Import explodes on Python 3.7

[vmarkovtsev]

import bblfsh.github.com.gogo.protobuf.gogoproto.gogo_pb2

fails with

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.7/site-packages/bblfsh/github/com/gogo/protobuf/gogoproto/gogo_pb2.py", line 670, in <module>
    google_dot_protobuf_dot_descriptor__pb2.EnumOptions.RegisterExtension(goproto_enum_prefix)
  File "/usr/local/lib/python3.7/site-packages/google/protobuf/internal/python_message.py", line 751, in RegisterExtension
    cls.DESCRIPTOR.file.pool.AddExtensionDescriptor(extension_handle)
  File "/usr/local/lib/python3.7/site-packages/google/protobuf/descriptor_pool.py", line 264, in AddExtensionDescriptor
    extension.containing_type.full_name, extension.number))
AssertionError: Extensions "gogoproto.goproto_enum_prefix" and "gogoproto.goproto_enum_prefix" both try to extend message type "google.protobuf.EnumOptions" with field number 62001.

Reproducible exclusively on Python 3.7.0 final (works fine with beta3). How to reproduce:

docker run -it --rm python:3.7.0-stretch bash
pip3 install bblfsh
python3 -c "import bblfsh.github.com.gogo.protobuf.gogoproto.gogo_pb2"

Related to protocolbuffers/protobuf#2533 but not really.

Looks like the top-level import of bblfsh is not visible to the import system and it imports the module twice. The workaround is to comment out that assertion inside protobuf.

[vmarkovtsev]

Yes, the problem is that import github.com.gogo.protobuf.gogoproto.gogo_pb2 with sweded sys.path and import bblfsh.github.com.gogo.protobuf.gogoproto.gogo_pb2 are different from 3.7's point of view. The solution is to make the internal imports absolute.