update collapsible when children change

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

@@ -228,6 +228,7 @@ export class IndexTreeModel<T extends Exclude<any, undefined>, TFilterData = voi
 		const nodesToInsertIterator = Iterable.map(toInsert, el => this.createTreeNode(el, parentNode, parentNode.visible ? TreeVisibility.Visible : TreeVisibility.Hidden, revealed, treeListElementsToInsert, onDidCreateNode));
 
 		const lastIndex = location[location.length - 1];
+		const lastHadChildren = parentNode.children.length > 0;
 
 		// figure out what's the visible child start index right before the
 		// splice point
@@ -296,6 +297,11 @@ export class IndexTreeModel<T extends Exclude<any, undefined>, TFilterData = voi
 			deletedNodes.forEach(visit);
 		}
 
+		const currentlyHasChildren = parentNode.children.length > 0;
+		if (lastHadChildren !== currentlyHasChildren) {
+			this.setCollapsible(location.slice(0, -1), currentlyHasChildren);
+		}
+
 		this._onDidSplice.fire({ insertedNodes: nodesToInsert, deletedNodes });
 
 		let node: IIndexTreeNode<T, TFilterData> | undefined = parentNode;

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

@@ -309,6 +309,30 @@ suite('IndexTreeModel', () => {
 		assert.deepEqual(list[2].depth, 1);
 	}));
 
+	test('updates collapsible', () => withSmartSplice(options => {
+		const list: ITreeNode<number>[] = [];
+		const model = new IndexTreeModel<number>('test', toList(list), -1);
+
+		model.splice([0], 0, [
+			{
+				element: 0, children: [
+					{ element: 1 },
+				]
+			},
+		], options);
+
+		assert.strictEqual(list[0].collapsible, true);
+		assert.strictEqual(list[1].collapsible, false);
+
+		model.splice([0, 0], 1, [], options);
+		assert.strictEqual(list[0].collapsible, false);
+		assert.strictEqual(list[1], undefined);
+
+		model.splice([0, 0], 0, [{ element: 1 }], options);
+		assert.strictEqual(list[0].collapsible, true);
+		assert.strictEqual(list[1].collapsible, false);
+	}));
+
 	test('expand', () => withSmartSplice(options => {
 		const list: ITreeNode<number>[] = [];
 		const model = new IndexTreeModel<number>('test', toList(list), -1);