Partially support isolated projects

plugin-gradle/CHANGES.md

@@ -3,6 +3,8 @@
 We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (starting after version `3.27.0`).
 
 ## [Unreleased]
+### Added
+- Partial support for isolated projects. They work if predeclared dependencies are not used. ([#2854](https://github.com/diffplug/spotless/pull/2854))
 ### Fixed
 - Fix the ability to specify a wildcard version (`*`) for external formatter executables, which did not work. ([#2848](https://github.com/diffplug/spotless/pull/2848))
 

plugin-gradle/README.md

@@ -1918,6 +1918,8 @@ Alternatively, you can also use `predeclareDepsFromBuildscript()` to resolve the
 
 If you use this feature, you will get an error if you use a formatter in a subproject which is not declared in the `spotlessPredeclare` block.
 
+Note that this feature is also incompatible with Isolated projects, because every project must reference the root project.
+
 <a name="preview"></a>
 
 ## How do I preview what `spotlessApply` will do?

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2023-2025 DiffPlug
+ * Copyright 2023-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,8 @@
 
 import javax.annotation.Nullable;
 
+import org.gradle.api.file.Directory;
+
 import com.diffplug.common.collect.ImmutableList;
 import com.diffplug.common.collect.ImmutableSortedMap;
 import com.diffplug.spotless.FileSignature;
@@ -160,7 +162,9 @@ private KtlintConfig(
 				Map<String, Object> editorConfigOverride,
 				List<String> customRuleSets) throws IOException {
 			Objects.requireNonNull(version);
-			File defaultEditorConfig = getProject().getRootProject().file(".editorconfig");
+			@SuppressWarnings("UnstableApiUsage")
+			Directory rootProjectDir = getProject().getIsolated().getRootProject().getProjectDirectory();
+			File defaultEditorConfig = rootProjectDir.file(".editorconfig").getAsFile();
 			FileSignature editorConfigPath = defaultEditorConfig.exists() ? FileSignature.signAsList(defaultEditorConfig) : null;
 			this.version = version;
 			this.editorConfigPath = editorConfigPath;

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

@@ -95,11 +95,11 @@ public FormatExtension(SpotlessExtension spotless) {
 	}
 
 	protected final Provisioner provisioner() {
-		return spotless.getRegisterDependenciesTask().getTaskService().get().provisionerFor(spotless);
+		return spotless.getSpotlessTaskService().get().provisionerFor(spotless);
 	}
 
 	protected final P2Provisioner p2Provisioner() {
-		return spotless.getRegisterDependenciesTask().getTaskService().get().p2ProvisionerFor(spotless);
+		return spotless.getSpotlessTaskService().get().p2ProvisionerFor(spotless);
 	}
 
 	private String formatName() {
@@ -1098,7 +1098,7 @@ protected void setupTask(SpotlessTask task) {
 		LineEnding lineEndings = getLineEndings();
 		task.setLineEndingsPolicy(
 				getProject().provider(() -> lineEndings.createPolicy(projectDir.getAsFile(), () -> totalTarget)));
-		spotless.getRegisterDependenciesTask().hookSubprojectTask(task);
+		spotless.getSpotlessTaskService().get().hookSubprojectTask(getProject(), task);
 		task.setupRatchet(getRatchetFrom() != null ? getRatchetFrom() : "");
 	}
 
@@ -1134,7 +1134,7 @@ public TaskProvider<SpotlessApply> createIndependentApplyTaskLazy(String taskNam
 				"Task name must not end with " + SpotlessExtension.APPLY);
 		TaskProvider<SpotlessTaskImpl> spotlessTask = spotless.project.getTasks()
 				.register(taskName + SpotlessTaskService.INDEPENDENT_HELPER, SpotlessTaskImpl.class, task -> {
-					task.init(spotless.getRegisterDependenciesTask().getTaskService());
+					task.init(spotless.getSpotlessTaskService());
 					setupTask(task);
 					// clean removes the SpotlessCache, so we have to run after clean
 					task.mustRunAfter(BasePlugin.CLEAN_TASK_NAME);

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025 DiffPlug
+ * Copyright 2025-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,24 +18,23 @@
 import javax.annotation.Nullable;
 
 import org.gradle.api.Project;
+import org.gradle.api.plugins.ExtraPropertiesExtension;
 
 public final class GradleCompat {
 	private GradleCompat() {}
 
 	@Nullable public static String findOptionalProperty(Project project, String propertyName) {
-		@Nullable String value = project.getProviders().gradleProperty(propertyName).getOrNull();
-		if (value != null) {
-			return value;
-		}
-		@Nullable Object property = project.findProperty(propertyName);
-		if (property != null) {
-			return property.toString();
+		ExtraPropertiesExtension extras = project.getExtensions().getByType(ExtraPropertiesExtension.class);
+		if (extras.has(propertyName)) {
+			@Nullable Object property = extras.get(propertyName);
+			if (property != null) {
+				return property.toString();
+			}
 		}
 		return null;
 	}
 
 	public static boolean isPropertyPresent(Project project, String propertyName) {
-		return project.getProviders().gradleProperty(propertyName).isPresent() ||
-				project.hasProperty(propertyName);
+		return project.getExtensions().getByType(ExtraPropertiesExtension.class).has(propertyName);
 	}
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2023 DiffPlug
+ * Copyright 2016-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,7 +25,6 @@
 
 import org.gradle.api.DefaultTask;
 import org.gradle.api.provider.Provider;
-import org.gradle.api.services.BuildServiceRegistry;
 import org.gradle.api.tasks.Input;
 import org.gradle.api.tasks.Internal;
 import org.gradle.api.tasks.OutputFile;
@@ -64,8 +63,7 @@ void hookSubprojectTask(SpotlessTask task) {
 	void setup() {
 		Preconditions.checkArgument(getProject().getRootProject() == getProject(), "Can only be used on the root project");
 		String compositeBuildSuffix = getName().substring(TASK_NAME.length()); // see https://github.com/diffplug/spotless/pull/1001
-		BuildServiceRegistry buildServices = getProject().getGradle().getSharedServices();
-		taskService = buildServices.registerIfAbsent("SpotlessTaskService" + compositeBuildSuffix, SpotlessTaskService.class, spec -> {});
+		taskService = SpotlessTaskService.registerIfAbsent(getProject(), compositeBuildSuffix);
 		usesService(taskService);
 		getBuildEventsListenerRegistry().onTaskCompletion(taskService);
 		unitOutput = new File(getProject().getLayout().getBuildDirectory().getAsFile().get(), "tmp/spotless-register-dependencies");

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2025 DiffPlug
+ * Copyright 2016-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,15 +27,14 @@
 import org.gradle.api.Action;
 import org.gradle.api.GradleException;
 import org.gradle.api.Project;
-import org.gradle.api.tasks.TaskContainer;
-import org.gradle.api.tasks.TaskProvider;
+import org.gradle.api.provider.Provider;
 import org.gradle.language.base.plugins.LifecycleBasePlugin;
 
 import com.diffplug.spotless.LineEnding;
 
 public abstract class SpotlessExtension {
 	final Project project;
-	private final RegisterDependenciesTask registerDependenciesTask;
+	private final Provider<SpotlessTaskService> spotlessTaskService;
 
 	protected static final String TASK_GROUP = LifecycleBasePlugin.VERIFICATION_GROUP;
 	protected static final String BUILD_SETUP_TASK_GROUP = "build setup";
@@ -52,11 +51,11 @@ public abstract class SpotlessExtension {
 
 	protected SpotlessExtension(Project project) {
 		this.project = requireNonNull(project);
-		this.registerDependenciesTask = findRegisterDepsTask().get();
+		this.spotlessTaskService = SpotlessTaskService.registerIfAbsent(project, "");
 	}
 
-	RegisterDependenciesTask getRegisterDependenciesTask() {
-		return registerDependenciesTask;
+	Provider<SpotlessTaskService> getSpotlessTaskService() {
+		return spotlessTaskService;
 	}
 
 	/** Line endings (if any). */
@@ -303,27 +302,6 @@ <T extends FormatExtension> T instantiateFormatExtension(Class<T> clazz) {
 
 	protected abstract void createFormatTasks(String name, FormatExtension formatExtension);
 
-	TaskProvider<RegisterDependenciesTask> findRegisterDepsTask() {
-		try {
-			return findRegisterDepsTask(RegisterDependenciesTask.TASK_NAME);
-		} catch (Exception e) {
-			// in a composite build there can be multiple Spotless plugins on the classpath, and they will each try to register
-			// a task on the root project with the same name. That will generate casting errors, which we can catch and try again
-			// with an identity-specific identifier.
-			// https://github.com/diffplug/spotless/pull/1001 for details
-			return findRegisterDepsTask(RegisterDependenciesTask.TASK_NAME + System.identityHashCode(RegisterDependenciesTask.class));
-		}
-	}
-
-	private TaskProvider<RegisterDependenciesTask> findRegisterDepsTask(String taskName) {
-		TaskContainer rootProjectTasks = project.getRootProject().getTasks();
-		if (!rootProjectTasks.getNames().contains(taskName)) {
-			return rootProjectTasks.register(taskName, RegisterDependenciesTask.class, RegisterDependenciesTask::setup);
-		} else {
-			return rootProjectTasks.named(taskName, RegisterDependenciesTask.class);
-		}
-	}
-
 	public void predeclareDepsFromBuildscript() {
 		if (project.getRootProject() != project) {
 			throw new GradleException("predeclareDepsFromBuildscript can only be called from the root project");

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

@@ -61,7 +61,7 @@ protected void createFormatTasks(String name, FormatExtension formatExtension) {
 		// create the SpotlessTask
 		String taskName = EXTENSION + SpotlessPlugin.capitalize(name);
 		TaskProvider<SpotlessTaskImpl> spotlessTask = tasks.register(taskName, SpotlessTaskImpl.class, task -> {
-			task.init(getRegisterDependenciesTask().getTaskService());
+			task.init(getSpotlessTaskService());
 			task.setGroup(TASK_GROUP);
 			task.getIdeHookState().set(ideHook);
 			// clean removes the SpotlessCache, so we have to run after clean

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

@@ -20,23 +20,28 @@
 
 import org.gradle.api.Action;
 import org.gradle.api.Project;
+import org.gradle.api.tasks.TaskProvider;
 
 import com.diffplug.spotless.LazyForwardingEquality;
 
 public class SpotlessExtensionPredeclare extends SpotlessExtension {
 	private final SortedMap<String, FormatExtension> toSetup = new TreeMap<>();
+	private final RegisterDependenciesTask registerDependenciesTask;
 
 	public SpotlessExtensionPredeclare(Project project, GradleProvisioner.Policy policy) {
 		super(project);
-		getRegisterDependenciesTask().getTaskService().get().predeclaredProvisioner = policy.dedupingProvisioner(project);
-		getRegisterDependenciesTask().getTaskService().get().predeclaredP2Provisioner = policy.dedupingP2Provisioner(project);
+		this.registerDependenciesTask = findRegisterDepsTask().get();
+		SpotlessTaskService taskService = getSpotlessTaskService().get();
+		taskService.isUsingPredeclared = true;
+		taskService.predeclaredProvisioner = policy.dedupingProvisioner(project);
+		taskService.predeclaredP2Provisioner = policy.dedupingP2Provisioner(project);
 		project.afterEvaluate(unused -> toSetup.forEach((name, formatExtension) -> {
 			for (Action<FormatExtension> lazyAction : formatExtension.lazyActions) {
 				lazyAction.execute(formatExtension);
 			}
-			getRegisterDependenciesTask().steps.addAll(formatExtension.steps);
+			registerDependenciesTask.steps.addAll(formatExtension.steps);
 			// needed to fix Deemon memory leaks (#1194), but this line came from https://github.com/diffplug/spotless/pull/1206
-			LazyForwardingEquality.unlazy(getRegisterDependenciesTask().steps);
+			LazyForwardingEquality.unlazy(registerDependenciesTask.steps);
 		}));
 	}
 
@@ -49,4 +54,21 @@ protected void createFormatTasks(String name, FormatExtension formatExtension) {
 	protected void predeclare(GradleProvisioner.Policy policy) {
 		throw new UnsupportedOperationException("predeclare can't be called from within `" + EXTENSION_PREDECLARE + "`");
 	}
+
+	private TaskProvider<RegisterDependenciesTask> findRegisterDepsTask() {
+		try {
+			return findRegisterDepsTask(RegisterDependenciesTask.TASK_NAME);
+		} catch (Exception e) {
+			// in a composite build there can be multiple Spotless plugins on the classpath, and they will each try to register
+			// a task on the root project with the same name. That will generate casting errors, which we can catch and try again
+			// with an identity-specific identifier.
+			// https://github.com/diffplug/spotless/pull/1001 for details
+			return findRegisterDepsTask(RegisterDependenciesTask.TASK_NAME + System.identityHashCode(RegisterDependenciesTask.class));
+		}
+	}
+
+	private TaskProvider<RegisterDependenciesTask> findRegisterDepsTask(String taskName) {
+		return project.getTasks().register(taskName, RegisterDependenciesTask.class, RegisterDependenciesTask::setup);
+	}
+
 }

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

@@ -28,6 +28,7 @@
 import javax.inject.Inject;
 
 import org.gradle.api.DefaultTask;
+import org.gradle.api.Project;
 import org.gradle.api.file.ConfigurableFileTree;
 import org.gradle.api.file.DirectoryProperty;
 import org.gradle.api.file.FileVisitDetails;
@@ -55,6 +56,7 @@
  * apply already did).
  */
 public abstract class SpotlessTaskService implements BuildService<BuildServiceParameters.None>, AutoCloseable, OperationCompletionListener {
+	protected boolean isUsingPredeclared = false;
 	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<>());
@@ -126,6 +128,21 @@ static void usesServiceTolerateTestFailure(DefaultTask task, Provider<SpotlessTa
 		}
 	}
 
+	public void hookSubprojectTask(Project project, SpotlessTask task) {
+		// This check allows isolated projects support by not accessing the root project tasks unless really needed
+		if (!isUsingPredeclared)
+			return;
+
+		project.getRootProject().getTasks().withType(RegisterDependenciesTask.class, (registerTask) -> {
+			registerTask.hookSubprojectTask(task);
+		});
+	}
+
+	public static Provider<SpotlessTaskService> registerIfAbsent(Project project, String suffix) {
+		return project.getGradle().getSharedServices()
+				.registerIfAbsent("SpotlessTaskService" + suffix, SpotlessTaskService.class, spec -> {});
+	}
+
 	abstract static class ClientTask extends DefaultTask {
 		@Internal
 		abstract Property<File> getSpotlessCleanDirectory();

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2025 DiffPlug
+ * Copyright 2016-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -136,10 +136,9 @@ private void expectSuccess() throws Exception {
 	private StringSelfie expectFailureAndConsoleToBe() throws Exception {
 		BuildResult result = gradleRunner().withArguments("check").buildAndFail();
 		String output = result.getOutput();
-		int register = output.indexOf(":spotlessInternalRegisterDependencies");
-		int firstNewlineAfterThat = output.indexOf('\n', register + 1);
+		int firstTask = output.indexOf("> Task");
 		int firstTry = output.indexOf("\n* Try:");
-		String useThisToMatch = output.substring(firstNewlineAfterThat, firstTry).trim();
+		String useThisToMatch = output.substring(firstTask, firstTry).trim();
 		return Selfie.expectSelfie(useThisToMatch);
 	}
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2025 DiffPlug
+ * Copyright 2016-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -197,7 +197,7 @@ private void taskIsUpToDate(String task, boolean upToDate) throws IOException {
 
 		List<String> expected = outcomes(buildResult, upToDate ? TaskOutcome.UP_TO_DATE : TaskOutcome.SUCCESS);
 		List<String> notExpected = outcomes(buildResult, upToDate ? TaskOutcome.SUCCESS : TaskOutcome.UP_TO_DATE);
-		boolean everythingAsExpected = !expected.isEmpty() && notExpected.isEmpty() && buildResult.getTasks().size() - 1 == expected.size();
+		boolean everythingAsExpected = !expected.isEmpty() && notExpected.isEmpty() && buildResult.getTasks().size() == expected.size();
 		if (!everythingAsExpected) {
 			fail("Expected all tasks to be " + (upToDate ? TaskOutcome.UP_TO_DATE : TaskOutcome.SUCCESS) + ", but instead was\n" + buildResultToString(buildResult));
 		}

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2025 DiffPlug
+ * Copyright 2016-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -151,4 +151,38 @@ public void predeclaredUndeclared() throws IOException {
 		Assertions.assertThat(gradleRunner().withArguments("spotlessApply").buildAndFail().getOutput())
 				.contains("Could not find method spotlessPredeclare() for arguments");
 	}
+
+	@Test
+	void nonPredeclaredSupportsIsolatedProjects() throws IOException {
+		setFile("build.gradle").toLines(
+				"plugins {",
+				"    id 'com.diffplug.spotless'",
+				"}",
+				"repositories { mavenCentral() }",
+				"",
+				"spotless {",
+				"    java {",
+				"        target file('test.java')",
+				"        googleJavaFormat('1.17.0')",
+				"    }",
+				"}");
+		createNSubprojects();
+		gradleRunner().withArguments("spotlessApply", "-Dorg.gradle.unsafe.isolated-projects=true").build();
+	}
+
+	@Test
+	void predeclaredRequiresNonIsolatedProjects() throws IOException {
+		setFile("build.gradle").toLines(
+				"plugins {",
+				"    id 'com.diffplug.spotless'",
+				"}",
+				"repositories { mavenCentral() }",
+				"spotless { predeclareDeps() }",
+				"spotlessPredeclare {",
+				" java { googleJavaFormat('1.17.0') }",
+				"}");
+		createNSubprojects();
+		Assertions.assertThat(gradleRunner().withArguments("spotlessApply", "-Dorg.gradle.unsafe.isolated-projects=true").buildAndFail().getOutput())
+				.containsAnyOf("Cannot access project", "cannot access 'Project.tasks'");
+	}
 }