Retain request dependencies only when discovery supplies the answer

core/src/ui/painter.rs

@@ -87,29 +87,37 @@ impl<'a> Painter<'a> {
         child: &StrongWidget<W>,
         axis: Axis,
     ) -> Option<RequestedLen> {
-        self.request_deps.push(child.id());
         if self.rsc.widgets().size_rules(child.id())[axis].bound() == crate::Bound::ANY
             && let Some(len) = self.size_hint(child, axis)
         {
+            self.request_deps.push(child.id());
             return Some(len.into());
         }
-        let rel_base = self.rel_base(axis);
+        let start = self.request_deps.len();
         let mut requests = SizeRequests {
             arena: &mut self.state.requests,
             measured: None,
             widgets: self.rsc.widgets(),
             dependencies: &mut self.request_deps,
-            rel_base,
+            rel_base: self.rel_base[axis],
         };
-        let request = requests.widget(child, axis)?;
-        // An intrinsic fixed answer still draws in the offered room and is
-        // moved afterwards. Only a declaration or a share chooses its ask box.
-        (request.has_leftover()
-            || matches!(
-                self.rsc.widgets().size_rules(child.id())[axis],
-                crate::SizeRule::Request(_)
-            ))
-        .then_some(request)
+        // Intrinsic fixed content must keep its offered box for wrapping;
+        // only a declaration or a share chooses the box it is drawn in.
+        let request = requests.widget(child, axis).filter(|request| {
+            request.has_leftover()
+                || matches!(
+                    self.rsc.widgets().size_rules(child.id())[axis],
+                    crate::SizeRule::Request(_)
+                )
+        });
+        if request.is_some() {
+            self.rel_base(axis);
+        } else {
+            // A discarded request contributes no dependency: the measured
+            // draw below records the size and box it actually used instead.
+            self.request_deps.truncate(start);
+        }
+        request
     }
 
     /// Completes discovery after a child was measured. Only this call may use
@@ -120,20 +128,32 @@ impl<'a> Painter<'a> {
         axis: Axis,
         len: LayoutLen,
     ) -> RequestedLen {
-        let rel_base = self.rel_base(axis);
+        let start = self.request_deps.len();
         let bound = self.rsc.widgets().size_rules(child.id())[axis].bound();
         let mut requests = SizeRequests {
             arena: &mut self.state.requests,
             measured: Some(&self.state.active),
             widgets: self.rsc.widgets(),
             dependencies: &mut self.request_deps,
-            rel_base,
+            rel_base: self.rel_base[axis],
         };
-        match requests.widget(child, axis) {
-            Some(request) if request.linear().is_none() && request.has_leftover() => request,
-            _ if len.leftover > Weight::ZERO => requests.bounded(len.into(), bound),
-            _ => len.into(),
+        if let Some(request) = requests.widget(child, axis)
+            && request.linear().is_none()
+            && request.has_leftover()
+        {
+            self.rel_base(axis);
+            return request;
         }
+        let request = if len.leftover > Weight::ZERO {
+            requests.bounded(len.into(), bound)
+        } else {
+            len.into()
+        };
+        self.request_deps.truncate(start);
+        if len.leftover > Weight::ZERO && bound != crate::Bound::ANY {
+            self.rel_base(axis);
+        }
+        request
     }
 
     /// A deferred comparison reads this window when the allocation is solved.