Allow new tree navigator to start from element

src/vs/base/browser/ui/tree/abstractTree.ts

@@ -491,8 +491,8 @@ export abstract class AbstractTree<T, TFilterData, TRef> implements IDisposable
 
 	protected abstract createModel(view: ISpliceable<ITreeNode<T, TFilterData>>, options: IAbstractTreeOptions<T, TFilterData>): ITreeModel<T, TFilterData, TRef>;
 
-	navigate(): ITreeNavigator<T> {
-		return new TreeNavigator(this.view, this.model);
+	navigate(start?: TRef): ITreeNavigator<T> {
+		return new TreeNavigator(this.view, this.model, start);
 	}
 
 	dispose(): void {
@@ -508,9 +508,15 @@ interface ITreeNavigatorView<T extends NonNullable<any>, TFilterData> {
 
 class TreeNavigator<T extends NonNullable<any>, TFilterData, TRef> implements ITreeNavigator<T> {
 
-	private index: number = -1;
+	private index: number;
 
-	constructor(private view: ITreeNavigatorView<T, TFilterData>, private model: ITreeModel<T, TFilterData, TRef>) { }
+	constructor(private view: ITreeNavigatorView<T, TFilterData>, private model: ITreeModel<T, TFilterData, TRef>, start?: TRef) {
+		if (start) {
+			this.index = this.model.getListIndex(start);
+		} else {
+			this.index = -1;
+		}
+	}
 
 	current(): T | null {
 		if (this.index < 0 || this.index >= this.view.length) {

src/vs/base/test/browser/ui/tree/objectTree.test.ts

@@ -151,5 +151,38 @@ suite('ObjectTree', function () {
 			assert.equal(navigator.first(), 0);
 			assert.equal(navigator.last(), 2);
 		});
+
+		test('should be able to start from node', () => {
+			tree.setChildren(null, Iterator.fromArray([
+				{
+					element: 0, children: Iterator.fromArray([
+						{ element: 10 },
+						{ element: 11 },
+						{ element: 12 },
+					])
+				},
+				{ element: 1 },
+				{ element: 2 }
+			]));
+
+			const navigator = tree.navigate(1);
+
+			assert.equal(navigator.current(), 1);
+			assert.equal(navigator.next(), 2);
+			assert.equal(navigator.current(), 2);
+			assert.equal(navigator.previous(), 1);
+			assert.equal(navigator.current(), 1);
+			assert.equal(navigator.previous(), 12);
+			assert.equal(navigator.previous(), 11);
+			assert.equal(navigator.previous(), 10);
+			assert.equal(navigator.previous(), 0);
+			assert.equal(navigator.previous(), null);
+			assert.equal(navigator.next(), 0);
+			assert.equal(navigator.next(), 10);
+			assert.equal(navigator.parent(), 0);
+			assert.equal(navigator.parent(), null);
+			assert.equal(navigator.first(), 0);
+			assert.equal(navigator.last(), 2);
+		});
 	});
 });
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