fix issue with key-based identity

src/idom/core/layout.py

@@ -234,15 +234,22 @@ def _render_model(
         raw_model: Any,
     ) -> None:
         new_state.model.current = {"tagName": raw_model["tagName"]}
-
-        self._render_model_attributes(old_state, new_state, raw_model)
-        self._render_model_children(old_state, new_state, raw_model.get("children", []))
-
         if "key" in raw_model:
-            new_state.model.current["key"] = raw_model["key"]
+            new_state.key = new_state.model.current["key"] = raw_model["key"]
         if "importSource" in raw_model:
             new_state.model.current["importSource"] = raw_model["importSource"]
 
+        if old_state is not None and old_state.key != new_state.key:
+            self._unmount_model_states([old_state])
+            if new_state.is_component_state:
+                self._model_states_by_life_cycle_state_id[
+                    new_state.life_cycle_state.id
+                ] = new_state
+            old_state = None
+
+        self._render_model_attributes(old_state, new_state, raw_model)
+        self._render_model_children(old_state, new_state, raw_model.get("children", []))
+
     def _render_model_attributes(
         self,
         old_state: Optional[_ModelState],
@@ -604,6 +611,9 @@ def parent(self) -> _ModelState:
         assert parent is not None, "detached model state"
         return parent
 
+    def __repr__(self) -> str:  # pragma: no cover
+        return f"ModelState({ {s: getattr(self, s, None) for s in self.__slots__} })"
+
 
 def _make_life_cycle_state(
     component: ComponentType,

temp.py

@@ -0,0 +1,23 @@
+from random import random
+
+from idom import component, hooks, html, run
+
+
+@component
+def Demo():
+    h = hooks.current_hook()
+    print("render")
+    return html.div(
+        html.button({"onClick": lambda event: h.schedule_render()}, "re-render"),
+        HasState(),
+        key=str(random()),
+    )
+
+
+@component
+def HasState():
+    state = hooks.use_state(random)[0]
+    return html.p(state)
+
+
+run(Demo)

tests/test_core/test_layout.py

@@ -1,5 +1,6 @@
 import asyncio
 import gc
+import random
 import re
 from weakref import finalize
 from weakref import ref as weakref
@@ -811,3 +812,29 @@ def SomeComponent():
         set_items.current([])
 
         await layout.render()
+
+
+async def test_changing_key_of_parent_element_unmounts_children():
+    random.seed(0)
+
+    root_hook = HookCatcher()
+    state = idom.Ref(None)
+
+    @idom.component
+    @root_hook.capture
+    def Root():
+        return idom.html.div(HasState(), key=str(random.random()))
+
+    @idom.component
+    def HasState():
+        state.current = idom.hooks.use_state(random.random)[0]
+        return idom.html.div()
+
+    with idom.Layout(Root()) as layout:
+        await layout.render()
+
+        for i in range(5):
+            last_state = state.current
+            root_hook.latest.schedule_render()
+            await layout.render()
+            assert last_state != state.current