Fix caching memory leak in lazy FormatterSteps.

Author: nedtwigg

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2020 DiffPlug
+ * Copyright 2016-2022 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -39,7 +39,7 @@ abstract class FormatterStepImpl<State extends Serializable> extends Strict<Stat
 	final transient String name;
 
 	/** Transient because only the state matters. */
-	final transient ThrowingEx.Supplier<State> stateSupplier;
+	transient ThrowingEx.Supplier<State> stateSupplier;
 
 	FormatterStepImpl(String name, ThrowingEx.Supplier<State> stateSupplier) {
 		this.name = Objects.requireNonNull(name);
@@ -53,7 +53,11 @@ public String getName() {
 
 	@Override
 	protected State calculateState() throws Exception {
-		return stateSupplier.get();
+		// LazyForwardingEquality guarantees that this will only be called once, and keeping toFormat
+		// causes a memory leak, see https://github.com/diffplug/spotless/issues/1194
+		State state = stateSupplier.get();
+		stateSupplier = null;
+		return state;
 	}
 
 	static final class Standard<State extends Serializable> extends FormatterStepImpl<State> {