Re: [PATCH] builtin-commit: avoid using reduce_heads()

> > Actually I think this would be ugly. MERGE_HEAD is about you can see
> > what will be merged once you commit the merge, but once you include HEAD
> > there, you can't easily check that. Maybe it's just me who sometimes
> > have a look at that file myself directly... :-)
> 
> The new semantic would be very simple.  If there is no MERGE_HEAD, it
> is an ordinary no-merge commit, and its only parent would be previous
> (current) version of HEAD.  If there is MERGE_HEAD it contains _all_
> parents in a merge commit, and only those heads which will be parents
> (_reduced_ heads); if HEAD is symref, we modify given branch so it
> points to newly created merge commit.
> 
> Currently parents of merge commits are 'reduce(HEAD + MERGE_HEAD)'
> in symbolic equation; I propose they would be simply 'MERGE_HEAD'.
> then we set this branch to new commit