develop-MLA-611-check-init (#3541)

.pre-commit-config.yaml

         language: script
         entry: utils/validate_versions.py
         files: ".*/__init__.py"
+    -   id: validate-init-py
+        name: validate __init__.py files
+        language: script
+        entry: utils/validate_inits.py
+        types: [python]
+

utils/validate_versions.py

-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import os
 import sys

utils/validate_inits.py

+#!/usr/bin/env python3
+
+import os
+import glob
+from setuptools import find_packages, PEP420PackageFinder
+
+
+class NonTrivialPEP420PackageFinder(PEP420PackageFinder):
+    """
+    The PEP420PackageFinder (used by find_namespace_packages) thinks everything
+    looks like a package, even if there are no python files in it. This is a
+    little stricter and only considers directories with python files in it.
+    """
+
+    @staticmethod
+    def _looks_like_package(path):
+        glob_path = os.path.join(path, "*.py")
+        return any(glob.iglob(glob_path))
+
+
+def validate_packages(root_dir):
+    """
+    Makes sure that all python files are discoverable by find_packages(), which
+    is what we use in setup.py. We could potentially use
+    find_namespace_packages instead, but depending on PEP420 has been flaky
+    in the past (particularly with regards to mypy).
+    """
+    exclude = ["*.tests", "*.tests.*", "tests.*", "tests"]
+    found_packages = find_packages(root_dir, exclude=exclude)
+    found_ns_packages = NonTrivialPEP420PackageFinder.find(root_dir, exclude=exclude)
+    assert found_packages, f"Couldn't find anything in directory {root_dir}"
+    if set(found_packages) != set(found_ns_packages):
+        raise RuntimeError(
+            "The following packages are not discoverable using found_packages():\n"
+            f"{set(found_ns_packages) - set(found_packages)}\n"
+            "Make sure you have an __init__.py file in the directories."
+        )
+    else:
+        print(f"__init__.py files for {root_dir} are OK.")
+
+
+def main():
+    for root_dir in ["ml-agents", "ml-agents-envs", "gym-unity"]:
+        validate_packages(root_dir)
+
+
+if __name__ == "__main__":
+    main()