Update layers when widget is updated without invalidating the layout

super_editor/lib/src/infrastructure/content_layers.dart

@@ -267,30 +267,45 @@ class ContentLayersElement extends RenderObjectElement {
     contentLayersLog.finer("ContentLayersElement - (re)building layers");
 
     owner!.buildScope(this, () {
-      final List<Element> underlays = List<Element>.filled(widget.underlays.length, _NullElement.instance);
-      for (int i = 0; i < underlays.length; i += 1) {
-        late final Element child;
-        if (i > _underlays.length - 1) {
-          child = inflateWidget(widget.underlays[i](this), _UnderlaySlot(i));
-        } else {
-          child = super.updateChild(_underlays[i], widget.underlays[i](this), _UnderlaySlot(i))!;
-        }
-        underlays[i] = child;
+      _buildLayersWithExistingScope();
+    });
+  }
+
+  /// Builds the underlays and overlays without establishing a new build scope.
+  ///
+  /// We build the layers in two situations:
+  ///
+  /// 1. When the content's layout is dirty. This happens during layout phase, when we need to
+  ///    establish a build scope. This is done when [buildLayers] is called.
+  /// 2. When the content's layout is clean. This happens when [update] is called, but only
+  ///    non-layout changes happened, like changing a color. In this case, we are already
+  ///    inside a build scope, so we can't try to establish a new one.
+  ///
+  /// See [BuildOwner.buildScope] for more information.
+  void _buildLayersWithExistingScope() {
+    final List<Element> underlays = List<Element>.filled(widget.underlays.length, _NullElement.instance);
+    for (int i = 0; i < underlays.length; i += 1) {
+      late final Element child;
+      if (i > _underlays.length - 1) {
+        child = inflateWidget(widget.underlays[i](this), _UnderlaySlot(i));
+      } else {
+        child = super.updateChild(_underlays[i], widget.underlays[i](this), _UnderlaySlot(i))!;
       }
-      _underlays = underlays;
-
-      final List<Element> overlays = List<Element>.filled(widget.overlays.length, _NullElement.instance);
-      for (int i = 0; i < overlays.length; i += 1) {
-        late final Element child;
-        if (i > _overlays.length - 1) {
-          child = inflateWidget(widget.overlays[i](this), _OverlaySlot(i));
-        } else {
-          child = super.updateChild(_overlays[i], widget.overlays[i](this), _OverlaySlot(i))!;
-        }
-        overlays[i] = child;
+      underlays[i] = child;
+    }
+    _underlays = underlays;
+
+    final List<Element> overlays = List<Element>.filled(widget.overlays.length, _NullElement.instance);
+    for (int i = 0; i < overlays.length; i += 1) {
+      late final Element child;
+      if (i > _overlays.length - 1) {
+        child = inflateWidget(widget.overlays[i](this), _OverlaySlot(i));
+      } else {
+        child = super.updateChild(_overlays[i], widget.overlays[i](this), _OverlaySlot(i))!;
       }
-      _overlays = overlays;
-    });
+      overlays[i] = child;
+    }
+    _overlays = overlays;
   }
 
   @override
@@ -331,6 +346,15 @@ class ContentLayersElement extends RenderObjectElement {
     assert(!debugChildrenHaveDuplicateKeys(widget, [newContent]));
 
     _content = updateChild(_content, newContent, _contentSlot);
+
+    if (!renderObject.contentNeedsLayout) {
+      // Layout has already run. No layout bounds changed. There might be a
+      // non-layout change that needs to be painted, e.g., change to theme brightness.
+      // Re-build all layers, which is safe to do because no layout constraints changed.
+      _buildLayersWithExistingScope();
+    }
+    // Else, dirty content layout will cause this whole widget to re-layout. The
+    // layers will be re-built during that layout pass.
   }
 
   @override