What happened here was the $codename = $::lsbdistcodename was removed from
init.pp and replaced with just $::lsbdistcodename whereever $codename was
used. Then in the sources.list.erb and preferences files things were changed
like this:
<pre>+### Debian current: <%= codename = scope.lookupvar('::lsbdistcodename') %>
...
-deb <%= debian_url %> <%= codename %> <%= repos %>
...
+deb <%= debian_url=scope.lookupvar('apt::debian_url') %> <%= codename %> <%= repos=scope.lookupvar('apt::repos') %>
</pre>
This meant that the codename was always set to lsbdistcodename, and you because
in newer puppet versions you cannot assign a value to a top-level facter
variable, it is not possible to change this.
Because we cannot change $lsbdistcodename, we have to fix this by allowing the
user to pass a different, non-top-level scoped variable to the class as a
parameter, which defaults to $::lsbdistcodename, so that upgrades can be
triggered.
This is documented in the README in an upgrade notice
