Fix list view npe when inserting whitespaces at top (microsoft#205311)

Author: rebornix

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

@@ -295,8 +295,8 @@ export class ListView<T> implements IListView<T> {
 	protected rangeMap: IRangeMap;
 	private cache: RowCache<T>;
 	private renderers = new Map<string, IListRenderer<any /* TODO@joao */, any>>();
-	private lastRenderTop: number;
-	private lastRenderHeight: number;
+	protected lastRenderTop: number;
+	protected lastRenderHeight: number;
 	private renderWidth = 0;
 	private rowsContainer: HTMLElement;
 	private scrollable: Scrollable;
@@ -1400,7 +1400,7 @@ export class ListView<T> implements IListView<T> {
 		return undefined;
 	}
 
-	private getRenderRange(renderTop: number, renderHeight: number): IRange {
+	protected getRenderRange(renderTop: number, renderHeight: number): IRange {
 		return {
 			start: this.rangeMap.indexAt(renderTop),
 			end: this.rangeMap.indexAfter(renderTop + renderHeight - 1)

src/vs/workbench/contrib/notebook/browser/view/notebookCellList.ts

@@ -594,7 +594,7 @@ export class NotebookCellList extends WorkbenchList<CellViewModel> implements ID
 
 		if (modelIndex >= this.hiddenRangesPrefixSum.getTotalSum()) {
 			// it's already after the last hidden range
-			return this.hiddenRangesPrefixSum.getTotalSum();
+			return Math.min(this.length, this.hiddenRangesPrefixSum.getTotalSum());
 		}
 
 		return this.hiddenRangesPrefixSum.getIndexOf(modelIndex).index;

src/vs/workbench/contrib/notebook/browser/view/notebookCellListView.ts

@@ -276,9 +276,14 @@ export class NotebookCellListView<T> extends ListView<T> {
 	insertWhitespace(afterPosition: number, size: number): string {
 		const scrollTop = this.scrollTop;
 		const id = `${++this._lastWhitespaceId}`;
+		const previousRenderRange = this.getRenderRange(this.lastRenderTop, this.lastRenderHeight);
+		const elementPosition = this.elementTop(afterPosition);
+		const aboveScrollTop = scrollTop > elementPosition;
 		this.notebookRangeMap.insertWhitespace(id, afterPosition, size);
 
-		this._rerender(scrollTop, this.renderHeight, false);
+		const newScrolltop = aboveScrollTop ? scrollTop + size : scrollTop;
+		this.render(previousRenderRange, newScrolltop, this.lastRenderHeight, undefined, undefined, false);
+		this._rerender(newScrolltop, this.renderHeight, false);
 		this.eventuallyUpdateScrollDimensions();
 
 		return id;

src/vs/workbench/contrib/notebook/browser/viewParts/notebookViewZones.ts

@@ -120,7 +120,8 @@ export class NotebookViewZones extends Disposable {
 	}
 
 	private _addZone(zone: INotebookViewZone): string {
-		const whitespaceId = this.listView.insertWhitespace(zone.afterModelPosition, zone.heightInPx);
+		const viewPosition = this.coordinator.convertModelIndexToViewIndex(zone.afterModelPosition);
+		const whitespaceId = this.listView.insertWhitespace(viewPosition, zone.heightInPx);
 		const isInHiddenArea = this._isInHiddenRanges(zone);
 		const myZone: IZoneWidget = {
 			whitespaceId: whitespaceId,

src/vs/workbench/contrib/notebook/test/browser/notebookViewZones.test.ts

@@ -346,6 +346,19 @@ suite('NotebookRangeMap with whitesspaces', () => {
 		instantiationService.stub(IConfigurationService, config);
 	});
 
+	test('simple', () => {
+		const rangeMap = new NotebookCellsLayout(0);
+		rangeMap.splice(0, 0, [{ size: 479 }, { size: 163 }, { size: 182 }, { size: 106 }, { size: 106 }, { size: 106 }, { size: 87 }]);
+
+		const start = rangeMap.indexAt(650);
+		const end = rangeMap.indexAfter(650 + 890 - 1);
+		assert.strictEqual(start, 2);
+		assert.strictEqual(end, 7);
+
+		rangeMap.insertWhitespace('1', 0, 18);
+		assert.strictEqual(rangeMap.indexAt(650), 1);
+	});
+
 	test('Whitespace CRUD', async function () {
 		const twenty = { size: 20 };