plugin to reweave history, inserting ghosts

[Jan Hudec]

On Mon, Oct 31, 2005 at 15:40:32 -0500, Martin Pool wrote:
> On 26/10/05, Jan Hudec <bulb at ucw.cz> wrote:
> > On Wed, Oct 26, 2005 at 18:30:12 +1000, Martin Pool wrote:
> > > On 26/10/05, Jan Hudec <bulb at ucw.cz> wrote:
> 
> > > You may not *know* the hash or contents of the parent at the time you
> > > create the child; this occurs all the time in arch.  You only know the
> > > id.
> >
> > I commented on the text in parenthesis -- that the fact it identifies
> > versions by hashes is irrelevant when it comes to whether it can have
> > ghost revisions or not.
> 
> Consider the case of upgrading an arch archive.  It is very common for
> them to contain records that revisions were merged from someone's
> private development archive, which may be only on their laptop and not
> mirrored.  That archive may not be accessible to the person doing the
> upgrade, and in fact may no longer exist at all.  Arch does not copy
> the contents of the revision when it merges, only the log headers. 
> There is, therefore, no way for the upgrade to know the hash of the
> merged revision; systems that use the hash of the inventory/manifest
> of the revision to identify it can't include that reference.  You
> could perhaps record it as a special kind of parent where only the id
> is known, but then you probably can't go back and make it a proper
> parent later.
> 
> Of course it's all about tradeoffs, and people might reasonably decide
> that they thing supporting this is not so important.  I'm not saying
> that every system has to do this; but we want to.

... which means it's not possible to convert Arch repository with ghost
revisions to Git or Mercurial or other system that only uses hashes. But if
some of those systems has ghost revisions, Bzr will have no trouble with
it...

-- 
						 Jan 'Bulb' Hudec <bulb at ucw.cz>
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