From 83c336d7d606a8d2c6f50c403a7fecc770e20cbe Mon Sep 17 00:00:00 2001
From: Henning Dieterichs <hdieterichs@microsoft.com>
Date: Fri, 20 Dec 2024 20:01:59 +0100
Subject: [PATCH] Log when a derived gets cleared (#236739)

---
 src/vs/base/common/observableInternal/derived.ts |  1 +
 src/vs/base/common/observableInternal/logging.ts | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/src/vs/base/common/observableInternal/derived.ts b/src/vs/base/common/observableInternal/derived.ts
index 5421b023df9..54a1e99296d 100644
--- a/src/vs/base/common/observableInternal/derived.ts
+++ b/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);
 		}
diff --git a/src/vs/base/common/observableInternal/logging.ts b/src/vs/base/common/observableInternal/logging.ts
index 8dc526a45be..f0bc82170d8 100644
--- a/src/vs/base/common/observableInternal/logging.ts
+++ b/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; }