Fix PyScript root component not hiding after render error

src/reactpy/executors/pyscript/layout_handler.py

@@ -28,6 +28,8 @@ def update_model(update, root_model):
         if update["path"]:
             set_pointer(root_model, update["path"], update["model"])
         else:
+            # clear old keys first, dict.update() alone would keep stale "children" around when the new model doesn't have any
+            root_model.clear()
             root_model.update(update["model"])
 
     def render_html(self, layout, model):

tests/test_pyscript/pyscript_components/root_error.py

@@ -0,0 +1,20 @@
+from reactpy import component, hooks, html
+
+
+@component
+def root():
+    count, set_count = hooks.use_state(0)
+
+    def increment(event):
+        set_count(count + 1)
+
+    # crash on purpose after a few clicks, same as the real bug report
+    if count == 3:
+        raise ValueError("This error should hide the root component")
+
+    return html.div(
+        html.button(
+            {"onClick": increment, "id": "incr", "data-count": count}, "Increment"
+        ),
+        html.p(f"PyScript Count: {count}"),
+    )

tests/test_pyscript/test_components.py

@@ -68,6 +68,33 @@ def CustomRootName():
     await display.page.wait_for_selector("#incr[data-count='3']")
 
 
+async def test_root_component_error_hides_component(display: DisplayFixture):
+    """A crash in the root render should hide it, not leave stale content stuck
+    on the page."""
+
+    @reactpy.component
+    def Counter():
+        return pyscript_component(
+            Path(__file__).parent / "pyscript_components" / "root_error.py",
+            initial=html.div({"id": "loading"}, "Loading..."),
+        )
+
+    await display.show(Counter)
+
+    await display.page.wait_for_selector("#loading")
+    await display.page.wait_for_selector("#incr")
+
+    await display.page.click("#incr")
+    await display.page.wait_for_selector("#incr[data-count='1']")
+
+    await display.page.click("#incr")
+    await display.page.wait_for_selector("#incr[data-count='2']")
+
+    # this click flips count to 3 -> root component raises -> button should vanish
+    await display.page.click("#incr")
+    await display.page.wait_for_selector("#incr", state="detached")
+
+
 def test_bad_file_path():
     with pytest.raises(ValueError):
         pyscript_component(initial=html.div({"id": "loading"}, "Loading...")).render()