lp-propose - API exceptions show an ugly error

[Robert Collins]

When the LP API server returns an error - such as
InvalidBranchMergeProposal
lp-propose reraises this as a plain Exception

This has two problems:
 - it shows a full traceback rather than a one-liner with the detail in .bzr.log
 - the actual backtrace on the server, which devs have access too, gets stripped.

So it makes it ugly and hard to debug.

Better to raise a BzrError of some sort - with internal set to false; and include in it the original error stringification so that when there is a traceback accessible it gets shown in .bzr.log

[Robert Collins (lifeless)]

For instance, this is the current output from a failed API call:
lp-propose lp:~ubuntu-website-community/ubuntu-website/light-drupal-theme -R ubuntu-website-community
lp:ubuntu-drupal-theme is already up-to-date.
bzr: ERROR: exceptions.Exception: InvalidBranchMergeProposal

Traceback (most recent call last):
  File "/home/michael/bzr-2.2b3/bzrlib/commands.py", line 909, in exception_to_return_code
    return the_callable(*args, **kwargs)
  File "/home/michael/bzr-2.2b3/bzrlib/commands.py", line 1107, in run_bzr
    ret = run(*run_argv)
  File "/home/michael/bzr-2.2b3/bzrlib/commands.py", line 687, in run_argv_aliases
    return self.run(**all_cmd_args)
  File "/home/michael/bzr-2.2b3/bzrlib/commands.py", line 702, in run
    return self._operation.run_simple(*args, **kwargs)
  File "/home/michael/bzr-2.2b3/bzrlib/cleanup.py", line 122, in run_simple
    self.cleanups, self.func, *args, **kwargs)
  File "/home/michael/bzr-2.2b3/bzrlib/cleanup.py", line 156, in _do_with_cleanups
    result = func(*args, **kwargs)
  File "/home/michael/bzr-2.2b3/bzrlib/plugins/launchpad/__init__.py", line 345, in run
    proposer.create_proposal()
  File "/home/michael/bzr-2.2b3/bzrlib/plugins/launchpad/lp_propose.py", line 208, in create_proposal
    review_types=review_types)
  File "/home/michael/bzr-2.2b3/bzrlib/plugins/launchpad/lp_propose.py", line 185, in call_webservice
    raise Exception(''.join(error_lines))
Exception: InvalidBranchMergeProposal

bzr 2.2b3 on python 2.6.5 (Linux-2.6.32-22-generic-i686-with-Ubuntu-10.04-lucid)
...

[Michael Lustfield (michaellustfield)]

Here's the error that's referred to.