fix(core): skip hydration for i18n nodes that were not projected (#57356)

This commit fixes an issue that happens when an i18n block is defined as a projectable content, but a parent component doesn't project it. With an extra check added in this commit, the code will be taking a regular "creation" pass instead of attempting hydration.

Resolves #57301.

PR Close #57356

packages/core/src/hydration/i18n.ts

@@ -26,6 +26,7 @@ import {IS_I18N_HYDRATION_ENABLED} from './tokens';
 import {
   getNgContainerSize,
   initDisconnectedNodes,
+  isDisconnectedNode,
   isSerializedElementContainer,
   processTextNodeBeforeSerialization,
 } from './utils';
@@ -407,15 +408,17 @@ function prepareI18nBlockForHydrationImpl(
   parentTNode: TNode | null,
   subTemplateIndex: number,
 ) {
-  if (
-    !isI18nHydrationSupportEnabled() ||
-    (parentTNode && isI18nInSkipHydrationBlock(parentTNode))
-  ) {
+  const hydrationInfo = lView[HYDRATION];
+  if (!hydrationInfo) {
     return;
   }
 
-  const hydrationInfo = lView[HYDRATION];
-  if (!hydrationInfo) {
+  if (
+    !isI18nHydrationSupportEnabled() ||
+    (parentTNode &&
+      (isI18nInSkipHydrationBlock(parentTNode) ||
+        isDisconnectedNode(hydrationInfo, parentTNode.index - HEADER_OFFSET)))
+  ) {
     return;
   }
 

packages/core/src/render3/instructions/element_container.ts

@@ -9,6 +9,7 @@ import {validateMatchingNode, validateNodeExists} from '../../hydration/error_ha
 import {locateNextRNode, siblingAfter} from '../../hydration/node_lookup_utils';
 import {
   getNgContainerSize,
+  isDisconnectedNode,
   markRNodeAsClaimedByHydration,
   setSegmentHead,
 } from '../../hydration/utils';
@@ -204,7 +205,11 @@ function locateOrCreateElementContainerNode(
 ): RComment {
   let comment: RComment;
   const hydrationInfo = lView[HYDRATION];
-  const isNodeCreationMode = !hydrationInfo || isInSkipHydrationBlock() || isDetachedByI18n(tNode);
+  const isNodeCreationMode =
+    !hydrationInfo ||
+    isInSkipHydrationBlock() ||
+    isDisconnectedNode(hydrationInfo, index) ||
+    isDetachedByI18n(tNode);
 
   lastNodeWasCreated(isNodeCreationMode);
 

packages/platform-server/test/hydration_spec.ts

@@ -2128,6 +2128,54 @@ describe('platform-server hydration integration', () => {
           expect(content.innerHTML).toBe('<span>two</span><div>one</div>');
         });
 
+        it('should work when i18n content is not projected', async () => {
+          @Component({
+            standalone: true,
+            selector: 'app-content',
+            template: `
+              @if (false) {
+                <ng-content />
+              }
+              Content outside of 'if'.
+            `,
+          })
+          class ContentComponent {}
+
+          @Component({
+            standalone: true,
+            selector: 'app',
+            template: `
+              <app-content>
+                <div i18n>Hello!</div>
+                <ng-container i18n>Hello again!</ng-container>
+              </app-content>
+            `,
+            imports: [ContentComponent],
+          })
+          class SimpleComponent {}
+
+          const hydrationFeatures = [withI18nSupport()] as unknown as HydrationFeature<any>[];
+          const html = await ssr(SimpleComponent, {hydrationFeatures});
+
+          const ssrContents = getAppContents(html);
+          expect(ssrContents).toContain('<app ngh');
+
+          resetTViewsFor(SimpleComponent, ContentComponent);
+
+          const appRef = await renderAndHydrate(doc, html, SimpleComponent, {hydrationFeatures});
+          const compRef = getComponentRef<SimpleComponent>(appRef);
+          appRef.tick();
+
+          const clientRootNode = compRef.location.nativeElement;
+          verifyAllNodesClaimedForHydration(clientRootNode);
+          verifyClientAndSSRContentsMatch(ssrContents, clientRootNode);
+
+          const content = clientRootNode.querySelector('app-content');
+          const text = content.textContent.trim();
+          expect(text).toBe("Content outside of 'if'.");
+          expect(text).not.toContain('Hello');
+        });
+
         it('should support interleaving projected content', async () => {
           @Component({
             standalone: true,