Fix missing parent directory entry link on lazy-load

When lazy-loading an existing directory structure, the
parent directory entry reference is not properly set. This
leads to issues traversing a directory structure bottom up.

CHANGELOG.rst

@@ -28,6 +28,7 @@ Changed
 * Lazy load directory entries for performance and `regex2fat <https://github.com/8051Enthusiast/regex2fat>`_ compatibility
    - Introduce ``lazy_load`` parameter to allow restoring previous behavior
    - `PR #32 <https://github.com/nathanhi/pyfatfs/pull/32>`_: Fix tree iteration on non-lazy load by `@zurcher <https://github.com/zurcher>`_ / `@Microsoft <https://github.com/Microsoft>`_
+   - `PR #33 <https://github.com/nathanhi/pyfatfs/pull/33>`_: Fix missing parent directory entry link on lazy-load by `@zurcher <https://github.com/zurcher>`_ / `@Microsoft <https://github.com/Microsoft>`_
 
 Removed
 ~~~~~~~

pyfatfs/FATDirectoryEntry.py

@@ -376,6 +376,8 @@ def __populate_dirs(self):
 
         clus = self.get_cluster()
         self.__dirs = self.__fs.parse_dir_entries_in_cluster_chain(clus)
+        for dir_entry in self.__dirs:
+            dir_entry._add_parent(self)
 
     def _get_entries_raw(self):
         """Get a full list of entries in current directory."""

tests/test_PyFatFS.py

@@ -55,6 +55,28 @@ def make_fs(self):  # pylint: disable=R0201
         """Create filesystem for PyFilesystem2 integration tests."""
         return _make_fs(self.FAT_TYPE)[0]
 
+    def test_lazy_load_dentry_parent_update(self):
+        """#33: Verify parent dentry is properly set on lazy-load."""
+        fs, in_memory_fs = _make_fs(self.FAT_TYPE, lazy_load=True)
+        fs.makedirs("/foo")
+        fs.touch("/foo/bar")
+        foo_dentry = fs.fs.root_dir.get_entry("foo")
+        foobar_dentry = fs.fs.root_dir.get_entry("foo/bar")
+        assert foo_dentry._parent == fs.fs.root_dir
+        assert foobar_dentry._parent == foo_dentry
+        assert foo_dentry.get_full_path() == "foo"
+        assert foobar_dentry.get_full_path() == "foo/bar"
+
+        in_memory_fs.seek(0)
+        fs = PyFatBytesIOFS(BytesIO(in_memory_fs.read()),
+                            encoding='UTF-8', lazy_load=True)
+        foo_dentry = fs.fs.root_dir.get_entry("foo")
+        foobar_dentry = fs.fs.root_dir.get_entry("foo/bar")
+        assert foo_dentry._parent == fs.fs.root_dir
+        assert foobar_dentry._parent == foo_dentry
+        assert foo_dentry.get_full_path() == "foo"
+        assert foobar_dentry.get_full_path() == "foo/bar"
+
     def test_lazy_vs_nonlazy_tree(self):
         """Compare directory tree between lazy and non-lazy loading."""
         fs1, in_memory_fs = _make_fs(self.FAT_TYPE, lazy_load=False)