Stop composer layout recursion on spaces

core/src/ui/render_state.rs

@@ -1217,18 +1217,50 @@ impl UiRenderState {
     /// newly grown subtree can retain the provisional (even inverted) region
     /// it was measured in until an unrelated later update redraws it.
     fn redraw_and_settle(&mut self, id: WidgetId, rsc: &mut dyn UiRsc) {
+        let Some((parent, changed)) = self.redraw_once(id, rsc) else {
+            return;
+        };
+        if changed {
+            if let Some(pid) = parent {
+                self.redraw_and_settle(pid, rsc);
+            }
+            // The parent pass above has now placed this widget in its final
+            // region. Draw it once more there; unchanged descendants still
+            // take draw_inner's retained fast path. This is deliberately one
+            // redraw rather than another settling pass: feeding its size
+            // back into the same upward walk can alternate between the
+            // provisional and final regions forever (a text edit first did
+            // that when an Android IME committed a space), overflowing the
+            // native thread's stack before Rust can report a panic.
+            let settled_size = self.active.get(&id).map(|active| active.size);
+            let _ = self.redraw_once(id, rsc);
+            debug_assert_eq!(
+                self.active.get(&id).map(|active| active.size),
+                settled_size,
+                "a widget changed size after its parent settled its final region"
+            );
+        }
+    }
+
+    /// Redraw `id` exactly once, returning its parent and whether the size it
+    /// reports changed. [`Self::redraw_and_settle`] owns any propagation; in
+    /// particular, its final downward redraw must not start another upward
+    /// pass through the same branch.
+    fn redraw_once(
+        &mut self,
+        id: WidgetId,
+        rsc: &mut dyn UiRsc,
+    ) -> Option<(Option<WidgetId>, bool)> {
         rsc.widgets_mut().needs_redraw.remove(&id);
         // An ancestor is drawing this widget right now, and that draw is
         // about to write fresh primitives for it. Drawing it a second time
         // here would leave one of the two copies on screen with nothing
         // owning it -- see `draw_started`'s own doc.
         if self.draw_started.contains(&id) {
-            return;
+            return None;
         }
 
-        let Some(active) = self.remove(id, false, true, rsc) else {
-            return;
-        };
+        let active = self.remove(id, false, true, rsc)?;
         let old_size = active.size;
         let parent = active.parent;
         // `old_move_slot` being `Some` below means the slot is reused in
@@ -1259,15 +1291,7 @@ impl UiRenderState {
         // there is no query left that answers "what size would this be"
         // without actually drawing (LAYOUT.md section 5).
         let changed = self.active.get(&id).map(|a| a.size) != Some(old_size);
-        if changed {
-            if let Some(pid) = parent {
-                self.redraw_and_settle(pid, rsc);
-            }
-            // The parent pass above has now placed this widget in its final
-            // region. Draw it once more there; unchanged descendants still
-            // take draw_inner's retained fast path.
-            self.redraw_and_settle(id, rsc);
-        }
+        Some((parent, changed))
     }
 }