fix safe_build crashing due to missing import

rio/app.py

@@ -30,25 +30,6 @@ __all__ = [
 ]
 
 
-def _validate_build_function(
-    build_function: Callable[[], rio.Component],
-) -> Callable[[], rio.Component]:
-    assert callable(
-        build_function
-    ), f"The App requires a function that returns a component, not {build_function!r}"
-
-    def wrapper():
-        component = build_function()
-
-        assert isinstance(
-            component, rio.Component
-        ), f"The `build` function passed to the App must return a `Component` instance, not {component!r}."
-
-        return component
-
-    return wrapper
-
-
 def make_default_connection_lost_component() -> rio.Component:
     class DefaultConnectionLostComponent(rio.Component):
         def build(self) -> rio.Component:
@@ -250,7 +231,7 @@ class App:
         self.assets_dir = main_file.parent / assets_dir
 
         self.name = name
-        self._build = _validate_build_function(build)
+        self._build = build
         self._icon = assets.Asset.from_image(icon)
         self.pages = tuple(pages)
         self._on_app_start = on_app_start

rio/common.py

@@ -312,9 +312,10 @@ def safe_build(build_function: Callable[[], rio.Component]) -> rio.Component:
         build_function_repr = _repr_build_function(build_function)
 
         rio._logger.exception(f"An exception occurred in `{build_function_repr}`")
-        return rio.components.build_failed.BuildFailed(
-            f"`{build_function_repr}` has crashed", repr(err)
-        )
+
+        from rio.components.build_failed import BuildFailed  # Screw circular imports
+
+        return BuildFailed(f"`{build_function_repr}` has crashed", repr(err))
 
     # Make sure the result meets expectations
     if not isinstance(build_result, rio.Component):  # type: ignore[unnecessary-isinstance]
@@ -324,7 +325,10 @@ def safe_build(build_function: Callable[[], rio.Component]) -> rio.Component:
             f"The output of `build` methods must be instances of"
             f" `rio.Component`, but `{build_function_repr}` returned `{build_result!r}`"
         )
-        return rio.components.build_failed.BuildFailed(
+
+        from rio.components.build_failed import BuildFailed  # Screw circular imports
+
+        return BuildFailed(
             f"`{build_function_repr}` has returned an invalid result",
             f"Build functions must return instances of `rio.Component`, but the result was {build_result!r}",
         )