Make Iris layout dependencies explicit

src/widget/position/lazy_span.rs

@@ -939,7 +939,7 @@ impl LazySpan {
             (Some(h), None) => {
                 let (lead, trail) = placement.edges(h);
                 let region = self.row_region(lead, trail);
-                let used = painter.widget_within(self.slot_widget(slot), region);
+                let used = painter.widget_within(self.slot_widget(slot), region).size();
                 let height = resolve(used);
                 if height != h {
                     let (new_lead, new_trail) = placement.edges(height);
@@ -957,7 +957,7 @@ impl LazySpan {
                     Placement::Trailing(_) => 0.0,
                 };
                 let first = self.row_region(measure_from, measure_from + GENEROUS_PADDING);
-                let height = resolve(painter.widget_within(self.slot_widget(slot), first));
+                let height = resolve(painter.widget_within(self.slot_widget(slot), first).size());
                 let (lead, trail) = placement.edges(height);
                 if is_anchor {
                     self.stabilize_lead(painter, measure_from, lead);
@@ -1072,7 +1072,7 @@ impl Widget for LazySpan {
         self.tick_fling(now)
     }
 
-    fn draw(&mut self, painter: &mut Painter) -> Size {
+    fn draw(&mut self, painter: &mut Painter) {
         let axis = self.dir.axis;
         let output_len = painter.output_size().axis(axis);
         self.viewport_len = painter.region().axis(axis).len().to_abs(output_len);
@@ -1081,7 +1081,8 @@ impl Widget for LazySpan {
         self.repair_anchor();
         if self.anchor.is_none() {
             self.extents.clear();
-            return Size::REST;
+            painter.set_size(Size::REST);
+            return;
         }
 
         // What a wheel, a drag or a fling asked for since the last frame,
@@ -1154,7 +1155,7 @@ impl Widget for LazySpan {
         self.rehome_anchor();
         self.update_snap_end();
         self.ctl.set_travel(self.travel());
-        Size::REST
+        painter.set_size(Size::REST);
     }
 
     fn size_hint(&self, _axis: Axis) -> Option<Len> {