Re: [PATCH] Update the documentation for git-merge-base

From: Fredrik Kuivinen <freku045@student.liu.se>
Date: 2006-05-16 16:54:52
On Mon, May 15, 2006 at 11:13:12PM -0700, Junio C Hamano wrote:
> Fredrik Kuivinen <freku045@student.liu.se> writes:
> 
> > Is the code guaranteed to return a least common ancestor? If that is
> > the case we should probably mention it in the documentation.
> 
> Unfortunately, no, if you mean by "least common" closest to the
> tips.
>

By "least" I mean the following:

C is a least common ancestor of A and B if:

* C is a common ancestor of A and B, and
* for every other common ancestor D (different from C) of A and B, C
  is not reacheable from D.

> See the big illustration at the top of the source for how you
> can construct pathological case to defeat an attempt to
> guarantee such.  --all guarantees that the output contains all
> interesting ones, but does not guarantee the output has no
> suboptimal merge bases.

There are two examples at the top of the source. In the first one a
least common ancestor is returned. As I interpret the second one, it
is an example of how the old algorithm without the postprocessing step
produced a common ancestor which is not least.

Am I wrong? Do we have any cases where the current merge-base
algorithm gives us common ancestors which are not least?

- Fredrik
-
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Received on Tue May 16 16:55:26 2006

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