feat: Introduce compatibility with native namespace packages (#201)

Similar to https://togithub.com/googleapis/google-auth-library-python/pull/1205
Also see https://packaging.python.org/en/latest/guides/packaging-namespace-packages/#native-namespace-packages

setup.py

@@ -30,6 +30,12 @@
 with io.open(readme_filename, encoding="utf-8") as readme_file:
     readme = readme_file.read()
 
+packages = [
+    package
+    for package in setuptools.find_namespace_packages()
+    if package.startswith("google")
+]
+
 setuptools.setup(
     name="google-cloud-documentai-toolbox",
     author="Google LLC",
@@ -39,8 +45,7 @@
     license="Apache 2.0",
     long_description=readme,
     long_description_content_type="text/x-rst",
-    packages=setuptools.PEP420PackageFinder.find(),
-    namespace_packages=("google", "google.cloud"),
+    packages=packages,
     platforms="Posix; MacOS X; Windows",
     include_package_data=True,
     package_data={

tests/unit/test_packaging.py

@@ -0,0 +1,37 @@
+# Copyright 2023 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import os
+import subprocess
+import sys
+
+
+def test_namespace_package_compat(tmp_path):
+    # The ``google`` namespace package should not be masked
+    # by the presence of ``google-cloud-documentai-toolbox``.
+    google = tmp_path / "google"
+    google.mkdir()
+    google.joinpath("othermod.py").write_text("")
+    env = dict(os.environ, PYTHONPATH=str(tmp_path))
+    cmd = [sys.executable, "-m", "google.othermod"]
+    subprocess.check_call(cmd, env=env)
+
+    # The ``google.cloud`` namespace package should not be masked
+    # by the presence of ``google-cloud-documentai-toolbox``.
+    google_cloud = tmp_path / "google" / "cloud"
+    google_cloud.mkdir()
+    google_cloud.joinpath("othermod.py").write_text("")
+    env = dict(os.environ, PYTHONPATH=str(tmp_path))
+    cmd = [sys.executable, "-m", "google.cloud.othermod"]
+    subprocess.check_call(cmd, env=env)