Make ConfigurationCacheHackList safe from Java's object serialization foibles.

Author: nedtwigg

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2024 DiffPlug
+ * Copyright 2024-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -15,6 +15,8 @@
  */
 package com.diffplug.spotless;
 
+import java.io.IOException;
+import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
@@ -48,8 +50,27 @@
  */
 public class ConfigurationCacheHackList implements java.io.Serializable {
 	private static final long serialVersionUID = 1L;
-	private final boolean optimizeForEquality;
-	private final ArrayList<Object> backingList = new ArrayList<>();
+	private boolean optimizeForEquality;
+	public ArrayList<Object> backingList = new ArrayList<>();
+
+	private void writeObject(java.io.ObjectOutputStream out) throws IOException {
+		out.writeBoolean(optimizeForEquality);
+		out.writeInt(backingList.size());
+		for (Object obj : backingList) {
+			// if write out the list on its own, we'll get java's non-deterministic object-graph serialization
+			// by writing each object to raw bytes independently, we avoid this
+			out.writeObject(LazyForwardingEquality.toBytes((Serializable) obj));
+		}
+	}
+
+	private void readObject(java.io.ObjectInputStream in) throws IOException, ClassNotFoundException {
+		optimizeForEquality = in.readBoolean();
+		backingList = new ArrayList<>();
+		int size = in.readInt();
+		for (int i = 0; i < size; i++) {
+			backingList.add(LazyForwardingEquality.fromBytes((byte[]) in.readObject()));
+		}
+	}
 
 	public static ConfigurationCacheHackList forEquality() {
 		return new ConfigurationCacheHackList(true);

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2023 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.
@@ -15,6 +15,7 @@
  */
 package com.diffplug.spotless;
 
+import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.ObjectInputStream;
@@ -112,6 +113,15 @@ static byte[] toBytes(Serializable obj) {
 		return byteOutput.toByteArray();
 	}
 
+	static Object fromBytes(byte[] bytes) {
+		ByteArrayInputStream byteOutput = new ByteArrayInputStream(bytes);
+		try (ObjectInputStream objectOutput = new ObjectInputStream(byteOutput)) {
+			return objectOutput.readObject();
+		} catch (IOException | ClassNotFoundException e) {
+			throw ThrowingEx.asRuntime(e);
+		}
+	}
+
 	/** Ensures that the lazy state has been evaluated. */
 	public static void unlazy(Object in) {
 		if (in instanceof LazyForwardingEquality) {

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

testlib/src/main/java/com/diffplug/spotless/StepHarnessWithFile.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.
@@ -98,4 +98,14 @@ public StringSelfie expectLintsOfResource(String filename, String resource) {
 			throw new AssertionError(e);
 		}
 	}
+
+	public StringSelfie expectLintsOfFileAndContent(String filename, String content) {
+		try {
+			File file = harness.setFile(filename).toContent(content);
+			LintState state = LintState.of(formatter(), file);
+			return StepHarness.expectLintsOf(state, formatter());
+		} catch (IOException e) {
+			throw new AssertionError(e);
+		}
+	}
 }

testlib/src/test/java/com/diffplug/spotless/generic/FenceStepTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2024 DiffPlug
+ * Copyright 2020-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,6 +24,7 @@
 import com.diffplug.spotless.FormatterStep;
 import com.diffplug.spotless.ResourceHarness;
 import com.diffplug.spotless.StepHarness;
+import com.diffplug.spotless.StepHarnessWithFile;
 
 class FenceStepTest extends ResourceHarness {
 	@Test
@@ -85,7 +86,7 @@ void broken() {
 		FormatterStep fence = FenceStep.named("fence").openClose("spotless:off", "spotless:on")
 				.preserveWithin(Arrays.asList(ReplaceStep.create("replace", "spotless:on", "REMOVED")));
 		// this fails because uppercase turns spotless:off into SPOTLESS:OFF, etc
-		StepHarness.forStep(fence).expectLintsOf(StringPrinter.buildStringFromLines("A B C",
+		StepHarnessWithFile.forStep(this, fence).expectLintsOfFileAndContent("README.md", StringPrinter.buildStringFromLines("A B C",
 				"spotless:off",
 				"D E F",
 				"spotless:on",