fix append to stale children ref (#807)

docs/source/about/changelog.rst

@@ -23,11 +23,13 @@ more info, see the :ref:`Contributor Guide <Creating a Changelog Entry>`.
 Unreleased
 ----------
 
-No changes.
+**Fixed**
 
+- :issue:`806` - child models after a component fail to render
 
-v0.40.0
--------
+
+v0.40.0 (yanked)
+----------------
 :octicon:`milestone` *released on 2022-08-13*
 
 **Fixed**

src/idom/core/layout.py

@@ -361,7 +361,7 @@ def _render_model_children(
                 [old_state.children_by_key[key] for key in old_keys]
             )
 
-        new_children = new_state.model.current["children"] = []
+        new_state.model.current["children"] = []
         for index, (child, child_type, key) in enumerate(child_type_key_tuples):
             old_child_state = old_state.children_by_key.get(key)
             if child_type is _DICT_TYPE:
@@ -388,7 +388,7 @@ def _render_model_children(
                             index,
                         )
                 self._render_model(exit_stack, old_child_state, new_child_state, child)
-                new_children.append(new_child_state.model.current)
+                new_state.append_child(new_child_state.model.current)
                 new_state.children_by_key[key] = new_child_state
             elif child_type is _COMPONENT_TYPE:
                 child = cast(ComponentType, child)
@@ -428,7 +428,7 @@ def _render_model_children(
                 old_child_state = old_state.children_by_key.get(key)
                 if old_child_state is not None:
                     self._unmount_model_states([old_child_state])
-                new_children.append(child)
+                new_state.append_child(child)
 
     def _render_model_children_without_old_state(
         self,
@@ -446,20 +446,20 @@ def _render_model_children_without_old_state(
                 f"Duplicate keys {duplicate_keys} at {new_state.patch_path or '/'!r}"
             )
 
-        new_children = new_state.model.current["children"] = []
+        new_state.model.current["children"] = []
         for index, (child, child_type, key) in enumerate(child_type_key_tuples):
             if child_type is _DICT_TYPE:
                 child_state = _make_element_model_state(new_state, index, key)
                 self._render_model(exit_stack, None, child_state, child)
-                new_children.append(child_state.model.current)
+                new_state.append_child(child_state.model.current)
                 new_state.children_by_key[key] = child_state
             elif child_type is _COMPONENT_TYPE:
                 child_state = _make_component_model_state(
                     new_state, index, key, child, self._rendering_queue.put
                 )
                 self._render_component(exit_stack, None, child_state, child)
             else:
-                new_children.append(child)
+                new_state.append_child(child)
 
     def _unmount_model_states(self, old_states: List[_ModelState]) -> None:
         to_unmount = old_states[::-1]  # unmount in reversed order of rendering
@@ -661,6 +661,9 @@ def parent(self) -> _ModelState:
         assert parent is not None, "detached model state"
         return parent
 
+    def append_child(self, child: Any) -> None:
+        self.model.current["children"].append(child)
+
     def __repr__(self) -> str:  # pragma: no cover
         return f"ModelState({ {s: getattr(self, s, None) for s in self.__slots__} })"
 

tests/test_core/test_layout.py

@@ -1207,3 +1207,43 @@ def bad_should_render(new):
             await layout.render()
             root_hook.latest.schedule_render()
             await layout.render()
+
+
+async def test_does_render_children_after_component():
+    """Regression test for bug where layout was appending children to a stale ref
+
+    The stale reference was created when a component got rendered. Thus, everything
+    after the component failed to display.
+    """
+
+    @idom.component
+    def Parent():
+        return html.div(
+            html.p("first"),
+            Child(),
+            html.p("third"),
+        )
+
+    @idom.component
+    def Child():
+        return html.p("second")
+
+    async with idom.Layout(Parent()) as layout:
+        update = await layout.render()
+        print(update.new)
+        assert update.new == {
+            "tagName": "",
+            "children": [
+                {
+                    "tagName": "div",
+                    "children": [
+                        {"tagName": "p", "children": ["first"]},
+                        {
+                            "tagName": "",
+                            "children": [{"tagName": "p", "children": ["second"]}],
+                        },
+                        {"tagName": "p", "children": ["third"]},
+                    ],
+                }
+            ],
+        }