Re: Strange behavior of git rev-list

[Jeff King <peff@peff.net>]

On Thu, Sep 07, 2017 at 11:20:15AM +0200, Paweł Marczewski wrote:

> I have an interesting case. In my repository, there are two commits,
> 'one' and 'two'. 'one' is reachable from 'two' (as evidenced by 'git
> rev-list two | grep $(giv rev-parse one)'). However, the output of
> 'git rev-list two..one' is not empty, as is 'git rev-list ^two one'.
> 
> Here is the repository: https://github.com/pwmarcz/git-wtf/
> 
> It seems that the commit dates influence this behavior, because when I
> edit all the dates to be the same, the output of 'git rev-list
> two..one' is empty. Pruning seemingly irrelevant parents also makes it
> empty.
> 
> I verified the behavior on git versions 2.14.1, 2.11.0, and on the
> 'next' branch (2.14.1.586.g1a2e63c10).

Yes, this is known. The commit dates are used as a proxy for graph
height (or generation numbers, if you prefer) so that we avoid having to
walk all the way down to a merge base before producing any output. But
it can give the wrong answer in the face of clock skew.

We walk back five extra commits more than we need to in order to avoid
small runs of skewed commits, but obviously you can have arbitrary-sized
runs.

-Peff