Fix infinite loop with very large ListView

internal/core/model.rs

@@ -1073,6 +1073,7 @@ impl<C: RepeatedItemTree + 'static> Repeater<C> {
             (inner.offset, first_item_y + vp_y)
         };
 
+        let mut loop_count = 0;
         loop {
             // If there is a gap before the new_offset and the beginning of the visible viewport,
             // try to fill it with items. First look at items that are before new_offset in the
@@ -1154,15 +1155,12 @@ impl<C: RepeatedItemTree + 'static> Repeater<C> {
                 inner.instances.push((RepeatedInstanceState::Clean, Some(new_instance)));
                 idx += 1;
             }
-            if y < listview_height && vp_y < zero {
+            if y < listview_height && vp_y < zero && loop_count < 3 {
                 assert!(idx >= row_count);
                 // we reached the end of the model, and we still have room. scroll a bit up.
-                let new_vp_y = vp_y + (listview_height - y);
-                // check that we actually did scroll (for very large lists we can exceed the precision of f32 and have an infinite loop)
-                if new_vp_y != vp_y {
-                    vp_y = new_vp_y;
-                    continue;
-                }
+                vp_y += listview_height - y;
+                loop_count += 1;
+                continue;
             }
 
             // Let's cleanup the instances that are not shown.

tests/cases/elements/listview-millions.slint

@@ -72,6 +72,10 @@ assert_eq!(clicked.borrow().as_slice(), &[210000012]);
 slint_testing::send_mouse_click(&instance, 5., 263.);
 slint_testing::send_mouse_click(&instance, 5., 239.);
 assert_eq!(clicked.borrow().as_slice(), &[210000012, 210000013, 210000011]);
+
+// go all the way to the end, it shouldn't crash or loop forever
+instance.set_viewport_y(-20. * (2130000000. - 5.));
+slint_testing::send_mouse_click(&instance, 5., 250.);
 ```
 
 ```cpp
@@ -124,6 +128,10 @@ assert.deepEqual(clicked, [210000012]);
 slintlib.private_api.send_mouse_click(instance, 5., 263.);
 slintlib.private_api.send_mouse_click(instance, 5., 239.);
 assert.deepEqual(clicked, [210000012, 210000013, 210000011]);
+
+// go all the way to the end, it shouldn't crash or loop forever
+instance.viewport_y=(-20. * (2130000000. - 5.));
+slintlib.private_api.send_mouse_click(instance, 5., 250.);
 ```