refactor(core): use HomescreenBase as a context manager

Instead of explicitly invoking `__del__()` to drop its `LayoutObj`.

[no changelog]

Author: romanz

core/src/apps/homescreen/__init__.py

@@ -14,11 +14,8 @@
 
 
 async def busyscreen() -> None:
-    obj = Busyscreen(busy_expiry_ms())
-    try:
+    with Busyscreen(busy_expiry_ms()) as obj:
         await obj.get_result()
-    finally:
-        obj.__del__()
 
 
 async def homescreen() -> None:
@@ -69,15 +66,12 @@ async def homescreen() -> None:
             False,
         )
 
-    obj = Homescreen(
+    with Homescreen(
         label=label,
         notification=notification,
         lockable=config.has_pin(),
-    )
-    try:
+    ) as obj:
         res = await obj.get_result()
-    finally:
-        obj.__del__()
 
     if utils.INTERNAL_MODEL == "T3W1":
         if res is trezorui_api.INFO:
@@ -94,14 +88,11 @@ async def _lockscreen(screensaver: bool = False) -> None:
     # Only show the lockscreen UI if the device can in fact be locked, or if it is
     # and OLED device (in which case the lockscreen is a screensaver).
     if can_lock_device() or screensaver:
-        obj = Lockscreen(
+        with Lockscreen(
             label=storage.device.get_label(),
             coinjoin_authorized=is_set_any_session(MessageType.AuthorizeCoinJoin),
-        )
-        try:
+        ) as obj:
             await obj.get_result()
-        finally:
-            obj.__del__()
     # Otherwise proceed directly to unlock() call. If the device is already unlocked,
     # it should be a no-op storage-wise, but it resets the internal configuration
     # to an unlocked state.

core/src/boot.py

@@ -55,9 +55,11 @@ def enforce_welcome_screen_duration() -> None:
 if not utils.USE_POWER_MANAGER:
 
     async def pin_unlock_sequence() -> None:
-        lockscreen = Lockscreen(label=storage.device.get_label(), bootscreen=True)
-        await lockscreen.get_result()
-        lockscreen.__del__()
+        with Lockscreen(
+            label=storage.device.get_label(),
+            bootscreen=True,
+        ) as lockscreen:
+            await lockscreen.get_result()
         await verify_user_pin()
 
 else:
@@ -70,9 +72,11 @@ async def wait_for_suspend() -> int:
 
     async def pin_unlock_sequence() -> None:
         while True:
-            lockscreen = Lockscreen(label=storage.device.get_label(), bootscreen=True)
-            await lockscreen.get_result()
-            lockscreen.__del__()
+            with Lockscreen(
+                label=storage.device.get_label(),
+                bootscreen=True,
+            ) as lockscreen:
+                await lockscreen.get_result()
             res = await loop.race(verify_user_pin(), wait_for_suspend())
             if res is _SUSPEND_MARKER:
                 # make some delay for the suspend

core/src/trezor/ui/__init__.py

@@ -564,6 +564,7 @@ def _start_task(self, task: loop.Task[None]) -> None:
         loop.schedule(task, finalizer=self._task_finalizer)
 
     def __del__(self) -> None:
+        # safe to call even if `self.layout` has been already dropped.
         self.layout.__del__()
 
 

core/src/trezor/ui/layouts/homescreen.py

@@ -9,6 +9,7 @@
     from typing import Any, Callable, Iterator, ParamSpec, Tuple, TypeVar
 
     from trezor import loop
+    from typing_extensions import Self
 
     P = ParamSpec("P")
     R = TypeVar("R")
@@ -57,7 +58,7 @@ def create_tasks(self) -> Iterator[loop.Task[None]]:
 class HomescreenBase(UsbAwareLayout):
     RENDER_INDICATOR: object | None = None
 
-    def __init__(self, layout: Any) -> None:
+    def __init__(self, layout: trezorui_api.LayoutObj[trezorui_api.UiResult]) -> None:
         super().__init__(layout=layout)
         self.should_resume = self._should_resume()
 
@@ -74,6 +75,14 @@ def _first_paint(self) -> None:
         else:
             self._paint()
 
+    def __enter__(self) -> Self:
+        self.layout.__enter__()
+        return self
+
+    def __exit__(self, exc_type: Any, exc_val: Any, exc_tb: Any) -> None:
+        """Drop internal Rust root component."""
+        self.layout.__exit__(exc_type, exc_val, exc_tb)
+
 
 class Homescreen(HomescreenBase):
     RENDER_INDICATOR = storage_cache.HOMESCREEN_ON