Wait for tree to be registered before disposing

This fixes the tree view rpc test
Fixes #116776

src/vs/workbench/api/browser/mainThreadTreeViews.ts

@@ -31,7 +31,7 @@ export class MainThreadTreeViews extends Disposable implements MainThreadTreeVie
 		this._proxy = extHostContext.getProxy(ExtHostContext.ExtHostTreeViews);
 	}
 
-	$registerTreeViewDataProvider(treeViewId: string, options: { showCollapseAll: boolean, canSelectMany: boolean }): void {
+	async $registerTreeViewDataProvider(treeViewId: string, options: { showCollapseAll: boolean, canSelectMany: boolean }): Promise<void> {
 		this.logService.trace('MainThreadTreeViews#$registerTreeViewDataProvider', treeViewId, options);
 
 		this.extensionService.whenInstalledExtensionsRegistered().then(() => {

src/vs/workbench/api/common/extHost.protocol.ts

@@ -285,7 +285,7 @@ export interface MainThreadTextEditorsShape extends IDisposable {
 }
 
 export interface MainThreadTreeViewsShape extends IDisposable {
-	$registerTreeViewDataProvider(treeViewId: string, options: { showCollapseAll: boolean, canSelectMany: boolean; }): void;
+	$registerTreeViewDataProvider(treeViewId: string, options: { showCollapseAll: boolean, canSelectMany: boolean; }): Promise<void>;
 	$refresh(treeViewId: string, itemsToRefresh?: { [treeItemHandle: string]: ITreeItem; }): Promise<void>;
 	$reveal(treeViewId: string, itemInfo: { item: ITreeItem, parentChain: ITreeItem[] } | undefined, options: IRevealOptions): Promise<void>;
 	$setMessage(treeViewId: string, message: string): void;

src/vs/workbench/api/common/extHostTreeViews.ts

@@ -84,7 +84,7 @@ export class ExtHostTreeViews implements ExtHostTreeViewsShape {
 		if (!options || !options.treeDataProvider) {
 			throw new Error('Options with treeDataProvider is mandatory');
 		}
-
+		const registerPromise = this._proxy.$registerTreeViewDataProvider(viewId, { showCollapseAll: !!options.showCollapseAll, canSelectMany: !!options.canSelectMany });
 		const treeView = this.createExtHostTreeView(viewId, options, extension);
 		return {
 			get onDidCollapseElement() { return treeView.onDidCollapseElement; },
@@ -110,7 +110,9 @@ export class ExtHostTreeViews implements ExtHostTreeViewsShape {
 			reveal: (element: T, options?: IRevealOptions): Promise<void> => {
 				return treeView.reveal(element, options);
 			},
-			dispose: () => {
+			dispose: async () => {
+				// Wait for the registration promise to finish before doing the dispose.
+				await registerPromise;
 				this.treeViews.delete(viewId);
 				treeView.dispose();
 			}
@@ -240,7 +242,6 @@ class ExtHostTreeView<T> extends Disposable {
 			}
 		}
 		this.dataProvider = options.treeDataProvider;
-		this.proxy.$registerTreeViewDataProvider(viewId, { showCollapseAll: !!options.showCollapseAll, canSelectMany: !!options.canSelectMany });
 		if (this.dataProvider.onDidChangeTreeData) {
 			this._register(this.dataProvider.onDidChangeTreeData(element => this._onDidChangeData.fire({ message: false, element })));
 		}

src/vs/workbench/test/browser/api/extHostTreeViews.test.ts

@@ -26,7 +26,7 @@ suite('ExtHostTreeView', function () {
 
 		onRefresh = new Emitter<{ [treeItemHandle: string]: ITreeItem }>();
 
-		$registerTreeViewDataProvider(treeViewId: string): void {
+		async $registerTreeViewDataProvider(treeViewId: string): Promise<void> {
 		}
 
 		$refresh(viewId: string, itemsToRefresh: { [treeItemHandle: string]: ITreeItem }): Promise<void> {