Add log on new FeatureClassLoader as it may help leak investigations (#1558)

Author: nedtwigg

lib/src/main/java/com/diffplug/spotless/SpotlessCache.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 DiffPlug
+ * Copyright 2016-2023 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,13 +27,18 @@
 
 import javax.annotation.Nullable;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 
 /**
  * Spotless' global cache. {@link SpotlessCache#clear()} should be called
  * when Spotless is no longer in use to release any resources it has grabbed.
  */
 public final class SpotlessCache {
+	private static final Logger LOGGER = LoggerFactory.getLogger(SpotlessCache.class);
+
 	/** Allows comparing keys based on their serialization. */
 	static final class SerializedKey {
 		final byte[] serialized;
@@ -68,7 +73,10 @@ synchronized ClassLoader classloader(JarState state) {
 	synchronized ClassLoader classloader(Serializable key, JarState state) {
 		SerializedKey serializedKey = new SerializedKey(key);
 		return cache
-				.computeIfAbsent(serializedKey, k -> new FeatureClassLoader(state.jarUrls(), this.getClass().getClassLoader()));
+				.computeIfAbsent(serializedKey, k -> {
+					LOGGER.debug("Allocating an additional FeatureClassLoader for key={} Cache.size was {}", key, cache.size());
+					return new FeatureClassLoader(state.jarUrls(), this.getClass().getClassLoader());
+				});
 	}
 
 	static SpotlessCache instance() {