fix(material/tree): aria-expanded attribute should not appear in the leaf node (#29096)

* fix(material/tree): fixed unit tests

fixed unit tests

Fixes #21922

* fix(material/tree): updated public api file

updated public api file

Fixes #21922

Author: DBowen33

src/cdk/tree/tree.spec.ts

@@ -145,20 +145,14 @@ describe('CdkTree', () => {
         let data = dataSource.data;
         dataSource.addChild(data[2]);
         fixture.detectChanges();
-        expect(
-          getNodes(treeElement).every(node => {
-            return node.getAttribute('aria-expanded') === 'false';
-          }),
-        ).toBe(true);
+        let ariaExpandedStates = getNodes(treeElement).map(n => n.getAttribute('aria-expanded'));
+        expect(ariaExpandedStates).toEqual([null, null, 'false', null]);
 
         component.treeControl.expandAll();
         fixture.detectChanges();
 
-        expect(
-          getNodes(treeElement).every(node => {
-            return node.getAttribute('aria-expanded') === 'true';
-          }),
-        ).toBe(true);
+        ariaExpandedStates = getNodes(treeElement).map(n => n.getAttribute('aria-expanded'));
+        expect(ariaExpandedStates).toEqual([null, null, 'true', null]);
       });
 
       it('with the right data', () => {
@@ -805,11 +799,8 @@ describe('CdkTree', () => {
       });
 
       it('with the right aria-expanded attrs', () => {
-        expect(
-          getNodes(treeElement).every(node => {
-            return node.getAttribute('aria-expanded') === 'false';
-          }),
-        ).toBe(true);
+        let ariaExpandedStates = getNodes(treeElement).map(n => n.getAttribute('aria-expanded'));
+        expect(ariaExpandedStates).toEqual([null, null, null]);
 
         component.toggleRecursively = false;
         fixture.changeDetectorRef.markForCheck();
@@ -822,7 +813,7 @@ describe('CdkTree', () => {
         fixture.detectChanges();
 
         const ariaExpanded = getNodes(treeElement).map(n => n.getAttribute('aria-expanded'));
-        expect(ariaExpanded).toEqual(['false', 'true', 'false', 'false']);
+        expect(ariaExpanded).toEqual([null, 'true', 'false', null]);
       });
 
       it('should expand/collapse the node multiple times', () => {
@@ -886,6 +877,7 @@ describe('CdkTree', () => {
       });
 
       it('should expand/collapse the node recursively', () => {
+        fixture.changeDetectorRef.markForCheck();
         let data = dataSource.data;
         const child = dataSource.addChild(data[1], false);
         dataSource.addChild(child, false);

src/cdk/tree/tree.ts

@@ -324,7 +324,7 @@ export class CdkTree<T, K = T> implements AfterContentChecked, CollectionViewer,
   exportAs: 'cdkTreeNode',
   host: {
     'class': 'cdk-tree-node',
-    '[attr.aria-expanded]': 'isExpanded',
+    '[attr.aria-expanded]': 'isLeafNode ? null : isExpanded',
   },
   standalone: true,
 })
@@ -375,6 +375,26 @@ export class CdkTreeNode<T, K = T> implements FocusableOption, OnDestroy, OnInit
     return this._tree.treeControl.isExpanded(this._data);
   }
 
+  /* If leaf node, return true to not assign aria-expanded attribute */
+  get isLeafNode(): boolean {
+    // If flat tree node data returns false for expandable property, it's a leaf node
+    if (
+      this._tree.treeControl.isExpandable !== undefined &&
+      !this._tree.treeControl.isExpandable(this._data)
+    ) {
+      return true;
+
+      // If nested tree node data returns 0 descendants, it's a leaf node
+    } else if (
+      this._tree.treeControl.isExpandable === undefined &&
+      this._tree.treeControl.getDescendants(this._data).length === 0
+    ) {
+      return true;
+    }
+
+    return false;
+  }
+
   get level(): number {
     // If the treeControl has a getLevel method, use it to get the level. Otherwise read the
     // aria-level off the parent node and use it as the level for this node (note aria-level is

src/material/tree/tree.spec.ts

@@ -78,20 +78,14 @@ describe('MatTree', () => {
         const data = underlyingDataSource.data;
         underlyingDataSource.addChild(data[2]);
         fixture.detectChanges();
-        expect(
-          getNodes(treeElement).every(node => {
-            return node.getAttribute('aria-expanded') === 'false';
-          }),
-        ).toBe(true);
+        let ariaExpandedStates = getNodes(treeElement).map(n => n.getAttribute('aria-expanded'));
+        expect(ariaExpandedStates).toEqual([null, null, 'false']);
 
         component.treeControl.expandAll();
         fixture.detectChanges();
 
-        expect(
-          getNodes(treeElement).every(node => {
-            return node.getAttribute('aria-expanded') === 'true';
-          }),
-        ).toBe(true);
+        ariaExpandedStates = getNodes(treeElement).map(n => n.getAttribute('aria-expanded'));
+        expect(ariaExpandedStates).toEqual([null, null, 'true', null]);
       });
 
       it('with the right data', () => {
@@ -470,11 +464,8 @@ describe('MatTree', () => {
       });
 
       it('with the right aria-expanded attrs', () => {
-        expect(
-          getNodes(treeElement).every(node => {
-            return node.getAttribute('aria-expanded') === 'false';
-          }),
-        ).toBe(true);
+        let ariaExpandedStates = getNodes(treeElement).map(n => n.getAttribute('aria-expanded'));
+        expect(ariaExpandedStates).toEqual([null, null, null]);
 
         component.toggleRecursively = false;
         const data = underlyingDataSource.data;
@@ -486,7 +477,7 @@ describe('MatTree', () => {
         fixture.detectChanges();
 
         const ariaExpanded = getNodes(treeElement).map(n => n.getAttribute('aria-expanded'));
-        expect(ariaExpanded).toEqual(['false', 'true', 'false', 'false']);
+        expect(ariaExpanded).toEqual([null, 'true', 'false', null]);
       });
 
       it('should expand/collapse the node', () => {

tools/public_api_guard/cdk/tree.md

@@ -127,6 +127,8 @@ export class CdkTreeNode<T, K = T> implements FocusableOption, OnDestroy, OnInit
     // (undocumented)
     get isExpanded(): boolean;
     // (undocumented)
+    get isLeafNode(): boolean;
+    // (undocumented)
     get level(): number;
     static mostRecentTreeNode: CdkTreeNode<any> | null;
     // (undocumented)