open extension url when all windows are closed

fixes #27343

src/vs/platform/windows/electron-main/windowsService.ts

@@ -37,10 +37,17 @@ export class WindowsService implements IWindowsService, IDisposable {
 		@ILifecycleService private lifecycleService: ILifecycleService,
 		@IHistoryMainService private historyService: IHistoryMainService
 	) {
+		// Catch file URLs
 		chain(urlService.onOpenURL)
 			.filter(uri => uri.authority === 'file' && !!uri.path)
 			.map(uri => URI.file(uri.fsPath))
 			.on(this.openFileForURI, this, this.disposables);
+
+		// Catch extension URLs when there are no windows open
+		chain(urlService.onOpenURL)
+			.filter(uri => /^extension/.test(uri.path))
+			.filter(() => this.windowsMainService.getWindowCount() === 0)
+			.on(this.openExtensionForURI, this, this.disposables);
 	}
 
 	openFileFolderPicker(windowId: number, forceNewWindow?: boolean, data?: ITelemetryData): TPromise<void> {
@@ -315,6 +322,16 @@ export class WindowsService implements IWindowsService, IDisposable {
 		return TPromise.as(null);
 	}
 
+	/**
+	 * This should only fire whenever an extension URL is open
+	 * and there are no windows to handle it.
+	 */
+	private openExtensionForURI(uri: URI): TPromise<void> {
+		const cli = assign(Object.create(null), this.environmentService.args);
+		this.windowsMainService.open({ context: OpenContext.API, cli });
+		return TPromise.as(null);
+	}
+
 	dispose(): void {
 		this.disposables = dispose(this.disposables);
 	}