Log when a derived gets cleared (microsoft#236739)

Author: hediet

src/vs/base/common/observableInternal/derived.ts

@@ -220,6 +220,7 @@ export class Derived<T, TChangeSummary = any> extends BaseObservable<T, void> im
 		 */
 		this.state = DerivedState.initial;
 		this.value = undefined;
+		getLogger()?.handleDerivedCleared(this);
 		for (const d of this.dependencies) {
 			d.removeObserver(this);
 		}

src/vs/base/common/observableInternal/logging.ts

@@ -48,6 +48,7 @@ export interface IObservableLogger {
 
 	handleDerivedCreated(observable: Derived<any>): void;
 	handleDerivedRecomputed(observable: Derived<any>, info: IChangeInformation): void;
+	handleDerivedCleared(observable: Derived<any>): void;
 
 	handleBeginTransaction(transaction: TransactionImpl): void;
 	handleEndTransaction(): void;
@@ -170,6 +171,15 @@ export class ConsoleObservableLogger implements IObservableLogger {
 		changedObservables.clear();
 	}
 
+	handleDerivedCleared(derived: Derived<unknown>): void {
+		if (!this._isIncluded(derived)) { return; }
+
+		console.log(...this.textToConsoleArgs([
+			formatKind('derived cleared'),
+			styled(derived.debugName, { color: 'BlueViolet' }),
+		]));
+	}
+
 	handleFromEventObservableTriggered(observable: FromEventObservable<any, any>, info: IChangeInformation): void {
 		if (!this._isIncluded(observable)) { return; }