Re: [PATCH 4/5] Head reduction before selecting merge strategy

[Jakub Narebski <jnareb@gmail.com>]

"Sverre Hvammen Johansen" <hvammen@gmail.com> writes:

> See the documentation for an explanation of this feature.

I think I get the idea now.

You want to generalize fast-forward merge, or what's equivalent make
fast-formard merge to be special case of head reduction.  This should
be written both in commit message and in documentation.  Do I
understand your goal correctly?

With head reduction comes three things:
 * the merge strategy used
 * recorded parents
 * generated merge commit message
The simplest way would be to use reduced head for all three things,
I think.

But I also think that this commit in series is the most controversial
one; is it realy needed for other commits?  I would put it then as the
last commit in series...
 
> +If more than one commit are specified on the command line, git will
> +try to reduce the number of commits used (reduced parents) by
> +eliminating commits than can be reached from other commits.  The
> +commit message will reflect the commits specified on the command line
> +but the merge strategy will be selected based on the reduced parents
> +including `HEAD`.  The reduced parents are the parents recorded in the
> +merge commit object.

Is it a correct solution, to use provided (specified) heads for
generation of merge commit message, but use reduced heads for
selecting merge strategy _and_ also as parents recorded in merge
commits?  Perhaps it is; but IMHO you should have written it in the
commit message, and defend this decision in commit message.

> +
> +The following shows master and three topic branches.  topicB is based
> +on topicA, topicA is previously branched off from master, and topicC
> +is based on the tip of the master branch:
> +
> +------------
> +                    o---o---o  topicB
> +                   /
> +          o---o---o  topicA
> +         /
> +    o---o---o---o---o---o  master
> +                         \
> +                          o---o  topicC
> +------------

I think I would start with simpler example without 'topicC', of
reduction of octopus to two-parent ordinary merge.

> diff --git a/git-merge.sh b/git-merge.sh
> index 7c34b6c..7c70c56 100755
> --- a/git-merge.sh
> +++ b/git-merge.sh
> @@ -337,11 +337,16 @@ set x $remoteheads ; shift
> 
>  find_reduced_parents "$@"
> 
> -actual_parents=$(git rev-parse "$@")

This was introduced by some of your earlier commits, isn't it?

[...]
-- 
Jakub Narebski
Poland
ShadeHawk on #git