remove fspath from StagingRegistry

This is to avoid likely footguns related to using os.path.join. Includes
test of error on os.path.join.

gufe/storage/stagingregistry.py

@@ -32,7 +32,7 @@ def _safe_to_delete_file(
 
 
 class StagingRegistry:
-    """PathLike local representation of an :class:`.ExternalStorage`.
+    """Local representation of an :class:`.ExternalStorage`.
 
     This connects objects on a local filesystem to the key-value store of a
     (possibly remote) :class:`.ExternalStorage`. It presents a FileLike
@@ -202,9 +202,6 @@ def _load_file_from_external(self, external: ExternalStorage,
     def __truediv__(self, path: Union[PathLike, str]):
         return StagingPath(root=self, path=path)
 
-    def __fspath__(self):
-        return str(self.staging_dir)
-
     def __repr__(self):
         return (
             f"{self.__class__.__name__}('{self.scratch}', {self.external})"

gufe/tests/storage/test_stagingregistry.py

@@ -42,7 +42,7 @@ def read_only_with_overwritten(root_with_contents):
         delete_staging=root_with_contents.delete_staging,
         read_only=True
     )
-    filename = pathlib.Path(read_only) / "old_unit/data.txt"
+    filename = (read_only / "old_unit/data.txt").as_path()
     assert not filename.exists()
     staged = read_only / "old_unit/data.txt"
     assert not filename.exists()
@@ -140,6 +140,12 @@ def test_repr(self, root):
         assert r.startswith("SharedStaging")
         assert "MemoryStorage" in r
 
+    def test_fspath_fail(self, root):
+        # ensure that we get an error on os.path.join (or really, anything
+        # that hits os.fspath)
+        with pytest.raises(TypeError):
+            os.path.join(root, "filename.txt")
+
     @pytest.mark.parametrize('pathlist', [
         ['file.txt'], ['dir', 'file.txt']
     ])
@@ -266,8 +272,7 @@ def test_transfer_read_only(self, read_only_with_overwritten, caplog):
 
     def test_cleanup(self, root_with_contents):
         root_with_contents.delete_staging = True  # slightly naughty
-        root_path = pathlib.Path(root_with_contents.__fspath__())
-        path = root_path / "new_unit/data.txt"
+        path = (root_with_contents / "new_unit/data.txt").as_path()
         assert path.exists()
         root_with_contents.cleanup()
         assert not path.exists()
@@ -303,7 +308,7 @@ def test_cleanup_directory(self, root, caplog):
         assert "During staging cleanup, the directory" in caplog.text
 
     def test_register_cleanup_preexisting_file(self, root):
-        filename = pathlib.Path(root.__fspath__()) / "new_unit/foo.txt"
+        filename = (root / "new_unit/foo.txt").as_path()
         filename.parent.mkdir(parents=True, exist_ok=True)
         filename.touch()
         root.external.store_bytes("new_unit/foo.txt", b"")
@@ -350,7 +355,7 @@ def test_delete_file_safe(self, tmp_path, is_safe):
         assert permanent._delete_file_safe(my_file) is is_safe
 
     def test_load_missing_for_transfer(self, permanent):
-        fname = pathlib.Path(permanent) / "old_unit/data.txt"
+        fname = (permanent / "old_unit/data.txt").as_path()
         assert not fname.exists()
         staging = permanent / "old_unit/data.txt"
         staging.__fspath__()