fix(core): preserve static class/styles on root component

Fix to preserve statically applied classes and styles on root component while using host binding.

Fixes angular#51460

packages/core/src/render3/component_ref.ts

@@ -57,6 +57,7 @@ import {ComponentDef, DirectiveDef, HostDirectiveDefs} from './interfaces/defini
 import {InputFlags} from './interfaces/input_flags';
 import {
   NodeInputBindings,
+  TAttributes,
   TContainerNode,
   TElementContainerNode,
   TElementNode,
@@ -89,6 +90,7 @@ import {getComponentLViewByIndex, getNativeByTNode, getTNode} from './util/view_
 import {ViewRef} from './view_ref';
 import {ChainedInjector} from './chained_injector';
 import {unregisterLView} from './interfaces/lview_tracking';
+import {AttributeMarker} from './interfaces/attribute_marker';
 
 export class ComponentFactoryResolver extends AbstractComponentFactoryResolver {
   /**
@@ -499,10 +501,29 @@ function createRootComponentTNode(lView: LView, rNode: RNode): TElementNode {
   ngDevMode && assertIndexInRange(lView, index);
   lView[index] = rNode;
 
+  let attr: TAttributes | null = null;
+  if (rNode && 'classList' in rNode && (rNode as any).classList?.length) {
+    attr = [AttributeMarker.Classes, ...(Array.from((rNode as any).classList) as string[])];
+  }
+  if (rNode && 'getAttribute' in rNode && (rNode as any).getAttribute('style')?.length) {
+    attr = attr?.length ? [...attr, AttributeMarker.Styles] : [AttributeMarker.Styles];
+    const styleAttribute = (rNode as any).getAttribute('style');
+
+    const styles: string[] = styleAttribute.split(';');
+
+    styles.forEach((style) => {
+      const [property, value] = style.split(':').map((s) => s.trim());
+
+      if (property && value) {
+        attr!.push(property, value);
+      }
+    });
+  }
+
   // '#host' is added here as we don't know the real host DOM name (we don't want to read it) and at
   // the same time we want to communicate the debug `TNode` that this is a special `TNode`
   // representing a host element.
-  return getOrCreateTNode(tView, index, TNodeType.Element, '#host', null);
+  return getOrCreateTNode(tView, index, TNodeType.Element, '#host', attr);
 }
 
 /**
@@ -576,7 +597,9 @@ function applyRootComponentStyling(
   for (const def of rootDirectives) {
     tNode.mergedAttrs = mergeHostAttrs(tNode.mergedAttrs, def.hostAttrs);
   }
-
+  if (tNode.attrs !== null) {
+    tNode.mergedAttrs = mergeHostAttrs(tNode.mergedAttrs, tNode.attrs);
+  }
   if (tNode.mergedAttrs !== null) {
     computeStaticStyling(tNode, tNode.mergedAttrs, true);
 

packages/core/test/acceptance/bootstrap_spec.ts

@@ -21,6 +21,7 @@ import {
   ViewEncapsulation,
   ɵNoopNgZone,
   ɵZONELESS_ENABLED,
+  ElementRef,
 } from '@angular/core';
 import {bootstrapApplication, BrowserModule} from '@angular/platform-browser';
 import {platformBrowserDynamic} from '@angular/platform-browser-dynamic';
@@ -82,6 +83,31 @@ describe('bootstrap', () => {
     }),
   );
 
+  it(
+    'should preserve static class and styles on root component',
+    withBody('<test-cmp class="foo" style="height: 100%"></test-cmp>', async () => {
+      @Component({
+        selector: 'test-cmp',
+        standalone: true,
+        template: '(test)',
+        host: {
+          class: 'baar',
+          style: 'width: 100%;',
+        },
+      })
+      class TestCmp {
+        constructor(public element: ElementRef) {}
+      }
+      const appRef = await bootstrapApplication(TestCmp);
+      expect(appRef.components[0].instance.element.nativeElement.className).toBe('baar foo');
+      expect(appRef.components[0].instance.element.nativeElement.getAttribute('style')).toBe(
+        'width: 100%; height: 100%;',
+      );
+
+      appRef.destroy();
+    }),
+  );
+
   describe('options', () => {
     function createComponentAndModule(
       options: {