Fix hover tabbing behaviour (microsoft#166657)

Ref microsoft#159088

* Focus back to last focused element when tabbing out of hover
* Add focus trap (tab loop) while focused on the hover

Author: rzhao271

src/vs/workbench/services/hover/browser/hoverService.ts

@@ -23,6 +23,8 @@ export class HoverService implements IHoverService {
 	private _currentHoverOptions: IHoverOptions | undefined;
 	private _currentHover: HoverWidget | undefined;
 
+	private _lastFocusedElementBeforeOpen: HTMLElement | undefined;
+
 	constructor(
 		@IInstantiationService private readonly _instantiationService: IInstantiationService,
 		@IContextViewService private readonly _contextViewService: IContextViewService,
@@ -37,10 +39,16 @@ export class HoverService implements IHoverService {
 			return undefined;
 		}
 		this._currentHoverOptions = options;
+		if (document.activeElement) {
+			this._lastFocusedElementBeforeOpen = document.activeElement as HTMLElement;
+		}
 
 		const hoverDisposables = new DisposableStore();
 		const hover = this._instantiationService.createInstance(HoverWidget, options);
 		hover.onDispose(() => {
+			// Required to handle cases such as closing the hover with the escape key
+			this._lastFocusedElementBeforeOpen?.focus();
+
 			// Only clear the current options if it's the current hover, the current options help
 			// reduce flickering when the same hover is shown multiple times
 			if (this._currentHoverOptions === options) {
@@ -64,11 +72,11 @@ export class HoverService implements IHoverService {
 			hoverDisposables.add(addDisposableListener(document, EventType.KEY_DOWN, e => this._keyDown(e, hover)));
 			hoverDisposables.add(addDisposableListener(focusedElement, EventType.KEY_UP, e => this._keyUp(e, hover)));
 			hoverDisposables.add(addDisposableListener(document, EventType.KEY_UP, e => this._keyUp(e, hover)));
-		}
-		if (options.hideOnKeyDown) {
-			const focusedElement = document.activeElement;
-			if (focusedElement) {
-				hoverDisposables.add(addDisposableListener(focusedElement, EventType.KEY_DOWN, () => this.hideHover()));
+			if (options.hideOnKeyDown) {
+				hoverDisposables.add(addDisposableListener(focusedElement, EventType.KEY_DOWN, () => {
+					this.hideHover();
+					this._lastFocusedElementBeforeOpen?.focus();
+				}));
 			}
 		}
 
@@ -110,7 +118,10 @@ export class HoverService implements IHoverService {
 		if (keybinding.getSingleModifierDispatchParts().some(value => !!value) || this._keybindingService.softDispatch(event, event.target)) {
 			return;
 		}
-		this.hideHover();
+		if (e.key !== 'Tab') {
+			this.hideHover();
+			this._lastFocusedElementBeforeOpen?.focus();
+		}
 	}
 
 	private _keyUp(e: KeyboardEvent, hover: HoverWidget) {
@@ -119,6 +130,7 @@ export class HoverService implements IHoverService {
 			// Hide if alt is released while the mouse os not over hover/target
 			if (!hover.isMouseIn) {
 				this.hideHover();
+				this._lastFocusedElementBeforeOpen?.focus();
 			}
 		}
 	}

src/vs/workbench/services/hover/browser/hoverWidget.ts

@@ -52,6 +52,7 @@ export class HoverWidget extends Widget {
 	private _x: number = 0;
 	private _y: number = 0;
 	private _isLocked: boolean = false;
+	private _addedFocusTrap: boolean = false;
 
 	get isDisposed(): boolean { return this._isDisposed; }
 	get isMouseIn(): boolean { return this._lockMouseTracker.isMouseIn; }
@@ -222,10 +223,55 @@ export class HoverWidget extends Widget {
 		}
 	}
 
+	private addFocusTrap() {
+		if (this._addedFocusTrap) {
+			return;
+		}
+		this._addedFocusTrap = true;
+
+		// Add a hover tab loop if the hover has at least one element with a valid tabIndex
+		const firstContainerFocusElement = this._hover.containerDomNode;
+		const lastContainerFocusElement = this.findLastFocusableChild(this._hover.contentsDomNode);
+		if (lastContainerFocusElement) {
+			const beforeContainerFocusElement = dom.prepend(this._hoverContainer, $('div'));
+			const afterContainerFocusElement = dom.append(this._hoverContainer, $('div'));
+			beforeContainerFocusElement.tabIndex = 0;
+			afterContainerFocusElement.tabIndex = 0;
+			this._register(dom.addDisposableListener(afterContainerFocusElement, 'focus', (e) => {
+				firstContainerFocusElement.focus();
+				e.preventDefault();
+			}));
+			this._register(dom.addDisposableListener(beforeContainerFocusElement, 'focus', (e) => {
+				lastContainerFocusElement.focus();
+				e.preventDefault();
+			}));
+		}
+	}
+
+	private findLastFocusableChild(root: Node): HTMLElement | undefined {
+		if (root.hasChildNodes()) {
+			for (let i = 0; i < root.childNodes.length; i++) {
+				const node = root.childNodes.item(root.childNodes.length - i - 1);
+				if (node.nodeType === node.ELEMENT_NODE) {
+					const parsedNode = node as HTMLElement;
+					if (typeof parsedNode.tabIndex === 'number' && parsedNode.tabIndex >= 0) {
+						return parsedNode;
+					}
+				}
+				const recursivelyFoundElement = this.findLastFocusableChild(node);
+				if (recursivelyFoundElement) {
+					return recursivelyFoundElement;
+				}
+			}
+		}
+		return undefined;
+	}
+
 	public render(container: HTMLElement): void {
 		container.appendChild(this._hoverContainer);
 
 		this.layout();
+		this.addFocusTrap();
 	}
 
 	public layout() {