Fix bug when joining cleared optional components

crates/re_query/src/archetype_view.rs

@@ -343,7 +343,9 @@ impl<A: Archetype> ArchetypeView<A> {
 
         let component = self.components.get(&C::name());
 
-        if let Some(component) = component {
+        let is_empty = component.map_or(true, |c| c.is_empty());
+
+        if let (Some(component), false) = (component, is_empty) {
             // NOTE(1): Autogenerated instance keys are interned behind datacells.
             // If two or more rows in the store share the same keys, then they will share
             // also the same cells.
@@ -357,6 +359,15 @@ impl<A: Archetype> ArchetypeView<A> {
             // - If the data isn't the same, the cost of the comparison will be dwarfed by the cost
             //   of the join anyway.
             if self.required_comp().instance_keys == component.instance_keys {
+                // This fast iterator is assumed to match the length of the primary component
+                // We shouldn't hit this if since the store should enforce matched lengths for
+                // non-empty components, and the outer if-guard should keep us from reaching this
+                // in the case of an empty component.
+                debug_assert!(
+                    self.required_comp().instance_keys.num_instances()
+                        == component.values.num_instances()
+                );
+
                 // NOTE: A component instance cannot be optional in itself, and if we're on this
                 // path then we know for a fact that both batches can be intersected 1-to-1.
                 // Therefore there cannot be any null values, therefore we can go through the fast

crates/re_query/tests/archetype_visit_tests.rs

@@ -285,3 +285,42 @@ fn joint_visit() {
     assert_eq!(positions, positions_out);
     assert_eq!(expected_colors, colors_out);
 }
+
+#[test]
+fn joint_visit_with_empty() {
+    let positions = vec![
+        Position2D::new(1.0, 2.0), //
+        Position2D::new(3.0, 4.0),
+        Position2D::new(5.0, 6.0),
+        Position2D::new(7.0, 8.0),
+        Position2D::new(9.0, 10.0),
+    ];
+
+    let shared_ids = InstanceKey::from_iter(0..5);
+
+    let colors: Vec<Color> = vec![];
+
+    let positions_comp =
+        ComponentWithInstances::from_native(shared_ids.clone(), positions.clone()).unwrap();
+    let colors_comp = ComponentWithInstances::from_native(shared_ids, colors).unwrap();
+
+    let arch_view =
+        ArchetypeView::<Points2D>::from_components(RowId::ZERO, [positions_comp, colors_comp]);
+
+    let mut positions_out = Vec::<Position2D>::new();
+    let mut colors_out = Vec::<Option<Color>>::new();
+
+    itertools::izip!(
+        arch_view.iter_required_component::<Position2D>().unwrap(),
+        arch_view.iter_optional_component::<Color>().unwrap()
+    )
+    .for_each(|(point, color)| {
+        positions_out.push(point);
+        colors_out.push(color);
+    });
+
+    let expected_colors = vec![None, None, None, None, None];
+
+    assert_eq!(positions, positions_out);
+    assert_eq!(expected_colors, colors_out);
+}