Make the diff a little smaller.

plugin-gradle/src/main/java/com/diffplug/gradle/spotless/SpotlessTaskService.java

@@ -44,27 +44,26 @@
  * apply already did).
  */
 public abstract class SpotlessTaskService implements BuildService<BuildServiceParameters.None>, AutoCloseable, OperationCompletionListener {
-	private Map<String, SpotlessApply> apply = Collections.synchronizedMap(new HashMap<>());
-	private Map<String, SpotlessTask> source = Collections.synchronizedMap(new HashMap<>());
-	private Map<String, Provisioner> provisioner = Collections.synchronizedMap(new HashMap<>());
-
-	void registerSourceAlreadyRan(SpotlessTask task) {
-		source.put(task.getPath(), task);
-	}
+	private final Map<String, SpotlessApply> apply = Collections.synchronizedMap(new HashMap<>());
+	private final Map<String, SpotlessTask> source = Collections.synchronizedMap(new HashMap<>());
+	private final Map<String, Provisioner> provisioner = Collections.synchronizedMap(new HashMap<>());
 
 	Provisioner provisionerFor(Project project) {
 		return provisioner.computeIfAbsent(project.getPath(), unused -> {
 			return GradleProvisioner.newDedupingProvisioner(project);
 		});
 	}
 
+	void registerSourceAlreadyRan(SpotlessTask task) {
+		source.put(task.getPath(), task);
+	}
+
 	void registerApplyAlreadyRan(SpotlessApply task) {
 		apply.put(task.sourceTaskPath(), task);
 	}
 
-	/////////////////
 	// <GitRatchet>
-	private GitRatchetGradle ratchet = new GitRatchetGradle();
+	private final GitRatchetGradle ratchet = new GitRatchetGradle();
 
 	GitRatchetGradle getRatchet() {
 		return ratchet;
@@ -80,7 +79,6 @@ public void close() throws Exception {
 		ratchet.close();
 	}
 	// </GitRatchet>
-	//////////////////
 
 	static String INDEPENDENT_HELPER = "Helper";
 

plugin-gradle/src/test/java/com/diffplug/gradle/spotless/ConfigurationCacheTest.java

@@ -17,6 +17,7 @@
 
 import java.io.IOException;
 
+import org.gradle.testkit.runner.BuildResult;
 import org.gradle.testkit.runner.GradleRunner;
 import org.junit.jupiter.api.Test;
 
@@ -59,4 +60,39 @@ public void helpConfiguresIfTasksAreCreated() throws IOException {
 				"tasks.named('spotlessJavaApply').get()");
 		gradleRunner().withArguments("help").build();
 	}
+
+	@Test
+	public void jvmLocalCache() throws IOException {
+		setFile("build.gradle").toLines(
+				"plugins {",
+				"    id 'com.diffplug.spotless'",
+				"}",
+				"repositories { mavenCentral() }",
+				"spotless {",
+				"    java {",
+				"        target file('test.java')",
+				"        googleJavaFormat('1.2')",
+				"    }",
+				"}");
+
+		// first run works
+		setFile("test.java").toResource("java/googlejavaformat/JavaCodeUnformatted.test");
+		gradleRunner().withArguments("spotlessApply").build();
+		assertFile("test.java").sameAsResource("java/googlejavaformat/JavaCodeFormatted.test");
+
+		// and it keeps working!
+		gradleRunner().withArguments("spotlessApply", "--stacktrace").build();
+		gradleRunner().withArguments("spotlessApply").build();
+		gradleRunner().withArguments("spotlessApply").build();
+
+		setFile("test.java").toResource("java/googlejavaformat/JavaCodeUnformatted.test");
+		gradleRunner().withArguments("spotlessCheck").buildAndFail();
+		gradleRunner().withArguments("spotlessApply").build();
+		assertFile("test.java").sameAsResource("java/googlejavaformat/JavaCodeFormatted.test");
+
+		BuildResult failure = gradleRunner().withDebug(true).withArguments("spotlessApply", "--stacktrace").buildAndFail();
+		failure.getOutput().contains("Spotless daemon-local cache is stale. Regenerate the cache with\n" +
+				"  rm -rf .gradle/configuration-cache\n" +
+				"For more information see #123\n");
+	}
 }