D3754: graft: introduce --abort flag to abort interrupted graft

[Yuya Nishihara]

> +def _abortgraft(ui, repo, graftstate):
> +    """abort the interrupted graft and rollbacks to the state before interrupted
> +    graft"""
> +    if not graftstate.exists():
> +        raise error.Abort(_("no interrupted graft to abort"))
> +    statedata = _readgraftstate(repo, graftstate)
> +    startnode = statedata.get('startnode')
> +    if not startnode:
> +        # and old graft state which does not have all the data required to abort
> +        # the graft
> +        raise error.Abort(_("cannot abort using an old graftstate"))
> +    newnodes = statedata.get('newnodes')
> +    hg.updaterepo(repo, startnode, True)
> +    if newnodes:

It's probably better to not updating to the startnode if we can't strip
grafted revisions.

> +        newnodes = [repo[r].rev() for r in newnodes]
> +
> +        # checking that none of the newnodes turned public or is public
> +        immutable = [c for c in newnodes if not repo[c].mutable()]
> +        if immutable:
> +            repo.ui.warn(_("cannot clean up public changesets %s\n")
> +                         % ','.join(bytes(repo[r]) for r in immutable),
> +                         hint=_("see 'hg help phases' for details"))
> +
> +        # checking that no new nodes are created on top of grafted revs
> +        desc = set(repo.changelog.descendants(newnodes))
> +        if desc - set(newnodes):
> +            repo.ui.warn(_("new changesets detected on destination "
> +                           "branch, can't strip\n"))
> +
> +        with repo.wlock(), repo.lock():
> +            # stripping the new nodes created
> +            strippoints = [c.node() for c in repo.set("roots(%ld)", newnodes)]
> +            repair.strip(repo.ui, repo, strippoints, False)
> +
> +    ui.write(_("graft aborted\nworking directory is now at %s\n")
> +             % repo[startnode].hex()[:12])
> +    graftstate.delete()
> +    return 0

This looks quite similar to rebase.abort(). Can we factor out a common part?
Maybe it's time to add a new module for rebase/graft thingy.