Do not re-populate directory structure from disk on pending entry change

When updating a dentry (e.g., adding a new file), the parent
directory will be re-read from disk on lazy-loading. This
causes the pending change to be reverted, leading to missing
newly added files.

To fix this, the directory entries __dirs list will only
be populated once.

CHANGELOG.rst

@@ -29,6 +29,7 @@ Changed
    - 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>`_
+   - `PR #33 <https://github.com/nathanhi/pyfatfs/pull/33>`_: Do not re-populate directory structure from disk on pending entry change by `@zurcher <https://github.com/zurcher>`_ / `@Microsoft <https://github.com/Microsoft>`_
 
 Removed
 ~~~~~~~

pyfatfs/FATDirectoryEntry.py

@@ -378,6 +378,7 @@ def __populate_dirs(self):
         self.__dirs = self.__fs.parse_dir_entries_in_cluster_chain(clus)
         for dir_entry in self.__dirs:
             dir_entry._add_parent(self)
+        self.__lazy_load = False
 
     def _get_entries_raw(self):
         """Get a full list of entries in current directory."""
@@ -497,8 +498,6 @@ def remove_dir_entry(self, name):
         **NOTE:** This will also remove special entries such
         as ».«, »..« and volume labels!
         """
-        self._verify_is_directory()
-        self.__populate_dirs()
         # Iterate all entries
         for dir_entry in self._get_entries_raw():
             sn = dir_entry.get_short_name()

tests/test_PyFatFS.py

@@ -77,6 +77,26 @@ def test_lazy_load_dentry_parent_update(self):
         assert foo_dentry.get_full_path() == "foo"
         assert foobar_dentry.get_full_path() == "foo/bar"
 
+    def test_update_dentry_no_repopulate(self):
+        """#33: Verify that update_dentry doesn't re-read entries from disk.
+
+        This is only problematic in case of lazy-loading, where
+        directory entries can be dynamically loaded, even when there
+        is a pending directory entry change; ultimately overwriting
+        the pending change.
+        """
+        fs, in_memory_fs = _make_fs(self.FAT_TYPE, lazy_load=True)
+        fs.makedirs("/foo")
+        fs.touch("/foo/bar")
+        assert fs.listdir("/foo") == ['bar']
+
+        in_memory_fs.seek(0)
+        fs = PyFatBytesIOFS(BytesIO(in_memory_fs.read()),
+                            encoding='UTF-8', lazy_load=True)
+        fs.touch("/foo/baz")
+        fs.remove("/foo/bar")
+        assert fs.listdir("/foo") == ['baz']
+
     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)