set aria-selected on focused and selected list items

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

@@ -180,19 +180,19 @@ class Trait<T> implements ISpliceable<boolean>, IDisposable {
 	}
 }
 
-class SelectionTrait<T> extends Trait<T> {
+class FocusTrait<T> extends Trait<T> {
 
-	constructor() {
-		super('selected');
+	constructor(private isAriaSelected: (index: number) => boolean) {
+		super('focused');
 	}
 
 	renderIndex(index: number, container: HTMLElement): void {
 		super.renderIndex(index, container);
 
-		if (this.contains(index)) {
+		if (this.contains(index) || this.isAriaSelected(index)) {
 			container.setAttribute('aria-selected', 'true');
 		} else {
-			container.removeAttribute('aria-selected');
+			container.setAttribute('aria-selected', 'false');
 		}
 	}
 }
@@ -1198,8 +1198,8 @@ export class List<T> implements ISpliceable<T>, IDisposable {
 		renderers: IListRenderer<any /* TODO@joao */, any>[],
 		private _options: IListOptions<T> = DefaultOptions
 	) {
-		this.focus = new Trait('focused');
-		this.selection = new SelectionTrait();
+		this.selection = new Trait('selected');
+		this.focus = new FocusTrait(this.selection.contains);
 
 		mixin(_options, defaultStyles, false);
 

src/vs/base/parts/tree/browser/treeView.ts

@@ -219,12 +219,9 @@ export class ViewItem implements IViewItem {
 		if (this.model.hasTrait('focused')) {
 			const base64Id = strings.safeBtoa(this.model.id);
 			this.element.setAttribute('id', base64Id);
-		} else {
-			this.element.removeAttribute('id');
-		}
-		if (this.model.hasTrait('selected')) {
 			this.element.setAttribute('aria-selected', 'true');
 		} else {
+			this.element.removeAttribute('id');
 			this.element.setAttribute('aria-selected', 'false');
 		}
 		if (this.model.hasChildren()) {