The TreeNodeIterator decodes nodes while iterating over a tree blob.
This should reduce peak memory usage as now only the serialized tree
blob and a single node have to alive at the same time. Using the
iterator has implications for the error handling however. Now it is
necessary that all loops that iterate through a tree check for errors
before using the node returned by the iterator.
The other change is that it is no longer possible to iterate over a tree
multiple times. Instead it must be loaded a second time. This only
affects the tree rewriting code.
This adds support for caching already rewritten trees, handling of load
errors and disabling the check that the serialization doesn't lead to
data loss.
The more generic RewriteNode callback replaces the SelectByName and
PrintExclude functions. The main part of this change is a preparation to
allow using the TreeRewriter for the `repair snapshots` command.
In principle, the JSON format of Tree objects is extensible without
requiring a format change. In order to not loose information just play
it safe and reject rewriting trees for which we could loose data.
Michael Eischer
Alex Johnson
Andrea Gelmini