
Christian.