listView.ts

/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/

import { DataTransfers, IDragAndDropData } from '../../dnd.js';
import { addDisposableListener, animate, Dimension, getActiveElement, getContentHeight, getContentWidth, getDocument, getTopLeftOffset, getWindow, isAncestor, isHTMLElement, isSVGElement, scheduleAtNextAnimationFrame } from '../../dom.js';
import { DomEmitter } from '../../event.js';
import { IMouseWheelEvent } from '../../mouseEvent.js';
import { EventType as TouchEventType, Gesture, GestureEvent } from '../../touch.js';
import { SmoothScrollableElement } from '../scrollbar/scrollableElement.js';
import { distinct, equals, splice } from '../../../common/arrays.js';
import { Delayer, disposableTimeout } from '../../../common/async.js';
import { memoize } from '../../../common/decorators.js';
import { Emitter, Event, IValueWithChangeEvent } from '../../../common/event.js';
import { Disposable, DisposableStore, IDisposable, toDisposable } from '../../../common/lifecycle.js';
import { IRange, Range } from '../../../common/range.js';
import { INewScrollDimensions, Scrollable, ScrollbarVisibility, ScrollEvent } from '../../../common/scrollable.js';
import { ISpliceable } from '../../../common/sequence.js';
import { IListDragAndDrop, IListDragEvent, IListGestureEvent, IListMouseEvent, IListRenderer, IListTouchEvent, IListVirtualDelegate, ListDragOverEffectPosition, ListDragOverEffectType } from './list.js';
import { IRangeMap, RangeMap, shift } from './rangeMap.js';
import { IRow, RowCache } from './rowCache.js';
import { BugIndicatingError } from '../../../common/errors.js';
import { AriaRole } from '../aria/aria.js';
import { ScrollableElementChangeOptions } from '../scrollbar/scrollableElementOptions.js';
import { clamp } from '../../../common/numbers.js';
import { applyDragImage } from '../dnd/dnd.js';

interface IItem<T> {
	readonly id: string;
	readonly element: T;
	readonly templateId: string;
	row: IRow | null;
	size: number;
	width: number | undefined;
	hasDynamicHeight: boolean;
	lastDynamicHeightWidth: number | undefined;
	uri: string | undefined;
	dropTarget: boolean;
	dragStartDisposable: IDisposable;
	checkedDisposable: IDisposable;
	stale: boolean;
}

const StaticDND = {
	CurrentDragAndDropData: undefined as IDragAndDropData | undefined
};

export interface IListViewDragAndDrop<T> extends IListDragAndDrop<T> {
	getDragElements(element: T): T[];
}

export const enum ListViewTargetSector {
	// drop position relative to the top of the item
	TOP = 0, 				// [0%-25%)
	CENTER_TOP = 1, 		// [25%-50%)
	CENTER_BOTTOM = 2, 		// [50%-75%)
	BOTTOM = 3				// [75%-100%)
}

export type CheckBoxAccessibleState = boolean | 'mixed';

export interface IListViewAccessibilityProvider<T> {
	getSetSize?(element: T, index: number, listLength: number): number;
	getPosInSet?(element: T, index: number): number;
	getRole?(element: T): AriaRole | undefined;
	isChecked?(element: T): CheckBoxAccessibleState | IValueWithChangeEvent<CheckBoxAccessibleState> | undefined;
}

export interface IListViewOptionsUpdate {
	readonly smoothScrolling?: boolean;
	readonly horizontalScrolling?: boolean;
	readonly scrollByPage?: boolean;
	readonly mouseWheelScrollSensitivity?: number;
	readonly fastScrollSensitivity?: number;
	readonly paddingTop?: number;
	readonly paddingBottom?: number;
}

export interface IListViewOptions<T> extends IListViewOptionsUpdate {
	readonly dnd?: IListViewDragAndDrop<T>;
	readonly useShadows?: boolean;
	readonly verticalScrollMode?: ScrollbarVisibility;
	readonly setRowLineHeight?: boolean;
	readonly setRowHeight?: boolean;
	readonly supportDynamicHeights?: boolean;
	readonly mouseSupport?: boolean;
	readonly userSelection?: boolean;
	readonly accessibilityProvider?: IListViewAccessibilityProvider<T>;
	readonly transformOptimization?: boolean;
	readonly alwaysConsumeMouseWheel?: boolean;
	readonly initialSize?: Dimension;
	readonly scrollToActiveElement?: boolean;
}

const DefaultOptions = {
	useShadows: true,
	verticalScrollMode: ScrollbarVisibility.Auto,
	setRowLineHeight: true,
	setRowHeight: true,
	supportDynamicHeights: false,
	dnd: {
		getDragElements<T>(e: T) { return [e]; },
		getDragURI() { return null; },
		onDragStart(): void { },
		onDragOver() { return false; },
		drop() { },
		dispose() { }
	},
	horizontalScrolling: false,
	transformOptimization: true,
	alwaysConsumeMouseWheel: true,
} satisfies IListViewOptions<any>;

export class ElementsDragAndDropData<T, TContext = void> implements IDragAndDropData {

	readonly elements: T[];

	private _context: TContext | undefined;
	public get context(): TContext | undefined {
		return this._context;
	}
	public set context(value: TContext | undefined) {
		this._context = value;
	}

	constructor(elements: T[]) {
		this.elements = elements;
	}

	update(): void { }

	getData(): T[] {
		return this.elements;
	}
}

export class ExternalElementsDragAndDropData<T> implements IDragAndDropData {

	readonly elements: T[];

	constructor(elements: T[]) {
		this.elements = elements;
	}

	update(): void { }

	getData(): T[] {
		return this.elements;
	}
}

export class NativeDragAndDropData implements IDragAndDropData {

	readonly types: any[];
	readonly files: any[];

	constructor() {
		this.types = [];
		this.files = [];
	}

	update(dataTransfer: DataTransfer): void {
		if (dataTransfer.types) {
			this.types.splice(0, this.types.length, ...dataTransfer.types);
		}

		if (dataTransfer.files) {
			this.files.splice(0, this.files.length);

			for (let i = 0; i < dataTransfer.files.length; i++) {
				const file = dataTransfer.files.item(i);

				if (file && (file.size || file.type)) {
					this.files.push(file);
				}
			}
		}
	}

	getData() {
		return {
			types: this.types,
			files: this.files
		};
	}
}

function equalsDragFeedback(f1: number[] | undefined, f2: number[] | undefined): boolean {
	if (Array.isArray(f1) && Array.isArray(f2)) {
		return equals(f1, f2);
	}

	return f1 === f2;
}

class ListViewAccessibilityProvider<T> implements Required<IListViewAccessibilityProvider<T>> {

	readonly getSetSize: (element: T, index: number, listLength: number) => number;
	readonly getPosInSet: (element: T, index: number) => number;
	readonly getRole: (element: T) => AriaRole | undefined;
	readonly isChecked: (element: T) => CheckBoxAccessibleState | IValueWithChangeEvent<CheckBoxAccessibleState> | undefined;

	constructor(accessibilityProvider?: IListViewAccessibilityProvider<T>) {
		if (accessibilityProvider?.getSetSize) {
			this.getSetSize = accessibilityProvider.getSetSize.bind(accessibilityProvider);
		} else {
			this.getSetSize = (e, i, l) => l;
		}

		if (accessibilityProvider?.getPosInSet) {
			this.getPosInSet = accessibilityProvider.getPosInSet.bind(accessibilityProvider);
		} else {
			this.getPosInSet = (e, i) => i + 1;
		}

		if (accessibilityProvider?.getRole) {
			this.getRole = accessibilityProvider.getRole.bind(accessibilityProvider);
		} else {
			this.getRole = _ => 'listitem';
		}

		if (accessibilityProvider?.isChecked) {
			this.isChecked = accessibilityProvider.isChecked.bind(accessibilityProvider);
		} else {
			this.isChecked = _ => undefined;
		}
	}
}

export interface IListView<T> extends ISpliceable<T>, IDisposable {
	readonly domId: string;
	readonly domNode: HTMLElement;
	readonly containerDomNode: HTMLElement;
	readonly scrollableElementDomNode: HTMLElement;
	readonly length: number;
	readonly contentHeight: number;
	readonly contentWidth: number;
	readonly onDidChangeContentHeight: Event<number>;
	readonly onDidChangeContentWidth: Event<number>;
	readonly renderHeight: number;
	readonly scrollHeight: number;
	readonly firstVisibleIndex: number;
	readonly firstMostlyVisibleIndex: number;
	readonly lastVisibleIndex: number;
	onDidScroll: Event<ScrollEvent>;
	onWillScroll: Event<ScrollEvent>;
	onMouseClick: Event<IListMouseEvent<T>>;
	onMouseDblClick: Event<IListMouseEvent<T>>;
	onMouseMiddleClick: Event<IListMouseEvent<T>>;
	onMouseUp: Event<IListMouseEvent<T>>;
	onMouseDown: Event<IListMouseEvent<T>>;
	onMouseOver: Event<IListMouseEvent<T>>;
	onMouseMove: Event<IListMouseEvent<T>>;
	onMouseOut: Event<IListMouseEvent<T>>;
	onContextMenu: Event<IListMouseEvent<T>>;
	onTouchStart: Event<IListTouchEvent<T>>;
	onTap: Event<IListGestureEvent<T>>;
	element(index: number): T;
	domElement(index: number): HTMLElement | null;
	getElementDomId(index: number): string;
	elementHeight(index: number): number;
	elementTop(index: number): number;
	indexOf(element: T): number;
	indexAt(position: number): number;
	indexAfter(position: number): number;
	updateOptions(options: IListViewOptionsUpdate): void;
	getScrollTop(): number;
	setScrollTop(scrollTop: number, reuseAnimation?: boolean): void;
	getScrollLeft(): number;
	setScrollLeft(scrollLeft: number): void;
	delegateScrollFromMouseWheelEvent(browserEvent: IMouseWheelEvent): void;
	delegateVerticalScrollbarPointerDown(browserEvent: PointerEvent): void;
	updateWidth(index: number): void;
	updateElementHeight(index: number, size: number | undefined, anchorIndex: number | null): void;
	rerender(): void;
	layout(height?: number, width?: number): void;
}

/**
 * The {@link ListView} is a virtual scrolling engine.
 *
 * Given that it only renders elements within its viewport, it can hold large
 * collections of elements and stay very performant. The performance bottleneck
 * usually lies within the user's rendering code for each element.
 *
 * @remarks It is a low-level widget, not meant to be used directly. Refer to the
 * List widget instead.
 */
export class ListView<T> implements IListView<T> {

	private static InstanceCount = 0;
	readonly domId = `list_id_${++ListView.InstanceCount}`;

	readonly domNode: HTMLElement;

	private items: IItem<T>[];
	private itemId: number;
	protected rangeMap: IRangeMap;
	private cache: RowCache<T>;
	private renderers = new Map<string, IListRenderer<any /* TODO@joao */, any>>();
	protected lastRenderTop: number;
	protected lastRenderHeight: number;
	private renderWidth = 0;
	private rowsContainer: HTMLElement;
	private scrollable: Scrollable;
	private scrollableElement: SmoothScrollableElement;
	private _scrollHeight: number = 0;
	private scrollableElementUpdateDisposable: IDisposable | null = null;
	private scrollableElementWidthDelayer = new Delayer<void>(50);
	private splicing = false;
	private dragOverAnimationDisposable: IDisposable | undefined;
	private dragOverAnimationStopDisposable: IDisposable = Disposable.None;
	private dragOverMouseY: number = 0;
	private setRowLineHeight: boolean;
	private setRowHeight: boolean;
	private supportDynamicHeights: boolean;
	private paddingBottom: number;
	private accessibilityProvider: ListViewAccessibilityProvider<T>;
	private scrollWidth: number | undefined;

	private dnd: IListViewDragAndDrop<T>;
	private canDrop: boolean = false;
	private currentDragData: IDragAndDropData | undefined;
	private currentDragFeedback: number[] | undefined;
	private currentDragFeedbackPosition: ListDragOverEffectPosition | undefined;
	private currentDragFeedbackDisposable: IDisposable = Disposable.None;
	private onDragLeaveTimeout: IDisposable = Disposable.None;
	private currentSelectionDisposable: IDisposable = Disposable.None;
	private currentSelectionBounds: IRange | undefined;
	private activeElement: HTMLElement | undefined;

	private readonly disposables: DisposableStore = new DisposableStore();

	private readonly _onDidChangeContentHeight = new Emitter<number>();
	private readonly _onDidChangeContentWidth = new Emitter<number>();
	readonly onDidChangeContentHeight: Event<number> = Event.latch(this._onDidChangeContentHeight.event, undefined, this.disposables);
	readonly onDidChangeContentWidth: Event<number> = Event.latch(this._onDidChangeContentWidth.event, undefined, this.disposables);
	get contentHeight(): number { return this.rangeMap.size; }
	get contentWidth(): number { return this.scrollWidth ?? 0; }

	get onDidScroll(): Event<ScrollEvent> { return this.scrollableElement.onScroll; }
	get onWillScroll(): Event<ScrollEvent> { return this.scrollableElement.onWillScroll; }
	get containerDomNode(): HTMLElement { return this.rowsContainer; }
	get scrollableElementDomNode(): HTMLElement { return this.scrollableElement.getDomNode(); }

	private _horizontalScrolling: boolean = false;
	private get horizontalScrolling(): boolean { return this._horizontalScrolling; }
	private set horizontalScrolling(value: boolean) {
		if (value === this._horizontalScrolling) {
			return;
		}

		if (value && this.supportDynamicHeights) {
			throw new Error('Horizontal scrolling and dynamic heights not supported simultaneously');
		}

		this._horizontalScrolling = value;
		this.domNode.classList.toggle('horizontal-scrolling', this._horizontalScrolling);

		if (this._horizontalScrolling) {
			for (const item of this.items) {
				this.measureItemWidth(item);
			}

			this.updateScrollWidth();
			this.scrollableElement.setScrollDimensions({ width: getContentWidth(this.domNode) });
			this.rowsContainer.style.width = `${Math.max(this.scrollWidth || 0, this.renderWidth)}px`;
		} else {
			this.scrollableElementWidthDelayer.cancel();
			this.scrollableElement.setScrollDimensions({ width: this.renderWidth, scrollWidth: this.renderWidth });
			this.rowsContainer.style.width = '';
		}
	}

	constructor(
		container: HTMLElement,
		private virtualDelegate: IListVirtualDelegate<T>,
		renderers: IListRenderer<any /* TODO@joao */, any>[],
		options: IListViewOptions<T> = DefaultOptions
	) {
		if (options.horizontalScrolling && options.supportDynamicHeights) {
			throw new Error('Horizontal scrolling and dynamic heights not supported simultaneously');
		}

		this.items = [];
		this.itemId = 0;
		this.rangeMap = this.createRangeMap(options.paddingTop ?? 0);

		for (const renderer of renderers) {
			this.renderers.set(renderer.templateId, renderer);
		}

		this.cache = this.disposables.add(new RowCache(this.renderers));

		this.lastRenderTop = 0;
		this.lastRenderHeight = 0;

		this.domNode = document.createElement('div');
		this.domNode.className = 'monaco-list';

		this.domNode.classList.add(this.domId);
		this.domNode.tabIndex = 0;

		this.domNode.classList.toggle('mouse-support', typeof options.mouseSupport === 'boolean' ? options.mouseSupport : true);

		this._horizontalScrolling = options.horizontalScrolling ?? DefaultOptions.horizontalScrolling;
		this.domNode.classList.toggle('horizontal-scrolling', this._horizontalScrolling);

		this.paddingBottom = typeof options.paddingBottom === 'undefined' ? 0 : options.paddingBottom;

		this.accessibilityProvider = new ListViewAccessibilityProvider(options.accessibilityProvider);

		this.rowsContainer = document.createElement('div');
		this.rowsContainer.className = 'monaco-list-rows';

		const transformOptimization = options.transformOptimization ?? DefaultOptions.transformOptimization;
		if (transformOptimization) {
			this.rowsContainer.style.transform = 'translate3d(0px, 0px, 0px)';
			this.rowsContainer.style.overflow = 'hidden';
			this.rowsContainer.style.contain = 'strict';
		}

		this.disposables.add(Gesture.addTarget(this.rowsContainer));

		this.scrollable = this.disposables.add(new Scrollable({
			forceIntegerValues: true,
			smoothScrollDuration: (options.smoothScrolling ?? false) ? 125 : 0,
			scheduleAtNextAnimationFrame: cb => scheduleAtNextAnimationFrame(getWindow(this.domNode), cb)
		}));
		this.scrollableElement = this.disposables.add(new SmoothScrollableElement(this.rowsContainer, {
			alwaysConsumeMouseWheel: options.alwaysConsumeMouseWheel ?? DefaultOptions.alwaysConsumeMouseWheel,
			horizontal: ScrollbarVisibility.Auto,
			vertical: options.verticalScrollMode ?? DefaultOptions.verticalScrollMode,
			useShadows: options.useShadows ?? DefaultOptions.useShadows,
			mouseWheelScrollSensitivity: options.mouseWheelScrollSensitivity,
			fastScrollSensitivity: options.fastScrollSensitivity,
			scrollByPage: options.scrollByPage
		}, this.scrollable));

		this.domNode.appendChild(this.scrollableElement.getDomNode());
		container.appendChild(this.domNode);

		this.scrollableElement.onScroll(this.onScroll, this, this.disposables);
		this.disposables.add(addDisposableListener(this.rowsContainer, TouchEventType.Change, e => this.onTouchChange(e as GestureEvent)));

		this.disposables.add(addDisposableListener(this.scrollableElement.getDomNode(), 'scroll', e => {
			// Make sure the active element is scrolled into view
			const element = (e.target as HTMLElement);
			const scrollValue = element.scrollTop;
			element.scrollTop = 0;
			if (options.scrollToActiveElement) {
				this.setScrollTop(this.scrollTop + scrollValue);
			}
		}));

		this.disposables.add(addDisposableListener(this.domNode, 'dragover', e => this.onDragOver(this.toDragEvent(e))));
		this.disposables.add(addDisposableListener(this.domNode, 'drop', e => this.onDrop(this.toDragEvent(e))));
		this.disposables.add(addDisposableListener(this.domNode, 'dragleave', e => this.onDragLeave(this.toDragEvent(e))));
		this.disposables.add(addDisposableListener(this.domNode, 'dragend', e => this.onDragEnd(e)));
		if (options.userSelection) {
			if (options.dnd) {
				throw new Error('DND and user selection cannot be used simultaneously');
			}
			this.disposables.add(addDisposableListener(this.domNode, 'mousedown', e => this.onPotentialSelectionStart(e)));
		}

		this.setRowLineHeight = options.setRowLineHeight ?? DefaultOptions.setRowLineHeight;
		this.setRowHeight = options.setRowHeight ?? DefaultOptions.setRowHeight;
		this.supportDynamicHeights = options.supportDynamicHeights ?? DefaultOptions.supportDynamicHeights;
		this.dnd = options.dnd ?? this.disposables.add(DefaultOptions.dnd);

		this.layout(options.initialSize?.height, options.initialSize?.width);
		if (options.scrollToActiveElement) {
			this._setupFocusObserver(container);
		}
	}

	private _setupFocusObserver(container: HTMLElement): void {
		this.disposables.add(addDisposableListener(container, 'focus', () => {
			const element = getActiveElement() as HTMLElement | null;
			if (this.activeElement !== element && element !== null) {
				this.activeElement = element;
				this._scrollToActiveElement(this.activeElement, container);
			}
		}, true));
	}

	private _scrollToActiveElement(element: HTMLElement, container: HTMLElement) {
		// The scroll event on the list only fires when scrolling down.
		// If the active element is above the viewport, we need to scroll up.
		const containerRect = container.getBoundingClientRect();
		const elementRect = element.getBoundingClientRect();

		const topOffset = elementRect.top - containerRect.top;

		if (topOffset < 0) {
			// Scroll up
			this.setScrollTop(this.scrollTop + topOffset);
		}
	}

	updateOptions(options: IListViewOptionsUpdate) {
		if (options.paddingBottom !== undefined) {
			this.paddingBottom = options.paddingBottom;
			this.scrollableElement.setScrollDimensions({ scrollHeight: this.scrollHeight });
		}

		if (options.smoothScrolling !== undefined) {
			this.scrollable.setSmoothScrollDuration(options.smoothScrolling ? 125 : 0);
		}

		if (options.horizontalScrolling !== undefined) {
			this.horizontalScrolling = options.horizontalScrolling;
		}

		let scrollableOptions: ScrollableElementChangeOptions | undefined;

		if (options.scrollByPage !== undefined) {
			scrollableOptions = { ...(scrollableOptions ?? {}), scrollByPage: options.scrollByPage };
		}

		if (options.mouseWheelScrollSensitivity !== undefined) {
			scrollableOptions = { ...(scrollableOptions ?? {}), mouseWheelScrollSensitivity: options.mouseWheelScrollSensitivity };
		}

		if (options.fastScrollSensitivity !== undefined) {
			scrollableOptions = { ...(scrollableOptions ?? {}), fastScrollSensitivity: options.fastScrollSensitivity };
		}

		if (scrollableOptions) {
			this.scrollableElement.updateOptions(scrollableOptions);
		}

		if (options.paddingTop !== undefined && options.paddingTop !== this.rangeMap.paddingTop) {
			// trigger a rerender
			const lastRenderRange = this.getRenderRange(this.lastRenderTop, this.lastRenderHeight);
			const offset = options.paddingTop - this.rangeMap.paddingTop;
			this.rangeMap.paddingTop = options.paddingTop;

			this.render(lastRenderRange, Math.max(0, this.lastRenderTop + offset), this.lastRenderHeight, undefined, undefined, true);
			this.setScrollTop(this.lastRenderTop);

			this.eventuallyUpdateScrollDimensions();

			if (this.supportDynamicHeights) {
				this._rerender(this.lastRenderTop, this.lastRenderHeight);
			}
		}
	}

	delegateScrollFromMouseWheelEvent(browserEvent: IMouseWheelEvent) {
		this.scrollableElement.delegateScrollFromMouseWheelEvent(browserEvent);
	}

	delegateVerticalScrollbarPointerDown(browserEvent: PointerEvent) {
		this.scrollableElement.delegateVerticalScrollbarPointerDown(browserEvent);
	}

	updateElementHeight(index: number, size: number | undefined, anchorIndex: number | null): void {
		if (index < 0 || index >= this.items.length) {
			return;
		}

		const originalSize = this.items[index].size;

		if (typeof size === 'undefined') {
			if (!this.supportDynamicHeights) {
				console.warn('Dynamic heights not supported', new Error().stack);
				return;
			}

			this.items[index].lastDynamicHeightWidth = undefined;
			size = originalSize + this.probeDynamicHeight(index);
		}

		if (originalSize === size) {
			return;
		}

		const lastRenderRange = this.getRenderRange(this.lastRenderTop, this.lastRenderHeight);

		let heightDiff = 0;

		if (index < lastRenderRange.start) {
			// do not scroll the viewport if resized element is out of viewport
			heightDiff = size - originalSize;
		} else {
			if (anchorIndex !== null && anchorIndex > index && anchorIndex < lastRenderRange.end) {
				// anchor in viewport
				// resized element in viewport and above the anchor
				heightDiff = size - originalSize;
			} else {
				heightDiff = 0;
			}
		}

		this.rangeMap.splice(index, 1, [{ size: size }]);
		this.items[index].size = size;

		this.render(lastRenderRange, Math.max(0, this.lastRenderTop + heightDiff), this.lastRenderHeight, undefined, undefined, true);
		this.setScrollTop(this.lastRenderTop);

		this.eventuallyUpdateScrollDimensions();

		if (this.supportDynamicHeights) {
			this._rerender(this.lastRenderTop, this.lastRenderHeight);
		} else {
			this._onDidChangeContentHeight.fire(this.contentHeight); // otherwise fired in _rerender()
		}
	}

	protected createRangeMap(paddingTop: number): IRangeMap {
		return new RangeMap(paddingTop);
	}

	splice(start: number, deleteCount: number, elements: readonly T[] = []): T[] {
		if (this.splicing) {
			throw new Error('Can\'t run recursive splices.');
		}

		this.splicing = true;

		try {
			return this._splice(start, deleteCount, elements);
		} finally {
			this.splicing = false;
			this._onDidChangeContentHeight.fire(this.contentHeight);
		}
	}

	private _splice(start: number, deleteCount: number, elements: readonly T[] = []): T[] {
		const previousRenderRange = this.getRenderRange(this.lastRenderTop, this.lastRenderHeight);
		const deleteRange = { start, end: start + deleteCount };
		const removeRange = Range.intersect(previousRenderRange, deleteRange);

		// try to reuse rows, avoid removing them from DOM
		const rowsToDispose = new Map<string, IRow[]>();
		for (let i = removeRange.end - 1; i >= removeRange.start; i--) {
			const item = this.items[i];
			item.dragStartDisposable.dispose();
			item.checkedDisposable.dispose();

			if (item.row) {
				let rows = rowsToDispose.get(item.templateId);

				if (!rows) {
					rows = [];
					rowsToDispose.set(item.templateId, rows);
				}

				const renderer = this.renderers.get(item.templateId);

				if (renderer && renderer.disposeElement) {
					renderer.disposeElement(item.element, i, item.row.templateData, { height: item.size });
				}

				rows.unshift(item.row);
			}

			item.row = null;
			item.stale = true;
		}

		const previousRestRange: IRange = { start: start + deleteCount, end: this.items.length };
		const previousRenderedRestRange = Range.intersect(previousRestRange, previousRenderRange);
		const previousUnrenderedRestRanges = Range.relativeComplement(previousRestRange, previousRenderRange);

		const inserted = elements.map<IItem<T>>(element => ({
			id: String(this.itemId++),
			element,
			templateId: this.virtualDelegate.getTemplateId(element),
			size: this.virtualDelegate.getHeight(element),
			width: undefined,
			hasDynamicHeight: !!this.virtualDelegate.hasDynamicHeight && this.virtualDelegate.hasDynamicHeight(element),
			lastDynamicHeightWidth: undefined,
			row: null,
			uri: undefined,
			dropTarget: false,
			dragStartDisposable: Disposable.None,
			checkedDisposable: Disposable.None,
			stale: false
		}));

		let deleted: IItem<T>[];

		// TODO@joao: improve this optimization to catch even more cases
		if (start === 0 && deleteCount >= this.items.length) {
			this.rangeMap = this.createRangeMap(this.rangeMap.paddingTop);
			this.rangeMap.splice(0, 0, inserted);
			deleted = this.items;
			this.items = inserted;
		} else {
			this.rangeMap.splice(start, deleteCount, inserted);
			deleted = splice(this.items, start, deleteCount, inserted);
		}

		const delta = elements.length - deleteCount;
		const renderRange = this.getRenderRange(this.lastRenderTop, this.lastRenderHeight);
		const renderedRestRange = shift(previousRenderedRestRange, delta);
		const updateRange = Range.intersect(renderRange, renderedRestRange);

		for (let i = updateRange.start; i < updateRange.end; i++) {
			this.updateItemInDOM(this.items[i], i);
		}

		const removeRanges = Range.relativeComplement(renderedRestRange, renderRange);

		for (const range of removeRanges) {
			for (let i = range.start; i < range.end; i++) {
				this.removeItemFromDOM(i);
			}
		}

		const unrenderedRestRanges = previousUnrenderedRestRanges.map(r => shift(r, delta));
		const elementsRange = { start, end: start + elements.length };
		const insertRanges = [elementsRange, ...unrenderedRestRanges].map(r => Range.intersect(renderRange, r)).reverse();

		for (const range of insertRanges) {
			for (let i = range.end - 1; i >= range.start; i--) {
				const item = this.items[i];
				const rows = rowsToDispose.get(item.templateId);
				const row = rows?.pop();
				this.insertItemInDOM(i, row);
			}
		}

		for (const rows of rowsToDispose.values()) {
			for (const row of rows) {
				this.cache.release(row);
			}
		}

		this.eventuallyUpdateScrollDimensions();

		if (this.supportDynamicHeights) {
			this._rerender(this.scrollTop, this.renderHeight);
		}

		return deleted.map(i => i.element);
	}

	protected eventuallyUpdateScrollDimensions(): void {
		this._scrollHeight = this.contentHeight;
		this.rowsContainer.style.height = `${this._scrollHeight}px`;

		if (!this.scrollableElementUpdateDisposable) {
			this.scrollableElementUpdateDisposable = scheduleAtNextAnimationFrame(getWindow(this.domNode), () => {
				this.scrollableElement.setScrollDimensions({ scrollHeight: this.scrollHeight });
				this.updateScrollWidth();
				this.scrollableElementUpdateDisposable = null;
			});
		}
	}

	private eventuallyUpdateScrollWidth(): void {
		if (!this.horizontalScrolling) {
			this.scrollableElementWidthDelayer.cancel();
			return;
		}

		this.scrollableElementWidthDelayer.trigger(() => this.updateScrollWidth());
	}

	private updateScrollWidth(): void {
		if (!this.horizontalScrolling) {
			return;
		}

		let scrollWidth = 0;

		for (const item of this.items) {
			if (typeof item.width !== 'undefined') {
				scrollWidth = Math.max(scrollWidth, item.width);
			}
		}

		this.scrollWidth = scrollWidth;
		this.scrollableElement.setScrollDimensions({ scrollWidth: scrollWidth === 0 ? 0 : (scrollWidth + 10) });
		this._onDidChangeContentWidth.fire(this.scrollWidth);
	}

	updateWidth(index: number): void {
		if (!this.horizontalScrolling || typeof this.scrollWidth === 'undefined') {
			return;
		}

		const item = this.items[index];
		this.measureItemWidth(item);

		if (typeof item.width !== 'undefined' && item.width > this.scrollWidth) {
			this.scrollWidth = item.width;
			this.scrollableElement.setScrollDimensions({ scrollWidth: this.scrollWidth + 10 });
			this._onDidChangeContentWidth.fire(this.scrollWidth);
		}
	}

	rerender(): void {
		if (!this.supportDynamicHeights) {
			return;
		}

		for (const item of this.items) {
			item.lastDynamicHeightWidth = undefined;
		}

		this._rerender(this.lastRenderTop, this.lastRenderHeight);
	}

	get length(): number {
		return this.items.length;
	}

	get renderHeight(): number {
		const scrollDimensions = this.scrollableElement.getScrollDimensions();
		return scrollDimensions.height;
	}

	get firstVisibleIndex(): number {
		const range = this.getVisibleRange(this.lastRenderTop, this.lastRenderHeight);
		return range.start;
	}

	get firstMostlyVisibleIndex(): number {
		const firstVisibleIndex = this.firstVisibleIndex;
		const firstElTop = this.rangeMap.positionAt(firstVisibleIndex);
		const nextElTop = this.rangeMap.positionAt(firstVisibleIndex + 1);
		if (nextElTop !== -1) {
			const firstElMidpoint = (nextElTop - firstElTop) / 2 + firstElTop;
			if (firstElMidpoint < this.scrollTop) {
				return firstVisibleIndex + 1;
			}
		}

		return firstVisibleIndex;
	}

	get lastVisibleIndex(): number {
		const range = this.getRenderRange(this.lastRenderTop, this.lastRenderHeight);
		return range.end - 1;
	}

	element(index: number): T {
		return this.items[index].element;
	}

	indexOf(element: T): number {
		return this.items.findIndex(item => item.element === element);
	}

	domElement(index: number): HTMLElement | null {
		const row = this.items[index].row;
		return row && row.domNode;
	}

	elementHeight(index: number): number {
		return this.items[index].size;
	}

	elementTop(index: number): number {
		return this.rangeMap.positionAt(index);
	}

	indexAt(position: number): number {
		return this.rangeMap.indexAt(position);
	}

	indexAfter(position: number): number {
		return this.rangeMap.indexAfter(position);
	}

	layout(height?: number, width?: number): void {
		const scrollDimensions: INewScrollDimensions = {
			height: typeof height === 'number' ? height : getContentHeight(this.domNode)
		};

		if (this.scrollableElementUpdateDisposable) {
			this.scrollableElementUpdateDisposable.dispose();
			this.scrollableElementUpdateDisposable = null;
			scrollDimensions.scrollHeight = this.scrollHeight;
		}

		this.scrollableElement.setScrollDimensions(scrollDimensions);

		if (typeof width !== 'undefined') {
			this.renderWidth = width;

			if (this.supportDynamicHeights) {
				this._rerender(this.scrollTop, this.renderHeight);
			}
		}

		if (this.horizontalScrolling) {
			this.scrollableElement.setScrollDimensions({
				width: typeof width === 'number' ? width : getContentWidth(this.domNode)
			});
		}
	}

	// Render

	protected render(previousRenderRange: IRange, renderTop: number, renderHeight: number, renderLeft: number | undefined, scrollWidth: number | undefined, updateItemsInDOM: boolean = false, onScroll: boolean = false): void {
		const renderRange = this.getRenderRange(renderTop, renderHeight);

		const rangesToInsert = Range.relativeComplement(renderRange, previousRenderRange).reverse();
		const rangesToRemove = Range.relativeComplement(previousRenderRange, renderRange);

		if (updateItemsInDOM) {
			const rangesToUpdate = Range.intersect(previousRenderRange, renderRange);

			for (let i = rangesToUpdate.start; i < rangesToUpdate.end; i++) {
				this.updateItemInDOM(this.items[i], i);
			}
		}

		this.cache.transact(() => {
			for (const range of rangesToRemove) {
				for (let i = range.start; i < range.end; i++) {
					this.removeItemFromDOM(i, onScroll);
				}
			}

			for (const range of rangesToInsert) {
				for (let i = range.end - 1; i >= range.start; i--) {
					this.insertItemInDOM(i);
				}
			}
		});

		if (renderLeft !== undefined) {
			this.rowsContainer.style.left = `-${renderLeft}px`;
		}

		this.rowsContainer.style.top = `-${renderTop}px`;

		if (this.horizontalScrolling && scrollWidth !== undefined) {
			this.rowsContainer.style.width = `${Math.max(scrollWidth, this.renderWidth)}px`;
		}

		this.lastRenderTop = renderTop;
		this.lastRenderHeight = renderHeight;
	}

	// DOM operations

	private insertItemInDOM(index: number, row?: IRow): void {
		const item = this.items[index];

		if (!item.row) {
			if (row) {
				item.row = row;
				item.stale = true;
			} else {
				const result = this.cache.alloc(item.templateId);
				item.row = result.row;
				item.stale ||= result.isReusingConnectedDomNode;
			}
		}

		const role = this.accessibilityProvider.getRole(item.element) || 'listitem';
		item.row.domNode.setAttribute('role', role);

		const checked = this.accessibilityProvider.isChecked(item.element);
		const toAriaState = (value: CheckBoxAccessibleState) => value === 'mixed' ? 'mixed' : String(!!value);

		if (typeof checked === 'boolean' || checked === 'mixed') {
			item.row.domNode.setAttribute('aria-checked', toAriaState(checked));
		} else if (checked) {
			const update = (value: CheckBoxAccessibleState) => item.row!.domNode.setAttribute('aria-checked', toAriaState(value));
			update(checked.value);
			item.checkedDisposable = checked.onDidChange(() => update(checked.value));
		}

		if (item.stale || !item.row.domNode.parentElement) {
			const referenceNode = this.items.at(index + 1)?.row?.domNode ?? null;
			if (item.row.domNode.parentElement !== this.rowsContainer || item.row.domNode.nextElementSibling !== referenceNode) {
				this.rowsContainer.insertBefore(item.row.domNode, referenceNode);
			}
			item.stale = false;
		}

		this.updateItemInDOM(item, index);

		const renderer = this.renderers.get(item.templateId);

		if (!renderer) {
			throw new Error(`No renderer found for template id ${item.templateId}`);
		}

		renderer?.renderElement(item.element, index, item.row.templateData, { height: item.size });

		const uri = this.dnd.getDragURI(item.element);
		item.dragStartDisposable.dispose();
		item.row.domNode.draggable = !!uri;

		if (uri) {
			item.dragStartDisposable = addDisposableListener(item.row.domNode, 'dragstart', event => this.onDragStart(item.element, uri, event));
		}

		if (this.horizontalScrolling) {
			this.measureItemWidth(item);
			this.eventuallyUpdateScrollWidth();
		}
	}

	private measureItemWidth(item: IItem<T>): void {
		if (!item.row || !item.row.domNode) {
			return;
		}

		item.row.domNode.style.width = 'fit-content';
		item.width = getContentWidth(item.row.domNode);
		const style = getWindow(item.row.domNode).getComputedStyle(item.row.domNode);

		if (style.paddingLeft) {
			item.width += parseFloat(style.paddingLeft);
		}

		if (style.paddingRight) {
			item.width += parseFloat(style.paddingRight);
		}

		item.row.domNode.style.width = '';
	}

	private updateItemInDOM(item: IItem<T>, index: number): void {
		item.row!.domNode.style.top = `${this.elementTop(index)}px`;

		if (this.setRowHeight) {
			item.row!.domNode.style.height = `${item.size}px`;
		}

		if (this.setRowLineHeight) {
			item.row!.domNode.style.lineHeight = `${item.size}px`;
		}

		item.row!.domNode.setAttribute('data-index', `${index}`);
		item.row!.domNode.setAttribute('data-last-element', index === this.length - 1 ? 'true' : 'false');
		item.row!.domNode.setAttribute('data-parity', index % 2 === 0 ? 'even' : 'odd');
		item.row!.domNode.setAttribute('aria-setsize', String(this.accessibilityProvider.getSetSize(item.element, index, this.length)));
		item.row!.domNode.setAttribute('aria-posinset', String(this.accessibilityProvider.getPosInSet(item.element, index)));
		item.row!.domNode.setAttribute('id', this.getElementDomId(index));

		item.row!.domNode.classList.toggle('drop-target', item.dropTarget);
	}

	private removeItemFromDOM(index: number, onScroll?: boolean): void {
		const item = this.items[index];
		item.dragStartDisposable.dispose();
		item.checkedDisposable.dispose();

		if (item.row) {
			const renderer = this.renderers.get(item.templateId);

			if (renderer && renderer.disposeElement) {
				renderer.disposeElement(item.element, index, item.row.templateData, { height: item.size, onScroll });
			}

			this.cache.release(item.row);
			item.row = null;
		}

		if (this.horizontalScrolling) {
			this.eventuallyUpdateScrollWidth();
		}
	}

	getScrollTop(): number {
		const scrollPosition = this.scrollableElement.getScrollPosition();
		return scrollPosition.scrollTop;
	}

	setScrollTop(scrollTop: number, reuseAnimation?: boolean): void {
		if (this.scrollableElementUpdateDisposable) {
			this.scrollableElementUpdateDisposable.dispose();
			this.scrollableElementUpdateDisposable = null;
			this.scrollableElement.setScrollDimensions({ scrollHeight: this.scrollHeight });
		}

		this.scrollableElement.setScrollPosition({ scrollTop, reuseAnimation });
	}

	getScrollLeft(): number {
		const scrollPosition = this.scrollableElement.getScrollPosition();
		return scrollPosition.scrollLeft;
	}

	setScrollLeft(scrollLeft: number): void {
		if (this.scrollableElementUpdateDisposable) {
			this.scrollableElementUpdateDisposable.dispose();
			this.scrollableElementUpdateDisposable = null;
			this.scrollableElement.setScrollDimensions({ scrollWidth: this.scrollWidth });
		}

		this.scrollableElement.setScrollPosition({ scrollLeft });
	}


	get scrollTop(): number {
		return this.getScrollTop();
	}

	set scrollTop(scrollTop: number) {
		this.setScrollTop(scrollTop);
	}

	get scrollHeight(): number {
		return this._scrollHeight + (this.horizontalScrolling ? 10 : 0) + this.paddingBottom;
	}

	// Events

	@memoize get onMouseClick(): Event<IListMouseEvent<T>> { return Event.map(this.disposables.add(new DomEmitter(this.domNode, 'click')).event, e => this.toMouseEvent(e), this.disposables); }
	@memoize get onMouseDblClick(): Event<IListMouseEvent<T>> { return Event.map(this.disposables.add(new DomEmitter(this.domNode, 'dblclick')).event, e => this.toMouseEvent(e), this.disposables); }
	@memoize get onMouseMiddleClick(): Event<IListMouseEvent<T>> { return Event.filter(Event.map(this.disposables.add(new DomEmitter(this.domNode, 'auxclick')).event, e => this.toMouseEvent(e as MouseEvent), this.disposables), e => e.browserEvent.button === 1, this.disposables); }
	@memoize get onMouseUp(): Event<IListMouseEvent<T>> { return Event.map(this.disposables.add(new DomEmitter(this.domNode, 'mouseup')).event, e => this.toMouseEvent(e), this.disposables); }
	@memoize get onMouseDown(): Event<IListMouseEvent<T>> { return Event.map(this.disposables.add(new DomEmitter(this.domNode, 'mousedown')).event, e => this.toMouseEvent(e), this.disposables); }
	@memoize get onMouseOver(): Event<IListMouseEvent<T>> { return Event.map(this.disposables.add(new DomEmitter(this.domNode, 'mouseover')).event, e => this.toMouseEvent(e), this.disposables); }
	@memoize get onMouseMove(): Event<IListMouseEvent<T>> { return Event.map(this.disposables.add(new DomEmitter(this.domNode, 'mousemove')).event, e => this.toMouseEvent(e), this.disposables); }
	@memoize get onMouseOut(): Event<IListMouseEvent<T>> { return Event.map(this.disposables.add(new DomEmitter(this.domNode, 'mouseout')).event, e => this.toMouseEvent(e), this.disposables); }
	@memoize get onContextMenu(): Event<IListMouseEvent<T> | IListGestureEvent<T>> { return Event.any<IListMouseEvent<any> | IListGestureEvent<any>>(Event.map(this.disposables.add(new DomEmitter(this.domNode, 'contextmenu')).event, e => this.toMouseEvent(e), this.disposables), Event.map(this.disposables.add(new DomEmitter(this.domNode, TouchEventType.Contextmenu)).event, e => this.toGestureEvent(e), this.disposables)); }
	@memoize get onTouchStart(): Event<IListTouchEvent<T>> { return Event.map(this.disposables.add(new DomEmitter(this.domNode, 'touchstart')).event, e => this.toTouchEvent(e), this.disposables); }
	@memoize get onTap(): Event<IListGestureEvent<T>> { return Event.map(this.disposables.add(new DomEmitter(this.rowsContainer, TouchEventType.Tap)).event, e => this.toGestureEvent(e), this.disposables); }

	private toMouseEvent(browserEvent: MouseEvent): IListMouseEvent<T> {
		const index = this.getItemIndexFromEventTarget(browserEvent.target || null);
		const item = typeof index === 'undefined' ? undefined : this.items[index];
		const element = item && item.element;
		return { browserEvent, index, element };
	}

	private toTouchEvent(browserEvent: TouchEvent): IListTouchEvent<T> {
		const index = this.getItemIndexFromEventTarget(browserEvent.target || null);
		const item = typeof index === 'undefined' ? undefined : this.items[index];
		const element = item && item.element;
		return { browserEvent, index, element };
	}

	private toGestureEvent(browserEvent: GestureEvent): IListGestureEvent<T> {
		const index = this.getItemIndexFromEventTarget(browserEvent.initialTarget || null);
		const item = typeof index === 'undefined' ? undefined : this.items[index];
		const element = item && item.element;
		return { browserEvent, index, element };
	}

	private toDragEvent(browserEvent: DragEvent): IListDragEvent<T> {
		const index = this.getItemIndexFromEventTarget(browserEvent.target || null);
		const item = typeof index === 'undefined' ? undefined : this.items[index];
		const element = item && item.element;
		const sector = this.getTargetSector(browserEvent, index);
		return { browserEvent, index, element, sector };
	}

	private onScroll(e: ScrollEvent): void {
		try {
			const previousRenderRange = this.getRenderRange(this.lastRenderTop, this.lastRenderHeight);
			this.render(previousRenderRange, e.scrollTop, e.height, e.scrollLeft, e.scrollWidth, undefined, true);

			if (this.supportDynamicHeights) {
				this._rerender(e.scrollTop, e.height, e.inSmoothScrolling);
			}
		} catch (err) {
			console.error('Got bad scroll event:', e);
			throw err;
		}
	}

	private onTouchChange(event: GestureEvent): void {
		event.preventDefault();
		event.stopPropagation();

		this.scrollTop -= event.translationY;
	}

	// DND

	private onDragStart(element: T, uri: string, event: DragEvent): void {
		if (!event.dataTransfer) {
			return;
		}

		const elements = this.dnd.getDragElements(element);

		event.dataTransfer.effectAllowed = 'copyMove';
		event.dataTransfer.setData(DataTransfers.TEXT, uri);

		let label: string | undefined;
		if (this.dnd.getDragLabel) {
			label = this.dnd.getDragLabel(elements, event);
		}
		if (typeof label === 'undefined') {
			label = String(elements.length);
		}

		applyDragImage(event, this.domNode, label, [this.domId /* add domId to get list specific styling */]);

		this.domNode.classList.add('dragging');
		this.currentDragData = new ElementsDragAndDropData(elements);
		StaticDND.CurrentDragAndDropData = new ExternalElementsDragAndDropData(elements);

		this.dnd.onDragStart?.(this.currentDragData, event);
	}

	private onPotentialSelectionStart(e: MouseEvent) {
		this.currentSelectionDisposable.dispose();
		const doc = getDocument(this.domNode);

		// Set up both the 'movement store' for watching the mouse, and the
		// 'selection store' which lasts as long as there's a selection, even
		// after the usr has stopped modifying it.
		const selectionStore = this.currentSelectionDisposable = new DisposableStore();
		const movementStore = selectionStore.add(new DisposableStore());

		// The selection events we get from the DOM are fairly limited and we lack a 'selection end' event.
		// Selection events also don't tell us where the input doing the selection is. So, make a poor
		// assumption that a user is using the mouse, and base our events on that.
		movementStore.add(addDisposableListener(this.domNode, 'selectstart', () => {
			movementStore.add(addDisposableListener(doc, 'mousemove', e => {
				if (doc.getSelection()?.isCollapsed === false) {
					this.setupDragAndDropScrollTopAnimation(e);
				}
			}));

			// The selection is cleared either on mouseup if there's no selection, or on next mousedown
			// when `this.currentSelectionDisposable` is reset.
			selectionStore.add(toDisposable(() => {
				const previousRenderRange = this.getRenderRange(this.lastRenderTop, this.lastRenderHeight);
				this.currentSelectionBounds = undefined;
				this.render(previousRenderRange, this.lastRenderTop, this.lastRenderHeight, undefined, undefined);
			}));
			selectionStore.add(addDisposableListener(doc, 'selectionchange', () => {
				const selection = doc.getSelection();
				// if the selection changed _after_ mouseup, it's from clearing the list or similar, so teardown
				if (!selection || selection.isCollapsed) {
					if (movementStore.isDisposed) {
						selectionStore.dispose();
					}
					return;
				}

				let start = this.getIndexOfListElement(selection.anchorNode as HTMLElement);
				let end = this.getIndexOfListElement(selection.focusNode as HTMLElement);
				if (start !== undefined && end !== undefined) {
					if (end < start) {
						[start, end] = [end, start];
					}
					this.currentSelectionBounds = { start, end };
				}
			}));
		}));

		movementStore.add(addDisposableListener(doc, 'mouseup', () => {
			movementStore.dispose();
			this.teardownDragAndDropScrollTopAnimation();

			if (doc.getSelection()?.isCollapsed !== false) {
				selectionStore.dispose();
			}
		}));
	}

	private getIndexOfListElement(element: HTMLElement | null): number | undefined {
		if (!element || !this.domNode.contains(element)) {
			return undefined;
		}

		while (element && element !== this.domNode) {
			if (element.dataset?.index) {
				return Number(element.dataset.index);
			}

			element = element.parentElement;
		}

		return undefined;
	}

	private onDragOver(event: IListDragEvent<T>): boolean {
		event.browserEvent.preventDefault(); // needed so that the drop event fires (https://stackoverflow.com/questions/21339924/drop-event-not-firing-in-chrome)

		this.onDragLeaveTimeout.dispose();

		if (StaticDND.CurrentDragAndDropData && StaticDND.CurrentDragAndDropData.getData() === 'vscode-ui') {
			return false;
		}

		this.setupDragAndDropScrollTopAnimation(event.browserEvent);

		if (!event.browserEvent.dataTransfer) {
			return false;
		}

		// Drag over from outside
		if (!this.currentDragData) {
			if (StaticDND.CurrentDragAndDropData) {
				// Drag over from another list
				this.currentDragData = StaticDND.CurrentDragAndDropData;

			} else {
				// Drag over from the desktop
				if (!event.browserEvent.dataTransfer.types) {
					return false;
				}

				this.currentDragData = new NativeDragAndDropData();
			}
		}

		const result = this.dnd.onDragOver(this.currentDragData, event.element, event.index, event.sector, event.browserEvent);
		this.canDrop = typeof result === 'boolean' ? result : result.accept;

		if (!this.canDrop) {
			this.currentDragFeedback = undefined;
			this.currentDragFeedbackDisposable.dispose();
			return false;
		}

		event.browserEvent.dataTransfer.dropEffect = (typeof result !== 'boolean' && result.effect?.type === ListDragOverEffectType.Copy) ? 'copy' : 'move';

		let feedback: number[];

		if (typeof result !== 'boolean' && result.feedback) {
			feedback = result.feedback;
		} else {
			if (typeof event.index === 'undefined') {
				feedback = [-1];
			} else {
				feedback = [event.index];
			}
		}

		// sanitize feedback list
		feedback = distinct(feedback).filter(i => i >= -1 && i < this.length).sort((a, b) => a - b);
		feedback = feedback[0] === -1 ? [-1] : feedback;

		let dragOverEffectPosition = typeof result !== 'boolean' && result.effect && result.effect.position ? result.effect.position : ListDragOverEffectPosition.Over;

		if (equalsDragFeedback(this.currentDragFeedback, feedback) && this.currentDragFeedbackPosition === dragOverEffectPosition) {
			return true;
		}

		this.currentDragFeedback = feedback;
		this.currentDragFeedbackPosition = dragOverEffectPosition;
		this.currentDragFeedbackDisposable.dispose();

		if (feedback[0] === -1) { // entire list feedback
			this.domNode.classList.add(dragOverEffectPosition);
			this.rowsContainer.classList.add(dragOverEffectPosition);
			this.currentDragFeedbackDisposable = toDisposable(() => {
				this.domNode.classList.remove(dragOverEffectPosition);
				this.rowsContainer.classList.remove(dragOverEffectPosition);
			});
		} else {

			if (feedback.length > 1 && dragOverEffectPosition !== ListDragOverEffectPosition.Over) {
				throw new Error('Can\'t use multiple feedbacks with position different than \'over\'');
			}

			// Make sure there is no flicker when moving between two items
			// Always use the before feedback if possible
			if (dragOverEffectPosition === ListDragOverEffectPosition.After) {
				if (feedback[0] < this.length - 1) {
					feedback[0] += 1;
					dragOverEffectPosition = ListDragOverEffectPosition.Before;
				}
			}

			for (const index of feedback) {
				const item = this.items[index];
				item.dropTarget = true;

				item.row?.domNode.classList.add(dragOverEffectPosition);
			}

			this.currentDragFeedbackDisposable = toDisposable(() => {
				for (const index of feedback) {
					const item = this.items[index];
					item.dropTarget = false;

					item.row?.domNode.classList.remove(dragOverEffectPosition);
				}
			});
		}

		return true;
	}

	private onDragLeave(event: IListDragEvent<T>): void {
		this.onDragLeaveTimeout.dispose();
		this.onDragLeaveTimeout = disposableTimeout(() => this.clearDragOverFeedback(), 100, this.disposables);
		if (this.currentDragData) {
			this.dnd.onDragLeave?.(this.currentDragData, event.element, event.index, event.browserEvent);
		}
	}

	private onDrop(event: IListDragEvent<T>): void {
		if (!this.canDrop) {
			return;
		}

		const dragData = this.currentDragData;
		this.teardownDragAndDropScrollTopAnimation();
		this.clearDragOverFeedback();
		this.domNode.classList.remove('dragging');
		this.currentDragData = undefined;
		StaticDND.CurrentDragAndDropData = undefined;

		if (!dragData || !event.browserEvent.dataTransfer) {
			return;
		}

		event.browserEvent.preventDefault();
		dragData.update(event.browserEvent.dataTransfer);
		this.dnd.drop(dragData, event.element, event.index, event.sector, event.browserEvent);
	}

	private onDragEnd(event: DragEvent): void {
		this.canDrop = false;
		this.teardownDragAndDropScrollTopAnimation();
		this.clearDragOverFeedback();
		this.domNode.classList.remove('dragging');
		this.currentDragData = undefined;
		StaticDND.CurrentDragAndDropData = undefined;

		this.dnd.onDragEnd?.(event);
	}

	private clearDragOverFeedback(): void {
		this.currentDragFeedback = undefined;
		this.currentDragFeedbackPosition = undefined;
		this.currentDragFeedbackDisposable.dispose();
		this.currentDragFeedbackDisposable = Disposable.None;
	}

	// DND scroll top animation

	private setupDragAndDropScrollTopAnimation(event: DragEvent | MouseEvent): void {
		if (!this.dragOverAnimationDisposable) {
			const viewTop = getTopLeftOffset(this.domNode).top;
			this.dragOverAnimationDisposable = animate(getWindow(this.domNode), this.animateDragAndDropScrollTop.bind(this, viewTop));
		}

		this.dragOverAnimationStopDisposable.dispose();
		this.dragOverAnimationStopDisposable = disposableTimeout(() => {
			if (this.dragOverAnimationDisposable) {
				this.dragOverAnimationDisposable.dispose();
				this.dragOverAnimationDisposable = undefined;
			}
		}, 1000, this.disposables);

		this.dragOverMouseY = event.pageY;
	}

	private animateDragAndDropScrollTop(viewTop: number): void {
		if (this.dragOverMouseY === undefined) {
			return;
		}

		const diff = this.dragOverMouseY - viewTop;
		const upperLimit = this.renderHeight - 35;

		if (diff < 35) {
			this.scrollTop += Math.max(-14, Math.floor(0.3 * (diff - 35)));
		} else if (diff > upperLimit) {
			this.scrollTop += Math.min(14, Math.floor(0.3 * (diff - upperLimit)));
		}
	}

	private teardownDragAndDropScrollTopAnimation(): void {
		this.dragOverAnimationStopDisposable.dispose();

		if (this.dragOverAnimationDisposable) {
			this.dragOverAnimationDisposable.dispose();
			this.dragOverAnimationDisposable = undefined;
		}
	}

	// Util

	private getTargetSector(browserEvent: DragEvent, targetIndex: number | undefined): ListViewTargetSector | undefined {
		if (targetIndex === undefined) {
			return undefined;
		}

		const relativePosition = browserEvent.offsetY / this.items[targetIndex].size;
		const sector = Math.floor(relativePosition / 0.25);
		return clamp(sector, 0, 3);
	}

	private getItemIndexFromEventTarget(target: EventTarget | null): number | undefined {
		const scrollableElement = this.scrollableElement.getDomNode();
		let element: HTMLElement | SVGElement | null = target as (HTMLElement | SVGElement | null);

		while ((isHTMLElement(element) || isSVGElement(element)) && element !== this.rowsContainer && scrollableElement.contains(element)) {
			const rawIndex = element.getAttribute('data-index');

			if (rawIndex) {
				const index = Number(rawIndex);

				if (!isNaN(index)) {
					return index;
				}
			}

			element = element.parentElement;
		}

		return undefined;
	}

	private getVisibleRange(renderTop: number, renderHeight: number): IRange {
		return {
			start: this.rangeMap.indexAt(renderTop),
			end: this.rangeMap.indexAfter(renderTop + renderHeight - 1)
		};
	}

	protected getRenderRange(renderTop: number, renderHeight: number): IRange {
		const range = this.getVisibleRange(renderTop, renderHeight);
		if (this.currentSelectionBounds) {
			const max = this.rangeMap.count;
			range.start = Math.min(range.start, this.currentSelectionBounds.start, max);
			range.end = Math.min(Math.max(range.end, this.currentSelectionBounds.end + 1), max);
		}

		return range;
	}

	/**
	 * Given a stable rendered state, checks every rendered element whether it needs
	 * to be probed for dynamic height. Adjusts scroll height and top if necessary.
	 */
	protected _rerender(renderTop: number, renderHeight: number, inSmoothScrolling?: boolean): void {
		const previousRenderRange = this.getRenderRange(renderTop, renderHeight);

		// Let's remember the second element's position, this helps in scrolling up
		// and preserving a linear upwards scroll movement
		let anchorElementIndex: number | undefined;
		let anchorElementTopDelta: number | undefined;

		if (renderTop === this.elementTop(previousRenderRange.start)) {
			anchorElementIndex = previousRenderRange.start;
			anchorElementTopDelta = 0;
		} else if (previousRenderRange.end - previousRenderRange.start > 1) {
			anchorElementIndex = previousRenderRange.start + 1;
			anchorElementTopDelta = this.elementTop(anchorElementIndex) - renderTop;
		}

		let heightDiff = 0;

		while (true) {
			const renderRange = this.getRenderRange(renderTop, renderHeight);

			let didChange = false;

			for (let i = renderRange.start; i < renderRange.end; i++) {
				const diff = this.probeDynamicHeight(i);

				if (diff !== 0) {
					this.rangeMap.splice(i, 1, [this.items[i]]);
				}

				heightDiff += diff;
				didChange = didChange || diff !== 0;
			}

			if (!didChange) {
				if (heightDiff !== 0) {
					this.eventuallyUpdateScrollDimensions();
				}

				const unrenderRanges = Range.relativeComplement(previousRenderRange, renderRange);

				for (const range of unrenderRanges) {
					for (let i = range.start; i < range.end; i++) {
						if (this.items[i].row) {
							this.removeItemFromDOM(i);
						}
					}
				}

				const renderRanges = Range.relativeComplement(renderRange, previousRenderRange).reverse();

				for (const range of renderRanges) {
					for (let i = range.end - 1; i >= range.start; i--) {
						this.insertItemInDOM(i);
					}
				}

				for (let i = renderRange.start; i < renderRange.end; i++) {
					if (this.items[i].row) {
						this.updateItemInDOM(this.items[i], i);
					}
				}

				if (typeof anchorElementIndex === 'number') {
					// To compute a destination scroll top, we need to take into account the current smooth scrolling
					// animation, and then reuse it with a new target (to avoid prolonging the scroll)
					// See https://github.com/microsoft/vscode/issues/104144
					// See https://github.com/microsoft/vscode/pull/104284
					// See https://github.com/microsoft/vscode/issues/107704
					const deltaScrollTop = this.scrollable.getFutureScrollPosition().scrollTop - renderTop;
					const newScrollTop = this.elementTop(anchorElementIndex) - anchorElementTopDelta! + deltaScrollTop;
					this.setScrollTop(newScrollTop, inSmoothScrolling);
				}

				this._onDidChangeContentHeight.fire(this.contentHeight);
				return;
			}
		}
	}

	private probeDynamicHeight(index: number): number {
		const item = this.items[index];
		const diff = this.probeDynamicHeightForItem(item, index);
		if (diff > 0) {
			this.virtualDelegate.setDynamicHeight?.(item.element, item.size);
		}

		return diff;
	}

	private probeDynamicHeightForItem(item: IItem<T>, index: number): number {
		if (!!this.virtualDelegate.getDynamicHeight) {
			const newSize = this.virtualDelegate.getDynamicHeight(item.element);
			if (newSize !== null) {
				const size = item.size;
				item.size = newSize;
				item.lastDynamicHeightWidth = this.renderWidth;
				return newSize - size;
			}
		}

		if (!item.hasDynamicHeight || item.lastDynamicHeightWidth === this.renderWidth) {
			return 0;
		}

		if (!!this.virtualDelegate.hasDynamicHeight && !this.virtualDelegate.hasDynamicHeight(item.element)) {
			return 0;
		}

		const size = item.size;

		if (item.row) {
			item.row.domNode.style.height = '';
			item.size = item.row.domNode.offsetHeight;
			if (item.size === 0) {
				if (!isAncestor(item.row.domNode, getWindow(item.row.domNode).document.body)) {
					console.warn('Measuring item node that is not in DOM! Add ListView to the DOM before measuring row height!', new Error().stack);
				} else {
					console.warn('Measured item node at 0px- ensure that ListView is not display:none before measuring row height!', new Error().stack);
				}
			}
			item.lastDynamicHeightWidth = this.renderWidth;
			return item.size - size;
		}

		const { row } = this.cache.alloc(item.templateId);
		row.domNode.style.height = '';
		this.rowsContainer.appendChild(row.domNode);

		const renderer = this.renderers.get(item.templateId);

		if (!renderer) {
			throw new BugIndicatingError('Missing renderer for templateId: ' + item.templateId);
		}

		renderer.renderElement(item.element, index, row.templateData);
		item.size = row.domNode.offsetHeight;
		renderer.disposeElement?.(item.element, index, row.templateData);

		item.lastDynamicHeightWidth = this.renderWidth;
		row.domNode.remove();
		this.cache.release(row);

		return item.size - size;
	}

	getElementDomId(index: number): string {
		return `${this.domId}_${index}`;
	}

	// Dispose

	dispose() {
		for (const item of this.items) {
			item.dragStartDisposable.dispose();
			item.checkedDisposable.dispose();

			if (item.row) {
				const renderer = this.renderers.get(item.row.templateId);
				if (renderer) {
					renderer.disposeElement?.(item.element, -1, item.row.templateData, undefined);
					renderer.disposeTemplate(item.row.templateData);
				}
			}
		}

		this.items = [];

		this.domNode?.remove();

		this.dragOverAnimationDisposable?.dispose();
		this.disposables.dispose();
	}
}