update scroll handler

src/vs/base/browser/ui/list/listWidget.ts

@@ -1311,7 +1311,7 @@ export class List<T> implements ISpliceable<T>, IDisposable {
 		this.eventBufferer.bufferEvents(() => this.spliceable.splice(start, deleteCount, elements));
 	}
 
-	public triggerScrollFromMouseWheelEvent(browserEvent: IMouseWheelEvent) {
+	triggerScrollFromMouseWheelEvent(browserEvent: IMouseWheelEvent) {
 		this.view.triggerScrollFromMouseWheelEvent(browserEvent);
 	}
 
@@ -1587,7 +1587,11 @@ export class List<T> implements ISpliceable<T>, IDisposable {
 		}
 	}
 
-	getElementTop(index: number): number {
+	getAbsoluteTop(index: number): number {
+		if (index < 0 || index >= this.length) {
+			throw new ListError(this.user, `Invalid index ${index}`);
+		}
+
 		return this.view.elementTop(index);
 	}
 

src/vs/vscode.proposed.d.ts

@@ -1478,7 +1478,7 @@ declare module 'vscode' {
 	}
 
 	//#endregion
-	//#region Language specific settings: https://github.com/microsoft/vscode/issues/26707
+
 	//#region color theme access
 
 	/**

src/vs/workbench/contrib/notebook/browser/notebookEditor.ts

@@ -186,17 +186,17 @@ export class NotebookEditor extends BaseEditor implements NotebookHandler {
 
 		if (!this.webview!.mapping.has(cell.id)) {
 			let index = this.model!.getNotebook().cells.indexOf(cell.cell);
-			let top = this.list?.getElementTop(index) || 0;
+			let top = this.list?.getAbsoluteTop(index) || 0;
 			this.webview!.createContentWidget(cell, offset, shadowContent, top + offset);
 			this.webview!.outputMapping.set(cell.id + `-${outputIndex}`, true);
 		} else if (!this.webview!.outputMapping.has(cell.id + `-${outputIndex}`)) {
 			let index = this.model!.getNotebook().cells.indexOf(cell.cell);
-			let top = this.list?.getElementTop(index) || 0;
+			let top = this.list?.getAbsoluteTop(index) || 0;
 			this.webview!.outputMapping.set(cell.id + `-${outputIndex}`, true);
 			this.webview!.createContentWidget(cell, offset, shadowContent, top + offset);
 		} else {
 			let index = this.model!.getNotebook().cells.indexOf(cell.cell);
-			let top = this.list?.getElementTop(index) || 0;
+			let top = this.list?.getAbsoluteTop(index) || 0;
 			let scrollTop = this.list?.scrollTop || 0;
 
 			this.webview!.updateViewScrollTop(-scrollTop, [{ id: cell.id, top: top + offset }]);
@@ -290,7 +290,7 @@ export class NotebookEditor extends BaseEditor implements NotebookHandler {
 					// const date = new Date();
 					this.webview?.mapping.forEach((item) => {
 						let index = this.model!.getNotebook().cells.indexOf(item.cell.cell);
-						let top = this.list?.getElementTop(index) || 0;
+						let top = this.list?.getAbsoluteTop(index) || 0;
 						let newTop = this.webview!.shouldRenderContentWidget(item.cell.id, top);
 
 						if (newTop !== undefined) {