Make the FormatterStep arguments a little bit more forgiving.

Author: nedtwigg

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2024 DiffPlug
+ * Copyright 2016-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -106,7 +106,7 @@ static <RoundtripState extends Serializable, EqualityState extends Serializable>
 			String name,
 			ThrowingEx.Supplier<RoundtripState> roundtripInit,
 			SerializedFunction<RoundtripState, EqualityState> equalityFunc,
-			SerializedFunction<EqualityState, FormatterFunc> formatterFunc) {
+			SerializedFunction<EqualityState, ? extends FormatterFunc> formatterFunc) {
 		return new FormatterStepSerializationRoundtrip<>(name, roundtripInit, equalityFunc, formatterFunc);
 	}
 
@@ -128,7 +128,7 @@ static <RoundtripState extends Serializable, EqualityState extends Serializable>
 			String name,
 			RoundtripState roundTrip,
 			SerializedFunction<RoundtripState, EqualityState> equalityFunc,
-			SerializedFunction<EqualityState, FormatterFunc> formatterFunc) {
+			SerializedFunction<EqualityState, ? extends FormatterFunc> formatterFunc) {
 		return createLazy(name, () -> roundTrip, equalityFunc, formatterFunc);
 	}
 

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2023-2024 DiffPlug
+ * Copyright 2023-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,9 +30,9 @@ final class FormatterStepSerializationRoundtrip<RoundtripState extends Serializa
 	private @Nullable RoundtripState roundtripStateInternal;
 	private @Nullable EqualityState equalityStateInternal;
 	private final SerializedFunction<RoundtripState, EqualityState> equalityStateExtractor;
-	private final SerializedFunction<EqualityState, FormatterFunc> equalityStateToFormatter;
+	private final SerializedFunction<EqualityState, ? extends FormatterFunc> equalityStateToFormatter;
 
-	FormatterStepSerializationRoundtrip(String name, ThrowingEx.Supplier<RoundtripState> initializer, SerializedFunction<RoundtripState, EqualityState> equalityStateExtractor, SerializedFunction<EqualityState, FormatterFunc> equalityStateToFormatter) {
+	FormatterStepSerializationRoundtrip(String name, ThrowingEx.Supplier<RoundtripState> initializer, SerializedFunction<RoundtripState, EqualityState> equalityStateExtractor, SerializedFunction<EqualityState, ? extends FormatterFunc> equalityStateToFormatter) {
 		this.name = name;
 		this.initializer = initializer;
 		this.equalityStateExtractor = equalityStateExtractor;