feat(cdk/tree): add cache of nodes to the tree

Author: BobobUnicorn

src/cdk/tree/tree.ts

@@ -60,6 +60,10 @@ function coerceObservable<T>(data: T | Observable<T>): Observable<T> {
   return data;
 }
 
+function isNotNullish<T>(val: T | null | undefined): val is T {
+  return val != null;
+}
+
 /**
  * CDK tree component that connects with a data source to retrieve data of type `T` and renders
  * dataNodes with hierarchy. Updates the dataNodes when new data is provided by the data source.
@@ -656,6 +660,22 @@ export class CdkTree<T, K = T> implements AfterContentChecked, CollectionViewer,
     return group.indexOf(dataNode) + 1;
   }
 
+  /**
+   * Adds the specified node component to the tree's internal registry.
+   *
+   * This primarily facilitates keyboard navigation.
+   */
+  _registerNode(node: CdkTreeNode<T, K>) {
+    this._nodes.value.set(this._trackExpansionKey(node.data), node);
+    this._nodes.next(this._nodes.value);
+  }
+
+  /** Removes the specified node component from the tree's internal registry. */
+  _unregisterNode(node: CdkTreeNode<T, K>) {
+    this._nodes.value.delete(this._trackExpansionKey(node.data));
+    this._nodes.next(this._nodes.value);
+  }
+
   private _getAllDescendants(): Observable<T[]> {
     return merge(...this._dataNodes.value.map(dataNode => this._getDescendants(dataNode)));
   }