fix: fix race condition on namespace package installation

src/poetry/installation/wheel_installer.py

@@ -39,16 +39,35 @@ def write_to_fs(
         stream: BinaryIO,
         is_executable: bool,
     ) -> RecordEntry:
+        import base64
+        import hashlib
+
         from installer.records import Hash
         from installer.records import RecordEntry
+        from installer.utils import _COPY_BUFSIZE
         from installer.utils import copyfileobj_with_hashing
         from installer.utils import make_file_executable
 
         target_path = Path(self.scheme_dict[scheme]) / path
         if target_path.exists():
             # Contrary to the base library we don't raise an error here since it can
             # break pkgutil-style and pkg_resource-style namespace packages.
-            logger.warning(f"Installing {target_path} over existing file")
+            # We instead log a warning and ignore it. See issue #9158.
+            logger.warning(f"{target_path} already exists. Ignoring.")
+            # Following is copied from copyfileobj_with_hashing, to calculate the hash
+            # without copying to the file again.
+            hasher = hashlib.new(self.hash_algorithm)
+            size = 0
+            while True:
+                buf = stream.read(_COPY_BUFSIZE)
+                if not buf:
+                    break
+                hasher.update(buf)
+                size += len(buf)
+            hash_ = (
+                base64.urlsafe_b64encode(hasher.digest()).decode("ascii").rstrip("=")
+            )
+            return RecordEntry(path, Hash(self.hash_algorithm, hash_), size)
 
         parent_folder = target_path.parent
         if not parent_folder.exists():