Merge remote-tracking branch 'FabricMC/dev/0.9' into dev/0.9

# Conflicts:
#	src/main/java/net/fabricmc/loom/LoomGradleExtension.java
#	src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java
#	src/main/java/net/fabricmc/loom/configuration/ide/RunConfig.java
#	src/main/java/net/fabricmc/loom/configuration/mods/ModProcessor.java
#	src/main/java/net/fabricmc/loom/configuration/providers/MinecraftProviderImpl.java
#	src/main/java/net/fabricmc/loom/configuration/providers/mappings/MappingsProviderImpl.java
#	src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftMappedProvider.java
#	src/main/java/net/fabricmc/loom/task/GenerateSourcesTask.java

52 files changed, 1411 insertions, 866 deletions

diff --git a/src/main/java/net/fabricmc/loom/LoomGradleExtension.java b/src/main/java/net/fabricmc/loom/LoomGradleExtension.java
index 6ea1a3ed..2705898c 100644
--- a/src/main/java/net/fabricmc/loom/LoomGradleExtension.java
+++ b/src/main/java/net/fabricmc/loom/LoomGradleExtension.java
@@ -25,563 +25,84 @@
 package net.fabricmc.loom;
 
 import java.io.File;
-import java.nio.file.Path;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.HashSet;
-import java.util.List;
-import java.util.Locale;
-import java.util.Objects;
 import java.util.Set;
-import java.util.function.Consumer;
-import java.util.function.Function;
 import java.util.function.Supplier;
-import java.util.stream.Collectors;
 
 import org.cadixdev.lorenz.MappingSet;
 import org.cadixdev.mercury.Mercury;
-import org.gradle.api.Action;
-import org.gradle.api.NamedDomainObjectContainer;
+import org.gradle.api.NamedDomainObjectProvider;
 import org.gradle.api.Project;
-import org.gradle.api.artifacts.Dependency;
+import org.gradle.api.artifacts.Configuration;
 import org.gradle.api.file.ConfigurableFileCollection;
-import org.gradle.api.plugins.BasePluginConvention;
-import org.gradle.api.plugins.JavaPluginConvention;
-import org.gradle.api.tasks.SourceSet;
-import org.jetbrains.annotations.ApiStatus;
 
-import net.fabricmc.loom.api.decompilers.LoomDecompiler;
+import net.fabricmc.loom.api.LoomGradleExtensionAPI;
 import net.fabricmc.loom.configuration.InstallerData;
 import net.fabricmc.loom.configuration.LoomDependencyManager;
-import net.fabricmc.loom.configuration.LoomProjectData;
-import net.fabricmc.loom.configuration.ide.RunConfig;
-import net.fabricmc.loom.configuration.ide.RunConfigSettings;
-import net.fabricmc.loom.configuration.launch.LaunchProviderSettings;
-import net.fabricmc.loom.configuration.processors.JarProcessor;
 import net.fabricmc.loom.configuration.processors.JarProcessorManager;
 import net.fabricmc.loom.configuration.providers.MinecraftProviderImpl;
-import net.fabricmc.loom.configuration.providers.forge.FieldMigratedMappingsProvider;
-import net.fabricmc.loom.configuration.providers.forge.ForgeProvider;
-import net.fabricmc.loom.configuration.providers.forge.ForgeUniversalProvider;
-import net.fabricmc.loom.configuration.providers.forge.ForgeUserdevProvider;
-import net.fabricmc.loom.configuration.providers.forge.McpConfigProvider;
-import net.fabricmc.loom.configuration.providers.forge.PatchProvider;
-import net.fabricmc.loom.configuration.providers.forge.SrgProvider;
-import net.fabricmc.loom.configuration.providers.minecraft.MinecraftMappedProvider;
-import net.fabricmc.loom.configuration.providers.mappings.GradleMappingContext;
-import net.fabricmc.loom.configuration.providers.mappings.LayeredMappingSpec;
-import net.fabricmc.loom.configuration.providers.mappings.LayeredMappingSpecBuilder;
-import net.fabricmc.loom.configuration.providers.mappings.LayeredMappingsDependency;
 import net.fabricmc.loom.configuration.providers.mappings.MappingsProviderImpl;
-import net.fabricmc.loom.configuration.providers.minecraft.MinecraftVersionMeta;
-import net.fabricmc.loom.util.ModPlatform;
-import net.fabricmc.loom.util.function.LazyBool;
-
-public class LoomGradleExtension {
-	private static final String FORGE_PROPERTY = "loom.forge";
-	private static final String PLATFORM_PROPERTY = "loom.platform";
-	private static final String INCLUDE_PROPERTY = "loom.forge.include";
-
-	public String refmapName;
-	public String loaderLaunchMethod;
-	public boolean remapMod = true;
-	public String customManifest = null;
-	public File accessWidener = null;
-	public Set<File> accessTransformers = new HashSet<>();
-	public Function<String, Object> intermediaryUrl = mcVer -> "https://maven.fabricmc.net/net/fabricmc/intermediary/" + mcVer + "/intermediary-" + mcVer + "-v2.jar";
-	public boolean shareCaches = false;
-	public List<String> mixinConfigs = new ArrayList<>(); // FORGE: Passed to Minecraft
-	public boolean useFabricMixin = true; // FORGE: Use Fabric Mixin for better refmap resolutions
-
-	private final ConfigurableFileCollection unmappedMods;
-	private final ConfigurableFileCollection log4jConfigs;
-
-	final List<LoomDecompiler> decompilers = new ArrayList<>();
-	private final List<JarProcessor> jarProcessors = new ArrayList<>();
-	private boolean silentMojangMappingsLicense = false;
-	public Boolean generateSrgTiny = null;
-
-	// Not to be set in the build.gradle
-	private final Project project;
-	private List<String> dataGenMods = new ArrayList<>();
-	private LoomDependencyManager dependencyManager;
-	private JarProcessorManager jarProcessorManager;
-	private InstallerData installerData;
-	private MappingSet[] srcMappingCache = new MappingSet[2];
-	private Mercury[] srcMercuryCache = new Mercury[2];
-	private ModPlatform platform;
-	private final LazyBool supportsInclude;
-	private Set<File> mixinMappings = Collections.synchronizedSet(new HashSet<>());
-	private final List<String> tasksBeforeRun = Collections.synchronizedList(new ArrayList<>());
-	public final List<Supplier<SourceSet>> forgeLocalMods = Collections.synchronizedList(new ArrayList<>(Collections.singletonList(new Supplier<SourceSet>() {
-		@Override
-		public SourceSet get() {
-			return project.getConvention().getPlugin(JavaPluginConvention.class).getSourceSets().getByName("main");
-		}
-	})));
-	@ApiStatus.Experimental
-	public final List<Consumer<RunConfig>> settingsPostEdit = new ArrayList<>();
-
-	@ApiStatus.Internal
-	private final LoomProjectData projectData;
-
-	private NamedDomainObjectContainer<RunConfigSettings> runConfigs;
-	private NamedDomainObjectContainer<LaunchProviderSettings> launchConfigs;
-
-	/**
-	 * Loom will generate a new genSources task (with a new name, based off of {@link LoomDecompiler#name()})
-	 * that uses the specified decompiler instead.
-	 */
-	public void addDecompiler(LoomDecompiler decompiler) {
-		decompilers.add(decompiler);
-	}
-
-	/**
-	 * Add a transformation over the mapped mc jar.
-	 * Adding any jar processor will cause mapped mc jars to be stored per-project so that
-	 * different transformation can be applied in different projects.
-	 * This means remapping will need to be done individually per-project, which is slower when developing
-	 * more than one project using the same minecraft version.
-	 */
-	public void addJarProcessor(JarProcessor processor) {
-		jarProcessors.add(processor);
-	}
-
-	public MappingSet getOrCreateSrcMappingCache(int id, Supplier<MappingSet> factory) {
-		if (id < 0 || id >= srcMappingCache.length) return factory.get();
-		return srcMappingCache[id] != null ? srcMappingCache[id] : (srcMappingCache[id] = factory.get());
-	}
-
-	public Mercury getOrCreateSrcMercuryCache(int id, Supplier<Mercury> factory) {
-		if (id < 0 || id >= srcMercuryCache.length) return factory.get();
-		return srcMercuryCache[id] != null ? srcMercuryCache[id] : (srcMercuryCache[id] = factory.get());
-	}
-
-	public void localMods(Action<SourceSetConsumer> action) {
-		if (!isForge()) {
-			throw new UnsupportedOperationException("Not running with Forge support.");
-		}
-
-		action.execute(new SourceSetConsumer());
-	}
-
-	public boolean isDataGenEnabled() {
-		return isForge() && !dataGenMods.isEmpty();
-	}
-
-	public List<String> getDataGenMods() {
-		return dataGenMods;
-	}
-
-	public class SourceSetConsumer {
-		public void add(Object... sourceSets) {
-			for (Object sourceSet : sourceSets) {
-				if (sourceSet instanceof SourceSet) {
-					forgeLocalMods.add(() -> (SourceSet) sourceSet);
-				} else {
-					forgeLocalMods.add(() -> project.getConvention().getPlugin(JavaPluginConvention.class).getSourceSets().findByName(String.valueOf(forgeLocalMods)));
-				}
-			}
-		}
-	}
-
-	public void dataGen(Action<DataGenConsumer> action) {
-		if (!isForge()) {
-			throw new UnsupportedOperationException("Not running with Forge support.");
-		}
-
-		action.execute(new DataGenConsumer());
-	}
-
-	public class DataGenConsumer {
-		public void mod(String... modIds) {
-			dataGenMods.addAll(Arrays.asList(modIds));
-
-			if (modIds.length > 0 && getRunConfigs().findByName("data") == null) {
-				getRunConfigs().create("data", RunConfigSettings::data);
-			}
-		}
-	}
-
-	public void addTaskBeforeRun(String task) {
-		this.tasksBeforeRun.add(task);
-	}
-
-	public List<String> getTasksBeforeRun() {
-		return tasksBeforeRun;
-	}
-
-	public void mixinConfig(String... config) {
-		mixinConfigs.addAll(Arrays.asList(config));
-	}
-
-	public void silentMojangMappingsLicense() {
-		this.silentMojangMappingsLicense = true;
-	}
-
-	public boolean isSilentMojangMappingsLicenseEnabled() {
-		return silentMojangMappingsLicense;
-	}
-
-	public Dependency officialMojangMappings() {
-		return layered(LayeredMappingSpecBuilder::officialMojangMappings);
-	}
-
-	public Dependency layered(Action<LayeredMappingSpecBuilder> action) {
-		LayeredMappingSpecBuilder builder = new LayeredMappingSpecBuilder(this);
-		action.execute(builder);
-		LayeredMappingSpec builtSpec = builder.build();
-		return new LayeredMappingsDependency(new GradleMappingContext(project, () -> {
-			MinecraftVersionMeta versionInfo = getMinecraftProvider().getVersionInfo();
-			return "layers/" + versionInfo.id() + "_" + builtSpec.getVersion().replace("+", "_").replace(".", "_");
-		}), builtSpec, builtSpec.getVersion());
-	}
-
-	public LoomGradleExtension(Project project) {
-		this.project = project;
-		this.unmappedMods = project.files();
-		this.supportsInclude = new LazyBool(() -> Boolean.parseBoolean(Objects.toString(project.findProperty(INCLUDE_PROPERTY))));
-		this.runConfigs = project.container(RunConfigSettings.class,
-				baseName -> new RunConfigSettings(project, baseName));
-		this.launchConfigs = project.container(LaunchProviderSettings.class,
-				baseName -> new LaunchProviderSettings(project, baseName));
-		this.log4jConfigs = project.files(getDefaultLog4jConfigFile());
-		projectData = new LoomProjectData(project);
-	}
-
-	/**
-	 * @see ConfigurableFileCollection#from(Object...)
-	 * @deprecated use {@link #getUnmappedModCollection()}{@code .from()} instead
-	 */
-	@Deprecated
-	public void addUnmappedMod(Path file) {
-		getUnmappedModCollection().from(file);
-	}
-
-	/**
-	 * @deprecated use {@link #getUnmappedModCollection()} instead
-	 */
-	@Deprecated
-	public List<Path> getUnmappedMods() {
-		return unmappedMods.getFiles().stream()
-				.map(File::toPath)
-				.collect(Collectors.toList());
-	}
-
-	public ConfigurableFileCollection getUnmappedModCollection() {
-		return unmappedMods;
-	}
-
-	public void setInstallerData(InstallerData data) {
-		this.installerData = data;
-	}
-
-	public InstallerData getInstallerData() {
-		return installerData;
-	}
-
-	public void accessWidener(Object file) {
-		this.accessWidener = project.file(file);
-	}
-
-	public void accessTransformer(Object file) {
-		this.accessTransformers.add(project.file(file));
-	}
-
-	public File getUserCache() {
-		File userCache = new File(project.getGradle().getGradleUserHomeDir(), "caches" + File.separator + "fabric-loom");
-
-		if (!userCache.exists()) {
-			userCache.mkdirs();
-		}
-
-		return userCache;
-	}
-
-	public File getRootProjectPersistentCache() {
-		File projectCache = new File(project.getRootProject().file(".gradle"), "loom-cache");
-
-		if (!projectCache.exists()) {
-			projectCache.mkdirs();
-		}
-
-		return projectCache;
-	}
-
-	public File getProjectPersistentCache() {
-		File projectCache = new File(project.file(".gradle"), "loom-cache");
-
-		if (!projectCache.exists()) {
-			projectCache.mkdirs();
-		}
-
-		return projectCache;
-	}
-
-	public File getRootProjectBuildCache() {
-		File projectCache = new File(project.getRootProject().getBuildDir(), "loom-cache");
-
-		if (!projectCache.exists()) {
-			projectCache.mkdirs();
-		}
-
-		return projectCache;
-	}
-
-	public File getProjectBuildCache() {
-		File projectCache = new File(project.getBuildDir(), "loom-cache");
-
-		if (!projectCache.exists()) {
-			projectCache.mkdirs();
-		}
-
-		return projectCache;
-	}
-
-	public File getRemappedModCache() {
-		File remappedModCache = new File(getRootProjectPersistentCache(), "remapped_mods");
-
-		if (!remappedModCache.exists()) {
-			remappedModCache.mkdir();
-		}
-
-		return remappedModCache;
-	}
-
-	public File getNestedModCache() {
-		File nestedModCache = new File(getRootProjectPersistentCache(), "nested_mods");
-
-		if (!nestedModCache.exists()) {
-			nestedModCache.mkdir();
-		}
+import net.fabricmc.loom.configuration.providers.minecraft.MinecraftMappedProvider;
+import net.fabricmc.loom.extension.LoomFiles;
+import net.fabricmc.loom.extension.LoomGradleExtensionImpl;
+import net.fabricmc.loom.extension.MixinApExtension;
 
-		return nestedModCache;
+public interface LoomGradleExtension extends LoomGradleExtensionAPI {
+	static LoomGradleExtension get(Project project) {
+		return project.getExtensions().getByType(LoomGradleExtensionImpl.class);
 	}
 
-	public File getNativesJarStore() {
-		File natives = new File(getUserCache(), "natives/jars");
+	LoomFiles getFiles();
 
-		if (!natives.exists()) {
-			natives.mkdirs();
-		}
+	NamedDomainObjectProvider<Configuration> createLazyConfiguration(String name);
 
-		return natives;
-	}
+	NamedDomainObjectProvider<Configuration> getLazyConfigurationProvider(String name);
 
-	public File getNativesDirectory() {
-		if (project.hasProperty("fabric.loom.natives.dir")) {
-			return new File((String) project.property("fabric.loom.natives.dir"));
-		}
+	MappingSet getOrCreateSrcMappingCache(int id, Supplier<MappingSet> factory);
 
-		File natives = new File(getUserCache(), "natives/" + getMinecraftProvider().minecraftVersion());
+	Mercury getOrCreateSrcMercuryCache(int id, Supplier<Mercury> factory);
 
-		if (!natives.exists()) {
-			natives.mkdirs();
-		}
+	ConfigurableFileCollection getUnmappedModCollection();
 
-		return natives;
-	}
+	void setInstallerData(InstallerData data);
 
-	public boolean hasCustomNatives() {
-		return project.getProperties().get("fabric.loom.natives.dir") != null;
-	}
+	InstallerData getInstallerData();
 
-	public File getDevLauncherConfig() {
-		return new File(getProjectPersistentCache(), "launch.cfg");
-	}
+	void setDependencyManager(LoomDependencyManager dependencyManager);
 
-	public String getLoaderLaunchMethod() {
-		return loaderLaunchMethod != null ? loaderLaunchMethod : "";
-	}
+	LoomDependencyManager getDependencyManager();
 
-	public LoomDependencyManager getDependencyManager() {
-		return dependencyManager;
-	}
+	void setJarProcessorManager(JarProcessorManager jarProcessorManager);
 
-	public PatchProvider getPatchProvider() {
-		return getDependencyManager().getProvider(PatchProvider.class);
-	}
+	JarProcessorManager getJarProcessorManager();
 
-	public MinecraftProviderImpl getMinecraftProvider() {
+	default MinecraftProviderImpl getMinecraftProvider() {
 		return getDependencyManager().getProvider(MinecraftProviderImpl.class);
 	}
 
-	public MinecraftMappedProvider getMinecraftMappedProvider() {
-		return getMappingsProvider().mappedProvider;
-	}
-
-	public MappingsProviderImpl getMappingsProvider() {
-		return getDependencyManager().getProvider(isForge() ? FieldMigratedMappingsProvider.class : MappingsProviderImpl.class);
-	}
-
-	public McpConfigProvider getMcpConfigProvider() {
-		return getDependencyManager().getProvider(McpConfigProvider.class);
+	default MappingsProviderImpl getMappingsProvider() {
+		return getDependencyManager().getProvider(MappingsProviderImpl.class);
 	}
 
-	public SrgProvider getSrgProvider() {
-		return getDependencyManager().getProvider(SrgProvider.class);
-	}
-
-	public ForgeUniversalProvider getForgeUniversalProvider() {
-		return getDependencyManager().getProvider(ForgeUniversalProvider.class);
-	}
-
-	public ForgeUserdevProvider getForgeUserdevProvider() {
-		return getDependencyManager().getProvider(ForgeUserdevProvider.class);
-	}
-
-	public ForgeProvider getForgeProvider() {
-		return getDependencyManager().getProvider(ForgeProvider.class);
-	}
-
-	public void setDependencyManager(LoomDependencyManager dependencyManager) {
-		this.dependencyManager = dependencyManager;
-	}
-
-	public JarProcessorManager getJarProcessorManager() {
-		return jarProcessorManager;
-	}
-
-	public void setJarProcessorManager(JarProcessorManager jarProcessorManager) {
-		this.jarProcessorManager = jarProcessorManager;
-	}
-
-	public List<JarProcessor> getJarProcessors() {
-		return jarProcessors;
+	default MinecraftMappedProvider getMinecraftMappedProvider() {
+		return getMappingsProvider().mappedProvider;
 	}
 
-	public String getRefmapName() {
-		if (refmapName == null || refmapName.isEmpty()) {
-			String defaultRefmapName;
+	File getNextMixinMappings();
 
-			if (isRootProject()) {
-				defaultRefmapName = project.getConvention().getPlugin(BasePluginConvention.class).getArchivesBaseName() + "-refmap.json";
-			} else {
-				defaultRefmapName = project.getConvention().getPlugin(BasePluginConvention.class).getArchivesBaseName() + "-" + project.getPath().replaceFirst(":", "").replace(':', '_') + "-refmap.json";
-			}
+	Set<File> getAllMixinMappings();
 
-			project.getLogger().info("Could not find refmap definition, will be using default name: " + defaultRefmapName);
-			refmapName = defaultRefmapName;
-		}
+	boolean isRootProject();
 
-		return refmapName;
-	}
+	boolean isShareCaches();
 
-	public boolean ideSync() {
+	default boolean ideSync() {
 		return Boolean.parseBoolean(System.getProperty("idea.sync.active", "false"));
 	}
 
-	// Ideally this should use maven, but this is a lot easier
-	public Function<String, String> getIntermediaryUrl() {
-		// Done like this to work around this possibly not being a java string...
-		return s -> intermediaryUrl.apply(s).toString();
-	}
-
-	public boolean isRootProject() {
-		return project.getRootProject() == project;
-	}
-
-	public LoomGradleExtension getRootGradleExtension() {
-		if (isRootProject()) {
-			return this;
-		}
-
-		return project.getRootProject().getExtensions().getByType(LoomGradleExtension.class);
-	}
-
-	public LoomGradleExtension getSharedGradleExtension() {
-		return isShareCaches() ? getRootGradleExtension() : this;
-	}
-
-	public boolean isShareCaches() {
-		return shareCaches;
-	}
-
-	@ApiStatus.Experimental
-	public ModPlatform getPlatform() {
-		if (platform == null) {
-			Object platformProperty = project.findProperty(PLATFORM_PROPERTY);
-
-			if (platformProperty != null) {
-				return platform = ModPlatform.valueOf(Objects.toString(platformProperty).toUpperCase(Locale.ROOT));
-			}
-
-			Object forgeProperty = project.findProperty(FORGE_PROPERTY);
-
-			if (forgeProperty != null) {
-				project.getLogger().warn("Project " + project.getPath() + " is using property " + FORGE_PROPERTY + " to enable forge mode. Please use '" + PLATFORM_PROPERTY + " = forge' instead!");
-				return platform = Boolean.parseBoolean(Objects.toString(forgeProperty)) ? ModPlatform.FORGE : ModPlatform.FABRIC;
-			}
-
-			platform = ModPlatform.FABRIC;
-		}
-
-		return platform;
-	}
-
-	public boolean isForge() {
-		return getPlatform() == ModPlatform.FORGE;
-	}
-
-	public boolean supportsInclude() {
-		return !isForge() || supportsInclude.getAsBoolean();
-	}
-
-	public boolean shouldGenerateSrgTiny() {
-		if (generateSrgTiny != null) {
-			return generateSrgTiny;
-		}
-
-		return isForge();
-	}
-
-	// Creates a new file each time its called, this is then held onto later when remapping the output jar
-	// Required as now when using parallel builds the old single file could be written by another sourceset compile task
-	public synchronized File getNextMixinMappings() {
-		File mixinMapping = new File(getProjectBuildCache(), "mixin-map-" + getMinecraftProvider().minecraftVersion() + "-" + getMappingsProvider().mappingsVersion + "." + mixinMappings.size() + ".tiny");
-		mixinMappings.add(mixinMapping);
-		return mixinMapping;
-	}
-
-	public Set<File> getAllMixinMappings() {
-		return Collections.unmodifiableSet(mixinMappings);
-	}
-
-	public List<LoomDecompiler> getDecompilers() {
-		return decompilers;
-	}
-
-	public File getDefaultLog4jConfigFile() {
-		return new File(getProjectPersistentCache(), "log4j.xml");
-	}
-
-	public File getUnpickLoggingConfigFile() {
-		return new File(getProjectPersistentCache(), "unpick-logging.properties");
-	}
-
-	public ConfigurableFileCollection getLog4jConfigs() {
-		return log4jConfigs;
-	}
-
-	public void runs(Action<NamedDomainObjectContainer<RunConfigSettings>> action) {
-		action.execute(runConfigs);
-	}
-
-	public void launches(Action<NamedDomainObjectContainer<LaunchProviderSettings>> action) {
-		action.execute(launchConfigs);
+	default String getIntermediaryUrl(String minecraftVersion) {
+		// TODO reimplement a way to change this, was never really supported api anyway
+		return String.format("https://maven.fabricmc.net/net/fabricmc/intermediary/%1$s/intermediary-%1$s-v2.jar", minecraftVersion);
 	}
 
-	public NamedDomainObjectContainer<RunConfigSettings> getRunConfigs() {
-		return runConfigs;
-	}
-
-	public NamedDomainObjectContainer<LaunchProviderSettings> getLaunchConfigs() {
-		return launchConfigs;
-	}
-
-	@ApiStatus.Internal
-	public LoomProjectData getProjectData() {
-		return projectData;
-	}
+	MixinApExtension getMixinApExtension();
 }
diff --git a/src/main/java/net/fabricmc/loom/LoomGradlePlugin.java b/src/main/java/net/fabricmc/loom/LoomGradlePlugin.java
index 3f7d710f..a79c5a8d 100644
--- a/src/main/java/net/fabricmc/loom/LoomGradlePlugin.java
+++ b/src/main/java/net/fabricmc/loom/LoomGradlePlugin.java
@@ -45,6 +45,8 @@ import net.fabricmc.loom.configuration.MavenPublication;
 import net.fabricmc.loom.configuration.ide.IdeConfiguration;
 import net.fabricmc.loom.configuration.providers.mappings.MappingsCache;
 import net.fabricmc.loom.decompilers.DecompilerConfiguration;
+import net.fabricmc.loom.extension.LoomGradleExtensionImpl;
+import net.fabricmc.loom.extension.LoomFilesImpl;
 import net.fabricmc.loom.task.LoomTasks;
 
 public class LoomGradlePlugin implements BootstrappedPlugin {
@@ -85,7 +87,7 @@ public class LoomGradlePlugin implements BootstrappedPlugin {
 		project.apply(ImmutableMap.of("plugin", "idea"));
 
 		// Setup extensions, loom shadows minecraft
-		project.getExtensions().create("minecraft", LoomGradleExtension.class, project);
+		project.getExtensions().create(LoomGradleExtension.class, "minecraft", LoomGradleExtensionImpl.class, project, new LoomFilesImpl(project));
 		project.getExtensions().add("loom", project.getExtensions().getByName("minecraft"));
 		project.getExtensions().create("fabricApi", FabricApiExtension.class, project);
 
diff --git a/src/main/java/net/fabricmc/loom/api/LoomGradleExtensionAPI.java b/src/main/java/net/fabricmc/loom/api/LoomGradleExtensionAPI.java
new file mode 100644
index 00000000..e4d3e930
--- /dev/null
+++ b/src/main/java/net/fabricmc/loom/api/LoomGradleExtensionAPI.java
@@ -0,0 +1,91 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021 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
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.api;
+
+import java.io.File;
+import java.util.List;
+
+import org.gradle.api.Action;
+import org.gradle.api.NamedDomainObjectContainer;
+import org.gradle.api.artifacts.Dependency;
+import org.gradle.api.file.ConfigurableFileCollection;
+import org.jetbrains.annotations.ApiStatus;
+
+import net.fabricmc.loom.api.decompilers.LoomDecompiler;
+import net.fabricmc.loom.configuration.ide.RunConfigSettings;
+import net.fabricmc.loom.configuration.processors.JarProcessor;
+import net.fabricmc.loom.configuration.providers.mappings.LayeredMappingSpecBuilder;
+
+/**
+ * This is the public api available exposed to build scripts.
+ */
+public interface LoomGradleExtensionAPI {
+	File getAccessWidener();
+
+	void setAccessWidener(Object file);
+
+	void setShareCaches(boolean shareCaches);
+
+	boolean isShareCaches();
+
+	default void shareCaches() {
+		setShareCaches(true);
+	}
+
+	List<LoomDecompiler> getDecompilers();
+
+	void addDecompiler(LoomDecompiler decompiler);
+
+	List<JarProcessor> getJarProcessors();
+
+	void addJarProcessor(JarProcessor processor);
+
+	ConfigurableFileCollection getLog4jConfigs();
+
+	default Dependency officialMojangMappings() {
+		return layered(LayeredMappingSpecBuilder::officialMojangMappings);
+	}
+
+	Dependency layered(Action<LayeredMappingSpecBuilder> action);
+
+	String getRefmapName();
+
+	void setRefmapName(String refmapName);
+
+	boolean isRemapMod();
+
+	void setRemapMod(boolean remapMod);
+
+	void runs(Action<NamedDomainObjectContainer<RunConfigSettings>> action);
+
+	NamedDomainObjectContainer<RunConfigSettings> getRunConfigs();
+
+	@ApiStatus.Experimental
+	void mixin(Action<MixinApExtensionAPI> action);
+
+	void setCustomManifest(String customManifest);
+
+	String getCustomManifest();
+}
diff --git a/src/main/java/net/fabricmc/loom/api/MixinApExtensionAPI.java b/src/main/java/net/fabricmc/loom/api/MixinApExtensionAPI.java
new file mode 100644
index 00000000..88b7fa79
--- /dev/null
+++ b/src/main/java/net/fabricmc/loom/api/MixinApExtensionAPI.java
@@ -0,0 +1,92 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021 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
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.api;
+
+import org.gradle.api.Action;
+import org.gradle.api.tasks.SourceSet;
+import org.gradle.api.tasks.util.PatternSet;
+import org.jetbrains.annotations.ApiStatus;
+
+@ApiStatus.Experimental
+public interface MixinApExtensionAPI {
+	/**
+	 * Apply Mixin AP to sourceSet.
+	 * @param sourceSet the sourceSet that applies Mixin AP.
+	 * @param refmapName the output ref-map name. By default this will
+	 *                      be {@link net.fabricmc.loom.LoomGradleExtension#getRefmapName()}
+	 * @param action used for filter the mixin json files. By default this will be all files
+	 *                  with name {@code *.mixins.json} that is inside the {@code resources} folder
+	 *                  of {@code sourceSet}.
+	 */
+	void add(SourceSet sourceSet, String refmapName, Action<PatternSet> action);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSet the sourceSet that applies Mixin AP.
+	 * @param refmapName the output ref-map name.
+	 */
+	void add(SourceSet sourceSet, String refmapName);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSet the sourceSet that applies Mixin AP.
+	 * @param action used for filter the mixin json files.
+	 */
+	void add(SourceSet sourceSet, Action<PatternSet> action);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSet the sourceSet that applies Mixin AP.
+	 */
+	void add(SourceSet sourceSet);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSetName the name of sourceSet that applies Mixin AP.
+	 * @param refmapName the output ref-map name.
+	 * @param action used for filter the mixin json files.
+	 */
+	void add(String sourceSetName, String refmapName, Action<PatternSet> action);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSetName the name of sourceSet that applies Mixin AP.
+	 * @param refmapName the output ref-map name.
+	 */
+	void add(String sourceSetName, String refmapName);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSetName the name of sourceSet that applies Mixin AP.
+	 * @param action used for filter the mixin json files.
+	 */
+	void add(String sourceSetName, Action<PatternSet> action);
+
+	/**
+	 * Apply Mixin AP to sourceSet. See {@link MixinApExtensionAPI#add(SourceSet, String, Action)} for more detail.
+	 * @param sourceSetName the name of sourceSet that applies Mixin AP.
+	 */
+	void add(String sourceSetName);
+}
diff --git a/src/main/java/net/fabricmc/loom/build/MixinRefmapHelper.java b/src/main/java/net/fabricmc/loom/build/MixinRefmapHelper.java
index bc775746..458a5ffb 100644
--- a/src/main/java/net/fabricmc/loom/build/MixinRefmapHelper.java
+++ b/src/main/java/net/fabricmc/loom/build/MixinRefmapHelper.java
@@ -25,71 +25,47 @@
 package net.fabricmc.loom.build;
 
 import java.io.File;
-import java.io.IOException;
-import java.io.InputStreamReader;
 import java.nio.file.Path;
-import java.util.HashSet;
-import java.util.Set;
+import java.util.Objects;
+import java.util.stream.Stream;
 import java.util.zip.ZipEntry;
 
 import com.google.gson.JsonObject;
+import org.gradle.api.Project;
 import org.zeroturnaround.zip.ZipUtil;
 import org.zeroturnaround.zip.transform.StringZipEntryTransformer;
 import org.zeroturnaround.zip.transform.ZipEntryTransformerEntry;
 
+import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.LoomGradlePlugin;
+import net.fabricmc.loom.extension.MixinApExtension;
 
 public final class MixinRefmapHelper {
 	private MixinRefmapHelper() { }
 
-	public static boolean addRefmapName(String filename, Path outputPath) {
+	public static boolean addRefmapName(Project project, Path outputPath) {
+		MixinApExtension mixin = LoomGradleExtension.get(project).getMixinApExtension();
 		File output = outputPath.toFile();
-		Set<String> mixinFilenames = findMixins(output, true);
 
-		if (mixinFilenames.size() > 0) {
-			return ZipUtil.transformEntries(output, mixinFilenames.stream().map((f) -> new ZipEntryTransformerEntry(f, new StringZipEntryTransformer("UTF-8") {
+		return mixin.getMixinSourceSetsStream().map(sourceSet -> {
+			MixinApExtension.MixinInformationContainer container = Objects.requireNonNull(
+					MixinApExtension.getMixinInformationContainer(sourceSet)
+			);
+			Stream<String> mixinJsonNames = container.getMixinJsonNames();
+			String refmapName = container.getRefmapName();
+
+			return ZipUtil.transformEntries(output, mixinJsonNames.map(f -> new ZipEntryTransformerEntry(f, new StringZipEntryTransformer("UTF-8") {
 				@Override
-				protected String transform(ZipEntry zipEntry, String input) throws IOException {
+				protected String transform(ZipEntry zipEntry, String input) {
 					JsonObject json = LoomGradlePlugin.GSON.fromJson(input, JsonObject.class);
 
 					if (!json.has("refmap")) {
-						json.addProperty("refmap", filename);
+						json.addProperty("refmap", refmapName);
 					}
 
 					return LoomGradlePlugin.GSON.toJson(json);
 				}
 			})).toArray(ZipEntryTransformerEntry[]::new));
-		} else {
-			return false;
-		}
-	}
-
-	private static Set<String> findMixins(File output, boolean onlyWithoutRefmap) {
-		// first, identify all of the mixin files
-		Set<String> mixinFilename = new HashSet<>();
-		// TODO: this is a lovely hack
-		ZipUtil.iterate(output, (stream, entry) -> {
-			if (!entry.isDirectory() && entry.getName().endsWith(".json") && !entry.getName().contains("/") && !entry.getName().contains("\\")) {
-				// JSON file in root directory
-				try (InputStreamReader inputStreamReader = new InputStreamReader(stream)) {
-					JsonObject json = LoomGradlePlugin.GSON.fromJson(inputStreamReader, JsonObject.class);
-
-					if (json != null) {
-						boolean hasMixins = json.has("mixins") && json.get("mixins").isJsonArray();
-						boolean hasClient = json.has("client") && json.get("client").isJsonArray();
-						boolean hasServer = json.has("server") && json.get("server").isJsonArray();
-
-						if (json.has("package") && (hasMixins || hasClient || hasServer)) {
-							if (!onlyWithoutRefmap || !json.has("refmap") || !json.has("minVersion")) {
-								mixinFilename.add(entry.getName());
-							}
-						}
-					}
-				} catch (Exception ignored) {
-					// ...
-				}
-			}
-		});
-		return mixinFilename;
+		}).reduce(false, Boolean::logicalOr);
 	}
 }
diff --git a/src/main/java/net/fabricmc/loom/build/ModCompileRemapper.java b/src/main/java/net/fabricmc/loom/build/ModCompileRemapper.java
index 4a4a808b..9533b343 100644
--- a/src/main/java/net/fabricmc/loom/build/ModCompileRemapper.java
+++ b/src/main/java/net/fabricmc/loom/build/ModCompileRemapper.java
@@ -51,7 +51,6 @@ import org.jetbrains.annotations.Nullable;
 
 import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.LoomGradlePlugin;
-import net.fabricmc.loom.configuration.LoomProjectData;
 import net.fabricmc.loom.configuration.RemappedConfigurationEntry;
 import net.fabricmc.loom.configuration.mods.ModProcessor;
 import net.fabricmc.loom.configuration.processors.dependency.ModDependencyInfo;
@@ -76,13 +75,11 @@ public class ModCompileRemapper {
 		DependencyHandler dependencies = project.getDependencies();
 		boolean refreshDeps = LoomGradlePlugin.refreshDeps;
 
-		final File modStore = extension.getRemappedModCache();
+		final File modStore = extension.getFiles().getRemappedModCache();
 		final RemapData remapData = new RemapData(mappingsSuffix, modStore);
 
-		final LoomProjectData data = extension.getProjectData();
-
 		for (RemappedConfigurationEntry entry : Constants.MOD_COMPILE_ENTRIES) {
-			data.getLazyConfigurationProvider(entry.getRemappedConfiguration()).configure(remappedConfig -> {
+			extension.getLazyConfigurationProvider(entry.getRemappedConfiguration()).configure(remappedConfig -> {
 				Configuration sourceConfig = project.getConfigurations().getByName(entry.sourceConfiguration());
 				Configuration regularConfig = project.getConfigurations().getByName(entry.getTargetConfiguration(project.getConfigurations()));
 
diff --git a/src/main/java/net/fabricmc/loom/build/mixin/AnnotationProcessorInvoker.java b/src/main/java/net/fabricmc/loom/build/mixin/AnnotationProcessorInvoker.java
index 07f7c09c..a9dca7f0 100644
--- a/src/main/java/net/fabricmc/loom/build/mixin/AnnotationProcessorInvoker.java
+++ b/src/main/java/net/fabricmc/loom/build/mixin/AnnotationProcessorInvoker.java
@@ -29,16 +29,17 @@ import java.io.IOException;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.Map;
-import java.util.stream.Stream;
+import java.util.Objects;
+import java.util.function.Function;
+import java.util.stream.Collectors;
 
 import org.gradle.api.Project;
 import org.gradle.api.Task;
 import org.gradle.api.artifacts.Configuration;
 import org.gradle.api.artifacts.ConfigurationContainer;
-import org.gradle.api.plugins.JavaPluginConvention;
 import org.gradle.api.tasks.SourceSet;
-import org.gradle.api.tasks.TaskCollection;
 
+import net.fabricmc.loom.extension.MixinApExtension;
 import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.util.Constants;
 
@@ -48,37 +49,46 @@ import net.fabricmc.loom.util.Constants;
  * See Java and Kapt implementations for a more deep understanding of the things passed by the children.
  */
 public abstract class AnnotationProcessorInvoker<T extends Task> {
+	public static final String JAVA = "java";
+	public static final String SCALA = "scala";
+
 	protected final Project project;
-	private final Collection<Configuration> annotationProcessorConfigurations;
-	protected final TaskCollection<T> invokerTasks;
+	protected final Map<SourceSet, T> invokerTasks;
+	private final Collection<Configuration> apConfigurations;
 
 	protected AnnotationProcessorInvoker(Project project,
-										Collection<Configuration> annotationProcessorConfigurations,
-										TaskCollection<T> invokerTasks) {
+										Collection<Configuration> apConfigurations,
+										Map<SourceSet, T> invokerTasks) {
 		this.project = project;
-		this.annotationProcessorConfigurations = annotationProcessorConfigurations;
+		this.apConfigurations = apConfigurations;
 		this.invokerTasks = invokerTasks;
 	}
 
+	protected static Collection<Configuration> getApConfigurations(Project project, Function<String, String> getApConfigNameFunc) {
+		MixinApExtension mixin = LoomGradleExtension.get(project).getMixinApExtension();
+		return mixin.getApConfigurationsStream(getApConfigNameFunc).collect(Collectors.toList());
+	}
+
 	protected abstract void passArgument(T compileTask, String key, String value);
 
-	protected abstract File getDestinationDir(T task);
+	protected abstract File getRefmapDestinationDir(T task);
 
-	protected final String getRefmapDestination(T task, LoomGradleExtension extension) throws IOException {
-		return new File(getDestinationDir(task), extension.getRefmapName()).getCanonicalPath();
+	protected final String getRefmapDestination(T task, String refmapName) throws IOException {
+		return new File(getRefmapDestinationDir(task), refmapName).getCanonicalPath();
 	}
 
-	private void passMixinArguments(T task) {
+	private void passMixinArguments(T task, SourceSet sourceSet) {
 		try {
-			LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+			LoomGradleExtension loom = LoomGradleExtension.get(project);
+			String refmapName = Objects.requireNonNull(MixinApExtension.getMixinInformationContainer(sourceSet)).getRefmapName();
 			Map<String, String> args = new HashMap<>() {{
-					put(Constants.MixinArguments.IN_MAP_FILE_NAMED_INTERMEDIARY, extension.getMappingsProvider().tinyMappings.getCanonicalPath());
-					put(Constants.MixinArguments.OUT_MAP_FILE_NAMED_INTERMEDIARY, extension.getNextMixinMappings().getCanonicalPath());
-					put(Constants.MixinArguments.OUT_REFMAP_FILE, getRefmapDestination(task, extension));
+					put(Constants.MixinArguments.IN_MAP_FILE_NAMED_INTERMEDIARY, loom.getMappingsProvider().tinyMappings.getCanonicalPath());
+					put(Constants.MixinArguments.OUT_MAP_FILE_NAMED_INTERMEDIARY, loom.getNextMixinMappings().getCanonicalPath());
+					put(Constants.MixinArguments.OUT_REFMAP_FILE, getRefmapDestination(task, refmapName));
 					put(Constants.MixinArguments.DEFAULT_OBFUSCATION_ENV, "named:intermediary");
 				}};
 
-			project.getLogger().debug("Outputting refmap to dir: " + getDestinationDir(task) + " for compile task: " + task);
+			project.getLogger().debug("Outputting refmap to dir: " + getRefmapDestinationDir(task) + " for compile task: " + task);
 			args.forEach((k, v) -> passArgument(task, k, v));
 		} catch (IOException e) {
 			project.getLogger().error("Could not configure mixin annotation processors", e);
@@ -87,10 +97,10 @@ public abstract class AnnotationProcessorInvoker<T extends Task> {
 
 	public void configureMixin() {
 		ConfigurationContainer configs = project.getConfigurations();
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 
 		if (!extension.ideSync()) {
-			for (Configuration processorConfig : annotationProcessorConfigurations) {
+			for (Configuration processorConfig : apConfigurations) {
 				project.getLogger().info("Adding mixin to classpath of AP config: " + processorConfig.getName());
 				// Pass named MC classpath to mixin AP classpath
 				processorConfig.extendsFrom(
@@ -109,14 +119,8 @@ public abstract class AnnotationProcessorInvoker<T extends Task> {
 			}
 		}
 
-		for (T task : invokerTasks) {
-			passMixinArguments(task);
+		for (Map.Entry<SourceSet, T> entry : invokerTasks.entrySet()) {
+			passMixinArguments(entry.getValue(), entry.getKey());
 		}
 	}
-
-	static Stream<SourceSet> getNonTestSourceSets(Project project) {
-		return project.getConvention().getPlugin(JavaPluginConvention.class).getSourceSets()
-						.stream()
-						.filter(sourceSet -> !sourceSet.getName().equals("test"));
-	}
 }
diff --git a/src/main/java/net/fabricmc/loom/build/mixin/JavaApInvoker.java b/src/main/java/net/fabricmc/loom/build/mixin/JavaApInvoker.java
index aa7d46a7..a449600a 100644
--- a/src/main/java/net/fabricmc/loom/build/mixin/JavaApInvoker.java
+++ b/src/main/java/net/fabricmc/loom/build/mixin/JavaApInvoker.java
@@ -25,17 +25,30 @@
 package net.fabricmc.loom.build.mixin;
 
 import java.io.File;
-import java.util.List;
+import java.util.Map;
+import java.util.Objects;
 import java.util.stream.Collectors;
 
 import org.gradle.api.Project;
-import org.gradle.api.artifacts.Configuration;
 import org.gradle.api.plugins.JavaPlugin;
+import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.compile.JavaCompile;
 
+import net.fabricmc.loom.LoomGradleExtension;
+import net.fabricmc.loom.extension.MixinApExtension;
+
 public class JavaApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 	public JavaApInvoker(Project project) {
-		super(project, getConfigurations(project), project.getTasks().withType(JavaCompile.class));
+		super(
+				project,
+				AnnotationProcessorInvoker.getApConfigurations(project, JavaApInvoker::getAptConfigurationName),
+				getInvokerTasks(project));
+	}
+
+	private static Map<SourceSet, JavaCompile> getInvokerTasks(Project project) {
+		MixinApExtension mixin = LoomGradleExtension.get(project).getMixinApExtension();
+		return mixin.getInvokerTasksStream(AnnotationProcessorInvoker.JAVA)
+				.collect(Collectors.toMap(Map.Entry::getKey, entry -> Objects.requireNonNull((JavaCompile) entry.getValue())));
 	}
 
 	@Override
@@ -44,18 +57,10 @@ public class JavaApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 	}
 
 	@Override
-	protected File getDestinationDir(JavaCompile task) {
+	protected File getRefmapDestinationDir(JavaCompile task) {
 		return task.getDestinationDir();
 	}
 
-	private static List<Configuration> getConfigurations(Project project) {
-		// java plugin generates an AP configuration for every source set based off of the getAptConfigurationName method.
-		return AnnotationProcessorInvoker.getNonTestSourceSets(project)
-						.map(sourceSet -> project.getConfigurations()
-										.getByName(getAptConfigurationName(sourceSet.getName()))
-						).collect(Collectors.toList());
-	}
-
 	private static String getAptConfigurationName(String sourceSet) {
 		// This is documented by the gradle 4.6 release notes https://docs.gradle.org/4.6/release-notes.html#potential-breaking-changes
 		return sourceSet.equals("main") ? JavaPlugin.ANNOTATION_PROCESSOR_CONFIGURATION_NAME : sourceSet + "AnnotationProcessor";
diff --git a/src/main/java/net/fabricmc/loom/build/mixin/KaptApInvoker.java b/src/main/java/net/fabricmc/loom/build/mixin/KaptApInvoker.java
index 5443855a..3fea3c6e 100644
--- a/src/main/java/net/fabricmc/loom/build/mixin/KaptApInvoker.java
+++ b/src/main/java/net/fabricmc/loom/build/mixin/KaptApInvoker.java
@@ -29,18 +29,18 @@ import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
-import java.util.List;
+import java.util.Map;
+import java.util.Objects;
 import java.util.stream.Collectors;
 
 import kotlin.Unit;
 import org.gradle.api.Project;
-import org.gradle.api.artifacts.Configuration;
 import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.compile.JavaCompile;
-import org.jetbrains.annotations.NotNull;
 import org.jetbrains.kotlin.gradle.plugin.KaptExtension;
 
 import net.fabricmc.loom.LoomGradleExtension;
+import net.fabricmc.loom.extension.MixinApExtension;
 
 public class KaptApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 	private final KaptExtension kaptExtension = project.getExtensions().getByType(KaptExtension.class);
@@ -48,7 +48,10 @@ public class KaptApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 	private final File dummyRefmapDirectory;
 
 	public KaptApInvoker(Project project) {
-		super(project, getConfigurations(project), project.getTasks().withType(JavaCompile.class));
+		super(
+				project,
+				AnnotationProcessorInvoker.getApConfigurations(project, KaptApInvoker::getKaptConfigurationName),
+				getInvokerTasks(project));
 
 		try {
 			dummyRefmapDirectory = Files.createTempDirectory("temp_refmap").toFile();
@@ -62,18 +65,26 @@ public class KaptApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 		kaptExtension.setIncludeCompileClasspath(false);
 	}
 
+	private static Map<SourceSet, JavaCompile> getInvokerTasks(Project project) {
+		MixinApExtension mixin = LoomGradleExtension.get(project).getMixinApExtension();
+		return mixin.getInvokerTasksStream(AnnotationProcessorInvoker.JAVA)
+				.collect(Collectors.toMap(Map.Entry::getKey, entry -> Objects.requireNonNull((JavaCompile) entry.getValue())));
+	}
+
 	@Override
 	public void configureMixin() {
 		super.configureMixin();
 
-		for (JavaCompile task : invokerTasks) {
+		for (Map.Entry<SourceSet, JavaCompile> entry : invokerTasks.entrySet()) {
 			// Kapt only allows specifying javac args to all annotation processors at once. So we need to specify some dummy
 			// target location for the refmap and then move it to the correct place for each sourceset
+			JavaCompile task = entry.getValue();
+			SourceSet sourceSet = entry.getKey();
 			task.doLast(t -> {
 				try {
-					LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
-					Path src = Paths.get(getRefmapDestination(task, extension));
-					Path dest = Paths.get(task.getDestinationDir().toString(), extension.getRefmapName());
+					String refmapName = Objects.requireNonNull(MixinApExtension.getMixinInformationContainer(sourceSet)).getRefmapName();
+					Path src = Paths.get(getRefmapDestination(task, refmapName));
+					Path dest = Paths.get(task.getDestinationDir().toString(), refmapName);
 
 					// Possible that no mixin annotations exist
 					if (Files.exists(src)) {
@@ -87,15 +98,6 @@ public class KaptApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 		}
 	}
 
-	@NotNull
-	private static List<Configuration> getConfigurations(Project project) {
-		// Kapt generates an AP configuration for every source set based off of the getKaptConfigurationName method.
-		return AnnotationProcessorInvoker.getNonTestSourceSets(project)
-						.map(sourceSet -> project.getConfigurations()
-										.getByName(getKaptConfigurationName(sourceSet.getName()))
-						).collect(Collectors.toList());
-	}
-
 	// Pulled out from the internal class: https://github.com/JetBrains/kotlin/blob/33a0ec9b4f40f3d6f1f96b2db504ade4c2fafe03/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/kapt/Kapt3KotlinGradleSubplugin.kt#L92
 	private static String getKaptConfigurationName(String sourceSetName) {
 		if (!sourceSetName.equals(SourceSet.MAIN_SOURCE_SET_NAME)) {
@@ -116,7 +118,7 @@ public class KaptApInvoker extends AnnotationProcessorInvoker<JavaCompile> {
 	}
 
 	@Override
-	protected File getDestinationDir(JavaCompile task) {
+	protected File getRefmapDestinationDir(JavaCompile task) {
 		return dummyRefmapDirectory;
 	}
 }
diff --git a/src/main/java/net/fabricmc/loom/build/mixin/ScalaApInvoker.java b/src/main/java/net/fabricmc/loom/build/mixin/ScalaApInvoker.java
index bc77e152..7a3238b7 100644
--- a/src/main/java/net/fabricmc/loom/build/mixin/ScalaApInvoker.java
+++ b/src/main/java/net/fabricmc/loom/build/mixin/ScalaApInvoker.java
@@ -25,17 +25,31 @@
 package net.fabricmc.loom.build.mixin;
 
 import java.io.File;
+import java.util.Map;
+import java.util.Objects;
+import java.util.stream.Collectors;
 
 import com.google.common.collect.ImmutableList;
 import org.gradle.api.Project;
+import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.scala.ScalaCompile;
 
+import net.fabricmc.loom.LoomGradleExtension;
+import net.fabricmc.loom.extension.MixinApExtension;
+
 public class ScalaApInvoker extends AnnotationProcessorInvoker<ScalaCompile> {
 	public ScalaApInvoker(Project project) {
-		super(project,
-						// Scala just uses the java AP configuration afaik. This of course assumes the java AP also gets configured.
-						ImmutableList.of(),
-						project.getTasks().withType(ScalaCompile.class));
+		super(
+				project,
+				// Scala just uses the java AP configuration afaik. This of course assumes the java AP also gets configured.
+				ImmutableList.of(),
+				getInvokerTasks(project));
+	}
+
+	private static Map<SourceSet, ScalaCompile> getInvokerTasks(Project project) {
+		MixinApExtension mixin = LoomGradleExtension.get(project).getMixinApExtension();
+		return mixin.getInvokerTasksStream(AnnotationProcessorInvoker.SCALA)
+				.collect(Collectors.toMap(Map.Entry::getKey, entry -> Objects.requireNonNull((ScalaCompile) entry.getValue())));
 	}
 
 	@Override
@@ -44,7 +58,7 @@ public class ScalaApInvoker extends AnnotationProcessorInvoker<ScalaCompile> {
 	}
 
 	@Override
-	protected File getDestinationDir(ScalaCompile task) {
+	protected File getRefmapDestinationDir(ScalaCompile task) {
 		return task.getDestinationDir();
 	}
 }
diff --git a/src/main/java/net/fabricmc/loom/build/nesting/NestedDependencyProvider.java b/src/main/java/net/fabricmc/loom/build/nesting/NestedDependencyProvider.java
index 2dae34f6..0ba7b5a0 100644
--- a/src/main/java/net/fabricmc/loom/build/nesting/NestedDependencyProvider.java
+++ b/src/main/java/net/fabricmc/loom/build/nesting/NestedDependencyProvider.java
@@ -157,8 +157,8 @@ public final class NestedDependencyProvider implements NestedJarProvider {
 
 			//A lib that doesnt have a mod.json, we turn it into a fake mod
 			if (!ZipUtil.containsEntry(file, "fabric.mod.json")) {
-				LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
-				File tempDir = new File(extension.getUserCache(), "temp/modprocessing");
+				LoomGradleExtension extension = LoomGradleExtension.get(project);
+				File tempDir = new File(extension.getFiles().getUserCache(), "temp/modprocessing");
 
 				if (!tempDir.exists()) {
 					tempDir.mkdirs();
diff --git a/src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java b/src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java
index 6b7e1f02..07a01118 100644
--- a/src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java
+++ b/src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java
@@ -33,6 +33,7 @@ import org.gradle.api.tasks.compile.JavaCompile;
 import org.gradle.api.tasks.javadoc.Javadoc;
 import org.gradle.jvm.tasks.Jar;
 
+import net.fabricmc.loom.extension.MixinApExtension;
 import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.build.mixin.JavaApInvoker;
 import net.fabricmc.loom.build.mixin.KaptApInvoker;
@@ -57,11 +58,11 @@ public final class CompileConfiguration {
 
 	public static void setupConfigurations(Project project) {
 		final ConfigurationContainer configurations = project.getConfigurations();
-		LoomProjectData data = project.getExtensions().getByType(LoomGradleExtension.class).getProjectData();
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 
 		project.afterEvaluate(project1 -> {
 			if (project.getExtensions().getByType(LoomGradleExtension.class).shouldGenerateSrgTiny()) {
-				data.createLazyConfiguration(Constants.Configurations.SRG).configure(configuration -> configuration.setTransitive(false));
+				extension.createLazyConfiguration(Constants.Configurations.SRG).configure(configuration -> configuration.setTransitive(false));
 			}
 
 			if (project.getExtensions().getByType(LoomGradleExtension.class).isDataGenEnabled()) {
@@ -71,21 +72,21 @@ public final class CompileConfiguration {
 			}
 		});
 
-		data.createLazyConfiguration(Constants.Configurations.MOD_COMPILE_CLASSPATH).configure(configuration -> configuration.setTransitive(true));
-		data.createLazyConfiguration(Constants.Configurations.MOD_COMPILE_CLASSPATH_MAPPED).configure(configuration -> configuration.setTransitive(false));
-		data.createLazyConfiguration(Constants.Configurations.MINECRAFT_NAMED).configure(configuration -> configuration.setTransitive(false)); // The launchers do not recurse dependencies
-		data.createLazyConfiguration(Constants.Configurations.MINECRAFT_DEPENDENCIES).configure(configuration -> configuration.setTransitive(false));
-		data.createLazyConfiguration(Constants.Configurations.LOADER_DEPENDENCIES).configure(configuration -> configuration.setTransitive(false));
-		data.createLazyConfiguration(Constants.Configurations.MINECRAFT).configure(configuration -> configuration.setTransitive(false));
+		extension.createLazyConfiguration(Constants.Configurations.MOD_COMPILE_CLASSPATH).configure(configuration -> configuration.setTransitive(true));
+		extension.createLazyConfiguration(Constants.Configurations.MOD_COMPILE_CLASSPATH_MAPPED).configure(configuration -> configuration.setTransitive(false));
+		extension.createLazyConfiguration(Constants.Configurations.MINECRAFT_NAMED).configure(configuration -> configuration.setTransitive(false)); // The launchers do not recurse dependencies
+		extension.createLazyConfiguration(Constants.Configurations.MINECRAFT_DEPENDENCIES).configure(configuration -> configuration.setTransitive(false));
+		extension.createLazyConfiguration(Constants.Configurations.LOADER_DEPENDENCIES).configure(configuration -> configuration.setTransitive(false));
+		extension.createLazyConfiguration(Constants.Configurations.MINECRAFT).configure(configuration -> configuration.setTransitive(false));
 
 		if (project.getExtensions().getByType(LoomGradleExtension.class).isForge()) {
-			data.createLazyConfiguration(Constants.Configurations.FORGE).configure(configuration -> configuration.setTransitive(false));
-			data.createLazyConfiguration(Constants.Configurations.FORGE_USERDEV).configure(configuration -> configuration.setTransitive(false));
-			data.createLazyConfiguration(Constants.Configurations.FORGE_INSTALLER).configure(configuration -> configuration.setTransitive(false));
-			data.createLazyConfiguration(Constants.Configurations.FORGE_UNIVERSAL).configure(configuration -> configuration.setTransitive(false));
-			data.createLazyConfiguration(Constants.Configurations.FORGE_DEPENDENCIES).configure(configuration -> configuration.setTransitive(false));
-			data.createLazyConfiguration(Constants.Configurations.FORGE_NAMED).configure(configuration -> configuration.setTransitive(false));
-			data.createLazyConfiguration(Constants.Configurations.MCP_CONFIG).configure(configuration -> configuration.setTransitive(false));
+			extension.createLazyConfiguration(Constants.Configurations.FORGE).configure(configuration -> configuration.setTransitive(false));
+			extension.createLazyConfiguration(Constants.Configurations.FORGE_USERDEV).configure(configuration -> configuration.setTransitive(false));
+			extension.createLazyConfiguration(Constants.Configurations.FORGE_INSTALLER).configure(configuration -> configuration.setTransitive(false));
+			extension.createLazyConfiguration(Constants.Configurations.FORGE_UNIVERSAL).configure(configuration -> configuration.setTransitive(false));
+			extension.createLazyConfiguration(Constants.Configurations.FORGE_DEPENDENCIES).configure(configuration -> configuration.setTransitive(false));
+			extension.createLazyConfiguration(Constants.Configurations.FORGE_NAMED).configure(configuration -> configuration.setTransitive(false));
+			extension.createLazyConfiguration(Constants.Configurations.MCP_CONFIG).configure(configuration -> configuration.setTransitive(false));
 
 			extendsFrom(Constants.Configurations.MINECRAFT_DEPENDENCIES, Constants.Configurations.FORGE_DEPENDENCIES, project);
 
@@ -96,24 +97,24 @@ public final class CompileConfiguration {
 		}
 
 		if (project.getExtensions().getByType(LoomGradleExtension.class).supportsInclude()) {
-			data.createLazyConfiguration(Constants.Configurations.INCLUDE).configure(configuration -> configuration.setTransitive(false)); // Dont get transitive deps
+			extension.createLazyConfiguration(Constants.Configurations.INCLUDE).configure(configuration -> configuration.setTransitive(false)); // Dont get transitive deps
 		}
 
-		data.createLazyConfiguration(Constants.Configurations.MAPPING_CONSTANTS);
+		extension.createLazyConfiguration(Constants.Configurations.MAPPING_CONSTANTS);
 
 		extendsFrom(JavaPlugin.COMPILE_ONLY_CONFIGURATION_NAME, Constants.Configurations.MAPPING_CONSTANTS, project);
 
-		data.createLazyConfiguration(Constants.Configurations.MAPPINGS);
-		data.createLazyConfiguration(Constants.Configurations.MAPPINGS_FINAL);
-		data.createLazyConfiguration(Constants.Configurations.LOOM_DEVELOPMENT_DEPENDENCIES);
-		data.createLazyConfiguration(Constants.Configurations.UNPICK_CLASSPATH);
+		extension.createLazyConfiguration(Constants.Configurations.MAPPINGS);
+		extension.createLazyConfiguration(Constants.Configurations.MAPPINGS_FINAL);
+		extension.createLazyConfiguration(Constants.Configurations.LOOM_DEVELOPMENT_DEPENDENCIES);
+		extension.createLazyConfiguration(Constants.Configurations.UNPICK_CLASSPATH);
 
 		for (RemappedConfigurationEntry entry : Constants.MOD_COMPILE_ENTRIES) {
-			data.createLazyConfiguration(entry.sourceConfiguration())
+			extension.createLazyConfiguration(entry.sourceConfiguration())
 					.configure(configuration -> configuration.setTransitive(true));
 
 			// Don't get transitive deps of already remapped mods
-			data.createLazyConfiguration(entry.getRemappedConfiguration())
+			extension.createLazyConfiguration(entry.getRemappedConfiguration())
 					.configure(configuration -> configuration.setTransitive(false));
 
 			extendsFrom(entry.getTargetConfiguration(configurations), entry.getRemappedConfiguration(), project);
@@ -152,7 +153,7 @@ public final class CompileConfiguration {
 		});
 
 		p.afterEvaluate(project -> {
-			LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+			LoomGradleExtension extension = LoomGradleExtension.get(project);
 
 			LoomDependencyManager dependencyManager = new LoomDependencyManager();
 			extension.setDependencyManager(dependencyManager);
@@ -187,7 +188,7 @@ public final class CompileConfiguration {
 			GenVsCodeProjectTask.generate(project);
 
 			// Enables the default mod remapper
-			if (extension.remapMod) {
+			if (extension.isRemapMod()) {
 				RemapConfiguration.setupDefaultRemap(project);
 			} else {
 				Jar jarTask = (Jar) project.getTasks().getByName("jar");
@@ -200,6 +201,9 @@ public final class CompileConfiguration {
 			System.setProperty("log4j.skipJansi", "true");
 
 			project.getLogger().info("Configuring compiler arguments for Java");
+			MixinApExtension mixinApExtension = LoomGradleExtension.get(project).getMixinApExtension();
+			mixinApExtension.init();
+
 			new JavaApInvoker(project).configureMixin();
 
 			if (project.getPluginManager().hasPlugin("scala")) {
diff --git a/src/main/java/net/fabricmc/loom/configuration/DependencyProvider.java b/src/main/java/net/fabricmc/loom/configuration/DependencyProvider.java
index 9f6d6db3..5017d54a 100644
--- a/src/main/java/net/fabricmc/loom/configuration/DependencyProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/DependencyProvider.java
@@ -49,6 +49,7 @@ import org.zeroturnaround.zip.ZipUtil;
 
 import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.LoomGradlePlugin;
+import net.fabricmc.loom.extension.LoomFiles;
 
 public abstract class DependencyProvider {
 	private LoomDependencyManager dependencyManager;
@@ -57,7 +58,7 @@ public abstract class DependencyProvider {
 
 	public DependencyProvider(Project project) {
 		this.project = project;
-		this.extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		this.extension = LoomGradleExtension.get(project);
 	}
 
 	public abstract void provide(DependencyInfo dependency, Consumer<Runnable> postPopulationScheduler) throws Exception;
@@ -88,6 +89,10 @@ public abstract class DependencyProvider {
 		return extension;
 	}
 
+	public LoomFiles getDirectories() {
+		return getExtension().getFiles();
+	}
+
 	public boolean isRefreshDeps() {
 		return LoomGradlePlugin.refreshDeps;
 	}
diff --git a/src/main/java/net/fabricmc/loom/configuration/FabricApiExtension.java b/src/main/java/net/fabricmc/loom/configuration/FabricApiExtension.java
index 59925bcb..15f5d2a0 100644
--- a/src/main/java/net/fabricmc/loom/configuration/FabricApiExtension.java
+++ b/src/main/java/net/fabricmc/loom/configuration/FabricApiExtension.java
@@ -103,9 +103,17 @@ public class FabricApiExtension {
 	}
 
 	private File getApiMavenPom(String fabricApiVersion) {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 
-		File mavenPom = new File(extension.getUserCache(), "fabric-api/" + fabricApiVersion + ".pom");
+		File mavenPom = new File(extension.getFiles().getUserCache(), "fabric-api/" + fabricApiVersion + ".pom");
+
+		if (project.getGradle().getStartParameter().isOffline()) {
+			if (!mavenPom.exists()) {
+				throw new RuntimeException("Cannot retrieve fabric-api pom due to being offline");
+			}
+
+			return mavenPom;
+		}
 
 		try {
 			URL url = new URL(String.format("https://maven.fabricmc.net/net/fabricmc/fabric-api/fabric-api/%1$s/fabric-api-%1$s.pom", fabricApiVersion));
diff --git a/src/main/java/net/fabricmc/loom/configuration/JarManifestConfiguration.java b/src/main/java/net/fabricmc/loom/configuration/JarManifestConfiguration.java
index 728a109f..408081d7 100644
--- a/src/main/java/net/fabricmc/loom/configuration/JarManifestConfiguration.java
+++ b/src/main/java/net/fabricmc/loom/configuration/JarManifestConfiguration.java
@@ -43,7 +43,7 @@ public final record JarManifestConfiguration(Project project) {
 			return;
 		}
 
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 
 		Attributes attributes = manifest.getMainAttributes();
 		var tinyRemapperVersion = Optional.ofNullable(TinyRemapper.class.getPackage().getImplementationVersion());
@@ -79,7 +79,7 @@ public final record JarManifestConfiguration(Project project) {
 	}
 
 	private Optional<String> getLoaderVersion() {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 
 		if (extension.getInstallerData() == null) {
 			project.getLogger().warn("Could not determine fabric loader version for jar manifest");
diff --git a/src/main/java/net/fabricmc/loom/configuration/LoomDependencyManager.java b/src/main/java/net/fabricmc/loom/configuration/LoomDependencyManager.java
index a33d7293..b0568731 100644
--- a/src/main/java/net/fabricmc/loom/configuration/LoomDependencyManager.java
+++ b/src/main/java/net/fabricmc/loom/configuration/LoomDependencyManager.java
@@ -89,7 +89,7 @@ public class LoomDependencyManager {
 		MappingsProviderImpl mappingsProvider = null;
 
 		project.getLogger().info(":setting up loom dependencies");
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 		Map<String, ProviderList> providerListMap = new HashMap<>();
 		List<ProviderList> targetProviders = new ArrayList<>();
 
@@ -178,7 +178,7 @@ public class LoomDependencyManager {
 	}
 
 	private static void handleInstallerJson(JsonObject jsonObject, Project project) {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 
 		JsonObject libraries = jsonObject.get("libraries").getAsJsonObject();
 		Configuration loaderDepsConfig = project.getConfigurations().getByName(Constants.Configurations.LOADER_DEPENDENCIES);
diff --git a/src/main/java/net/fabricmc/loom/configuration/LoomProjectData.java b/src/main/java/net/fabricmc/loom/configuration/LoomProjectData.java
deleted file mode 100644
index a45df51c..00000000
--- a/src/main/java/net/fabricmc/loom/configuration/LoomProjectData.java
+++ /dev/null
@@ -1,70 +0,0 @@
-/*
- * This file is part of fabric-loom, licensed under the MIT License (MIT).
- *
- * Copyright (c) 2016-2021 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
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all
- * copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
- * SOFTWARE.
- */
-
-package net.fabricmc.loom.configuration;
-
-import java.util.HashMap;
-import java.util.Map;
-import java.util.Objects;
-
-import org.gradle.api.NamedDomainObjectProvider;
-import org.gradle.api.Project;
-import org.gradle.api.artifacts.Configuration;
-import org.jetbrains.annotations.ApiStatus;
-
-@ApiStatus.Internal
-/**
- * This class is stored in the gradle extension, and should not be used outside of loom.
- * It contains data/info related to the current project
- */
-public final class LoomProjectData {
-	private final Project project;
-	private final Map<String, NamedDomainObjectProvider<Configuration>> lazyConfigurations = new HashMap<>();
-
-	public LoomProjectData(Project project) {
-		this.project = Objects.requireNonNull(project);
-	}
-
-	public NamedDomainObjectProvider<Configuration> createLazyConfiguration(String name) {
-		NamedDomainObjectProvider<Configuration> provider = project.getConfigurations().register(name);
-
-		if (lazyConfigurations.containsKey(name)) {
-			throw new IllegalStateException("Duplicate configuration name" + name);
-		}
-
-		lazyConfigurations.put(name, provider);
-
-		return provider;
-	}
-
-	public NamedDomainObjectProvider<Configuration> getLazyConfigurationProvider(String name) {
-		NamedDomainObjectProvider<Configuration> provider = lazyConfigurations.get(name);
-
-		if (provider == null) {
-			throw new NullPointerException("Could not find provider with name: " + name);
-		}
-
-		return provider;
-	}
-}
diff --git a/src/main/java/net/fabricmc/loom/configuration/RemapConfiguration.java b/src/main/java/net/fabricmc/loom/configuration/RemapConfiguration.java
index 62935326..e1f60180 100644
--- a/src/main/java/net/fabricmc/loom/configuration/RemapConfiguration.java
+++ b/src/main/java/net/fabricmc/loom/configuration/RemapConfiguration.java
@@ -65,7 +65,7 @@ public class RemapConfiguration {
 
 	// isDefaultRemap is set to true for the standard remap task, some defaults are left out when this is false.
 	private static void setupRemap(Project project, boolean isDefaultRemap, String jarTaskName, String sourcesJarTaskName, String remapJarTaskName, String remapSourcesJarTaskName, String remapAllJarsTaskName, String remapAllSourcesTaskName) {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 		AbstractArchiveTask jarTask = (AbstractArchiveTask) project.getTasks().getByName(jarTaskName);
 		RemapJarTask remapJarTask = (RemapJarTask) project.getTasks().findByName(remapJarTaskName);
 
diff --git a/src/main/java/net/fabricmc/loom/configuration/accesswidener/AccessWidenerJarProcessor.java b/src/main/java/net/fabricmc/loom/configuration/accesswidener/AccessWidenerJarProcessor.java
index 0d428bac..ef2f37e1 100644
--- a/src/main/java/net/fabricmc/loom/configuration/accesswidener/AccessWidenerJarProcessor.java
+++ b/src/main/java/net/fabricmc/loom/configuration/accesswidener/AccessWidenerJarProcessor.java
@@ -72,15 +72,15 @@ public class AccessWidenerJarProcessor implements JarProcessor {
 
 	@Override
 	public void setup() {
-		LoomGradleExtension loomGradleExtension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension loomGradleExtension = LoomGradleExtension.get(project);
 
-		if (!loomGradleExtension.accessWidener.exists()) {
-			throw new RuntimeException("Could not find access widener file @ " + loomGradleExtension.accessWidener.getAbsolutePath());
+		if (!loomGradleExtension.getAccessWidener().exists()) {
+			throw new RuntimeException("Could not find access widener file @ " + loomGradleExtension.getAccessWidener().getAbsolutePath());
 		}
 
-		inputHash = Checksum.sha256(loomGradleExtension.accessWidener);
+		inputHash = Checksum.sha256(loomGradleExtension.getAccessWidener());
 
-		try (BufferedReader reader = new BufferedReader(new FileReader(loomGradleExtension.accessWidener))) {
+		try (BufferedReader reader = new BufferedReader(new FileReader(loomGradleExtension.getAccessWidener()))) {
 			accessWidenerReader.read(reader);
 		} catch (IOException e) {
 			throw new RuntimeException("Failed to read project access widener file");
diff --git a/src/main/java/net/fabricmc/loom/configuration/ide/RunConfig.java b/src/main/java/net/fabricmc/loom/configuration/ide/RunConfig.java
index 0d31192d..f3a83ef0 100644
--- a/src/main/java/net/fabricmc/loom/configuration/ide/RunConfig.java
+++ b/src/main/java/net/fabricmc/loom/configuration/ide/RunConfig.java
@@ -28,10 +28,8 @@ import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.charset.StandardCharsets;
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.List;
 import java.util.Map;
+import java.util.HashMap;
 import java.util.Objects;
 import java.util.UUID;
 import java.util.function.Consumer;
@@ -41,7 +39,6 @@ import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
 import com.google.common.base.Strings;
-import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
@@ -53,7 +50,6 @@ import org.w3c.dom.Element;
 import org.w3c.dom.Node;
 
 import net.fabricmc.loom.LoomGradleExtension;
-import net.fabricmc.loom.util.Constants;
 import net.fabricmc.loom.util.OperatingSystem;
 
 public class RunConfig {
@@ -131,13 +127,8 @@ public class RunConfig {
 		runConfig.vmArgs = "";
 		runConfig.programArgs = "";
 
-		if ("launchwrapper".equals(extension.getLoaderLaunchMethod())) {
-			runConfig.mainClass = "net.minecraft.launchwrapper.Launch"; // TODO What about custom tweakers for run configs?
-			runConfig.programArgs += "--tweakClass " + ("client".equals(environment) ? Constants.LaunchWrapper.DEFAULT_FABRIC_CLIENT_TWEAKER : Constants.LaunchWrapper.DEFAULT_FABRIC_SERVER_TWEAKER);
-		} else {
-			runConfig.mainClass = "net.fabricmc.devlaunchinjector.Main";
-			runConfig.vmArgs = "-XX:+ShowCodeDetailsInExceptionMessages -Dfabric.dli.config=" + encodeEscaped(extension.getDevLauncherConfig().getAbsolutePath()) + " -Dfabric.dli.env=" + environment.toLowerCase();
-		}
+		runConfig.mainClass = "net.fabricmc.devlaunchinjector.Main";
+		runConfig.vmArgs = "-XX:+ShowCodeDetailsInExceptionMessages -Dfabric.dli.config=" + encodeEscaped(extension.getFiles().getDevLauncherConfig().getAbsolutePath()) + " -Dfabric.dli.env=" + environment.toLowerCase();
 
 		if (extension.isForge()) {
 			List<String> modClasses = new ArrayList<>();
@@ -155,35 +146,6 @@ public class RunConfig {
 
 			runConfig.envVariables.put("MOD_CLASSES", String.join(File.pathSeparator, modClasses));
 		}
-
-		if (extension.getLoaderLaunchMethod().equals("launchwrapper")) {
-			// if installer.json found...
-			JsonObject installerJson = extension.getInstallerData().installerJson();
-
-			if (installerJson != null) {
-				List<String> sideKeys = ImmutableList.of(environment, "common");
-
-				// copy launchwrapper tweakers
-				if (installerJson.has("launchwrapper")) {
-					JsonObject launchwrapperJson = installerJson.getAsJsonObject("launchwrapper");
-
-					if (launchwrapperJson.has("tweakers")) {
-						JsonObject tweakersJson = launchwrapperJson.getAsJsonObject("tweakers");
-						StringBuilder builder = new StringBuilder();
-
-						for (String s : sideKeys) {
-							if (tweakersJson.has(s)) {
-								for (JsonElement element : tweakersJson.getAsJsonArray(s)) {
-									builder.append(" --tweakClass ").append(element.getAsString());
-								}
-							}
-						}
-
-						runConfig.programArgs += builder.toString();
-					}
-				}
-			}
-		}
 	}
 
 	// Turns camelCase/PascalCase into Capital Case
@@ -197,7 +159,7 @@ public class RunConfig {
 	}
 
 	public static RunConfig runConfig(Project project, RunConfigSettings settings) {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 		String name = settings.getName();
 
 		String configName = settings.getConfigName();
@@ -325,11 +287,6 @@ public class RunConfig {
 			return mainClassName;
 		}
 
-		// Fallback to default class names, happens when in a loader dev env
-		if ("launchwrapper".equals(extension.getLoaderLaunchMethod())) {
-			return "net.minecraft.launchwrapper.Launch";
-		}
-
 		return defaultMainClass;
 	}
 
diff --git a/src/main/java/net/fabricmc/loom/configuration/ide/RunConfigSettings.java b/src/main/java/net/fabricmc/loom/configuration/ide/RunConfigSettings.java
index 66956521..28f2f2f6 100644
--- a/src/main/java/net/fabricmc/loom/configuration/ide/RunConfigSettings.java
+++ b/src/main/java/net/fabricmc/loom/configuration/ide/RunConfigSettings.java
@@ -100,7 +100,7 @@ public final class RunConfigSettings implements Named {
 	public RunConfigSettings(Project project, String baseName) {
 		this.baseName = baseName;
 		this.project = project;
-		this.extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		this.extension = LoomGradleExtension.get(project);
 		this.ideConfigGenerated = extension.isRootProject();
 
 		source("main");
diff --git a/src/main/java/net/fabricmc/loom/configuration/ide/SetupIntelijRunConfigs.java b/src/main/java/net/fabricmc/loom/configuration/ide/SetupIntelijRunConfigs.java
index 5bc388a5..db815e94 100644
--- a/src/main/java/net/fabricmc/loom/configuration/ide/SetupIntelijRunConfigs.java
+++ b/src/main/java/net/fabricmc/loom/configuration/ide/SetupIntelijRunConfigs.java
@@ -37,7 +37,7 @@ import net.fabricmc.loom.configuration.providers.minecraft.assets.MinecraftAsset
 
 public class SetupIntelijRunConfigs {
 	public static void setup(Project project) {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 
 		File projectDir = project.getRootProject().file(".idea");
 
@@ -54,7 +54,7 @@ public class SetupIntelijRunConfigs {
 
 	private static void generate(Project project) throws IOException {
 		Project rootProject = project.getRootProject();
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 
 		if (extension.ideSync()) {
 			//Ensures the assets are downloaded when idea is syncing a project
diff --git a/src/main/java/net/fabricmc/loom/configuration/mods/ModProcessor.java b/src/main/java/net/fabricmc/loom/configuration/mods/ModProcessor.java
index b13cf0ea..b7b37506 100644
--- a/src/main/java/net/fabricmc/loom/configuration/mods/ModProcessor.java
+++ b/src/main/java/net/fabricmc/loom/configuration/mods/ModProcessor.java
@@ -137,7 +137,7 @@ public class ModProcessor {
 	}
 
 	private static void remapJars(Project project, List<ModDependencyInfo> processList) throws IOException {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 		String fromM = extension.isForge() ? "srg" : "intermediary";
 		String toM = "named";
 
@@ -277,28 +277,15 @@ public class ModProcessor {
 
 	public static JsonObject readInstallerJson(File file, Project project) {
 		try {
-			LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
-			String launchMethod = extension.getLoaderLaunchMethod();
+			LoomGradleExtension extension = LoomGradleExtension.get(project);
 
 			String jsonStr;
 
 			try (JarFile jarFile = new JarFile(file)) {
-				ZipEntry entry = null;
-
-				if (!launchMethod.isEmpty()) {
-					entry = jarFile.getEntry("fabric-installer." + launchMethod + ".json");
-
-					if (entry == null) {
-						project.getLogger().warn("Could not find loader launch method '" + launchMethod + "', falling back");
-					}
-				}
+				ZipEntry entry = jarFile.getEntry("fabric-installer.json");
 
 				if (entry == null) {
-					entry = jarFile.getEntry("fabric-installer.json");
-
-					if (entry == null) {
-						return null;
-					}
+					return null;
 				}
 
 				try (InputStream inputstream = jarFile.getInputStream(entry)) {
diff --git a/src/main/java/net/fabricmc/loom/configuration/processors/MinecraftProcessedProvider.java b/src/main/java/net/fabricmc/loom/configuration/processors/MinecraftProcessedProvider.java
index 22badc39..4e28f52a 100644
--- a/src/main/java/net/fabricmc/loom/configuration/processors/MinecraftProcessedProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/processors/MinecraftProcessedProvider.java
@@ -72,7 +72,7 @@ public class MinecraftProcessedProvider extends MinecraftMappedProvider {
 	}
 
 	private void invalidateJars() {
-		File dir = getJarDirectory(getExtension().getUserCache(), projectMappedClassifier);
+		File dir = getJarDirectory(getExtension().getFiles().getUserCache(), projectMappedClassifier);
 
 		if (dir.exists()) {
 			getProject().getLogger().warn("Invalidating project jars");
@@ -89,7 +89,7 @@ public class MinecraftProcessedProvider extends MinecraftMappedProvider {
 	public void initFiles(MinecraftProviderImpl minecraftProvider, MappingsProviderImpl mappingsProvider) {
 		super.initFiles(minecraftProvider, mappingsProvider);
 
-		projectMappedJar = new File(getJarDirectory(getExtension().getRootProjectPersistentCache(), projectMappedClassifier), "minecraft-" + getJarVersionString(projectMappedClassifier) + ".jar");
+		projectMappedJar = new File(getJarDirectory(getExtension().getFiles().getRootProjectPersistentCache(), projectMappedClassifier), "minecraft-" + getJarVersionString(projectMappedClassifier) + ".jar");
 	}
 
 	@Override
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/LaunchProvider.java b/src/main/java/net/fabricmc/loom/configuration/providers/LaunchProvider.java
index 1690fa64..03a08d10 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/LaunchProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/LaunchProvider.java
@@ -59,13 +59,13 @@ public class LaunchProvider extends DependencyProvider {
 				.property("fabric.remapClasspathFile", getRemapClasspathFile().getAbsolutePath())
 				.property("log4j.configurationFile", getAllLog4JConfigFiles())
 
-				.property("client", "java.library.path", getExtension().getNativesDirectory().getAbsolutePath())
-				.property("client", "org.lwjgl.librarypath", getExtension().getNativesDirectory().getAbsolutePath())
+				.property("client", "java.library.path", getDirectories().getNativesDirectory(getExtension().getMinecraftProvider()).getAbsolutePath())
+				.property("client", "org.lwjgl.librarypath", getDirectories().getNativesDirectory(getExtension().getMinecraftProvider()).getAbsolutePath())
 
 				.argument("client", "--assetIndex")
 				.argument("client", getExtension().getMinecraftProvider().getVersionInfo().assetIndex().fabricId(getExtension().getMinecraftProvider().minecraftVersion()))
 				.argument("client", "--assetsDir")
-				.argument("client", new File(getExtension().getUserCache(), "assets").getAbsolutePath());
+				.argument("client", new File(getDirectories().getUserCache(), "assets").getAbsolutePath());
 
 		if (getExtension().isForge()) {
 			launchConfig
@@ -127,7 +127,7 @@ public class LaunchProvider extends DependencyProvider {
 		}
 
 		writeLog4jConfig();
-		FileUtils.writeStringToFile(getExtension().getDevLauncherConfig(), launchConfig.asString(), StandardCharsets.UTF_8);
+		FileUtils.writeStringToFile(getDirectories().getDevLauncherConfig(), launchConfig.asString(), StandardCharsets.UTF_8);
 
 		addDependency(Constants.Dependencies.DEV_LAUNCH_INJECTOR + Constants.Dependencies.Versions.DEV_LAUNCH_INJECTOR, Constants.Configurations.LOOM_DEVELOPMENT_DEPENDENCIES);
 		addDependency(Constants.Dependencies.TERMINAL_CONSOLE_APPENDER + Constants.Dependencies.Versions.TERMINAL_CONSOLE_APPENDER, Constants.Configurations.LOOM_DEVELOPMENT_DEPENDENCIES);
@@ -143,7 +143,7 @@ public class LaunchProvider extends DependencyProvider {
 	}
 
 	private File getLog4jConfigFile() {
-		return getExtension().getDefaultLog4jConfigFile();
+		return getDirectories().getDefaultLog4jConfigFile();
 	}
 
 	private String getAllLog4JConfigFiles() {
@@ -153,7 +153,7 @@ public class LaunchProvider extends DependencyProvider {
 	}
 
 	private File getRemapClasspathFile() {
-		return new File(getExtension().getDevLauncherConfig().getParentFile(), "remapClasspath.txt");
+		return new File(getDirectories().getDevLauncherConfig().getParentFile(), "remapClasspath.txt");
 	}
 
 	private void writeLog4jConfig() {
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/MinecraftProviderImpl.java b/src/main/java/net/fabricmc/loom/configuration/providers/MinecraftProviderImpl.java
index 0ecb49ff..fa6e5703 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/MinecraftProviderImpl.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/MinecraftProviderImpl.java
@@ -59,6 +59,7 @@ public class MinecraftProviderImpl extends DependencyProvider implements Minecra
 	public File minecraftServerJar;
 	private File minecraftMergedJar;
 	private File versionManifestJson;
+	private File experimentalVersionsJson;
 	private String jarSuffix = "";
 
 	public MinecraftProviderImpl(Project project) {
@@ -117,17 +118,20 @@ public class MinecraftProviderImpl extends DependencyProvider implements Minecra
 	}
 
 	private void initFiles() {
-		minecraftJson = new File(getExtension().getUserCache(), "minecraft-" + minecraftVersion + "-info.json");
-		minecraftClientJar = new File(getExtension().getUserCache(), "minecraft-" + minecraftVersion + "-client.jar");
-		minecraftServerJar = new File(getExtension().getUserCache(), "minecraft-" + minecraftVersion + "-server.jar");
-		minecraftMergedJar = new File(getExtension().getUserCache(), "minecraft-" + minecraftVersion + "-merged.jar");
-		versionManifestJson = new File(getExtension().getUserCache(), "version_manifest.json");
+		minecraftJson = new File(getDirectories().getUserCache(), "minecraft-" + minecraftVersion + "-info.json");
+		minecraftClientJar = new File(getDirectories().getUserCache(), "minecraft-" + minecraftVersion + "-client.jar");
+		minecraftServerJar = new File(getDirectories().getUserCache(), "minecraft-" + minecraftVersion + "-server.jar");
+		minecraftMergedJar = new File(getDirectories().getUserCache(), "minecraft-" + minecraftVersion + "-merged.jar");
+		versionManifestJson = new File(getDirectories().getUserCache(), "version_manifest.json");
+		experimentalVersionsJson = new File(getDirectories().getUserCache(), "experimental_version_manifest.json");
 	}
 
 	public void deleteFiles() {
 		DownloadUtil.delete(minecraftClientJar);
 		DownloadUtil.delete(minecraftServerJar);
 		DownloadUtil.delete(minecraftMergedJar);
+		DownloadUtil.delete(versionManifestJson);
+		DownloadUtil.delete(experimentalVersionsJson);
 	}
 
 	private void downloadMcJson(boolean offline) throws IOException {
@@ -155,16 +159,20 @@ public class MinecraftProviderImpl extends DependencyProvider implements Minecra
 
 		Optional<ManifestVersion.Versions> optionalVersion = Optional.empty();
 
-		if (getExtension().customManifest != null) {
+		if (getExtension().getCustomManifest() != null) {
 			ManifestVersion.Versions customVersion = new ManifestVersion.Versions();
 			customVersion.id = minecraftVersion;
-			customVersion.url = getExtension().customManifest;
+			customVersion.url = getExtension().getCustomManifest();
 			optionalVersion = Optional.of(customVersion);
 			getProject().getLogger().lifecycle("Using custom minecraft manifest");
 		}
 
-		if (!optionalVersion.isPresent()) {
+		if (optionalVersion.isEmpty()) {
 			optionalVersion = mcManifest.versions().stream().filter(versions -> versions.id.equalsIgnoreCase(minecraftVersion)).findFirst();
+
+			if (optionalVersion.isEmpty()) {
+				optionalVersion = findExperimentalVersion(offline);
+			}
 		}
 
 		if (optionalVersion.isPresent()) {
@@ -194,8 +202,31 @@ public class MinecraftProviderImpl extends DependencyProvider implements Minecra
 		}
 	}
 
+	// This attempts to find the version from fabric's own fallback version manifest json.
+	private Optional<ManifestVersion.Versions> findExperimentalVersion(boolean offline) throws IOException {
+		if (offline) {
+			if (!experimentalVersionsJson.exists()) {
+				getProject().getLogger().warn("Skipping download of experimental versions jsons due to being offline.");
+				return Optional.empty();
+			}
+		} else {
+			DownloadUtil.downloadIfChanged(new URL(Constants.EXPERIMENTAL_VERSIONS), experimentalVersionsJson, getProject().getLogger());
+		}
+
+		String expVersionManifest = Files.asCharSource(experimentalVersionsJson, StandardCharsets.UTF_8).read();
+		ManifestVersion expManifest = LoomGradlePlugin.OBJECT_MAPPER.readValue(expVersionManifest, ManifestVersion.class);
+
+		var result = expManifest.versions().stream().filter(versions -> versions.id.equalsIgnoreCase(minecraftVersion)).findFirst();
+
+		if (result.isPresent()) {
+			getProject().getLogger().lifecycle("Using fallback experimental version {}", minecraftVersion);
+		}
+
+		return result;
+	}
+
 	private boolean hasRecentValidManifest() throws IOException {
-		if (getExtension().customManifest != null) {
+		if (getExtension().getCustomManifest() != null) {
 			return false;
 		}
 
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/mappings/GradleMappingContext.java b/src/main/java/net/fabricmc/loom/configuration/providers/mappings/GradleMappingContext.java
index f2f928bc..db478671 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/mappings/GradleMappingContext.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/mappings/GradleMappingContext.java
@@ -41,7 +41,7 @@ public class GradleMappingContext implements MappingContext {
 
 	public GradleMappingContext(Project project, Supplier<String> workingDirName) {
 		this.project = project;
-		this.extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		this.extension = LoomGradleExtension.get(project);
 		this.workingDirName = workingDirName;
 	}
 
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/mappings/MappingsProviderImpl.java b/src/main/java/net/fabricmc/loom/configuration/providers/mappings/MappingsProviderImpl.java
index 36837ccf..1de460e8 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/mappings/MappingsProviderImpl.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/mappings/MappingsProviderImpl.java
@@ -113,7 +113,7 @@ public class MappingsProviderImpl extends DependencyProvider implements Mappings
 
 	public MappingsProviderImpl(Project project) {
 		super(project);
-		mappingsDir = getExtension().getUserCache().toPath().resolve("mappings");
+		mappingsDir = getDirectories().getUserCache().toPath().resolve("mappings");
 		mappingsStepsDir = mappingsDir.resolve("steps");
 	}
 
@@ -214,7 +214,7 @@ public class MappingsProviderImpl extends DependencyProvider implements Mappings
 		Path mappedVersionedDir = getMappedVersionedDir(removeSuffix);
 		tinyMappings = mappedVersionedDir.resolve("mappings.tiny").toFile();
 		unpickDefinitionsFile = mappedVersionedDir.resolve("definitions.unpick").toFile();
-		tinyMappingsJar = new File(getExtension().getUserCache(), removeSuffix + "-" + jarClassifier + ".jar");
+		tinyMappingsJar = new File(getDirectories().getUserCache(), removeSuffix + "-" + jarClassifier + ".jar");
 		tinyMappingsWithSrg = mappedVersionedDir.resolve("mappings-srg.tiny");
 		mixinTinyMappingsWithSrg = mappedVersionedDir.resolve("mappings-mixin-srg.tiny").toFile();
 		srgToNamedSrg = mappedVersionedDir.resolve("mappings-srg-named.srg").toFile();
@@ -277,7 +277,7 @@ public class MappingsProviderImpl extends DependencyProvider implements Mappings
 
 		LoomGradleExtension extension = getExtension();
 
-		if (extension.accessWidener != null) {
+		if (extension.getAccessWidener() != null) {
 			extension.addJarProcessor(new AccessWidenerJarProcessor(getProject()));
 		}
 
@@ -545,7 +545,7 @@ public class MappingsProviderImpl extends DependencyProvider implements Mappings
 
 				// Download and extract intermediary
 				String encodedMinecraftVersion = UrlEscapers.urlFragmentEscaper().escape(minecraftVersion);
-				String intermediaryArtifactUrl = getExtension().getIntermediaryUrl().apply(encodedMinecraftVersion);
+				String intermediaryArtifactUrl = getExtension().getIntermediaryUrl(encodedMinecraftVersion);
 				Path intermediaryJar = getMappingsVersionedDir().resolve("intermediary-v2.jar");
 				DownloadUtil.downloadIfChanged(new URL(intermediaryArtifactUrl), intermediaryJar.toFile(), getProject().getLogger());
 
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftLibraryProvider.java b/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftLibraryProvider.java
index 0089b935..53c9412d 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftLibraryProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftLibraryProvider.java
@@ -48,7 +48,7 @@ public class MinecraftLibraryProvider {
 	}
 
 	private void initFiles(Project project, MinecraftProviderImpl minecraftProvider) {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
-		MINECRAFT_LIBS = new File(extension.getUserCache(), "libraries");
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
+		MINECRAFT_LIBS = new File(extension.getFiles().getUserCache(), "libraries");
 	}
 }
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftMappedProvider.java b/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftMappedProvider.java
index 1fd45815..6c6ceee5 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftMappedProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftMappedProvider.java
@@ -352,9 +352,9 @@ public class MinecraftMappedProvider extends DependencyProvider {
 
 	public void initFiles(MinecraftProviderImpl minecraftProvider, MappingsProviderImpl mappingsProvider) {
 		this.minecraftProvider = minecraftProvider;
-		minecraftIntermediaryJar = new File(getExtension().getUserCache(), "minecraft-" + getJarVersionString("intermediary") + ".jar");
+		minecraftIntermediaryJar = new File(getDirectories().getUserCache(), "minecraft-" + getJarVersionString("intermediary") + ".jar");
 		minecraftSrgJar = !getExtension().isForge() ? null : new File(getExtension().getUserCache(), "minecraft-" + getJarVersionString("srg") + ".jar");
-		minecraftMappedJar = new File(getJarDirectory(getExtension().getUserCache(), "mapped"), "minecraft-" + getJarVersionString("mapped") + ".jar");
+		minecraftMappedJar = new File(getJarDirectory(getDirectories().getUserCache(), "mapped"), "minecraft-" + getJarVersionString("mapped") + ".jar");
 		inputJar = getExtension().isForge() ? mappingsProvider.patchedProvider.getMergedJar() : minecraftProvider.getMergedJar();
 
 		if (getExtension().isForge()) {
@@ -398,7 +398,7 @@ public class MinecraftMappedProvider extends DependencyProvider {
 	}
 
 	public File getUnpickedJar() {
-		return new File(getJarDirectory(getExtension().getUserCache(), "mapped"), "minecraft-" + getJarVersionString("unpicked") + ".jar");
+		return new File(getJarDirectory(getDirectories().getUserCache(), "mapped"), "minecraft-" + getJarVersionString("unpicked") + ".jar");
 	}
 
 	@Override
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftNativesProvider.java b/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftNativesProvider.java
index 587c42ab..868b5651 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftNativesProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/MinecraftNativesProvider.java
@@ -49,10 +49,10 @@ public class MinecraftNativesProvider {
 
 	public MinecraftNativesProvider(Project project) {
 		this.project = project;
-		extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		extension = LoomGradleExtension.get(project);
 
-		nativesDir = extension.getNativesDirectory();
-		jarStore = extension.getNativesJarStore();
+		nativesDir = extension.getFiles().getNativesDirectory(extension.getMinecraftProvider());
+		jarStore = extension.getFiles().getNativesJarStore();
 	}
 
 	public static void provide(Project project) throws IOException {
@@ -60,7 +60,7 @@ public class MinecraftNativesProvider {
 	}
 
 	private void provide() throws IOException {
-		if (extension.hasCustomNatives()) {
+		if (extension.getFiles().hasCustomNatives()) {
 			if (!nativesDir.exists()) {
 				throw new RuntimeException("Could no find custom natives directory at " + nativesDir.getAbsolutePath());
 			}
diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/assets/MinecraftAssetsProvider.java b/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/assets/MinecraftAssetsProvider.java
index edc3aea8..13fc8f0f 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/assets/MinecraftAssetsProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/minecraft/assets/MinecraftAssetsProvider.java
@@ -50,14 +50,14 @@ import net.fabricmc.loom.util.HashedDownloadUtil;
 
 public class MinecraftAssetsProvider {
 	public static void provide(MinecraftProviderImpl minecraftProvider, Project project) throws IOException {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 		boolean offline = project.getGradle().getStartParameter().isOffline();
 
 		MinecraftVersionMeta versionInfo = minecraftProvider.getVersionInfo();
 		MinecraftVersionMeta.AssetIndex assetIndex = versionInfo.assetIndex();
 
 		// get existing cache files
-		File assets = new File(extension.getUserCache(), "assets");
+		File assets = new File(extension.getFiles().getUserCache(), "assets");
 
 		if (!assets.exists()) {
 			assets.mkdirs();
diff --git a/src/main/java/net/fabricmc/loom/decompilers/DecompilerConfiguration.java b/src/main/java/net/fabricmc/loom/decompilers/DecompilerConfiguration.java
index 322e6dc3..40380a4d 100644
--- a/src/main/java/net/fabricmc/loom/decompilers/DecompilerConfiguration.java
+++ b/src/main/java/net/fabricmc/loom/decompilers/DecompilerConfiguration.java
@@ -35,7 +35,7 @@ public final class DecompilerConfiguration {
 	}
 
 	public static void setup(Project project) {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 		extension.addDecompiler(new FabricFernFlowerDecompiler(project));
 		extension.addDecompiler(new FabricCFRDecompiler(project));
 	}
diff --git a/src/main/java/net/fabricmc/loom/extension/LoomFiles.java b/src/main/java/net/fabricmc/loom/extension/LoomFiles.java
new file mode 100644
index 00000000..b24352a8
--- /dev/null
+++ b/src/main/java/net/fabricmc/loom/extension/LoomFiles.java
@@ -0,0 +1,43 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021 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
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.extension;
+
+import java.io.File;
+
+import net.fabricmc.loom.configuration.providers.MinecraftProvider;
+
+public interface LoomFiles {
+	File getUserCache();
+	File getRootProjectPersistentCache();
+	File getProjectPersistentCache();
+	File getProjectBuildCache();
+	File getRemappedModCache();
+	File getNativesJarStore();
+	boolean hasCustomNatives();
+	File getNativesDirectory(MinecraftProvider minecraftProvider);
+	File getDefaultLog4jConfigFile();
+	File getDevLauncherConfig();
+	File getUnpickLoggingConfigFile();
+}
diff --git a/src/main/java/net/fabricmc/loom/extension/LoomFilesImpl.java b/src/main/java/net/fabricmc/loom/extension/LoomFilesImpl.java
new file mode 100644
index 00000000..1dac177d
--- /dev/null
+++ b/src/main/java/net/fabricmc/loom/extension/LoomFilesImpl.java
@@ -0,0 +1,128 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021 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
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.extension;
+
+import java.io.File;
+
+import org.gradle.api.Project;
+
+import net.fabricmc.loom.configuration.providers.MinecraftProvider;
+
+public final class LoomFilesImpl implements LoomFiles {
+	private final Project project;
+
+	private final File userCache;
+	private final File rootProjectPersistentCache;
+	private final File projectPersistentCache;
+	private final File projectBuildCache;
+	private final File remappedModCache;
+	private final File nativesJarStore;
+
+	public LoomFilesImpl(Project project) {
+		this.project = project;
+
+		this.userCache = createFile(project.getGradle().getGradleUserHomeDir(), "caches" + File.separator + "fabric-loom");
+		this.rootProjectPersistentCache = createFile(project.getRootProject().file(".gradle"), "loom-cache");
+		this.projectPersistentCache = createFile(project.file(".gradle"), "loom-cache");
+		this.projectBuildCache = createFile(project.getBuildDir(), "loom-cache");
+		this.remappedModCache = createFile(getRootProjectPersistentCache(), "remapped_mods");
+		this.nativesJarStore = createFile(getUserCache(), "natives/jars");
+	}
+
+	private File createFile(File parent, String child) {
+		File file = new File(parent, child);
+
+		if (!file.exists()) {
+			file.mkdirs();
+		}
+
+		return file;
+	}
+
+	@Override
+	public File getUserCache() {
+		return userCache;
+	}
+
+	@Override
+	public File getRootProjectPersistentCache() {
+		return rootProjectPersistentCache;
+	}
+
+	@Override
+	public File getProjectPersistentCache() {
+		return projectPersistentCache;
+	}
+
+	@Override
+	public File getProjectBuildCache() {
+		return projectBuildCache;
+	}
+
+	@Override
+	public File getRemappedModCache() {
+		return remappedModCache;
+	}
+
+	@Override
+	public File getNativesJarStore() {
+		return nativesJarStore;
+	}
+
+	@Override
+	public boolean hasCustomNatives() {
+		return project.getProperties().get("fabric.loom.natives.dir") != null;
+	}
+
+	@Override
+	public File getNativesDirectory(MinecraftProvider minecraftProvider) {
+		if (hasCustomNatives()) {
+			return new File((String) project.property("fabric.loom.natives.dir"));
+		}
+
+		File natives = new File(getUserCache(), "natives/" + minecraftProvider.minecraftVersion());
+
+		if (!natives.exists()) {
+			natives.mkdirs();
+		}
+
+		return natives;
+	}
+
+	@Override
+	public File getDefaultLog4jConfigFile() {
+		return new File(getProjectPersistentCache(), "log4j.xml");
+	}
+
+	@Override
+	public File getDevLauncherConfig() {
+		return new File(getProjectPersistentCache(), "launch.cfg");
+	}
+
+	@Override
+	public File getUnpickLoggingConfigFile() {
+		return new File(getProjectPersistentCache(), "unpick-logging.properties");
+	}
+}
diff --git a/src/main/java/net/fabricmc/loom/extension/LoomGradleExtensionApiImpl.java b/src/main/java/net/fabricmc/loom/extension/LoomGradleExtensionApiImpl.java
new file mode 100644
index 00000000..3d9ca87d
--- /dev/null
+++ b/src/main/java/net/fabricmc/loom/extension/LoomGradleExtensionApiImpl.java
@@ -0,0 +1,207 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021 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
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.extension;
+
+import java.io.File;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+
+import org.gradle.api.Action;
+import org.gradle.api.NamedDomainObjectContainer;
+import org.gradle.api.Project;
+import org.gradle.api.artifacts.Dependency;
+import org.gradle.api.file.ConfigurableFileCollection;
+import org.gradle.api.plugins.BasePluginConvention;
+
+import net.fabricmc.loom.api.MixinApExtensionAPI;
+import net.fabricmc.loom.api.decompilers.LoomDecompiler;
+import net.fabricmc.loom.api.LoomGradleExtensionAPI;
+import net.fabricmc.loom.configuration.ide.RunConfigSettings;
+import net.fabricmc.loom.configuration.processors.JarProcessor;
+import net.fabricmc.loom.configuration.providers.mappings.GradleMappingContext;
+import net.fabricmc.loom.configuration.providers.mappings.LayeredMappingSpec;
+import net.fabricmc.loom.configuration.providers.mappings.LayeredMappingSpecBuilder;
+import net.fabricmc.loom.configuration.providers.mappings.LayeredMappingsDependency;
+
+/**
+ * This class implements the public extension api.
+ */
+public abstract class LoomGradleExtensionApiImpl implements LoomGradleExtensionAPI {
+	protected final List<LoomDecompiler> decompilers = new ArrayList<>();
+	protected final List<JarProcessor> jarProcessors = new ArrayList<>();
+	protected final ConfigurableFileCollection log4jConfigs;
+
+	protected File accessWidener = null;
+	protected boolean shareCaches = false;
+	protected String refmapName = null;
+	protected boolean remapMod = true;
+	protected String customManifest;
+
+	private NamedDomainObjectContainer<RunConfigSettings> runConfigs;
+
+	protected LoomGradleExtensionApiImpl(Project project, LoomFiles directories) {
+		this.runConfigs = project.container(RunConfigSettings.class,
+				baseName -> new RunConfigSettings(project, baseName));
+		this.log4jConfigs = project.files(directories.getDefaultLog4jConfigFile());
+	}
+
+	@Override
+	public File getAccessWidener() {
+		return accessWidener;
+	}
+
+	@Override
+	public void setAccessWidener(Object file) {
+		Objects.requireNonNull(file, "Access widener file cannot be null");
+		this.accessWidener = getProject().file(file);
+	}
+
+	@Override
+	public void setShareCaches(boolean shareCaches) {
+		this.shareCaches = shareCaches;
+	}
+
+	@Override
+	public boolean isShareCaches() {
+		return shareCaches;
+	}
+
+	@Override
+	public List<LoomDecompiler> getDecompilers() {
+		return decompilers;
+	}
+
+	@Override
+	public void addDecompiler(LoomDecompiler decompiler) {
+		Objects.requireNonNull(decompiler, "Decompiler cannot be null");
+		decompilers.add(decompiler);
+	}
+
+	@Override
+	public List<JarProcessor> getJarProcessors() {
+		return jarProcessors;
+	}
+
+	@Override
+	public void addJarProcessor(JarProcessor processor) {
+		Objects.requireNonNull(processor, "Jar processor cannot be null");
+		jarProcessors.add(processor);
+	}
+
+	@Override
+	public Dependency layered(Action<LayeredMappingSpecBuilder> action) {
+		LayeredMappingSpecBuilder builder = new LayeredMappingSpecBuilder();
+		action.execute(builder);
+		LayeredMappingSpec builtSpec = builder.build();
+		return new LayeredMappingsDependency(new GradleMappingContext(getProject(), "layers_" + builtSpec.getVersion().replace("+", "_").replace(".", "_")), builtSpec, builtSpec.getVersion());
+	}
+
+	@Override
+	public String getRefmapName() {
+		if (refmapName == null || refmapName.isEmpty()) {
+			String defaultRefmapName = getProject().getConvention().getPlugin(BasePluginConvention.class).getArchivesBaseName() + "-refmap.json";
+			getProject().getLogger().info("Could not find refmap definition, will be using default name: " + defaultRefmapName);
+			refmapName = defaultRefmapName;
+		}
+
+		return refmapName;
+	}
+
+	@Override
+	public void setRefmapName(String refmapName) {
+		this.refmapName = refmapName;
+	}
+
+	@Override
+	public void setRemapMod(boolean remapMod) {
+		this.remapMod = remapMod;
+	}
+
+	@Override
+	public void runs(Action<NamedDomainObjectContainer<RunConfigSettings>> action) {
+		action.execute(runConfigs);
+	}
+
+	@Override
+	public NamedDomainObjectContainer<RunConfigSettings> getRunConfigs() {
+		return runConfigs;
+	}
+
+	@Override
+	public ConfigurableFileCollection getLog4jConfigs() {
+		return log4jConfigs;
+	}
+
+	@Override
+	public boolean isRemapMod() {
+		return remapMod;
+	}
+
+	@Override
+	public void mixin(Action<MixinApExtensionAPI> action) {
+		action.execute(getMixinApExtension());
+	}
+
+	@Override
+	public void setCustomManifest(String customManifest) {
+		Objects.requireNonNull(customManifest, "Custom manifest cannot be null");
+		this.customManifest = customManifest;
+	}
+
+	@Override
+	public String getCustomManifest() {
+		return customManifest;
+	}
+
+	protected abstract Project getProject();
+
+	protected abstract LoomFiles getFiles();
+
+	protected abstract MixinApExtension getMixinApExtension();
+
+	// This is here to ensure that LoomGradleExtensionApiImpl compiles without any unimplemented methods
+	private final class EnsureCompile extends LoomGradleExtensionApiImpl {
+		private EnsureCompile() {
+			super(null, null);
+			throw new RuntimeException();
+		}
+
+		@Override
+		protected Project getProject() {
+			throw new RuntimeException("Yeah... something is really wrong");
+		}
+
+		@Override
+		protected LoomFiles getFiles() {
+			throw new RuntimeException("Yeah... something is really wrong");
+		}
+
+		@Override
+		protected MixinApExtension getMixinApExtension() {
+			throw new RuntimeException("Yeah... something is really wrong");
+		}
+	}
+}
diff --git a/src/main/java/net/fabricmc/loom/extension/LoomGradleExtensionImpl.java b/src/main/java/net/fabricmc/loom/extension/LoomGradleExtensionImpl.java
new file mode 100644
index 00000000..436f9b6b
--- /dev/null
+++ b/src/main/java/net/fabricmc/loom/extension/LoomGradleExtensionImpl.java
@@ -0,0 +1,170 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021 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
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.extension;
+
+import java.io.File;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.function.Supplier;
+
+import org.cadixdev.lorenz.MappingSet;
+import org.cadixdev.mercury.Mercury;
+import org.gradle.api.NamedDomainObjectProvider;
+import org.gradle.api.Project;
+import org.gradle.api.artifacts.Configuration;
+import org.gradle.api.file.ConfigurableFileCollection;
+
+import net.fabricmc.loom.LoomGradleExtension;
+import net.fabricmc.loom.configuration.InstallerData;
+import net.fabricmc.loom.configuration.LoomDependencyManager;
+import net.fabricmc.loom.configuration.processors.JarProcessorManager;
+
+public class LoomGradleExtensionImpl extends LoomGradleExtensionApiImpl implements LoomGradleExtension {
+	private final Project project;
+	private final MixinApExtension mixinApExtension;
+	private final LoomFiles loomFiles;
+	private final ConfigurableFileCollection unmappedMods;
+
+	private final Set<File> mixinMappings = Collections.synchronizedSet(new HashSet<>());
+	private final MappingSet[] srcMappingCache = new MappingSet[2];
+	private final Mercury[] srcMercuryCache = new Mercury[2];
+	private final Map<String, NamedDomainObjectProvider<Configuration>> lazyConfigurations = new HashMap<>();
+
+	private LoomDependencyManager dependencyManager;
+	private JarProcessorManager jarProcessorManager;
+	private InstallerData installerData;
+
+	public LoomGradleExtensionImpl(Project project, LoomFiles files) {
+		super(project, files);
+		this.project = project;
+		this.mixinApExtension = new MixinApExtensionImpl(project);
+		this.loomFiles = files;
+		this.unmappedMods = project.files();
+	}
+
+	@Override
+	protected Project getProject() {
+		return project;
+	}
+
+	@Override
+	public LoomFiles getFiles() {
+		return loomFiles;
+	}
+
+	@Override
+	public synchronized File getNextMixinMappings() {
+		File mixinMapping = new File(getFiles().getProjectBuildCache(), "mixin-map-" + getMinecraftProvider().minecraftVersion() + "-" + getMappingsProvider().mappingsVersion + "." + mixinMappings.size() + ".tiny");
+		mixinMappings.add(mixinMapping);
+		return mixinMapping;
+	}
+
+	@Override
+	public Set<File> getAllMixinMappings() {
+		return mixinMappings;
+	}
+
+	@Override
+	public void setDependencyManager(LoomDependencyManager dependencyManager) {
+		this.dependencyManager = dependencyManager;
+	}
+
+	@Override
+	public LoomDependencyManager getDependencyManager() {
+		return Objects.requireNonNull(dependencyManager, "Cannot get LoomDependencyManager before it has been setup");
+	}
+
+	@Override
+	public void setJarProcessorManager(JarProcessorManager jarProcessorManager) {
+		this.jarProcessorManager = jarProcessorManager;
+	}
+
+	@Override
+	public JarProcessorManager getJarProcessorManager() {
+		return Objects.requireNonNull(jarProcessorManager, "Cannot get JarProcessorManager before it has been setup");
+	}
+
+	@Override
+	public MappingSet getOrCreateSrcMappingCache(int id, Supplier<MappingSet> factory) {
+		return srcMappingCache[id] != null ? srcMappingCache[id] : (srcMappingCache[id] = factory.get());
+	}
+
+	@Override
+	public Mercury getOrCreateSrcMercuryCache(int id, Supplier<Mercury> factory) {
+		return srcMercuryCache[id] != null ? srcMercuryCache[id] : (srcMercuryCache[id] = factory.get());
+	}
+
+	@Override
+	public ConfigurableFileCollection getUnmappedModCollection() {
+		return unmappedMods;
+	}
+
+	public void setInstallerData(InstallerData object) {
+		this.installerData = object;
+	}
+
+	@Override
+	public InstallerData getInstallerData() {
+		return installerData;
+	}
+
+	@Override
+	public boolean isRootProject() {
+		return project.getRootProject() == project;
+	}
+
+	@Override
+	public NamedDomainObjectProvider<Configuration> createLazyConfiguration(String name) {
+		NamedDomainObjectProvider<Configuration> provider = project.getConfigurations().register(name);
+
+		if (lazyConfigurations.containsKey(name)) {
+			throw new IllegalStateException("Duplicate configuration name" + name);
+		}
+
+		lazyConfigurations.put(name, provider);
+
+		return provider;
+	}
+
+	@Override
+	public NamedDomainObjectProvider<Configuration> getLazyConfigurationProvider(String name) {
+		NamedDomainObjectProvider<Configuration> provider = lazyConfigurations.get(name);
+
+		if (provider == null) {
+			throw new NullPointerException("Could not find provider with name: " + name);
+		}
+
+		return provider;
+	}
+
+	@Override
+	public MixinApExtension getMixinApExtension() {
+		return this.mixinApExtension;
+	}
+}
diff --git a/src/main/java/net/fabricmc/loom/extension/MixinApExtension.java b/src/main/java/net/fabricmc/loom/extension/MixinApExtension.java
new file mode 100644
index 00000000..e63700b1
--- /dev/null
+++ b/src/main/java/net/fabricmc/loom/extension/MixinApExtension.java
@@ -0,0 +1,126 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2016-2017 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
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.extension;
+
+import java.util.Collection;
+import java.util.Map;
+import java.util.Objects;
+import java.util.function.Function;
+import java.util.stream.Stream;
+
+import org.gradle.api.InvalidUserDataException;
+import org.gradle.api.Task;
+import org.gradle.api.artifacts.Configuration;
+import org.gradle.api.plugins.ExtraPropertiesExtension;
+import org.gradle.api.tasks.Input;
+import org.gradle.api.tasks.SourceSet;
+import org.gradle.api.tasks.util.PatternSet;
+import org.jetbrains.annotations.ApiStatus;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import net.fabricmc.loom.api.MixinApExtensionAPI;
+
+/**
+ * A gradle extension to configure mixin annotation processor.
+ */
+@ApiStatus.Experimental
+public interface MixinApExtension extends MixinApExtensionAPI {
+	String MIXIN_INFORMATION_CONTAINER = "mixin";
+
+	/**
+	 * An information container stores necessary information
+	 * for configuring the mixin annotation processor. It's stored
+	 * in [SourceSet].ext.mixin.
+	 */
+	final class MixinInformationContainer {
+		private final SourceSet sourceSet;
+		private final String refmapName;
+		private Stream<String> mixinJsonNames;
+
+		final PatternSet mixinJsonPattern;
+
+		public MixinInformationContainer(@NotNull SourceSet sourceSet,
+										@NotNull String refmapName,
+										@NotNull PatternSet mixinJsonPattern) {
+			this.sourceSet = sourceSet;
+			this.refmapName = refmapName;
+			this.mixinJsonPattern = mixinJsonPattern;
+		}
+
+		void setMixinJsonNames(@NotNull Stream<String> mixinJsonNames) {
+			if (this.mixinJsonNames == null) {
+				this.mixinJsonNames = mixinJsonNames;
+			}
+		}
+
+		@NotNull
+		public Stream<String> getMixinJsonNames() {
+			return Objects.requireNonNull(mixinJsonNames);
+		}
+
+		@NotNull
+		public SourceSet getSourceSet() {
+			return sourceSet;
+		}
+
+		@NotNull
+		public String getRefmapName() {
+			return refmapName;
+		}
+	}
+
+	@Nullable
+	static MixinInformationContainer getMixinInformationContainer(SourceSet sourceSet) {
+		ExtraPropertiesExtension extra = sourceSet.getExtensions().getExtraProperties();
+		return extra.has(MIXIN_INFORMATION_CONTAINER) ? (MixinInformationContainer) extra.get(MIXIN_INFORMATION_CONTAINER) : null;
+	}
+
+	static void setMixinInformationContainer(SourceSet sourceSet, MixinInformationContainer container) {
+		ExtraPropertiesExtension extra = sourceSet.getExtensions().getExtraProperties();
+
+		if (extra.has(MIXIN_INFORMATION_CONTAINER)) {
+			throw new InvalidUserDataException("The sourceSet " + sourceSet.getName()
+					+ " has been configured for mixin annotation processor multiple times");
+		}
+
+		extra.set(MIXIN_INFORMATION_CONTAINER, container);
+	}
+
+	@NotNull
+	Stream<SourceSet> getMixinSourceSetsStream();
+
+	@NotNull
+	Stream<Configuration> getApConfigurationsStream(Function<String, String> getApConfigNameFunc);
+
+	@NotNull
+	Stream<Map.Entry<SourceSet, Task>> getInvokerTasksStream(String compileTaskLanguage);
+
+	@NotNull
+	@Input
+	Collection<SourceSet> getMixinSourceSets();
+
+	void init();
+}
diff --git a/src/main/java/net/fabricmc/loom/extension/MixinApExtensionApiImpl.java b/src/main/java/net/fabricmc/loom/extension/MixinApExtensionApiImpl.java
new file mode 100644
index 00000000..76326380
--- /dev/null
+++ b/src/main/java/net/fabricmc/loom/extension/MixinApExtensionApiImpl.java
@@ -0,0 +1,110 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021 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
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.extension;
+
+import org.gradle.api.Action;
+import org.gradle.api.InvalidUserDataException;
+import org.gradle.api.Project;
+import org.gradle.api.plugins.JavaPluginConvention;
+import org.gradle.api.tasks.SourceSet;
+import org.gradle.api.tasks.util.PatternSet;
+
+import net.fabricmc.loom.LoomGradleExtension;
+import net.fabricmc.loom.api.MixinApExtensionAPI;
+
+public abstract class MixinApExtensionApiImpl implements MixinApExtensionAPI {
+	protected abstract Project getProject();
+	protected abstract PatternSet add0(SourceSet sourceSet, String refmapName);
+
+	@Override
+	public void add(SourceSet sourceSet, String refmapName, Action<PatternSet> action) {
+		PatternSet pattern = add0(sourceSet, refmapName);
+		action.execute(pattern);
+	}
+
+	@Override
+	public void add(SourceSet sourceSet, String refmapName) {
+		add(sourceSet, refmapName, x -> { });
+	}
+
+	@Override
+	public void add(String sourceSetName, String refmapName, Action<PatternSet> action) {
+		// try to find sourceSet with name sourceSetName in this project
+		SourceSet sourceSet = getProject().getConvention().getPlugin(JavaPluginConvention.class)
+				.getSourceSets().findByName(sourceSetName);
+
+		if (sourceSet == null) {
+			throw new InvalidUserDataException("No sourceSet " + sourceSetName + " was found");
+		}
+
+		PatternSet pattern = add0(sourceSet, refmapName);
+		action.execute(pattern);
+	}
+
+	@Override
+	public void add(String sourceSetName, String refmapName) {
+		add(sourceSetName, refmapName, x -> { });
+	}
+
+	@Override
+	public void add(SourceSet sourceSet, Action<PatternSet> action) {
+		LoomGradleExtension extension = LoomGradleExtension.get(getProject());
+		add(sourceSet, extension.getRefmapName(), action);
+	}
+
+	@Override
+	public void add(SourceSet sourceSet) {
+		add(sourceSet, x -> { });
+	}
+
+	@Override
+	public void add(String sourceSetName, Action<PatternSet> action) {
+		LoomGradleExtension extension = LoomGradleExtension.get(getProject());
+		add(sourceSetName, extension.getRefmapName(), action);
+	}
+
+	@Override
+	public void add(String sourceSetName) {
+		add(sourceSetName, x -> { });
+	}
+
+	// This is here to ensure that LoomGradleExtensionApiImpl compiles without any unimplemented methods
+	private final class EnsureCompile extends MixinApExtensionApiImpl {
+		private EnsureCompile() {
+			super();
+			throw new RuntimeException();
+		}
+
+		@Override
+		protected Project getProject() {
+			throw new RuntimeException("Yeah... something is really wrong");
+		}
+
+		@Override
+		protected PatternSet add0(SourceSet sourceSet, String refmapName) {
+			throw new RuntimeException("Yeah... something is really wrong");
+		}
+	}
+}
diff --git a/src/main/java/net/fabricmc/loom/extension/MixinApExtensionImpl.java b/src/main/java/net/fabricmc/loom/extension/MixinApExtensionImpl.java
new file mode 100644
index 00000000..fd541106
--- /dev/null
+++ b/src/main/java/net/fabricmc/loom/extension/MixinApExtensionImpl.java
@@ -0,0 +1,125 @@
+/*
+ * This file is part of fabric-loom, licensed under the MIT License (MIT).
+ *
+ * Copyright (c) 2021 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
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package net.fabricmc.loom.extension;
+
+import java.io.File;
+import java.util.AbstractMap;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import org.gradle.api.Project;
+import org.gradle.api.Task;
+import org.gradle.api.UnknownTaskException;
+import org.gradle.api.artifacts.Configuration;
+import org.gradle.api.plugins.JavaPluginConvention;
+import org.gradle.api.tasks.Input;
+import org.gradle.api.tasks.SourceSet;
+import org.gradle.api.tasks.util.PatternSet;
+import org.jetbrains.annotations.NotNull;
+
+public class MixinApExtensionImpl extends MixinApExtensionApiImpl implements MixinApExtension {
+	private boolean isDefault;
+	private final Project project;
+
+	public MixinApExtensionImpl(Project project) {
+		this.isDefault = true;
+		this.project = project;
+	}
+
+	@Override
+	public Project getProject() {
+		return this.project;
+	}
+
+	@Override
+	protected PatternSet add0(SourceSet sourceSet, String refmapName) {
+		PatternSet pattern = new PatternSet().setIncludes(Collections.singletonList("*.mixins.json"));
+		MixinApExtension.setMixinInformationContainer(sourceSet, new MixinApExtension.MixinInformationContainer(sourceSet, refmapName, pattern));
+
+		isDefault = false;
+
+		return pattern;
+	}
+
+	@Override
+	@NotNull
+	public Stream<SourceSet> getMixinSourceSetsStream() {
+		return project.getConvention().getPlugin(JavaPluginConvention.class).getSourceSets().stream()
+				.filter(sourceSet -> {
+					MixinApExtension.MixinInformationContainer container = MixinApExtension.getMixinInformationContainer(sourceSet);
+
+					if (container != null) {
+						PatternSet pattern = container.mixinJsonPattern;
+						Stream<String> mixinJsonNames = sourceSet.getResources()
+								.matching(pattern).getFiles().stream().map(File::getName);
+						container.setMixinJsonNames(mixinJsonNames);
+						return true;
+					}
+
+					return false;
+				});
+	}
+
+	@Override
+	@NotNull
+	public Stream<Configuration> getApConfigurationsStream(Function<String, String> getApConfigNameFunc) {
+		return getMixinSourceSetsStream()
+				.map(sourceSet -> project.getConfigurations().getByName(getApConfigNameFunc.apply(sourceSet.getName())));
+	}
+
+	@Override
+	@NotNull
+	public Stream<Map.Entry<SourceSet, Task>> getInvokerTasksStream(String compileTaskLanguage) {
+		return getMixinSourceSetsStream()
+				.flatMap(sourceSet -> {
+					try {
+						Task task = project.getTasks().getByName(sourceSet.getCompileTaskName(compileTaskLanguage));
+						return Stream.of(new AbstractMap.SimpleEntry<>(sourceSet, task));
+					} catch (UnknownTaskException ignored) {
+						return Stream.empty();
+					}
+				});
+	}
+
+	@Override
+	@NotNull
+	@Input
+	public Collection<SourceSet> getMixinSourceSets() {
+		return getMixinSourceSetsStream().collect(Collectors.toList());
+	}
+
+	@Override
+	public void init() {
+		if (isDefault) {
+			project.getConvention().getPlugin(JavaPluginConvention.class).getSourceSets().forEach(this::add);
+		}
+
+		isDefault = false;
+	}
+}
diff --git a/src/main/java/net/fabricmc/loom/task/AbstractLoomTask.java b/src/main/java/net/fabricmc/loom/task/AbstractLoomTask.java
index 430416f8..d9216042 100644
--- a/src/main/java/net/fabricmc/loom/task/AbstractLoomTask.java
+++ b/src/main/java/net/fabricmc/loom/task/AbstractLoomTask.java
@@ -37,6 +37,6 @@ public abstract class AbstractLoomTask extends DefaultTask {
 
 	@Internal
 	protected LoomGradleExtension getExtension() {
-		return getProject().getExtensions().getByType(LoomGradleExtension.class);
+		return LoomGradleExtension.get(getProject());
 	}
 }
diff --git a/src/main/java/net/fabricmc/loom/task/GenerateSourcesTask.java b/src/main/java/net/fabricmc/loom/task/GenerateSourcesTask.java
index 93739c07..22a4af8f 100644
--- a/src/main/java/net/fabricmc/loom/task/GenerateSourcesTask.java
+++ b/src/main/java/net/fabricmc/loom/task/GenerateSourcesTask.java
@@ -83,10 +83,6 @@ public class GenerateSourcesTask extends AbstractLoomTask {
 			Files.copy(linemappedJarDestination, runtimeJar, StandardCopyOption.REPLACE_EXISTING);
 			Files.delete(linemappedJarDestination);
 		}
-
-		if (getExtension().isForge()) {
-			ForgeSourcesRemapper.addForgeSources(getProject(), sourcesDestination);
-		}
 	}
 
 	private void remapLineNumbers(Path oldCompiledJar, Path linemap, Path linemappedJarDestination) throws IOException {
@@ -114,7 +110,7 @@ public class GenerateSourcesTask extends AbstractLoomTask {
 	}
 
 	public static File getMappedJarFileWithSuffix(Project project, String suffix, boolean forgeJar) {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(getProject());
 		MappingsProviderImpl mappingsProvider = extension.getMappingsProvider();
 		File mappedJar = forgeJar ? mappingsProvider.mappedProvider.getForgeMappedJar() : mappingsProvider.mappedProvider.getMappedJar();
 		String path = mappedJar.getAbsolutePath();
diff --git a/src/main/java/net/fabricmc/loom/task/LoomTasks.java b/src/main/java/net/fabricmc/loom/task/LoomTasks.java
index 4c7c46a6..f827b000 100644
--- a/src/main/java/net/fabricmc/loom/task/LoomTasks.java
+++ b/src/main/java/net/fabricmc/loom/task/LoomTasks.java
@@ -89,7 +89,7 @@ public final class LoomTasks {
 	}
 
 	private static void registerRunTasks(TaskContainer tasks, Project project) {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 
 		Preconditions.checkArgument(extension.getRunConfigs().size() == 0, "Run configurations must not be registered before loom");
 
@@ -122,7 +122,7 @@ public final class LoomTasks {
 	}
 
 	private static void registerDecompileTasks(TaskContainer tasks, Project project) {
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 
 		project.afterEvaluate(p -> {
 			MappingsProviderImpl mappingsProvider = extension.getMappingsProvider();
diff --git a/src/main/java/net/fabricmc/loom/task/MigrateMappingsTask.java b/src/main/java/net/fabricmc/loom/task/MigrateMappingsTask.java
index 28410b1f..6febed33 100644
--- a/src/main/java/net/fabricmc/loom/task/MigrateMappingsTask.java
+++ b/src/main/java/net/fabricmc/loom/task/MigrateMappingsTask.java
@@ -120,7 +120,7 @@ public class MigrateMappingsTask extends AbstractLoomTask {
 
 		try {
 			if (mappings.startsWith("net.minecraft:mappings:") || mappings.startsWith("net.mojang.minecraft:mappings:")) {
-				if (!mappings.endsWith(":" + project.getExtensions().getByType(LoomGradleExtension.class).getMinecraftProvider().minecraftVersion())) {
+				if (!mappings.endsWith(":" + LoomGradleExtension.get(project).getMinecraftProvider().minecraftVersion())) {
 					throw new UnsupportedOperationException("Migrating Mojang mappings is currently only supported for the specified minecraft version");
 				}
 
diff --git a/src/main/java/net/fabricmc/loom/task/RemapJarTask.java b/src/main/java/net/fabricmc/loom/task/RemapJarTask.java
index 963b35f3..3a06ff49 100644
--- a/src/main/java/net/fabricmc/loom/task/RemapJarTask.java
+++ b/src/main/java/net/fabricmc/loom/task/RemapJarTask.java
@@ -137,7 +137,7 @@ public class RemapJarTask extends Jar {
 			jarRemapper = new JarRemapper();
 		}
 
-		scheduleRemap(singleRemap || getProject().getExtensions().getByType(LoomGradleExtension.class).isRootProject());
+		scheduleRemap(singleRemap || LoomGradleExtension.get(getProject()).isRootProject());
 
 		if (singleRemap) {
 			jarRemapper.remap(getProject());
@@ -212,7 +212,7 @@ public class RemapJarTask extends Jar {
 
 	public void scheduleRemap(boolean isMainRemapTask) throws Throwable {
 		Project project = getProject();
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(getProject());
 		Path input = this.getInput().getAsFile().get().toPath();
 		Path output = this.getArchivePath().toPath();
 
@@ -248,7 +248,7 @@ public class RemapJarTask extends Jar {
 
 		jarRemapper.scheduleRemap(input, output)
 				.supplyAccessWidener((remapData, remapper) -> {
-					if (getRemapAccessWidener().getOrElse(false) && extension.accessWidener != null) {
+					if (getRemapAccessWidener().getOrElse(false) && extension.getAccessWidener() != null) {
 						AccessWidenerJarProcessor accessWidenerJarProcessor = extension.getJarProcessorManager().getByType(AccessWidenerJarProcessor.class);
 						byte[] data;
 
@@ -271,7 +271,7 @@ public class RemapJarTask extends Jar {
 						throw new RuntimeException("Failed to remap " + input + " to " + output + " - file missing!");
 					}
 
-					if (MixinRefmapHelper.addRefmapName(extension.getRefmapName(), output)) {
+					if (MixinRefmapHelper.addRefmapName(project, output)) {
 						project.getLogger().debug("Transformed mixin reference maps in output JAR!");
 					}
 
diff --git a/src/main/java/net/fabricmc/loom/task/RunClientTask.java b/src/main/java/net/fabricmc/loom/task/RunClientTask.java
index da895b0a..cfe50a05 100644
--- a/src/main/java/net/fabricmc/loom/task/RunClientTask.java
+++ b/src/main/java/net/fabricmc/loom/task/RunClientTask.java
@@ -31,7 +31,7 @@ import net.fabricmc.loom.configuration.ide.RunConfig;
 public class RunClientTask extends AbstractRunTask {
 	public RunClientTask() {
 		super(project -> {
-			LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+			LoomGradleExtension extension = LoomGradleExtension.get(project);
 			return RunConfig.runConfig(project, extension.getRunConfigs().getByName("client"));
 		});
 	}
diff --git a/src/main/java/net/fabricmc/loom/task/RunServerTask.java b/src/main/java/net/fabricmc/loom/task/RunServerTask.java
index fea4223d..748d4180 100644
--- a/src/main/java/net/fabricmc/loom/task/RunServerTask.java
+++ b/src/main/java/net/fabricmc/loom/task/RunServerTask.java
@@ -31,7 +31,7 @@ import net.fabricmc.loom.configuration.ide.RunConfig;
 public class RunServerTask extends AbstractRunTask {
 	public RunServerTask() {
 		super(project -> {
-			LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+			LoomGradleExtension extension = LoomGradleExtension.get(project);
 			return RunConfig.runConfig(project, extension.getRunConfigs().getByName("client"));
 		});
 	}
diff --git a/src/main/java/net/fabricmc/loom/task/UnpickJarTask.java b/src/main/java/net/fabricmc/loom/task/UnpickJarTask.java
index 2d4bd3cc..93c71747 100644
--- a/src/main/java/net/fabricmc/loom/task/UnpickJarTask.java
+++ b/src/main/java/net/fabricmc/loom/task/UnpickJarTask.java
@@ -36,6 +36,7 @@ import org.gradle.api.tasks.OutputFile;
 
 import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.configuration.providers.LaunchProvider;
+import net.fabricmc.loom.extension.LoomFiles;
 import net.fabricmc.loom.util.Constants;
 
 public class UnpickJarTask extends JavaExec {
@@ -60,15 +61,15 @@ public class UnpickJarTask extends JavaExec {
 		fileArg(getMinecraftDependencies());
 
 		writeUnpickLogConfig();
-		systemProperty("java.util.logging.config.file", getExtension().getUnpickLoggingConfigFile().getAbsolutePath());
+		systemProperty("java.util.logging.config.file", getDirectories().getUnpickLoggingConfigFile().getAbsolutePath());
 
 		super.exec();
 	}
 
 	private void writeUnpickLogConfig() {
 		try (InputStream is = LaunchProvider.class.getClassLoader().getResourceAsStream("unpick-logging.properties")) {
-			Files.deleteIfExists(getExtension().getUnpickLoggingConfigFile().toPath());
-			Files.copy(is, getExtension().getUnpickLoggingConfigFile().toPath());
+			Files.deleteIfExists(getDirectories().getUnpickLoggingConfigFile().toPath());
+			Files.copy(is, getDirectories().getUnpickLoggingConfigFile().toPath());
 		} catch (IOException e) {
 			throw new RuntimeException("Failed to copy unpick logging config", e);
 		}
@@ -121,6 +122,10 @@ public class UnpickJarTask extends JavaExec {
 
 	@Internal
 	protected LoomGradleExtension getExtension() {
-		return getProject().getExtensions().getByType(LoomGradleExtension.class);
+		return LoomGradleExtension.get(getProject());
+	}
+
+	private LoomFiles getDirectories() {
+		return getExtension().getFiles();
 	}
 }
diff --git a/src/main/java/net/fabricmc/loom/util/Constants.java b/src/main/java/net/fabricmc/loom/util/Constants.java
index 56887417..7d46245f 100644
--- a/src/main/java/net/fabricmc/loom/util/Constants.java
+++ b/src/main/java/net/fabricmc/loom/util/Constants.java
@@ -37,6 +37,7 @@ public class Constants {
 	public static final String LIBRARIES_BASE = "https://libraries.minecraft.net/";
 	public static final String RESOURCES_BASE = "https://resources.download.minecraft.net/";
 	public static final String VERSION_MANIFESTS = "https://launchermeta.mojang.com/mc/game/version_manifest_v2.json";
+	public static final String EXPERIMENTAL_VERSIONS = "https://maven.fabricmc.net/net/minecraft/experimental_versions.json";
 
 	public static final String SYSTEM_ARCH = System.getProperty("os.arch").equals("64") ? "64" : "32";
 	public static final String TASK_CATEGORY = "loom";
@@ -127,14 +128,6 @@ public class Constants {
 		}
 	}
 
-	public static final class LaunchWrapper {
-		public static final String DEFAULT_FABRIC_CLIENT_TWEAKER = "net.fabricmc.loader.launch.FabricClientTweaker";
-		public static final String DEFAULT_FABRIC_SERVER_TWEAKER = "net.fabricmc.loader.launch.FabricServerTweaker";
-
-		private LaunchWrapper() {
-		}
-	}
-
 	public static final class Knot {
 		public static final String KNOT_CLIENT = "net.fabricmc.loader.launch.knot.KnotClient";
 		public static final String KNOT_SERVER = "net.fabricmc.loader.launch.knot.KnotServer";
diff --git a/src/main/java/net/fabricmc/loom/util/DownloadUtil.java b/src/main/java/net/fabricmc/loom/util/DownloadUtil.java
index 1da65ae5..56ccf8d3 100644
--- a/src/main/java/net/fabricmc/loom/util/DownloadUtil.java
+++ b/src/main/java/net/fabricmc/loom/util/DownloadUtil.java
@@ -26,9 +26,11 @@ package net.fabricmc.loom.util;
 
 import java.io.File;
 import java.io.IOException;
+import java.io.InputStream;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
+import java.util.zip.GZIPInputStream;
 
 import com.google.common.io.Files;
 import org.apache.commons.io.FileUtils;
@@ -110,7 +112,13 @@ public class DownloadUtil {
 		}
 
 		try { // Try download to the output
-			FileUtils.copyInputStreamToFile(connection.getInputStream(), to);
+			InputStream inputStream = connection.getInputStream();
+
+			if ("gzip".equals(connection.getContentEncoding())) {
+				inputStream = new GZIPInputStream(inputStream);
+			}
+
+			FileUtils.copyInputStreamToFile(inputStream, to);
 		} catch (IOException e) {
 			delete(to); // Probably isn't good if it fails to copy/save
 			throw e;
diff --git a/src/main/java/net/fabricmc/loom/util/HashedDownloadUtil.java b/src/main/java/net/fabricmc/loom/util/HashedDownloadUtil.java
index 712043da..a9b77ab4 100644
--- a/src/main/java/net/fabricmc/loom/util/HashedDownloadUtil.java
+++ b/src/main/java/net/fabricmc/loom/util/HashedDownloadUtil.java
@@ -27,9 +27,11 @@ package net.fabricmc.loom.util;
 import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.IOException;
+import java.io.InputStream;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.nio.charset.StandardCharsets;
+import java.util.zip.GZIPInputStream;
 
 import javax.annotation.Nullable;
 
@@ -106,7 +108,13 @@ public class HashedDownloadUtil {
 		}
 
 		try { // Try download to the output
-			FileUtils.copyInputStreamToFile(connection.getInputStream(), to);
+			InputStream inputStream = connection.getInputStream();
+
+			if ("gzip".equals(connection.getContentEncoding())) {
+				inputStream = new GZIPInputStream(inputStream);
+			}
+
+			FileUtils.copyInputStreamToFile(inputStream, to);
 		} catch (IOException e) {
 			delete(to); // Probably isn't good if it fails to copy/save
 			throw e;
diff --git a/src/main/java/net/fabricmc/loom/util/SourceRemapper.java b/src/main/java/net/fabricmc/loom/util/SourceRemapper.java
index f79ccd3f..fb46d53b 100644
--- a/src/main/java/net/fabricmc/loom/util/SourceRemapper.java
+++ b/src/main/java/net/fabricmc/loom/util/SourceRemapper.java
@@ -171,7 +171,7 @@ public class SourceRemapper {
 			return this.mercury;
 		}
 
-		LoomGradleExtension extension = project.getExtensions().getByType(LoomGradleExtension.class);
+		LoomGradleExtension extension = LoomGradleExtension.get(project);
 		MappingsProviderImpl mappingsProvider = extension.getMappingsProvider();
 
 		String intermediary = extension.isForge() ? "srg" : "intermediary";