Add missing __init__.py files for editable PARs

Summary:
As per when building the full wheel, make sure we fill in missing
`__init__.py` files.

Reviewed By: asp2insp

Differential Revision: D69825146

fbshipit-source-id: 80084843db8f2132e6c76b789646754fc5b69da9

prelude/python/tools/create_link_tree.py

@@ -10,6 +10,7 @@
 import argparse
 import json
 import os
+from typing import Set
 
 
 def main() -> None:
@@ -20,14 +21,36 @@ def main() -> None:
 
     os.makedirs(args.output)
 
+    pkgs: Set[str] = set()
+    pkgs_with_init: Set[str] = set()
+
+    def _add_pkg(pkg: str) -> None:
+        pkgs.add(pkg)
+        parent = os.path.dirname(pkg)
+        if parent:
+            _add_pkg(parent)
+
     for manifest in args.manifests:
         with open(manifest, "r") as f:
             for dst, src, _ in json.load(f):
+                # Record pkgs and the ones w/ `__init__.py` files already.
+                if dst.endswith((".py", ".so")):
+                    pkg = os.path.dirname(dst)
+                    _add_pkg(pkg)
+                    if os.path.basename(dst) == "__init__.py":
+                        pkgs_with_init.add(pkg)
+
+                # Create symlink.
                 dst = os.path.join(args.output, dst)
                 os.makedirs(os.path.dirname(dst), exist_ok=True)
                 src = os.path.relpath(src, start=os.path.dirname(dst))
                 os.symlink(src, dst)
 
+    # Create any missing ones.
+    for pkg in pkgs - pkgs_with_init:
+        with open(os.path.join(pkg, "__init__.py"), "wb") as _:
+            pass
+
 
 if __name__ == "__main__":
     main()