[MERGE] Make cmd_branch check the destination before doing any I/O on the source.

[Andrew Bennetts]

On Tue, Jul 25, 2006 at 01:48:31PM -0500, John Arbash Meinel wrote:
[...]
> The only thing it really means is that if we get an exception, and then
> delete_tree() also raises, it will hide the original exception.
> The only way I know around it is:
> 
> except Exception, e:
>   try:
>     to_transport.delete_tree('.')
>   except:
>     raise e
>   raise
> 
> That will raise the original exception delete_tree() fails, though you
> lose the traceback. And if delete_tree() succeeds, it raises the
> original exception with the original traceback.

You can do slightly better with sys.exc_info():

except Exception, e:
  exc_value, exc_type, exc_tb = sys.exc_info()
  try:
    to_transport.delete_tree('.')
  except:
    raise exc_value, exc_type, exc_tb
  raise

This preserves the original exception, although the code is a bit uglier.

-Andrew.