fixes delete_mag for symlink mags (#1300)

Author: normanrz

webknossos/Changelog.md

@@ -19,6 +19,7 @@ For upgrade instructions, please check the respective _Breaking Changes_ section
 ### Changed
 
 ### Fixed
+- Fixed deletion of symlinked mags. [#1300](https://github.com/scalableminds/webknossos-libs/pull/1300)
 
 
 ## [2.3.3](https://github.com/scalableminds/webknossos-libs/releases/tag/v2.3.3) - 2025-05-06

webknossos/tests/dataset/test_dataset.py

@@ -1997,6 +1997,11 @@ def test_add_symlink_mag(data_format: DataFormat) -> None:
     assure_exported_properties(ds)
     assure_exported_properties(original_ds)
 
+    layer.delete_mag(4)
+    assert Mag(4) not in layer.mags
+    assert not (symlink_path / "color" / "4").exists()
+    assert (ds_path / "color" / "4").exists()
+
 
 @pytest.mark.parametrize("data_format", [DataFormat.Zarr, DataFormat.Zarr3])
 def test_remote_add_symlink_layer(data_format: DataFormat) -> None:

webknossos/webknossos/dataset/layer.py

@@ -860,15 +860,25 @@ def delete_mag(self, mag: MagLike) -> None:
             raise IndexError(
                 f"Deleting mag {mag} failed. There is no mag with this name"
             )
+        mag_view = self.get_mag(mag)
 
         full_path = self._mags[mag].path
         del self._mags[mag]
         self._properties.mags = [
             res for res in self._properties.mags if Mag(res.mag) != mag
         ]
         self.dataset._export_as_json()
-        # delete files on disk
-        rmtree(full_path)
+        if not mag_view.is_foreign:
+            # delete files on disk
+            rmtree(full_path)
+        else:
+            # delete symlinks only
+            short_mag_file_path = self.path / mag.to_layer_name()
+            long_mag_file_path = self.path / mag.to_long_layer_name()
+            if short_mag_file_path.exists():
+                short_mag_file_path.unlink()
+            elif long_mag_file_path.exists():
+                long_mag_file_path.unlink()
 
     def add_copy_mag(
         self,