Merge with Fabric 0.13, stage 1

bootstrap/test-project/build.gradle

@@ -1,5 +1,5 @@
 plugins {
-	id 'dev.architectury.loom' version '0.12.local'
+	id 'dev.architectury.loom' version '0.13.local'
 }
 
 dependencies {

build.gradle

@@ -30,7 +30,7 @@ tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).all {
 
 group = "dev.architectury"
 archivesBaseName = project.name
-def baseVersion = '0.12.0'
+def baseVersion = '0.13.0'
 def runNumber = System.getenv("GITHUB_RUN_NUMBER") ?: "9999"
 
 def isSnapshot = System.getenv("PR_NUM") != null
@@ -55,7 +55,6 @@ repositories {
 			excludeGroupByRegex "org\\.eclipse\\.?.*"
 		}
 	}
-	mavenLocal()
 }
 
 configurations {
@@ -82,7 +81,7 @@ dependencies {
 	// libraries
 	implementation ('commons-io:commons-io:2.11.0')
 	implementation ('com.google.code.gson:gson:2.9.0')
-	implementation ('com.fasterxml.jackson.core:jackson-databind:2.13.2.2')
+	implementation ('com.fasterxml.jackson.core:jackson-databind:2.13.3')
 	implementation ('com.google.guava:guava:31.1-jre')
 	implementation ('org.ow2.asm:asm:9.3')
 	implementation ('org.ow2.asm:asm-analysis:9.3')
@@ -99,6 +98,7 @@ dependencies {
 
 	// tinyfile management
 	implementation ('dev.architectury:tiny-remapper:1.7.19')
+	// TODO: implementation ('net.fabricmc:tiny-remapper:0.8.5')
 	implementation 'net.fabricmc:access-widener:2.1.0'
 	implementation 'net.fabricmc:mapping-io:0.2.1'
 
@@ -135,11 +135,11 @@ dependencies {
 		exclude module: 'groovy-all'
 	}
 	testImplementation 'org.junit.jupiter:junit-jupiter-engine:5.8.2'
-	testImplementation ('io.javalin:javalin:4.4.0') {
+	testImplementation ('io.javalin:javalin:4.6.1') {
 		exclude group: 'org.jetbrains.kotlin'
 	}
 	testImplementation 'net.fabricmc:fabric-installer:0.9.0'
-	testImplementation 'org.mockito:mockito-core:4.4.0'
+	testImplementation 'org.mockito:mockito-core:4.6.1'
 
 	compileOnly 'org.jetbrains:annotations:23.0.0'
 	testCompileOnly 'org.jetbrains:annotations:23.0.0'
@@ -212,6 +212,11 @@ test {
 	maxHeapSize = "1536m"
 	useJUnitPlatform()
 	maxParallelForks = Runtime.runtime.availableProcessors() ?: 1
+
+	// Forward system prop onto tests.
+	if (System.getProperty("fabric.loom.test.homeDir")) {
+		systemProperty "fabric.loom.test.homeDir", System.getProperty("fabric.loom.test.homeDir")
+	}
 }
 
 import org.gradle.util.GradleVersion

src/main/java/net/fabricmc/loom/build/MixinRefmapHelper.java

@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2018-2021 FabricMC
+ * Copyright (c) 2018-2022 FabricMC
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -24,46 +24,21 @@
 
 package net.fabricmc.loom.build;
 
-import java.io.File;
-import java.io.IOException;
-import java.io.InputStreamReader;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.stream.Collectors;
 import java.util.stream.StreamSupport;
-import java.util.zip.ZipEntry;
-import java.util.zip.ZipFile;
 
 import com.google.gson.JsonArray;
 import com.google.gson.JsonObject;
 import com.google.gson.JsonPrimitive;
 import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
-
-import net.fabricmc.loom.LoomGradlePlugin;
 
 public final class MixinRefmapHelper {
 	private MixinRefmapHelper() { }
 
 	private static final String FABRIC_MOD_JSON = "fabric.mod.json";
 
-	@Nullable
-	public static JsonObject readFabricModJson(File output) {
-		try (ZipFile zip = new ZipFile(output)) {
-			ZipEntry entry = zip.getEntry(FABRIC_MOD_JSON);
-
-			if (entry == null) {
-				return null;
-			}
-
-			try (InputStreamReader reader = new InputStreamReader(zip.getInputStream(entry))) {
-				return LoomGradlePlugin.GSON.fromJson(reader, JsonObject.class);
-			}
-		} catch (IOException e) {
-			throw new RuntimeException("Cannot read file fabric.mod.json in the jar.", e);
-		}
-	}
-
 	@NotNull
 	public static Collection<String> getMixinConfigurationFiles(JsonObject fabricModJson) {
 		JsonArray mixins = fabricModJson.getAsJsonArray("mixins");

src/main/java/net/fabricmc/loom/configuration/ide/RunConfig.java

@@ -24,7 +24,6 @@
 
 package net.fabricmc.loom.configuration.ide;
 
-import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.charset.StandardCharsets;
@@ -44,6 +43,9 @@ import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
 import org.apache.tools.ant.util.StringUtils;
 import org.gradle.api.Project;
+import org.gradle.api.artifacts.ModuleVersionIdentifier;
+import org.gradle.api.artifacts.ResolvedArtifact;
+import org.gradle.api.artifacts.ResolvedModuleVersion;
 import org.gradle.api.tasks.SourceSet;
 import org.gradle.plugins.ide.eclipse.model.EclipseModel;
 import org.w3c.dom.Document;
@@ -296,14 +298,6 @@ public class RunConfig {
 	}
 
 	public List<String> getExcludedLibraryPaths(Project project) {
-		if (true) {
-			/*
-				This whole excluded libraries idea breaks down when the server library version does not match the client.
-				This is a quick change to disable it meanwhile a proper solution is sorted.
-			 */
-			return Collections.emptyList();
-		}
-
 		if (!environment.equals("server")) {
 			return Collections.emptyList();
 		}
@@ -315,19 +309,32 @@ public class RunConfig {
 			return Collections.emptyList();
 		}
 
-		final Set<File> allLibraries = project.getConfigurations().getByName(Constants.Configurations.MINECRAFT_DEPENDENCIES).getFiles();
+		final Set<ResolvedArtifact> allLibraries = getArtifacts(project, Constants.Configurations.MINECRAFT_DEPENDENCIES);
-		final Set<File> serverLibraries = project.getConfigurations().getByName(Constants.Configurations.MINECRAFT_SERVER_DEPENDENCIES).getFiles();
+		final Set<ResolvedArtifact> serverLibraries = getArtifacts(project, Constants.Configurations.MINECRAFT_SERVER_DEPENDENCIES);
 		final List<String> clientOnlyLibraries = new LinkedList<>();
 
-		for (File commonLibrary : allLibraries) {
+		for (ResolvedArtifact library : allLibraries) {
-			if (!serverLibraries.contains(commonLibrary)) {
+			if (!containsLibrary(serverLibraries, library.getModuleVersion().getId())) {
-				clientOnlyLibraries.add(commonLibrary.getAbsolutePath());
+				clientOnlyLibraries.add(library.getFile().getAbsolutePath());
 			}
 		}
 
 		return clientOnlyLibraries;
 	}
 
+	private static Set<ResolvedArtifact> getArtifacts(Project project, String configuration) {
+		return project.getConfigurations().getByName(configuration)
+				.getResolvedConfiguration()
+				.getResolvedArtifacts();
+	}
+
+	private static boolean containsLibrary(Set<ResolvedArtifact> artifacts, ModuleVersionIdentifier identifier) {
+		return artifacts.stream()
+				.map(ResolvedArtifact::getModuleVersion)
+				.map(ResolvedModuleVersion::getId)
+				.anyMatch(test -> test.getGroup().equals(identifier.getGroup()) && test.getName().equals(identifier.getName()));
+	}
+
 	private static String encodeEscaped(String s) {
 		StringBuilder ret = new StringBuilder();
 

src/main/java/net/fabricmc/loom/configuration/providers/mappings/MappingsProviderImpl.java

@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2016-2021 FabricMC
+ * Copyright (c) 2016-2022 FabricMC
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -67,6 +67,7 @@ import net.fabricmc.loom.configuration.providers.minecraft.MergedMinecraftProvid
 import net.fabricmc.loom.configuration.providers.minecraft.MinecraftProvider;
 import net.fabricmc.loom.util.Constants;
 import net.fabricmc.loom.util.DeletingFileVisitor;
+import net.fabricmc.loom.util.FileSystemUtil;
 import net.fabricmc.loom.util.ZipUtils;
 import net.fabricmc.loom.util.service.SharedService;
 import net.fabricmc.loom.util.service.SharedServiceManager;
@@ -299,9 +300,9 @@ public class MappingsProviderImpl implements MappingsProvider, SharedService {
 			return;
 		}
 
-		try (FileSystem fileSystem = FileSystems.newFileSystem(inputJar, (ClassLoader) null)) {
+		try (FileSystemUtil.Delegate delegate = FileSystemUtil.getJarFileSystem(inputJar)) {
-			extractMappings(fileSystem, baseTinyMappings);
+			extractMappings(delegate.fs(), baseTinyMappings);
-			extractExtras(fileSystem);
+			extractExtras(delegate.fs());
 		}
 
 		if (areMappingsMergedV2(baseTinyMappings)) {
@@ -383,8 +384,8 @@ public class MappingsProviderImpl implements MappingsProvider, SharedService {
 	}
 
 	public static void extractMappings(Path jar, Path extractTo) throws IOException {
-		try (FileSystem unmergedIntermediaryFs = FileSystems.newFileSystem(jar, (ClassLoader) null)) {
+		try (FileSystemUtil.Delegate delegate = FileSystemUtil.getJarFileSystem(jar)) {
-			extractMappings(unmergedIntermediaryFs, extractTo);
+			extractMappings(delegate.fs(), extractTo);
 		}
 	}
 

src/main/java/net/fabricmc/loom/configuration/providers/mappings/extras/signatures/SignatureFixesLayerImpl.java

@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2021 FabricMC
+ * Copyright (c) 2022 FabricMC
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -25,17 +25,13 @@
 package net.fabricmc.loom.configuration.providers.mappings.extras.signatures;
 
 import java.io.IOException;
-import java.io.InputStreamReader;
 import java.nio.file.Path;
 import java.util.Map;
-import java.util.Objects;
-import java.util.zip.ZipEntry;
-import java.util.zip.ZipFile;
 
 import org.jetbrains.annotations.ApiStatus;
 
-import net.fabricmc.loom.LoomGradlePlugin;
 import net.fabricmc.loom.api.mappings.layered.MappingLayer;
+import net.fabricmc.loom.util.ZipUtils;
 import net.fabricmc.mappingio.MappingVisitor;
 
 @ApiStatus.Experimental
@@ -49,14 +45,9 @@ public record SignatureFixesLayerImpl(Path mappingsFile) implements MappingLayer
 
 	@Override
 	public Map<String, String> getSignatureFixes() {
-		try (var zipFile = new ZipFile(mappingsFile().toFile())) {
+		try {
-			ZipEntry zipFileEntry = zipFile.getEntry(SIGNATURE_FIXES_PATH);
+			//noinspection unchecked
-			Objects.requireNonNull(zipFileEntry, "Could not find %s in file".formatted(SIGNATURE_FIXES_PATH));
+			return ZipUtils.unpackJackson(mappingsFile(), SIGNATURE_FIXES_PATH, Map.class);
-
-			try (var reader = new InputStreamReader(zipFile.getInputStream(zipFileEntry))) {
-				//noinspection unchecked
-				return LoomGradlePlugin.OBJECT_MAPPER.readValue(reader, Map.class);
-			}
 		} catch (IOException e) {
 			throw new RuntimeException("Failed to extract signature fixes", e);
 		}

src/main/java/net/fabricmc/loom/configuration/providers/mappings/parchment/ParchmentMappingLayer.java

@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2016-2021 FabricMC
+ * Copyright (c) 2016-2022 FabricMC
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -25,15 +25,11 @@
 package net.fabricmc.loom.configuration.providers.mappings.parchment;
 
 import java.io.IOException;
-import java.io.InputStreamReader;
 import java.nio.file.Path;
-import java.util.Objects;
-import java.util.zip.ZipEntry;
-import java.util.zip.ZipFile;
 
-import net.fabricmc.loom.LoomGradlePlugin;
 import net.fabricmc.loom.api.mappings.layered.MappingLayer;
 import net.fabricmc.loom.api.mappings.layered.MappingsNamespace;
+import net.fabricmc.loom.util.ZipUtils;
 import net.fabricmc.mappingio.MappingVisitor;
 
 public record ParchmentMappingLayer(Path parchmentFile, boolean removePrefix) implements MappingLayer {
@@ -51,13 +47,6 @@ public record ParchmentMappingLayer(Path parchmentFile, boolean removePrefix) im
 	}
 
 	private ParchmentTreeV1 getParchmentData() throws IOException {
-		try (var zipFile = new ZipFile(parchmentFile().toFile())) {
+		return ZipUtils.unpackJackson(parchmentFile, PARCHMENT_DATA_FILE_NAME, ParchmentTreeV1.class);
-			ZipEntry zipFileEntry = zipFile.getEntry(PARCHMENT_DATA_FILE_NAME);
-			Objects.requireNonNull(zipFileEntry, "Could not find %s in parchment data file".formatted(PARCHMENT_DATA_FILE_NAME));
-
-			try (var reader = new InputStreamReader(zipFile.getInputStream(zipFileEntry))) {
-				return LoomGradlePlugin.OBJECT_MAPPER.readValue(reader, ParchmentTreeV1.class);
-			}
-		}
 	}
 }

src/main/java/net/fabricmc/loom/configuration/providers/mappings/tiny/TinyJarInfo.java

@@ -27,13 +27,12 @@ package net.fabricmc.loom.configuration.providers.mappings.tiny;
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.UncheckedIOException;
-import java.nio.file.FileSystem;
-import java.nio.file.FileSystems;
 import java.nio.file.Files;
 import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
 import java.util.Optional;
 
+import net.fabricmc.loom.util.FileSystemUtil;
 import net.fabricmc.mappingio.MappingReader;
 import net.fabricmc.mappingio.format.MappingFormat;
 
@@ -47,8 +46,8 @@ public record TinyJarInfo(boolean v2, Optional<String> minecraftVersionId) {
 	}
 
 	private static boolean doesJarContainV2Mappings(Path path) throws IOException {
-		try (FileSystem fs = FileSystems.newFileSystem(path, (ClassLoader) null)) {
+		try (FileSystemUtil.Delegate delegate = FileSystemUtil.getJarFileSystem(path)) {
-			try (BufferedReader reader = Files.newBufferedReader(fs.getPath("mappings", "mappings.tiny"))) {
+			try (BufferedReader reader = Files.newBufferedReader(delegate.fs().getPath("mappings", "mappings.tiny"))) {
 				return MappingReader.detectFormat(reader) == MappingFormat.TINY_2;
 			}
 		} catch (NoSuchFileException e) {

src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftLibraryProvider.java

@@ -75,8 +75,6 @@ public class MinecraftLibraryProvider {
 				if (runtimeOnlyLog4j && library.name().startsWith("org.apache.logging.log4j")) {
 					// Make log4j a runtime only dep to force slf4j.
 					project.getDependencies().add(Constants.Configurations.MINECRAFT_RUNTIME_DEPENDENCIES, library.name());
-				} else if (serverBundleMetadata != null && isLibraryInBundle(serverBundleMetadata, library)) {
-					project.getDependencies().add(Constants.Configurations.MINECRAFT_SERVER_DEPENDENCIES, library.name());
 				} else if (jarConfiguration.getSupportedEnvironments().contains("client")) {
 					// Client only library, or legacy version
 					project.getDependencies().add(Constants.Configurations.MINECRAFT_DEPENDENCIES, library.name());
@@ -117,6 +115,12 @@ public class MinecraftLibraryProvider {
 			}
 		}
 
+		if (serverBundleMetadata != null) {
+			for (BundleMetadata.Entry library : serverBundleMetadata.libraries()) {
+				project.getDependencies().add(Constants.Configurations.MINECRAFT_SERVER_DEPENDENCIES, library.name());
+			}
+		}
+
 		if (overrideLWJGL) {
 			LWJGLVersionOverride.DEPENDENCIES.forEach(s -> project.getDependencies().add(Constants.Configurations.MINECRAFT_DEPENDENCIES, s));
 			LWJGLVersionOverride.NATIVES.forEach(s -> project.getDependencies().add(Constants.Configurations.MINECRAFT_NATIVES, s));
@@ -132,8 +136,4 @@ public class MinecraftLibraryProvider {
 			project.getDependencies().add("modLocalRuntime", dependency);
 		}
 	}
-
-	private static boolean isLibraryInBundle(BundleMetadata bundleMetadata, MinecraftVersionMeta.Library library) {
-		return bundleMetadata.libraries().stream().anyMatch(entry -> entry.name().equals(library.name()));
-	}
 }

src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftSourceSets.java

@@ -209,12 +209,14 @@ public abstract sealed class MinecraftSourceSets permits MinecraftSourceSets.Sin
 				);
 			});
 
-			if (project.getTasks().findByName(mainSourceSet.getSourcesJarTaskName()) == null) {
+			// The sources task can be registered at a later time.
-				// No sources.
+			project.getTasks().configureEach(task -> {
-				return;
+				if (!mainSourceSet.getSourcesJarTaskName().equals(task.getName()) || !(task instanceof Jar jar)) {
-			}
+					// Not the sources task we are looking for.
+					return;
+				}
 
-			project.getTasks().named(mainSourceSet.getSourcesJarTaskName(), Jar.class).configure(jar -> {
+				// The client only sources to the combined sources jar.
 				jar.from(clientOnlySourceSet.getAllSource());
 			});
 		}
@@ -224,7 +226,7 @@ public abstract sealed class MinecraftSourceSets permits MinecraftSourceSets.Sin
 		}
 
 		public static SourceSet getClientSourceSet(Project project) {
-			Preconditions.checkArgument(LoomGradleExtension.get(project).areEnvironmentSourceSetsSplit());
+			Preconditions.checkArgument(LoomGradleExtension.get(project).areEnvironmentSourceSetsSplit(), "Cannot get client only sourceset as project is not split");
 
 			final JavaPluginExtension javaExtension = project.getExtensions().getByType(JavaPluginExtension.class);
 			return javaExtension.getSourceSets().getByName(CLIENT_ONLY_SOURCE_SET_NAME);

src/main/java/net/fabricmc/loom/decompilers/fernflower/FernFlowerUtils.java

@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2016-2020 FabricMC
+ * Copyright (c) 2016-2022 FabricMC
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -26,11 +26,11 @@ package net.fabricmc.loom.decompilers.fernflower;
 
 import java.io.File;
 import java.io.IOException;
-import java.util.zip.ZipEntry;
-import java.util.zip.ZipFile;
 
 import org.jetbrains.java.decompiler.util.InterpreterUtil;
 
+import net.fabricmc.loom.util.ZipUtils;
+
 public class FernFlowerUtils {
 	public static byte[] getBytecode(String externalPath, String internalPath) throws IOException {
 		File file = new File(externalPath);
@@ -38,15 +38,7 @@ public class FernFlowerUtils {
 		if (internalPath == null) {
 			return InterpreterUtil.getBytes(file);
 		} else {
-			try (ZipFile archive = new ZipFile(file)) {
+			return ZipUtils.unpack(file.toPath(), internalPath);
-				ZipEntry entry = archive.getEntry(internalPath);
-
-				if (entry == null) {
-					throw new IOException("Entry not found: " + internalPath);
-				}
-
-				return InterpreterUtil.getBytes(archive, entry);
-			}
 		}
 	}
 }

src/main/java/net/fabricmc/loom/task/AbstractRemapJarTask.java

@@ -24,18 +24,30 @@
 
 package net.fabricmc.loom.task;
 
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.File;
 import java.io.IOException;
 import java.nio.file.Path;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Function;
+import java.util.jar.Manifest;
 
 import javax.inject.Inject;
 
+import com.google.common.base.Preconditions;
 import org.gradle.api.Action;
 import org.gradle.api.file.ConfigurableFileCollection;
 import org.gradle.api.file.RegularFileProperty;
+import org.gradle.api.provider.ListProperty;
+import org.gradle.api.provider.MapProperty;
 import org.gradle.api.provider.Property;
 import org.gradle.api.tasks.Input;
 import org.gradle.api.tasks.InputFile;
 import org.gradle.api.tasks.InputFiles;
+import org.gradle.api.tasks.Internal;
 import org.gradle.jvm.tasks.Jar;
 import org.gradle.workers.WorkAction;
 import org.gradle.workers.WorkParameters;
@@ -44,9 +56,14 @@ import org.gradle.workers.WorkerExecutor;
 
 import net.fabricmc.loom.api.mappings.layered.MappingsNamespace;
 import net.fabricmc.loom.build.IntermediaryNamespaces;
+import net.fabricmc.loom.task.service.JarManifestService;
 import net.fabricmc.loom.util.ZipReprocessorUtil;
+import net.fabricmc.loom.util.ZipUtils;
 
 public abstract class AbstractRemapJarTask extends Jar {
+	public static final String MANIFEST_PATH = "META-INF/MANIFEST.MF";
+	public static final String MANIFEST_NAMESPACE_KEY = "Fabric-Mapping-Namespace";
+
 	@InputFile
 	public abstract RegularFileProperty getInputFile();
 
@@ -68,11 +85,15 @@ public abstract class AbstractRemapJarTask extends Jar {
 	@Inject
 	protected abstract WorkerExecutor getWorkerExecutor();
 
+	@Input
+	public abstract Property<Boolean> getIncludesClientOnlyClasses();
+
 	@Inject
 	public AbstractRemapJarTask() {
 		getSourceNamespace().convention(MappingsNamespace.NAMED.toString()).finalizeValueOnRead();
 		getTargetNamespace().convention(IntermediaryNamespaces.intermediary(getProject())).finalizeValueOnRead();
 		getRemapperIsolation().convention(true).finalizeValueOnRead();
+		getIncludesClientOnlyClasses().convention(false).finalizeValueOnRead();
 	}
 
 	public final <P extends AbstractRemapParams> void submitWork(Class<? extends AbstractRemapAction<P>> workAction, Action<P> action) {
@@ -88,10 +109,21 @@ public abstract class AbstractRemapJarTask extends Jar {
 			params.getArchivePreserveFileTimestamps().set(isPreserveFileTimestamps());
 			params.getArchiveReproducibleFileOrder().set(isReproducibleFileOrder());
 
+			params.getJarManifestService().set(JarManifestService.get(getProject()));
+
+			if (getIncludesClientOnlyClasses().get()) {
+				final List<String> clientOnlyEntries = getClientOnlyEntries();
+				applyClientOnlyManifestAttributes(params, clientOnlyEntries);
+				params.getClientOnlyEntries().set(clientOnlyEntries.stream().filter(s -> s.endsWith(".class")).toList());
+			}
+
 			action.execute(params);
 		});
 	}
 
+	@Internal
+	protected abstract List<String> getClientOnlyEntries();
+
 	public interface AbstractRemapParams extends WorkParameters {
 		RegularFileProperty getInputFile();
 		RegularFileProperty getOutputFile();
@@ -101,6 +133,18 @@ public abstract class AbstractRemapJarTask extends Jar {
 
 		Property<Boolean> getArchivePreserveFileTimestamps();
 		Property<Boolean> getArchiveReproducibleFileOrder();
+
+		Property<JarManifestService> getJarManifestService();
+		MapProperty<String, String> getManifestAttributes();
+
+		ListProperty<String> getClientOnlyEntries();
+	}
+
+	protected void applyClientOnlyManifestAttributes(AbstractRemapParams params, List<String> entries) {
+		params.getManifestAttributes().set(Map.of(
+				"Fabric-Loom-Split-Environment", "true",
+				"Fabric-Loom-Client-Only-Entries", String.join(";", entries)
+		));
 	}
 
 	public abstract static class AbstractRemapAction<T extends AbstractRemapParams> implements WorkAction<T> {
@@ -113,6 +157,21 @@ public abstract class AbstractRemapJarTask extends Jar {
 			outputFile = getParameters().getOutputFile().getAsFile().get().toPath();
 		}
 
+		protected void modifyJarManifest() throws IOException {
+			int count = ZipUtils.transform(outputFile, Map.of(MANIFEST_PATH, bytes -> {
+				var manifest = new Manifest(new ByteArrayInputStream(bytes));
+
+				getParameters().getJarManifestService().get().apply(manifest, getParameters().getManifestAttributes().get());
+				manifest.getMainAttributes().putValue(MANIFEST_NAMESPACE_KEY, getParameters().getTargetNamespace().get());
+
+				ByteArrayOutputStream out = new ByteArrayOutputStream();
+				manifest.write(out);
+				return out.toByteArray();
+			}));
+
+			Preconditions.checkState(count > 0, "Did not transform any jar manifest");
+		}
+
 		protected void rewriteJar() throws IOException {
 			final boolean isReproducibleFileOrder = getParameters().getArchiveReproducibleFileOrder().get();
 			final boolean isPreserveFileTimestamps = getParameters().getArchivePreserveFileTimestamps().get();
@@ -128,4 +187,31 @@ public abstract class AbstractRemapJarTask extends Jar {
 	public RegularFileProperty getInput() {
 		return getInputFile();
 	}
+
+	protected static List<String> getRootPaths(Set<File> files) {
+		return files.stream()
+				.map(root -> {
+					String rootPath = root.getAbsolutePath().replace("\\", "/");
+
+					if (rootPath.charAt(rootPath.length() - 1) != '/') {
+						rootPath += '/';
+					}
+
+					return rootPath;
+				}).toList();
+	}
+
+	protected static Function<File, String> relativePath(List<String> rootPaths) {
+		return file -> {
+			String s = file.getAbsolutePath().replace("\\", "/");
+
+			for (String rootPath : rootPaths) {
+				if (s.startsWith(rootPath)) {
+					s = s.substring(rootPath.length());
+				}
+			}
+
+			return s;
+		};
+	}
 }

src/main/java/net/fabricmc/loom/task/MigrateMappingsTask.java

@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2019-2021 FabricMC
+ * Copyright (c) 2019-2022 FabricMC
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -26,8 +26,6 @@ package net.fabricmc.loom.task;
 
 import java.io.File;
 import java.io.IOException;
-import java.nio.file.FileSystem;
-import java.nio.file.FileSystems;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.Set;
@@ -51,6 +49,7 @@ import net.fabricmc.loom.api.mappings.layered.MappingsNamespace;
 import net.fabricmc.loom.api.mappings.layered.spec.LayeredMappingSpecBuilder;
 import net.fabricmc.loom.configuration.providers.mappings.LayeredMappingsDependency;
 import net.fabricmc.loom.configuration.providers.mappings.MappingsProviderImpl;
+import net.fabricmc.loom.util.FileSystemUtil;
 import net.fabricmc.loom.util.SourceRemapper;
 import net.fabricmc.lorenztiny.TinyMappingsJoiner;
 import net.fabricmc.mappingio.MappingReader;
@@ -117,7 +116,7 @@ public class MigrateMappingsTask extends AbstractLoomTask {
 		Set<File> files;
 
 		try {
-			if (mappings.startsWith("net.minecraft:mappings:") || mappings.startsWith("net.mojang.minecraft:mappings:")) {
+			if (mappings.startsWith("net.minecraft:mappings:")) {
 				if (!mappings.endsWith(":" + LoomGradleExtension.get(project).getMinecraftProvider().minecraftVersion())) {
 					throw new UnsupportedOperationException("Migrating Mojang mappings is currently only supported for the specified minecraft version");
 				}
@@ -149,8 +148,8 @@ public class MigrateMappingsTask extends AbstractLoomTask {
 	private static MemoryMappingTree getMappings(File mappings) throws IOException {
 		MemoryMappingTree mappingTree = new MemoryMappingTree();
 
-		try (FileSystem fileSystem = FileSystems.newFileSystem(mappings.toPath(), (ClassLoader) null)) {
+		try (FileSystemUtil.Delegate delegate = FileSystemUtil.getJarFileSystem(mappings.toPath())) {
-			MappingReader.read(fileSystem.getPath("mappings/mappings.tiny"), mappingTree);
+			MappingReader.read(delegate.fs().getPath("mappings/mappings.tiny"), mappingTree);
 		}
 
 		return mappingTree;

src/main/java/net/fabricmc/loom/task/RemapJarTask.java

@@ -26,7 +26,6 @@ package net.fabricmc.loom.task;
 
 import java.io.BufferedReader;
 import java.io.ByteArrayInputStream;
-import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStreamReader;
@@ -47,7 +46,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
-import java.util.function.Function;
 import java.util.function.Supplier;
 import java.util.jar.Attributes;
 import java.util.jar.JarFile;
@@ -58,7 +56,6 @@ import java.util.stream.StreamSupport;
 
 import javax.inject.Inject;
 
-import com.google.common.base.Preconditions;
 import com.google.common.base.Suppliers;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
@@ -73,7 +70,6 @@ import org.gradle.api.file.FileCollection;
 import org.gradle.api.file.RegularFileProperty;
 import org.gradle.api.plugins.JavaPlugin;
 import org.gradle.api.provider.ListProperty;
-import org.gradle.api.provider.MapProperty;
 import org.gradle.api.provider.Property;
 import org.gradle.api.provider.Provider;
 import org.gradle.api.provider.SetProperty;
@@ -100,7 +96,6 @@ import net.fabricmc.loom.build.nesting.JarNester;
 import net.fabricmc.loom.configuration.accesswidener.AccessWidenerFile;
 import net.fabricmc.loom.configuration.providers.minecraft.MinecraftSourceSets;
 import net.fabricmc.loom.extension.MixinExtension;
-import net.fabricmc.loom.task.service.JarManifestService;
 import net.fabricmc.loom.task.service.MappingsService;
 import net.fabricmc.loom.task.service.TinyRemapperService;
 import net.fabricmc.loom.util.Constants;
@@ -108,6 +103,7 @@ import net.fabricmc.loom.util.ExceptionUtil;
 import net.fabricmc.loom.util.FileSystemUtil;
 import net.fabricmc.loom.util.LfWriter;
 import net.fabricmc.loom.util.ModPlatform;
+import net.fabricmc.loom.util.ModUtils;
 import net.fabricmc.loom.util.Pair;
 import net.fabricmc.loom.util.SidedClassVisitor;
 import net.fabricmc.loom.util.ZipUtils;
@@ -116,9 +112,6 @@ import net.fabricmc.loom.util.service.UnsafeWorkQueueHelper;
 import net.fabricmc.lorenztiny.TinyMappingsReader;
 
 public abstract class RemapJarTask extends AbstractRemapJarTask {
-	public static final String MANIFEST_PATH = "META-INF/MANIFEST.MF";
-	public static final String MANIFEST_NAMESPACE_KEY = "Fabric-Mapping-Namespace";
-
 	@InputFiles
 	public abstract ConfigurableFileCollection getNestedJars();
 
@@ -128,9 +121,6 @@ public abstract class RemapJarTask extends AbstractRemapJarTask {
 	@Input
 	public abstract Property<Boolean> getAddNestedDependencies();
 
-	@Input
-	public abstract Property<Boolean> getIncludesClientOnlyClasses();
-
 	/**
 	 * Gets the jar paths to the access wideners that will be converted to ATs for Forge runtime.
 	 * If you specify multiple files, they will be merged into one.
@@ -170,7 +160,6 @@ public abstract class RemapJarTask extends AbstractRemapJarTask {
 
 		getClasspath().from(getProject().getConfigurations().getByName(JavaPlugin.COMPILE_CLASSPATH_CONFIGURATION_NAME));
 		getAddNestedDependencies().convention(true).finalizeValueOnRead();
-		getIncludesClientOnlyClasses().convention(false).finalizeValueOnRead();
 		getReadMixinConfigsFromManifest().convention(LoomGradleExtension.get(getProject()).isForge()).finalizeValueOnRead();
 		getInjectAccessWidener().convention(false);
 
@@ -221,7 +210,6 @@ public abstract class RemapJarTask extends AbstractRemapJarTask {
 				}
 			}
 
-			params.getJarManifestService().set(JarManifestService.get(getProject()));
 			params.getTinyRemapperBuildServiceUuid().set(UnsafeWorkQueueHelper.create(getProject(), tinyRemapperService.get()));
 			params.getRemapClasspath().from(getClasspath());
 
@@ -246,20 +234,6 @@ public abstract class RemapJarTask extends AbstractRemapJarTask {
 			if (!getAtAccessWideners().get().isEmpty()) {
 				params.getMappingBuildServiceUuid().set(UnsafeWorkQueueHelper.create(getProject(), MappingsService.createDefault(getProject(), getSourceNamespace().get(), getTargetNamespace().get())));
 			}
-
-			if (getIncludesClientOnlyClasses().get()) {
-				if (!extension.areEnvironmentSourceSetsSplit()) {
-					throw new UnsupportedOperationException("Jar cannot include client only classes as the sources are not split");
-				}
-
-				final List<String> clientOnlyJarEntries = getClientOnlyJarEntries();
-				params.getManifestAttributes().set(Map.of(
-						"Fabric-Loom-Split-Environment", "true",
-						"Fabric-Loom-Client-Only-Entries", String.join(";", clientOnlyJarEntries)
-				));
-
-				params.getClientOnlyClasses().set(clientOnlyJarEntries.stream().filter(s -> s.endsWith(".class")).toList());
-			}
 		});
 	}
 
@@ -268,7 +242,7 @@ public abstract class RemapJarTask extends AbstractRemapJarTask {
 		final MixinExtension mixinExtension = extension.getMixin();
 		Collection<String> allMixinConfigs = null;
 
-		final JsonObject fabricModJson = extension.getPlatform().get() == ModPlatform.FABRIC ? MixinRefmapHelper.readFabricModJson(getInputFile().getAsFile().get()) : null;
+		final JsonObject fabricModJson = extension.getPlatform().get() == ModPlatform.FABRIC ? ModUtils.getFabricModJson(getInputFile().getAsFile().get().toPath()) : null;
 
 		if (fabricModJson == null) {
 			if (extension.getPlatform().get() == ModPlatform.QUILT) {
@@ -374,12 +348,8 @@ public abstract class RemapJarTask extends AbstractRemapJarTask {
 		record RefmapData(List<String> mixinConfigs, String refmapName) implements Serializable { }
 		ListProperty<RefmapData> getMixinData();
 
-		Property<JarManifestService> getJarManifestService();
 		Property<String> getTinyRemapperBuildServiceUuid();
 		Property<String> getMappingBuildServiceUuid();
-
-		MapProperty<String, String> getManifestAttributes();
-		ListProperty<String> getClientOnlyClasses();
 	}
 
 	public abstract static class RemapAction extends AbstractRemapAction<RemapParams> {
@@ -401,7 +371,7 @@ public abstract class RemapJarTask extends AbstractRemapJarTask {
 
 				remap();
 
-				if (getParameters().getClientOnlyClasses().isPresent()) {
+				if (getParameters().getClientOnlyEntries().isPresent()) {
 					markClientOnlyClasses();
 				}
 
@@ -439,7 +409,7 @@ public abstract class RemapJarTask extends AbstractRemapJarTask {
 		}
 
 		private void markClientOnlyClasses() throws IOException {
-			final Stream<Pair<String, ZipUtils.UnsafeUnaryOperator<byte[]>>> tranformers = getParameters().getClientOnlyClasses().get().stream()
+			final Stream<Pair<String, ZipUtils.UnsafeUnaryOperator<byte[]>>> tranformers = getParameters().getClientOnlyEntries().get().stream()
 					.map(s -> new Pair<>(s,
 							(ZipUtils.AsmClassOperator) classVisitor -> SidedClassVisitor.CLIENT.insertApplyVisitor(null, classVisitor)
 					));
@@ -564,21 +534,6 @@ public abstract class RemapJarTask extends AbstractRemapJarTask {
 			JarNester.nestJars(jars, forgeNestedJars.getOrElse(List.of()), outputFile.toFile(), getParameters().getPlatform().get(), LOGGER);
 		}
 
-		private void modifyJarManifest() throws IOException {
-			int count = ZipUtils.transform(outputFile, Map.of(MANIFEST_PATH, bytes -> {
-				var manifest = new Manifest(new ByteArrayInputStream(bytes));
-
-				getParameters().getJarManifestService().get().apply(manifest, getParameters().getManifestAttributes().get());
-				manifest.getMainAttributes().putValue(MANIFEST_NAMESPACE_KEY, getParameters().getTargetNamespace().get());
-
-				ByteArrayOutputStream out = new ByteArrayOutputStream();
-				manifest.write(out);
-				return out.toByteArray();
-			}));
-
-			Preconditions.checkState(count > 0, "Did not transform any jar manifest");
-		}
-
 		private void addRefmaps() throws IOException {
 			if (getParameters().getUseMixinExtension().get()) {
 				return;
@@ -596,7 +551,8 @@ public abstract class RemapJarTask extends AbstractRemapJarTask {
 		}
 	}
 
-	private List<String> getClientOnlyJarEntries() {
+	@Override
+	protected List<String> getClientOnlyEntries() {
 		final SourceSet clientSourceSet = MinecraftSourceSets.Split.getClientSourceSet(getProject());
 
 		final ConfigurableFileCollection output = getProject().getObjects().fileCollection();
@@ -613,33 +569,6 @@ public abstract class RemapJarTask extends AbstractRemapJarTask {
 				.toList();
 	}
 
-	private static List<String> getRootPaths(Set<File> files) {
-		return files.stream()
-			.map(root -> {
-				String rootPath = root.getAbsolutePath().replace("\\", "/");
-
-				if (rootPath.charAt(rootPath.length() - 1) != '/') {
-					rootPath += '/';
-				}
-
-				return rootPath;
-			}).toList();
-	}
-
-	private static Function<File, String> relativePath(List<String> rootPaths) {
-		return file -> {
-			String s = file.getAbsolutePath().replace("\\", "/");
-
-			for (String rootPath : rootPaths) {
-				if (s.startsWith(rootPath)) {
-					s = s.substring(rootPath.length());
-				}
-			}
-
-			return s;
-		};
-	}
-
 	@Internal
 	public TinyRemapperService getTinyRemapperService() {
 		return tinyRemapperService.get();

src/main/java/net/fabricmc/loom/task/RemapSourcesJarTask.java

@@ -26,15 +26,18 @@ package net.fabricmc.loom.task;
 
 import java.io.IOException;
 import java.nio.file.Files;
+import java.util.List;
 
 import javax.inject.Inject;
 
 import org.gradle.api.plugins.JavaPlugin;
 import org.gradle.api.provider.Property;
+import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.TaskAction;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import net.fabricmc.loom.configuration.providers.minecraft.MinecraftSourceSets;
 import net.fabricmc.loom.task.service.SourceRemapperService;
 import net.fabricmc.loom.util.service.UnsafeWorkQueueHelper;
 
@@ -53,6 +56,15 @@ public abstract class RemapSourcesJarTask extends AbstractRemapJarTask {
 		});
 	}
 
+	@Override
+	protected List<String> getClientOnlyEntries() {
+		final SourceSet clientSourceSet = MinecraftSourceSets.Split.getClientSourceSet(getProject());
+
+		return clientSourceSet.getAllSource().getFiles().stream()
+				.map(relativePath(getRootPaths(clientSourceSet.getAllSource().getSrcDirs())))
+				.toList();
+	}
+
 	public interface RemapSourcesParams extends AbstractRemapParams {
 		Property<String> getSourcesRemapperServiceUuid();
 	}
@@ -73,6 +85,7 @@ public abstract class RemapSourcesJarTask extends AbstractRemapJarTask {
 			try {
 				sourceRemapperService.remapSourcesJar(inputFile, outputFile);
 
+				modifyJarManifest();
 				rewriteJar();
 			} catch (Exception e) {
 				try {

src/main/java/net/fabricmc/loom/task/RemapTaskConfiguration.java

@@ -150,6 +150,7 @@ public class RemapTaskConfiguration {
 
 			task.dependsOn(sourcesJarTask);
 			task.getInputFile().convention(sourcesJarTask.getArchiveFile());
+			task.getIncludesClientOnlyClasses().set(project.provider(extension::areEnvironmentSourceSetsSplit));
 		});
 
 		tasks.named(BasePlugin.ASSEMBLE_TASK_NAME).configure(task -> task.dependsOn(remapSourcesTask));

src/main/java/net/fabricmc/loom/util/FileSystemUtil.java

@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2016-2017 FabricMC
+ * Copyright (c) 2016-2022 FabricMC
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -27,20 +27,17 @@ package net.fabricmc.loom.util;
 import java.io.File;
 import java.io.IOException;
 import java.net.URI;
-import java.net.URISyntaxException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.FileSystem;
-import java.nio.file.FileSystemAlreadyExistsException;
-import java.nio.file.FileSystems;
 import java.nio.file.Files;
 import java.nio.file.NoSuchFileException;
 import java.nio.file.Path;
-import java.util.Collections;
-import java.util.Map;
 import java.util.function.Supplier;
 
+import net.fabricmc.tinyremapper.FileSystemReference;
+
 public final class FileSystemUtil {
-	public record Delegate(FileSystem fs, boolean owner) implements AutoCloseable, Supplier<FileSystem> {
+	public record Delegate(FileSystemReference reference) implements AutoCloseable, Supplier<FileSystem> {
 		public byte[] readAllBytes(String path) throws IOException {
 			Path fsPath = get().getPath(path);
 
@@ -57,50 +54,36 @@ public final class FileSystemUtil {
 
 		@Override
 		public void close() throws IOException {
-			if (owner) {
+			reference.close();
-				fs.close();
-			}
 		}
 
 		@Override
 		public FileSystem get() {
-			return fs;
+			return reference.getFs();
+		}
+
+		// TODO cleanup
+		public FileSystem fs() {
+			return get();
 		}
 	}
 
 	private FileSystemUtil() {
 	}
 
-	private static final Map<String, String> jfsArgsCreate = Map.of("create", "true");
-	private static final Map<String, String> jfsArgsEmpty = Collections.emptyMap();
-
 	public static Delegate getJarFileSystem(File file, boolean create) throws IOException {
-		return getJarFileSystem(file.toURI(), create);
+		return new Delegate(FileSystemReference.openJar(file.toPath(), create));
 	}
 
 	public static Delegate getJarFileSystem(Path path, boolean create) throws IOException {
-		return getJarFileSystem(path.toUri(), create);
+		return new Delegate(FileSystemReference.openJar(path, create));
 	}
 
 	public static Delegate getJarFileSystem(Path path) throws IOException {
-		return getJarFileSystem(path, false);
+		return new Delegate(FileSystemReference.openJar(path));
 	}
 
 	public static Delegate getJarFileSystem(URI uri, boolean create) throws IOException {
-		URI jarUri;
+		return new Delegate(FileSystemReference.open(uri, create));
-
-		try {
-			jarUri = new URI("jar:" + uri.getScheme(), uri.getHost(), uri.getPath(), uri.getFragment());
-		} catch (URISyntaxException e) {
-			throw new IOException(e);
-		}
-
-		try {
-			return new Delegate(FileSystems.newFileSystem(jarUri, create ? jfsArgsCreate : jfsArgsEmpty), true);
-		} catch (FileSystemAlreadyExistsException e) {
-			return new Delegate(FileSystems.getFileSystem(jarUri), false);
-		} catch (IOException e) {
-			throw new IOException("Could not create JAR file system for " + uri + " (create: " + create + ")", e);
-		}
 	}
 }

src/main/java/net/fabricmc/loom/util/ModUtils.java

@@ -27,15 +27,12 @@ package net.fabricmc.loom.util;
 import java.io.File;
 import java.io.IOException;
 import java.io.UncheckedIOException;
-import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
 
 import com.google.gson.JsonObject;
 import org.gradle.api.logging.Logger;
 import org.jetbrains.annotations.Nullable;
 
-import net.fabricmc.loom.LoomGradlePlugin;
-
 public final class ModUtils {
 	private ModUtils() {
 	}
@@ -56,19 +53,11 @@ public final class ModUtils {
 
 	@Nullable
 	public static JsonObject getFabricModJson(Path path) {
-		final byte[] modJsonBytes;
-
 		try {
-			modJsonBytes = ZipUtils.unpackNullable(path, "fabric.mod.json");
+			return ZipUtils.unpackGsonNullable(path, "fabric.mod.json", JsonObject.class);
 		} catch (IOException e) {
 			throw new UncheckedIOException("Failed to extract fabric.mod.json from " + path, e);
 		}
-
-		if (modJsonBytes == null) {
-			return null;
-		}
-
-		return LoomGradlePlugin.GSON.fromJson(new String(modJsonBytes, StandardCharsets.UTF_8), JsonObject.class);
 	}
 
 	public static boolean shouldRemapMod(Logger logger, File input, Object id, ModPlatform platform, String config) {

src/main/java/net/fabricmc/loom/util/ZipUtils.java

@@ -107,6 +107,25 @@ public class ZipUtils {
 		}
 	}
 
+	public static <T> T unpackGson(Path zip, String path, Class<T> clazz) throws IOException {
+		final byte[] bytes = unpack(zip, path);
+		return LoomGradlePlugin.GSON.fromJson(new String(bytes, StandardCharsets.UTF_8), clazz);
+	}
+
+	@Nullable
+	public static <T> T unpackGsonNullable(Path zip, String path, Class<T> clazz) throws IOException {
+		try {
+			return unpackGson(zip, path, clazz);
+		} catch (NoSuchFileException e) {
+			return null;
+		}
+	}
+
+	public static <T> T unpackJackson(Path zip, String path, Class<T> clazz) throws IOException {
+		final byte[] bytes = unpack(zip, path);
+		return LoomGradlePlugin.OBJECT_MAPPER.readValue(new String(bytes, StandardCharsets.UTF_8), clazz);
+	}
+
 	public static void pack(Path from, Path zip) throws IOException {
 		Files.deleteIfExists(zip);
 

src/test/groovy/net/fabricmc/loom/test/util/GradleProjectTestTrait.groovy

@@ -46,6 +46,13 @@ trait GradleProjectTestTrait {
         File projectDir = options.projectDir as File ?: options.sharedFiles ? sharedProjectDir : File.createTempDir()
         File gradleHomeDir = options.gradleHomeDir as File ?: options.sharedFiles ? sharedGradleHomeDir : File.createTempDir()
 
+		// Useful for faster local testing.
+		def homeDirOverride = System.getProperty("fabric.loom.test.homeDir")
+
+		if (homeDirOverride) {
+			gradleHomeDir = new File(homeDirOverride)
+		}
+
         setupProject(options, projectDir)
 
         println([