fix(cdk/tree): fix template context not updating with trackBy

src/cdk/tree/tree.spec.ts

@@ -564,6 +564,15 @@ describe('CdkTree', () => {
         component.dataSource.addData();
       }
 
+      function mutateProperties() {
+        const copiedData = component.dataSource.data.slice();
+        copiedData[0] = new TestData('topping_something_new');
+        copiedData[1] = new TestData('topping_something_new_1');
+        component.dataSource.data = copiedData;
+        fixture.changeDetectorRef.markForCheck();
+        fixture.detectChanges();
+      }
+
       it('should add/remove/move nodes with reference-based trackBy', () => {
         createTrackByTestComponent('reference');
         mutateData();
@@ -613,6 +622,16 @@ describe('CdkTree', () => {
         expect(changedNodes[1].getAttribute('initialIndex')).toBe('1');
         expect(changedNodes[2].getAttribute('initialIndex')).toBe(null);
       });
+
+      it('should update templated data if object changes', () => {
+        createTrackByTestComponent('index');
+        mutateProperties();
+
+        const changedNodes = getNodes(treeElement);
+        expect(changedNodes.length).toBe(3);
+        expect(changedNodes[0].textContent).toContain('topping_something_new');
+        expect(changedNodes[1].textContent).toContain('topping_something_new_1');
+      });
     });
 
     it('should pick up indirect descendant node definitions', () => {

src/cdk/tree/tree.ts

@@ -31,6 +31,7 @@ import {
   Directive,
   ElementRef,
   EventEmitter,
+  EmbeddedViewRef,
   Input,
   IterableChangeRecord,
   IterableDiffer,
@@ -538,6 +539,16 @@ export class CdkTree<T, K = T>
       },
     );
 
+    // If the data itself changes, but keeps the same trackBy, we need to update the templates'
+    // context to reflect the new object.
+    changes?.forEachIdentityChange((record: IterableChangeRecord<T>) => {
+      const newData = record.item;
+      if (record.currentIndex != undefined) {
+        const view = viewContainer.get(record.currentIndex);
+        (view as EmbeddedViewRef<any>).context.$implicit = newData;
+      }
+    });
+
     // TODO: change to `this._changeDetectorRef.markForCheck()`, or just switch this component to
     // use signals.
     this._changeDetectorRef.detectChanges();

src/components-examples/cdk/tree/cdk-tree-complex/cdk-tree-complex-example.html

@@ -15,7 +15,7 @@
         (expandedChange)="onExpand(node, $event)">
       <!-- Spinner when node is loading children; this replaces the expand button. -->
       @if (node.areChildrenLoading()) {
-        <mat-spinner mode="indeterminate"></mat-spinner>
+        <mat-spinner diameter="48" mode="indeterminate"></mat-spinner>
       }
 
       @if (!node.areChildrenLoading() && node.isExpandable()) {