Fire only once per item (fixes #46669 and #46671)

src/vs/base/common/event.ts

@@ -365,6 +365,7 @@ export interface IChainableEvent<T> {
 	map<O>(fn: (i: T) => O): IChainableEvent<O>;
 	forEach(fn: (i: T) => void): IChainableEvent<T>;
 	filter(fn: (e: T) => boolean): IChainableEvent<T>;
+	latch(): IChainableEvent<T>;
 	on(listener: (e: T) => any, thisArgs?: any, disposables?: IDisposable[]): IDisposable;
 }
 
@@ -398,6 +399,10 @@ class ChainableEvent<T> implements IChainableEvent<T> {
 		return new ChainableEvent(filterEvent(this._event, fn));
 	}
 
+	latch(): IChainableEvent<T> {
+		return new ChainableEvent(latch(this._event));
+	}
+
 	on(listener: (e: T) => any, thisArgs: any, disposables: IDisposable[]) {
 		return this._event(listener, thisArgs, disposables);
 	}

src/vs/workbench/browser/parts/quickinput/quickInput.ts

@@ -29,6 +29,7 @@ import { CountBadge } from 'vs/base/browser/ui/countBadge/countBadge';
 import { attachBadgeStyler, attachProgressBarStyler } from 'vs/platform/theme/common/styler';
 import { IEnvironmentService } from 'vs/platform/environment/common/environment';
 import { ProgressBar } from 'vs/base/browser/ui/progressbar/progressbar';
+import { chain } from 'vs/base/common/event';
 
 const $ = dom.$;
 
@@ -127,11 +128,13 @@ export class QuickInputService extends Component implements IQuickInputService {
 				this.inputBox.setFocus();
 			}, 0);
 		}));
-		this.toUnbind.push(this.checkboxList.onFocusChange(e => {
-			if (this.progress && e.length) {
-				this.progress(e[0]);
-			}
-		}));
+		this.toUnbind.push(
+			chain(this.checkboxList.onFocusChange)
+				.map(e => e[0])
+				.filter(e => !!e)
+				.latch()
+				.on(e => this.progress && this.progress(e))
+		);
 
 		this.toUnbind.push(dom.addDisposableListener(this.container, 'focusout', (e: FocusEvent) => {
 			for (let element = <Element>e.relatedTarget; element; element = element.parentElement) {

src/vs/workbench/browser/parts/quickinput/quickInputCheckboxList.ts

@@ -21,6 +21,7 @@ import { KeyCode } from 'vs/base/common/keyCodes';
 import { StandardKeyboardEvent } from 'vs/base/browser/keyboardEvent';
 import { IconLabel, IIconLabelValueOptions } from 'vs/base/browser/ui/iconLabel/iconLabel';
 import { HighlightedLabel } from 'vs/base/browser/ui/highlightedlabel/highlightedLabel';
+import { memoize } from 'vs/base/common/decorators';
 
 const $ = dom.$;
 
@@ -181,6 +182,7 @@ export class QuickInputCheckboxList {
 		}));
 	}
 
+	@memoize
 	get onFocusChange() {
 		return mapEvent(this.list.onFocusChange, e => e.elements.map(e => e.item));
 	}