From 950ca05d5c9fe4a7cc356b7cb02dc08d895d8b02 Mon Sep 17 00:00:00 2001
From: Alex Ross <38270282+alexr00@users.noreply.github.com>
Date: Fri, 12 Dec 2025 18:01:41 +0100
Subject: [PATCH] Reapply element already registered race condition fix
 (#283079)

Fixes microsoft/vscode-pull-request-github#8073
---
 .../src/singlefolder-tests/tree.test.ts       |  2 +-
 .../workbench/api/common/extHostTreeViews.ts  | 19 ++++++++++++++++---
 .../workbench/browser/parts/views/treeView.ts | 12 +++++++++---
 3 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/extensions/vscode-api-tests/src/singlefolder-tests/tree.test.ts b/extensions/vscode-api-tests/src/singlefolder-tests/tree.test.ts
index cfbd8bff51c..5382fb5777e 100644
--- a/extensions/vscode-api-tests/src/singlefolder-tests/tree.test.ts
+++ b/extensions/vscode-api-tests/src/singlefolder-tests/tree.test.ts
@@ -18,7 +18,7 @@ suite('vscode API - tree', () => {
 		assertNoRpc();
 	});
 
-	test.skip('TreeView - element already registered', async function () {
+	test('TreeView - element already registered', async function () {
 		this.timeout(60_000);
 
 		type TreeElement = { readonly kind: 'leaf' };
diff --git a/src/vs/workbench/api/common/extHostTreeViews.ts b/src/vs/workbench/api/common/extHostTreeViews.ts
index f21f207f426..f50257579be 100644
--- a/src/vs/workbench/api/common/extHostTreeViews.ts
+++ b/src/vs/workbench/api/common/extHostTreeViews.ts
@@ -863,10 +863,23 @@ class ExtHostTreeView<T> extends Disposable {
 	}
 
 	private _createAndRegisterTreeNode(element: T, extTreeItem: vscode.TreeItem, parentNode: TreeNode | Root): TreeNode {
-		const node = this._createTreeNode(element, extTreeItem, parentNode);
-		if (extTreeItem.id && this._elements.has(node.item.handle)) {
-			throw new Error(localize('treeView.duplicateElement', 'Element with id {0} is already registered', extTreeItem.id));
+		const duplicateHandle = extTreeItem.id ? `${ExtHostTreeView.ID_HANDLE_PREFIX}/${extTreeItem.id}` : undefined;
+		if (duplicateHandle) {
+			const existingElement = this._elements.get(duplicateHandle);
+			if (existingElement) {
+				if (existingElement !== element) {
+					throw new Error(localize('treeView.duplicateElement', 'Element with id {0} is already registered', extTreeItem.id));
+				}
+				const existingNode = this._nodes.get(existingElement);
+				if (existingNode) {
+					const newNode = this._createTreeNode(element, extTreeItem, parentNode);
+					this._updateNodeCache(element, newNode, existingNode, parentNode);
+					existingNode.dispose();
+					return newNode;
+				}
+			}
 		}
+		const node = this._createTreeNode(element, extTreeItem, parentNode);
 		this._addNodeToCache(element, node);
 		this._addNodeToParentCache(node, parentNode);
 		return node;
diff --git a/src/vs/workbench/browser/parts/views/treeView.ts b/src/vs/workbench/browser/parts/views/treeView.ts
index 48c342e84fa..c8cae02f383 100644
--- a/src/vs/workbench/browser/parts/views/treeView.ts
+++ b/src/vs/workbench/browser/parts/views/treeView.ts
@@ -693,7 +693,7 @@ abstract class AbstractTreeView extends Disposable implements ITreeView {
 		const treeMenus = this.treeDisposables.add(this.instantiationService.createInstance(TreeMenus, this.id));
 		this.treeLabels = this.treeDisposables.add(this.instantiationService.createInstance(ResourceLabels, this));
 		const dataSource = this.instantiationService.createInstance(TreeDataSource, this, <T>(task: Promise<T>) => this.progressService.withProgress({ location: this.id }, () => task));
-		const aligner = this.treeDisposables.add(new Aligner(this.themeService));
+		const aligner = this.treeDisposables.add(new Aligner(this.themeService, this.logService));
 		const checkboxStateHandler = this.treeDisposables.add(new CheckboxStateHandler());
 		const renderer = this.treeDisposables.add(this.instantiationService.createInstance(TreeRenderer, this.id, treeMenus, this.treeLabels, actionViewItemProvider, aligner, checkboxStateHandler, () => this.manuallyManageCheckboxes));
 		this.treeDisposables.add(renderer.onDidChangeCheckboxState(e => this._onDidChangeCheckboxState.fire(e)));
@@ -1631,7 +1631,7 @@ class TreeRenderer extends Disposable implements ITreeRenderer<ITreeItem, FuzzyS
 class Aligner extends Disposable {
 	private _tree: WorkbenchAsyncDataTree<ITreeItem, ITreeItem, FuzzyScore> | undefined;
 
-	constructor(private themeService: IThemeService) {
+	constructor(private themeService: IThemeService, private logService: ILogService) {
 		super();
 	}
 
@@ -1649,7 +1649,13 @@ class Aligner extends Disposable {
 
 		if (this._tree) {
 			const root = this._tree.getInput();
-			const parent: ITreeItem = this._tree.getParentElement(treeItem) || root;
+			let parent: ITreeItem;
+			try {
+				parent = this._tree.getParentElement(treeItem) || root;
+			} catch (error) {
+				this.logService.error(`[TreeView] Failed to resolve parent for ${treeItem.handle}`, error);
+				return false;
+			}
 			if (this.hasIconOrCheckbox(parent)) {
 				return !!parent.children && parent.children.some(c => c.collapsibleState !== TreeItemCollapsibleState.None && !this.hasIconOrCheckbox(c));
 			}