Don't show infinite notebook progress if webview fails to init

src/vs/workbench/contrib/notebook/browser/view/renderers/backLayerWebView.ts

@@ -497,10 +497,10 @@ export class BackLayerWebView<T extends ICommonCellInfo> extends Themable {
 		return !!this.webview;
 	}
 
-	createWebview(): void {
+	createWebview(): Promise<void> {
 		const baseUrl = this.asWebviewUri(this.getNotebookBaseUri(), undefined);
 		const htmlContent = this.generateContent(baseUrl.toString());
-		this._initialize(htmlContent);
+		return this._initialize(htmlContent);
 	}
 
 	private getNotebookBaseUri() {
@@ -535,7 +535,7 @@ export class BackLayerWebView<T extends ICommonCellInfo> extends Themable {
 		];
 	}
 
-	private _initialize(content: string) {
+	private _initialize(content: string): Promise<void> {
 		if (!document.body.contains(this.element)) {
 			throw new Error('Element is already detached from the DOM tree');
 		}
@@ -546,6 +546,12 @@ export class BackLayerWebView<T extends ICommonCellInfo> extends Themable {
 
 		this._register(new WebviewWindowDragMonitor(() => this.webview));
 
+		const initializePromise = new DeferredPromise<void>();
+
+		this._register(this.webview.onFatalError(e => {
+			initializePromise.error(new Error(`Could not initialize webview: ${e.message}}`));
+		}));
+
 		this._register(this.webview.onMessage(async (message) => {
 			const data: FromWebviewMessage | { readonly __vscode_notebook_message: undefined } = message.message;
 			if (this._disposed) {
@@ -558,6 +564,7 @@ export class BackLayerWebView<T extends ICommonCellInfo> extends Themable {
 
 			switch (data.type) {
 				case 'initialized': {
+					initializePromise.complete();
 					this.initializeWebViewState();
 					break;
 				}
@@ -828,6 +835,8 @@ export class BackLayerWebView<T extends ICommonCellInfo> extends Themable {
 				}
 			}
 		}));
+
+		return initializePromise.p;
 	}
 
 	private _handleNotebookCellResource(uri: URI) {

src/vs/workbench/contrib/webview/browser/overlayWebview.ts

@@ -222,6 +222,7 @@ export class OverlayWebview extends Disposable implements IOverlayWebview {
 			this._webviewEvents.add(webview.onMissingCsp(x => { this._onMissingCsp.fire(x); }));
 			this._webviewEvents.add(webview.onDidWheel(x => { this._onDidWheel.fire(x); }));
 			this._webviewEvents.add(webview.onDidReload(() => { this._onDidReload.fire(); }));
+			this._webviewEvents.add(webview.onFatalError(x => { this._onFatalError.fire(x); }));
 
 			this._webviewEvents.add(webview.onDidScroll(x => {
 				this._initialScrollProgress = x.scrollYPercentage;
@@ -320,6 +321,9 @@ export class OverlayWebview extends Disposable implements IOverlayWebview {
 	private readonly _onDidWheel = this._register(new Emitter<IMouseWheelEvent>());
 	public readonly onDidWheel = this._onDidWheel.event;
 
+	private readonly _onFatalError = this._register(new Emitter<{ readonly message: string }>());
+	public onFatalError = this._onFatalError.event;
+
 	public async postMessage(message: any, transfer?: readonly ArrayBuffer[]): Promise<boolean> {
 		if (this._webview.value) {
 			return this._webview.value.postMessage(message, transfer);

src/vs/workbench/contrib/webview/browser/webview.ts

@@ -215,16 +215,27 @@ export interface IWebview extends IDisposable {
 
 	readonly onDidFocus: Event<void>;
 	readonly onDidBlur: Event<void>;
+
+	/**
+	 * Fired when the webview is disposed of.
+	 */
 	readonly onDidDispose: Event<void>;
 
 	readonly onDidClickLink: Event<string>;
 	readonly onDidScroll: Event<{ readonly scrollYPercentage: number }>;
 	readonly onDidWheel: Event<IMouseWheelEvent>;
+
 	readonly onDidUpdateState: Event<string | undefined>;
 	readonly onDidReload: Event<void>;
-	readonly onMessage: Event<WebviewMessageReceivedEvent>;
+
+	/**
+	 * Fired when the webview cannot be loaded or is now in a non-functional state.
+	 */
+	readonly onFatalError: Event<{ readonly message: string }>;
 	readonly onMissingCsp: Event<ExtensionIdentifier>;
 
+	readonly onMessage: Event<WebviewMessageReceivedEvent>;
+
 	postMessage(message: any, transfer?: readonly ArrayBuffer[]): Promise<boolean>;
 
 	focus(): void;

src/vs/workbench/contrib/webview/browser/webviewElement.ts

@@ -261,6 +261,7 @@ export class WebviewElement extends Disposable implements IWebview, WebviewFindD
 
 		this._register(this.on('fatal-error', (e) => {
 			notificationService.error(localize('fatalErrorMessage', "Error loading webview: {0}", e.message));
+			this._onFatalError.fire({ message: e.message });
 		}));
 
 		this._register(this.on('did-keydown', (data) => {
@@ -403,6 +404,9 @@ export class WebviewElement extends Disposable implements IWebview, WebviewFindD
 	private readonly _onDidBlur = this._register(new Emitter<void>());
 	public readonly onDidBlur = this._onDidBlur.event;
 
+	private readonly _onFatalError = this._register(new Emitter<{ readonly message: string }>());
+	public readonly onFatalError = this._onFatalError.event;
+
 	private readonly _onDidDispose = this._register(new Emitter<void>());
 	public readonly onDidDispose = this._onDidDispose.event;