Add __init__.py to directories created by grpcio

src/python/pants/backend/codegen/grpcio/python/BUILD

@@ -14,6 +14,7 @@ python_library(
     'src/python/pants/build_graph',
     'src/python/pants/subsystem',
     'src/python/pants/util:contextutil',
+    'src/python/pants/util:memo',
     'src/python/pants/task',
   ],
-)
+)

src/python/pants/backend/codegen/grpcio/python/grpcio_run.py

@@ -3,9 +3,11 @@
 
 import functools
 import logging
+from pathlib import Path
 
 from pants.backend.codegen.grpcio.python.grpcio_prep import GrpcioPrep
 from pants.backend.codegen.grpcio.python.python_grpcio_library import PythonGrpcioLibrary
+from pants.backend.python.subsystems.pex_build_util import identify_missing_init_files
 from pants.backend.python.targets.python_library import PythonLibrary
 from pants.base.build_environment import get_buildroot
 from pants.base.exceptions import TaskError
@@ -45,6 +47,12 @@ def execute_codegen(self, target, target_workdir):
       if exit_code != 0:
         raise TaskError('{} ... exited non-zero ({}).'.format(cmdline, exit_code),
                         exit_code=exit_code)
+      # Create __init__.py in each subdirectory of the target directory so that setup_py recognizes
+      # them as modules.
+      target_workdir_path = Path(target_workdir)
+      sources = [str(p.relative_to(target_workdir_path)) for p in target_workdir_path.rglob("*.py")]
+      for missing_init in identify_missing_init_files(sources):
+        (target_workdir_path / missing_init).touch()
       logging.info("Grpcio finished code generation into: [{}]".format(target_workdir))
 
   def build_args(self, target, target_workdir):

tests/python/pants_test/backend/codegen/grpcio/test_multiple_grpcio_gen.py

@@ -55,9 +55,13 @@ def test_multiple_dependent_protobufs(self):
     # then
     self.assertIsNotNone(synthetic_target)
     self.assertEqual(2, len(synthetic_target))
-    self.assertEqual({'com/foo/foo_example_pb2_grpc.py',
+    self.assertEqual({'com/__init__.py',
+                      'com/foo/__init__.py',
+                      'com/foo/foo_example_pb2_grpc.py',
                       'com/foo/foo_example_pb2.py'},
                      set(synthetic_target[0].sources_relative_to_source_root()))
-    self.assertEqual({'com/bar/bar_example_pb2_grpc.py',
+    self.assertEqual({'com/__init__.py',
+                      'com/bar/__init__.py',
+                      'com/bar/bar_example_pb2_grpc.py',
                       'com/bar/bar_example_pb2.py'},
                      set(synthetic_target[1].sources_relative_to_source_root()))

tests/python/pants_test/backend/codegen/grpcio/test_single_grpcio_gen.py

@@ -34,6 +34,8 @@ def test_single_protobuf(self):
 
     # then
     self.assertEqual(1, len(synthetic_target))
-    self.assertEqual({'com/example/example_pb2_grpc.py',
+    self.assertEqual({'com/__init__.py',
+                      'com/example/__init__.py',
+                      'com/example/example_pb2_grpc.py',
                       'com/example/example_pb2.py'},
                      set(synthetic_target[0].sources_relative_to_source_root()))