Regression in 1.3+ with Branch5 and mismatched bzr versions

[John Arbash Meinel]

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So, I just spent a long time today debugging this. The symptoms are really odd.

The bug is:
~  https://bugs.launchpad.net/bzr/+bug/214894

Looking into this, the problem is with the RemoteRepository.get_parent_map() code.

Specifically, if the server doesn't support get_parent_map() it falls back to
just calling get_revision_graph().

However, for nodes with 0 parents, get_parent_map() returns ('null:',) while
get_revision_graph() just returns ().
for get_parent_map(), a return of () means that the revision is a ghost.

This shows up for Branch5, because it checks the normalization of history when
you call set_last_revision_info(). And the _lefthand_history() code iterates
backwards, stopping when it finds a ghost.

So when you "bzr push bzr+ssh://" a Branch5 (dirstate) it checks the length of
the remote history, and doesn't include the first revision (because it thinks it
is a ghost).

The fix isn't very hard, you just need to filter the get_revision_graph() call
and substitute ('null:',) for any () nodes.

I'll work up a patch. This is probably worthy of a 1.3.2 fix if we really want
to allow bzr >1.2 to interoperate with bzr <1.2 (and 1.3.2 because that is
easier to get into Hardy than asking them to release 1.5)

John
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