fix(core): handle missing withI18nSupport() call for components that use i18n blocks (#56175)

This commit updates hydration serialization logic to handle a case when the `withI18nSupport()` call is not present for an application that has a component that uses i18n blocks. Note: the issue is only reproducible for components that also inject `ViewContainerRef`, since it triggers a special serialization code path.

Resolves #56074.

PR Close #56175

packages/core/src/hydration/annotate.ts

@@ -182,6 +182,14 @@ function annotateLContainerForHydration(lContainer: LContainer, context: Hydrati
   // Serialize the root component itself.
   const componentLViewNghIndex = annotateComponentLViewForHydration(componentLView, context);
 
+  if (componentLViewNghIndex === null) {
+    // Component was not serialized (for example, if hydration was skipped by adding
+    // the `ngSkipHydration` attribute or this component uses i18n blocks in the template,
+    // but `withI18nSupport()` was not added), avoid annotating host element with the `ngh`
+    // attribute.
+    return;
+  }
+
   const hostElement = unwrapRNode(componentLView[HOST]!) as HTMLElement;
 
   // Serialize all views within this view container.

packages/platform-server/test/hydration_spec.ts

@@ -1964,6 +1964,29 @@ describe('platform-server hydration integration', () => {
           clearTranslations();
         });
 
+        it('should append skip hydration flag if component uses i18n blocks and no `withI18nSupport()` call present', async () => {
+          @Component({
+            standalone: true,
+            selector: 'app',
+            template: '<div i18n>Hi!</div>',
+          })
+          class SimpleComponent {
+            // Having `ViewContainerRef` here is important: it triggers
+            // a code path that serializes top-level `LContainer`s.
+            vcr = inject(ViewContainerRef);
+          }
+
+          const hydrationFeatures = [] as unknown as HydrationFeature<any>[];
+          const html = await ssr(SimpleComponent, {hydrationFeatures});
+
+          const ssrContents = getAppContents(html);
+
+          // Since `withI18nSupport()` was not included and a component has i18n blocks -
+          // we expect that the `ngSkipHydration` attribute was added during serialization.
+          expect(ssrContents).not.toContain('ngh="');
+          expect(ssrContents).toContain('ngskiphydration="');
+        });
+
         it('should not append skip hydration flag if component uses i18n blocks', async () => {
           @Component({
             standalone: true,