Add default URI if not provided in dialog API

Fixes #111585

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

@@ -23,12 +23,20 @@ export class MainThreadDialogs implements MainThreadDiaglogsShape {
 		//
 	}
 
-	$showOpenDialog(options?: MainThreadDialogOpenOptions): Promise<URI[] | undefined> {
-		return Promise.resolve(this._fileDialogService.showOpenDialog(MainThreadDialogs._convertOpenOptions(options)));
+	async $showOpenDialog(options?: MainThreadDialogOpenOptions): Promise<URI[] | undefined> {
+		const convertedOptions = MainThreadDialogs._convertOpenOptions(options);
+		if (!convertedOptions.defaultUri) {
+			convertedOptions.defaultUri = await this._fileDialogService.defaultFilePath();
+		}
+		return Promise.resolve(this._fileDialogService.showOpenDialog(convertedOptions));
 	}
 
-	$showSaveDialog(options?: MainThreadDialogSaveOptions): Promise<URI | undefined> {
-		return Promise.resolve(this._fileDialogService.showSaveDialog(MainThreadDialogs._convertSaveOptions(options)));
+	async $showSaveDialog(options?: MainThreadDialogSaveOptions): Promise<URI | undefined> {
+		const convertedOptions = MainThreadDialogs._convertSaveOptions(options);
+		if (!convertedOptions.defaultUri) {
+			convertedOptions.defaultUri = await this._fileDialogService.defaultFilePath();
+		}
+		return Promise.resolve(this._fileDialogService.showSaveDialog(convertedOptions));
 	}
 
 	private static _convertOpenOptions(options?: MainThreadDialogOpenOptions): IOpenDialogOptions {

src/vs/workbench/services/dialogs/browser/simpleFileDialog.ts

@@ -221,7 +221,7 @@ export class SimpleFileDialog {
 	}
 
 	private getScheme(available: readonly string[] | undefined, defaultUri: URI | undefined): string {
-		if (available) {
+		if (available && available.length > 0) {
 			if (defaultUri && (available.indexOf(defaultUri.scheme) >= 0)) {
 				return defaultUri.scheme;
 			}