So many repo formats

[Andrew Bennetts]

Stefan Monnier wrote:
> >> So, what's the downside?
> > Upgrading from a non-rich-root format to a rich-root format is more
> > resource-intensive and one-way (you can't convert from a
> > rich-root-format to a non-rich-root-format, since that would lose data).
> 
> I don't understand why its one way: losing data is usually the easier path.

Because then you'd have two revisions claiming to have the same revision
ID, but with different data.  That's a fairly fundamental constraint
that we cannot break.  So it's not possible to store rich-root revisions
in a non-rich-root repository

-Andrew.