fix(ivy): fix styling context resolution for host bindings on containers (#28221)

Previous to this change, the isStylingContext() function was improperly
returning true for LContainers because it used the presence of an array
at index 2 to determine whether it was a styling context. Unfortunately,
LContainers also contain arrays at index 2, so this would return a false
positive. This led to other errors down the line because we would treat
nodes with containers as if they already had styling contexts (even if
they did not), so the proper initialization logic for styling contexts
was not run.

This commit fixes the isStylingContext() function to use LCONTAINER_LENGTH
as a marker rather than the presence of an array, which in turn fixes
host bindings to styles on nodes with containers.

PR Close #28221

packages/core/src/render3/styling/util.ts

@@ -9,7 +9,7 @@ import '../../util/ng_dev_mode';
 
 import {StyleSanitizeFn} from '../../sanitization/style_sanitizer';
 import {getLContext} from '../context_discovery';
-import {LContainer} from '../interfaces/container';
+import {LCONTAINER_LENGTH, LContainer} from '../interfaces/container';
 import {LContext} from '../interfaces/context';
 import {AttributeMarker, TAttributes, TNode, TNodeFlags} from '../interfaces/node';
 import {PlayState, Player, PlayerContext, PlayerIndex} from '../interfaces/player';
@@ -96,7 +96,7 @@ export function getStylingContext(index: number, viewData: LView): StylingContex
 export function isStylingContext(value: any): value is StylingContext {
   // Not an LView or an LContainer
   return Array.isArray(value) && typeof value[StylingIndex.MasterFlagPosition] === 'number' &&
-      Array.isArray(value[StylingIndex.InitialStyleValuesPosition]);
+      value.length !== LCONTAINER_LENGTH;
 }
 
 export function isAnimationProp(name: string): boolean {

packages/core/test/render3/host_binding_spec.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {ElementRef, QueryList} from '@angular/core';
+import {ElementRef, QueryList, ViewContainerRef} from '@angular/core';
 
 import {AttributeMarker, defineComponent, template, defineDirective, InheritDefinitionFeature, ProvidersFeature} from '../../src/render3/index';
 import {allocHostVars, bind, directiveInject, element, elementAttribute, elementEnd, elementProperty, elementStyleProp, elementStyling, elementStylingApply, elementStart, listener, load, text, textBinding, loadQueryList, registerContentQuery, elementHostAttrs} from '../../src/render3/instructions';
@@ -1131,6 +1131,58 @@ describe('host bindings', () => {
       expect(hostBindingEl.style.width).toEqual('5px');
     });
 
+    it('should bind to host styles on containers', () => {
+      let hostBindingDir !: HostBindingToStyles;
+      /**
+       * host: {
+       *   '[style.width.px]': 'width'
+       * }
+       */
+      class HostBindingToStyles {
+        width = 2;
+
+        static ngDirectiveDef = defineDirective({
+          type: HostBindingToStyles,
+          selectors: [['', 'hostStyles', '']],
+          factory: () => hostBindingDir = new HostBindingToStyles(),
+          hostBindings: (rf: RenderFlags, ctx: HostBindingToStyles, elIndex: number) => {
+            if (rf & RenderFlags.Create) {
+              elementStyling(null, ['width'], null, ctx);
+            }
+            if (rf & RenderFlags.Update) {
+              elementStyleProp(0, 0, ctx.width, 'px', ctx);
+              elementStylingApply(0, ctx);
+            }
+          }
+        });
+      }
+
+      class ContainerDir {
+        constructor(public vcr: ViewContainerRef) {}
+
+        static ngDirectiveDef = defineDirective({
+          type: ContainerDir,
+          selectors: [['', 'containerDir', '']],
+          factory: () => new ContainerDir(directiveInject(ViewContainerRef as any)),
+        });
+      }
+
+      /** <div hostStyles containerDir></div> */
+      const App = createComponent('app', (rf: RenderFlags, ctx: any) => {
+        if (rf & RenderFlags.Create) {
+          element(0, 'div', ['containerDir', '', 'hostStyles', '']);
+        }
+      }, 1, 0, [ContainerDir, HostBindingToStyles]);
+
+      const fixture = new ComponentFixture(App);
+      const hostBindingEl = fixture.hostElement.querySelector('div') as HTMLElement;
+      expect(hostBindingEl.style.width).toEqual('2px');
+
+      hostBindingDir.width = 5;
+      fixture.update();
+      expect(hostBindingEl.style.width).toEqual('5px');
+    });
+
     it('should apply static host classes', () => {
       /**
        * host: {