failure to lazy-load a plugin repository format should not be fatal

[Martin Pool]

If we fail to lazy-load something from a registry, we should possibly give a warning rather than a fatal error. In the case below this format is not relevant to the command I'm trying to run.

mbp@grace% bzr info
bbzr: ERROR: exceptions.ImportError: failed to load bzrlib.plugins.groupcompress.repofmt.RepositoryFormatPackGCRichRoot: No module named index2.btree_index

Traceback (most recent call last):
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 857, in run_bzr_catch_errors
    return run_bzr(argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 797, in run_bzr
    ret = run(*run_argv)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 499, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/usr/lib/python2.5/site-packages/bzrlib/commands.py", line 818, in ignore_pipe
    result = func(*args, **kwargs)
  File "/usr/lib/python2.5/site-packages/bzrlib/builtins.py", line 1049, in run
    verbose=noise_level, outfile=self.outf)
  File "/usr/lib/python2.5/site-packages/bzrlib/info.py", line 346, in show_bzrdir_info
    outfile)
  File "/usr/lib/python2.5/site-packages/bzrlib/info.py", line 361, in show_component_info
    format = describe_format(control, repository, branch, working)
  File "/usr/lib/python2.5/site-packages/bzrlib/info.py", line 449, in describe_format
    format = bzrdir.format_registry.make_bzrdir(key)
  File "/usr/lib/python2.5/site-packages/bzrlib/bzrdir.py", line 2707, in make_bzrdir
    return self.get(key)()
  File "/usr/lib/python2.5/site-packages/bzrlib/bzrdir.py", line 2659, in helper
    bd.repository_format = _load(repository_format)
  File "/usr/lib/python2.5/site-packages/bzrlib/bzrdir.py", line 2644, in _load
    raise ImportError('failed to load %s: %s' % (full_name, e))
ImportError: failed to load bzrlib.plugins.groupcompress.repofmt.RepositoryFormatPackGCRichRoot: No module named index2.btree_index

bzr 1.6b3 on python 2.5.2 (linux2)
arguments: ['/usr/bin/bzr', 'info']
encoding: 'UTF-8', fsenc: 'UTF-8', lang: 'en_AU.UTF-8'
plugins:
  bzrtools /usr/lib/python2.5/site-packages/bzrlib/plugins/bzrtools [1.5.0]
  groupcompress /home/mbp/.bazaar/plugins/groupcompress [unknown]
  gtk /home/mbp/.bazaar/plugins/gtk [0.95.0dev1]
  launchpad /usr/lib/python2.5/site-packages/bzrlib/plugins/launchpad [unknown]
  loom /home/mbp/.bazaar/plugins/loom [1.4.0dev0]
  pqm /home/mbp/.bazaar/plugins/pqm [1.3.0dev0]
*** Bazaar has encountered an internal error.
    Please report a bug at https://bugs.launchpad.net/bzr/+filebug
    including this traceback, and a description of what you
    were doing when the error occurred.

[John A Meinel (jameinel)]

I agree, though as these are development formats, I don't think it is critical to fix this yet.