fix bug in element key identity

old children by key were being copied for elements.
as a result we were attempting to delete elements
more than once.

Author: rmorshea

src/idom/core/_fixed_jsonpatch.py

@@ -0,0 +1,54 @@
+"""A patched version of jsonpatch
+
+We need this because of: https://github.com/stefankoegl/python-json-patch/issues/138
+
+The core of this patch is in `DiffBuilder._item_removed`. The rest is just boilerplate
+that's been copied over with little to no changes.
+"""
+
+from jsonpatch import _ST_REMOVE
+from jsonpatch import DiffBuilder as _DiffBuilder
+from jsonpatch import JsonPatch as _JsonPatch
+from jsonpatch import JsonPointer, RemoveOperation, _path_join
+
+
+def apply_patch(doc, patch, in_place=False, pointer_cls=JsonPointer):
+    if isinstance(patch, (str, bytes)):
+        patch = JsonPatch.from_string(patch, pointer_cls=pointer_cls)
+    else:
+        patch = JsonPatch(patch, pointer_cls=pointer_cls)
+    return patch.apply(doc, in_place)
+
+
+def make_patch(src, dst, pointer_cls=JsonPointer):
+    return JsonPatch.from_diff(src, dst, pointer_cls=pointer_cls)
+
+
+class JsonPatch(_JsonPatch):
+    @classmethod
+    def from_diff(
+        cls,
+        src,
+        dst,
+        optimization=True,
+        dumps=None,
+        pointer_cls=JsonPointer,
+    ):
+        json_dumper = dumps or cls.json_dumper
+        builder = DiffBuilder(src, dst, json_dumper, pointer_cls=pointer_cls)
+        builder._compare_values("", None, src, dst)
+        ops = list(builder.execute())
+        return cls(ops, pointer_cls=pointer_cls)
+
+
+class DiffBuilder(_DiffBuilder):
+    def _item_removed(self, path, key, item):
+        new_op = RemoveOperation(
+            {
+                "op": "remove",
+                "path": _path_join(path, key),
+            },
+            pointer_cls=self.pointer_cls,
+        )
+        new_index = self.insert(new_op)
+        self.store_index(item, new_index, _ST_REMOVE)

src/idom/core/dispatcher.py

@@ -19,10 +19,10 @@
 from weakref import WeakSet
 
 from anyio import create_task_group
-from jsonpatch import apply_patch, make_patch
 
 from idom.utils import Ref
 
+from ._fixed_jsonpatch import apply_patch, make_patch
 from .layout import LayoutEvent, LayoutUpdate
 from .proto import LayoutType, VdomJson
 

src/idom/core/layout.py

@@ -538,7 +538,7 @@ def _update_element_model_state(
         key=old_model_state.key,
         model=Ref(),  # does not copy the model
         patch_path=old_model_state.patch_path,
-        children_by_key=old_model_state.children_by_key.copy(),
+        children_by_key={},
         targets_by_event={},
     )