# Strange reachability inconsistency (apparently, at least...)

3 messages from 2015-02-19 to 2015-02-23. Participants: ydirson@free.fr, Junio C Hamano.
Thread: https://gitlist.dev/t/38603

## ydirson@free.fr, 2015-02-19 15:03

Subject: Strange reachability inconsistency (apparently, at least...)
Message-ID: <324985759.551780546.1424358217833.JavaMail.root@zimbra39-e7.priv.proxad.net>
URL: https://gitlist.dev/e/324985759.551780546.1424358217833.JavaMail.root%40zimbra39-e7.priv.proxad.net
In-Reply-To: <144640746.551672305.1424355582540.JavaMail.root@zimbra39-e7.priv.proxad.net>

```
I have a (fsck-clean) git tree in which for 2 commits A and B:

* "git merge-base --is-ancestor A B" returns 0
* "git log B..A" returns a non-empty set of commits

I get this behaviour with 2.3.0 as well as with 2.1.3 and 1.7.12.

Is that a real bug or am I just misinterpreting something ?

```

## Junio C Hamano, 2015-02-22 23:30

Subject: Re: Strange reachability inconsistency (apparently, at least...)
Message-ID: <CAPc5daW=OeNmPVMVWQvp3rfYzfV7z6c1=26E26y0SaRQH7JooA@mail.gmail.com>
URL: https://gitlist.dev/e/CAPc5daW%3DOeNmPVMVWQvp3rfYzfV7z6c1%3D26E26y0SaRQH7JooA%40mail.gmail.com
In-Reply-To: <324985759.551780546.1424358217833.JavaMail.root@zimbra39-e7.priv.proxad.net>

```
On Thu, Feb 19, 2015 at 7:03 AM,  <ydirson@free.fr> wrote:
> I have a (fsck-clean) git tree in which for 2 commits A and B:
>
> * "git merge-base --is-ancestor A B" returns 0
> * "git log B..A" returns a non-empty set of commits
>
> I get this behaviour with 2.3.0 as well as with 2.1.3 and 1.7.12.
>
> Is that a real bug or am I just misinterpreting something ?

Sounds strange. Is it possible to share the repository (or an
anonymised copy of it)?

```

## Junio C Hamano, 2015-02-23 06:44

Subject: Re: Strange reachability inconsistency (apparently, at least...)
Message-ID: <xmqq1tlhunxs.fsf@gitster.dls.corp.google.com>
URL: https://gitlist.dev/e/xmqq1tlhunxs.fsf%40gitster.dls.corp.google.com
In-Reply-To: <CAPc5daW=OeNmPVMVWQvp3rfYzfV7z6c1=26E26y0SaRQH7JooA@mail.gmail.com>

```
Junio C Hamano <gitster@pobox.com> writes:

> On Thu, Feb 19, 2015 at 7:03 AM,  <ydirson@free.fr> wrote:
>> I have a (fsck-clean) git tree in which for 2 commits A and B:
>>
>> * "git merge-base --is-ancestor A B" returns 0
>> * "git log B..A" returns a non-empty set of commits
>>
>> I get this behaviour with 2.3.0 as well as with 2.1.3 and 1.7.12.
>>
>> Is that a real bug or am I just misinterpreting something ?
>
> Sounds strange. Is it possible to share the repository (or an
> anonymised copy of it)?

Actually it does not sound all that strange.

I suspect that B is indeed a proper descendant of A, but you have
commits with screwed-up committer timestamps between these two
commits that break the cut-off heuristic used by log and reb-list.

Grab the output from "git rev-list B..A".  These are supposed to be
ahead of B (i.e. should not be reachable from B).  Then look at the
output from "git log B" (no lower bound) and see if these commits
appear there, perhaps like:

    $ git rev-list B..A | sed -e 's/^/^/' >phantoms
    $ git log --format='%H %ct' B | grep -C2 -f phantoms

Hits from the latter "grep" would indicate that what the traversal
B..A claimed that are not reachable from B contained some commits
that are indeed reachable from B.

```