$ ./pants run bonsai/.buildkite
Exception caught: (<class 'pants.build_graph.address_mapper.InvalidBuildFileReference'>)

Exception message: [...]/bonsai/.buildkite does not contain any BUILD files.
  when translating spec bonsai/.buildkite

$ cat bonsai/.buildkite/BUILD
python_binary(
  name = 'generate-backend-deploy-step',
  dependencies=[
    '3rdparty/python/sh',
  ],
  source='generate-backend-deploy-step.py',
)