Running

./pants filter 3rdparty::

blows up with a super helpful error message:

Traceback (most recent call last):
  File "/Users/gmalmquist/Src/Pants/src/python/pants/build_graph/build_file_address_mapper.py", line 278, in _scan_spec
    addresses.update(self.addresses_in_spec_path(build_file.spec_path))
  File "/Users/gmalmquist/Src/Pants/src/python/pants/build_graph/build_file_address_mapper.py", line 161, in addresses_in_spec_path
    return self._address_map_from_spec_path(spec_path).keys()
  File "/Users/gmalmquist/Src/Pants/src/python/pants/build_graph/build_file_address_mapper.py", line 153, in _address_map_from_spec_path
    .format(message=e, spec_path=spec_path))
AddressLookupError: string indices must be integers, not str
 while executing BUILD file BuildFile(3rdparty/BUILD.gen, FileSystemProjectTree(/Users/gmalmquist/Development/java))
 Loading addresses from '3rdparty' failed.

Exception message: string indices must be integers, not str
 while executing BUILD file BuildFile(3rdparty/BUILD.gen, FileSystemProjectTree(/Users/gmalmquist/Development/java))
 Loading addresses from '3rdparty' failed.
Invalid BUILD files for [3rdparty::]

(Having trouble with Pants and think you've found a bug?  Let us know with ./pants bug-report)