[darcs-users] rebase feedback and amend-record flexibility

[Michael Hendricks]

Hi Ben.  Thanks for the feedback.


> >    - rewording commit messages, changing author, changing date, etc
> >       - amend-record does this, it's just not smart enough yet
> >       - rewording a patch needs no commute operations
> >       - dependencies should never prevent a reword operation
> >       - rewording a buried darcs patch only modifies other patches if
> >       there are "record --ask-deps" dependencies (which appear easy to
> >       adjust automatically)
>
> No, no, no! This is not possible, changing the meta data will change the
> patch identity of an arbitrary number of other patches! I definitely want
> to
> have this disabled by default. Note that currently amend-record does not
> mutate any patches other than the one I have explicitly chosen.
>

If I want to change the meta data for patch P, three are three possible
scenarios: no patches depend on P, a patch Q implicitly depends on P, a
patch Q explicitly depends on P (via darcs record --ask-deps).  The first
scenario is trivial and amend-record handles it well today.  The second
doesn't mutate Q, so Darcs should handle allow it but doesn't. The third
triggers the cascading effects you mention.  I agree that it should be
disabled by default or generate a loud warning so the user isn't surprised.
 In any case, the changes are easy, so a fancy rebase mechanism isn't
needed.

Unfortunately, since Darcs refers to patches by their entire meta data, the
cascading effect is worse than it needs to be.  A unique patch identifier,
independent of other metadata, would let us correct typos in P without
mutating Q at all.  Ignore-this "junk" might make a decent identifier, but
that's for another discussion.


> I'd say that even the existing version of amend-record would be improved by
> issuing a warning (with a request for confirmation) if I change a patch
> that
> is also present in the default-repo.
>
> "Warning: This operation modifies a patch the exists in the default remote
> repo. Are you sure? [yN]"
>

I agree.


> >    - combining arbitrary, adjacent patches
> >       - Darcs internals call this coalesce, but we have no UI for it
> >       - current amend-record is a special case of this, applied to only
> >       the top two patches
>
> To clarify: no, amend-record works fine for all patches that have no
> dependents yet.
>

Right.  One can view the current amend-record behavior as following these
steps: commute patch A to the front, record working copy changes as patch
C, coalesce A and C into A'.  In that sense, today's amend-record is a
special case of combining patches, namely the top two.

Combining arbitrary, adjacent patches is a more general case.  As long as A
and C can be commuted to adjacent positions somewhere in the patch list,
amend-record should work.

For example, imagine having patches A and B where B depends on A.  I want
to amend changes C into A.  C does not depend on B.  Today's darcs fails
this case because A can't commute to the front.  However, we could commute
C backwards to get ACB, then combine into A'B

-- 
Michael
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