show a spinner if the Output box is out of date

src/vs/editor/contrib/rtv/browser/RTVDisplay.ts

@@ -309,6 +309,10 @@ class RTVOutputDisplayBox {
 			throw new Error('Cannot find Monaco Editor');
 		}
 
+		if (this._outOfDate) {
+			this.setSpinner();
+		}
+
 		this._box.style.display = 'inline-block';
 		this._box.style.opacity = '1';
 		editor_div.appendChild(this._box);
@@ -338,6 +342,15 @@ class RTVOutputDisplayBox {
 		this._outOfDate = true;
 	}
 
+	public setSpinner() {
+		this.setContent(
+			`<div class="d-flex justify-content-center align-items-center mt-5">
+				<div class="spinner-border" role="status">
+					<span class="sr-only">Loading...</span>
+				</div>
+			</div>`);
+	}
+
 	public update(outputMsg: string, errorMsg: string, parsedResults: any) {
 		this._outOfDate = false;
 
@@ -2987,6 +3000,7 @@ export class RTVController implements IRTVController {
 
 		this._eventEmitter.fire(new BoxUpdateEvent(true, false, false));
 
+		this.getOutputBox().outOfDate();
 		this.hideOutputBox();
 
 		const [outputMsg, errorMsg, parsedResult] = await this.runProgram();