Defer dependency resolution using LazyFiles

Author: simonlebras

lib-extra/src/main/java/com/diffplug/spotless/extra/EquoBasedStepBuilder.java

@@ -139,7 +139,7 @@ public FormatterStep build() {
 			mavenDeps.add("dev.equo.ide:solstice:1.8.1");
 			mavenDeps.add("com.diffplug.durian:durian-swt.os:4.3.1");
 			mavenDeps.addAll(query.getJarsOnMavenCentral());
-			classpath.addAll(mavenProvisioner.provisionWithTransitives(false, mavenDeps));
+			classpath.addAll(mavenProvisioner.provisionWithTransitives(false, mavenDeps).files());
 			classpath.addAll(query.getJarsNotOnMavenCentral());
 			for (var nested : NestedJars.inFiles(query.getJarsNotOnMavenCentral()).extractAllNestedJars()) {
 				classpath.add(nested.getValue());

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

@@ -129,7 +129,7 @@ public static JarState withoutTransitives(Collection<String> mavenCoordinates, P
 	private static JarState provisionWithTransitives(boolean withTransitives, Collection<String> mavenCoordinates, Provisioner provisioner) throws IOException {
 		Objects.requireNonNull(mavenCoordinates, "mavenCoordinates");
 		Objects.requireNonNull(provisioner, "provisioner");
-		Set<File> jars = provisioner.provisionWithTransitives(withTransitives, mavenCoordinates);
+		Set<File> jars = provisioner.provisionWithTransitives(withTransitives, mavenCoordinates).files();
 		if (jars.isEmpty()) {
 			throw new NoSuchElementException("Resolved to an empty result: " + String.join(", ", mavenCoordinates));
 		}

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

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2025 DiffPlug
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.diffplug.spotless;
+
+import java.io.File;
+import java.util.Set;
+
+/**
+ * A lazy provider of a set of files, to allow build systems
+ * to defer resolution of dependencies.
+ */
+@FunctionalInterface
+public interface LazyFiles {
+	Set<File> files();
+
+	static LazyFiles of(Set<File> files) {
+		return () -> files;
+	}
+}

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2020 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.
@@ -15,27 +15,25 @@
  */
 package com.diffplug.spotless;
 
-import java.io.File;
 import java.util.Arrays;
 import java.util.Collection;
-import java.util.Set;
 
 /**
  * Many spotless steps require third-party libraries, but we want to keep
  * Spotless' dependencies minimal.
  */
 public interface Provisioner {
 	/**
-	 * Given a set of Maven coordinates, returns a set of jars which include all
+	 * Given a set of Maven coordinates, returns a lazy set of jars which include all
 	 * of the specified coordinates and optionally their transitive dependencies.
 	 */
-	public default Set<File> provisionWithTransitives(boolean withTransitives, String... mavenCoordinates) {
+	public default LazyFiles provisionWithTransitives(boolean withTransitives, String... mavenCoordinates) {
 		return provisionWithTransitives(withTransitives, Arrays.asList(mavenCoordinates));
 	}
 
 	/**
-	 * Given a set of Maven coordinates, returns a set of jars which include all
+	 * Given a set of Maven coordinates, returns a lazy set of jars which include all
 	 * of the specified coordinates and optionally their transitive dependencies.
 	 */
-	public Set<File> provisionWithTransitives(boolean withTransitives, Collection<String> mavenCoordinates);
+	public LazyFiles provisionWithTransitives(boolean withTransitives, Collection<String> mavenCoordinates);
 }

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

@@ -15,26 +15,27 @@
  */
 package com.diffplug.gradle.spotless;
 
-import java.io.File;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.Map;
-import java.util.Set;
 
 import org.gradle.api.GradleException;
+import org.gradle.api.NamedDomainObjectProvider;
 import org.gradle.api.Project;
 import org.gradle.api.artifacts.Configuration;
 import org.gradle.api.artifacts.ConfigurationContainer;
 import org.gradle.api.artifacts.dsl.DependencyHandler;
 import org.gradle.api.attributes.Bundling;
 import org.gradle.api.attributes.Category;
 import org.gradle.api.attributes.java.TargetJvmEnvironment;
+import org.gradle.api.file.FileCollection;
 import org.gradle.api.initialization.dsl.ScriptHandler;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import com.diffplug.common.base.Unhandled;
 import com.diffplug.common.collect.ImmutableList;
+import com.diffplug.spotless.LazyFiles;
 import com.diffplug.spotless.Provisioner;
 
 /** Should be package-private. */
@@ -59,16 +60,16 @@ public DedupingProvisioner dedupingProvisioner(Project project) {
 
 	static class DedupingProvisioner implements Provisioner {
 		private final Provisioner provisioner;
-		private final Map<Request, Set<File>> cache = new HashMap<>();
+		private final Map<Request, LazyFiles> cache = new HashMap<>();
 
 		DedupingProvisioner(Provisioner provisioner) {
 			this.provisioner = provisioner;
 		}
 
 		@Override
-		public Set<File> provisionWithTransitives(boolean withTransitives, Collection<String> mavenCoordinates) {
+		public LazyFiles provisionWithTransitives(boolean withTransitives, Collection<String> mavenCoordinates) {
 			Request req = new Request(withTransitives, mavenCoordinates);
-			Set<File> result;
+			LazyFiles result;
 			synchronized (cache) {
 				result = cache.get(req);
 			}
@@ -89,7 +90,7 @@ public Set<File> provisionWithTransitives(boolean withTransitives, Collection<St
 		/** A child Provisioner which retries cached elements only. */
 		final Provisioner cachedOnly = (withTransitives, mavenCoordinates) -> {
 			Request req = new Request(withTransitives, mavenCoordinates);
-			Set<File> result;
+			LazyFiles result;
 			synchronized (cache) {
 				result = cache.get(req);
 			}
@@ -113,22 +114,25 @@ static Provisioner forRootProjectBuildscript(Project project) {
 	private static Provisioner forConfigurationContainer(Project project, ConfigurationContainer configurations, DependencyHandler dependencies) {
 		return (withTransitives, mavenCoords) -> {
 			try {
-				Configuration config = configurations.create("spotless"
-						+ new Request(withTransitives, mavenCoords).hashCode());
-				mavenCoords.stream()
-						.map(dependencies::create)
-						.forEach(config.getDependencies()::add);
-				config.setDescription(mavenCoords.toString());
-				config.setTransitive(withTransitives);
-				config.setCanBeConsumed(false);
-				config.setVisible(false);
-				config.attributes(attr -> {
-					attr.attribute(Category.CATEGORY_ATTRIBUTE, project.getObjects().named(Category.class, Category.LIBRARY));
-					attr.attribute(Bundling.BUNDLING_ATTRIBUTE, project.getObjects().named(Bundling.class, Bundling.EXTERNAL));
-					// Add this attribute for resolving Guava dependency, see https://github.com/google/guava/issues/6801.
-					attr.attribute(TargetJvmEnvironment.TARGET_JVM_ENVIRONMENT_ATTRIBUTE, project.getObjects().named(TargetJvmEnvironment.class, TargetJvmEnvironment.STANDARD_JVM));
-				});
-				return config.resolve();
+				NamedDomainObjectProvider<Configuration> config = configurations.register(
+						"spotless" + new Request(withTransitives, mavenCoords).hashCode(),
+						files -> {
+							mavenCoords.stream()
+									.map(dependencies::create)
+									.forEach(files.getDependencies()::add);
+							files.setDescription(mavenCoords.toString());
+							files.setTransitive(withTransitives);
+							files.setCanBeConsumed(false);
+							files.setVisible(false);
+							files.attributes(attr -> {
+								attr.attribute(Category.CATEGORY_ATTRIBUTE, project.getObjects().named(Category.class, Category.LIBRARY));
+								attr.attribute(Bundling.BUNDLING_ATTRIBUTE, project.getObjects().named(Bundling.class, Bundling.EXTERNAL));
+								attr.attribute(TargetJvmEnvironment.TARGET_JVM_ENVIRONMENT_ATTRIBUTE, project.getObjects().named(TargetJvmEnvironment.class, TargetJvmEnvironment.STANDARD_JVM));
+							});
+						});
+
+				final FileCollection configFiles = project.files(config);
+				return configFiles::getFiles;
 			} catch (Exception e) {
 				String projName = project.getPath().substring(1).replace(':', '/');
 				if (!projName.isEmpty()) {

testlib/src/main/java/com/diffplug/spotless/TestProvisioner.java

@@ -23,6 +23,7 @@
 import java.util.Comparator;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Set;
 import java.util.function.Consumer;
 import java.util.function.Supplier;
 
@@ -77,22 +78,24 @@ private static Provisioner createWithRepositories(Consumer<RepositoryHandler> re
 				// Add this attribute for resolving Guava dependency, see https://github.com/google/guava/issues/6801.
 				attr.attribute(TargetJvmEnvironment.TARGET_JVM_ENVIRONMENT_ATTRIBUTE, project.getObjects().named(TargetJvmEnvironment.class, TargetJvmEnvironment.STANDARD_JVM));
 			});
-			try {
-				return config.resolve();
-			} catch (ResolveException e) {
-				/* Provide Maven coordinates in exception message instead of static string 'detachedConfiguration' */
-				throw new RuntimeException("Error resolving configuration: " + config.getDescription(), e);
-			} finally {
-				// delete the temp dir
+			return (LazyFiles) () -> {
 				try {
-					java.nio.file.Files.walk(tempDir.toPath())
-							.sorted(Comparator.reverseOrder())
-							.map(Path::toFile)
-							.forEach(File::delete);
-				} catch (IOException e) {
-					throw Errors.asRuntime(e);
+					return config.resolve();
+				} catch (ResolveException e) {
+					/* Provide Maven coordinates in exception message instead of static string 'detachedConfiguration' */
+					throw new RuntimeException("Error resolving configuration: " + config.getDescription(), e);
+				} finally {
+					// delete the temp dir
+					try {
+						java.nio.file.Files.walk(tempDir.toPath())
+								.sorted(Comparator.reverseOrder())
+								.map(Path::toFile)
+								.forEach(File::delete);
+					} catch (IOException e) {
+						throw Errors.asRuntime(e);
+					}
 				}
-			}
+			};
 		};
 	}
 
@@ -125,15 +128,15 @@ private static Provisioner caching(String name, Supplier<Provisioner> input) {
 				// double-check that depcache pruning hasn't removed them since our cache cached them
 				boolean needsToBeSet = result == null || !result.stream().allMatch(file -> file.exists() && file.isFile() && file.length() > 0);
 				if (needsToBeSet) {
-					result = ImmutableSet.copyOf(input.get().provisionWithTransitives(withTransitives, mavenCoords));
+					result = ImmutableSet.copyOf(input.get().provisionWithTransitives(withTransitives, mavenCoords).files());
 					cached.put(mavenCoords, result);
 					try (ObjectOutputStream outputStream = new ObjectOutputStream(Files.asByteSink(cacheFile).openBufferedStream())) {
 						outputStream.writeObject(cached);
 					} catch (IOException e) {
 						throw Errors.asRuntime(e);
 					}
 				}
-				return result;
+				return LazyFiles.of(result);
 			}
 		};
 	}