fix(scroll-frame): handle empty canvas bbox during wheel scroll

Also guard scroll handling when the canvas has no bbox yet.

Author: amilcarlucas

ardupilot_methodic_configurator/frontend_tkinter_scroll_frame.py

@@ -71,12 +71,6 @@ def on_frame_configure(self, _event) -> None:  # noqa: ANN001
         """Reset the scroll region to encompass the inner frame."""
         # Whenever the size of the frame changes, alter the scroll region respectively.
         self.canvas.configure(scrollregion=self.canvas.bbox("all"))
-        # Calculate the bounding box for the scroll region, starting from the second row
-        # bbox = self.canvas.bbox("all")
-        # if bbox:
-        #     # Adjust the bounding box to start from the second row
-        #     bbox = (bbox[0], bbox[1] + self.canvas.winfo_reqheight(), bbox[2], bbox[3])
-        #     self.canvas.configure(scrollregion=bbox)
 
     def on_canvas_configure(self, event: tk.Event) -> None:
         """Reset the canvas window to encompass inner frame when required."""
@@ -86,7 +80,8 @@ def on_canvas_configure(self, event: tk.Event) -> None:
 
     def on_mouse_wheel(self, event: tk.Event) -> None:  # cross platform scroll wheel event
         canvas_height = self.canvas.winfo_height()
-        rows_height = self.canvas.bbox("all")[3]
+        bbox = self.canvas.bbox("all")
+        rows_height = bbox[3] if bbox is not None else 0
 
         if rows_height > canvas_height:  # only scroll if the rows overflow the frame
             if platform_system() == "Windows":

tests/test_frontend_tkinter_scroll_frame.py

@@ -154,6 +154,25 @@ def test_user_does_not_scroll_when_all_content_is_visible(self, scrollable_frame
         # Verify no scrolling occurred
         scrollable_frame.canvas.yview_scroll.assert_not_called()
 
+    def test_user_does_not_crash_when_canvas_has_no_items(self, scrollable_frame) -> None:
+        """
+        User does not hit a crash when scrolling before any canvas items exist.
+
+        GIVEN: A ScrollFrame whose canvas reports no bounding box yet
+        WHEN: The user scrolls
+        THEN: No scrolling occurs and no exception is raised
+        """
+        scrollable_frame.canvas.winfo_height.return_value = 100
+        scrollable_frame.canvas.bbox.return_value = None
+
+        event = MagicMock()
+        event.delta = 120
+
+        with patch("ardupilot_methodic_configurator.frontend_tkinter_scroll_frame.platform_system", return_value="Windows"):
+            scrollable_frame.on_mouse_wheel(event)
+
+        scrollable_frame.canvas.yview_scroll.assert_not_called()
+
     def test_user_mouse_events_are_properly_managed_on_enter_leave(self, scrollable_frame) -> None:
         """
         User mouse events are properly bound and unbound as cursor enters/leaves the scroll area.