[*] Rework registration of TweedExtensions

buildSrc/src/main/kotlin/de.siphalor.tweed5.base-module.gradle.kts

@@ -11,8 +11,8 @@ group = rootProject.group
 version = rootProject.version
 
 java {
-    sourceCompatibility = JavaVersion.toVersion(libs.versions.java.get())
+    sourceCompatibility = JavaVersion.toVersion(libs.versions.java.main.get())
-    targetCompatibility = JavaVersion.toVersion(libs.versions.java.get())
+    targetCompatibility = JavaVersion.toVersion(libs.versions.java.main.get())
 }
 
 repositories {
@@ -52,6 +52,10 @@ dependencies {
     testImplementation(libs.assertj)
 }
 
+tasks.compileTestJava {
+    sourceCompatibility = libs.versions.java.test.get()
+    targetCompatibility = libs.versions.java.test.get()
+}
 
 tasks.test {
     dependsOn(testAgentClasspath)

gradle/libs.versions.toml

@@ -2,7 +2,8 @@
 assertj = "3.26.3"
 asm = "9.7"
 autoservice = "1.1.1"
-java = "8"
+java-main = "8"
+java-test = "21"
 jetbrains-annotations = "26.0.1"
 jspecify = "1.0.0"
 junit = "5.12.0"

tweed5-core/src/main/java/de/siphalor/tweed5/core/api/container/ConfigContainer.java

@@ -9,6 +9,7 @@ import org.jspecify.annotations.Nullable;
 
 import java.util.Collection;
 import java.util.Map;
+import java.util.Optional;
 
 /**
  * The main wrapper for a config tree.<br />
@@ -20,16 +21,14 @@ public interface ConfigContainer<T> {
 	@SuppressWarnings("rawtypes")
 	TweedConstructFactory<ConfigContainer> FACTORY = TweedConstructFactory.builder(ConfigContainer.class).build();
 
-	default void registerExtensions(TweedExtension... extensions) {
+	default void registerExtensions(Class<? extends TweedExtension>... extensionClasses) {
-		for (TweedExtension extension : extensions) {
+		for (Class<? extends TweedExtension> extensionClass : extensionClasses) {
-			registerExtension(extension);
+			registerExtension(extensionClass);
 		}
 	}
+	void registerExtension(Class<? extends TweedExtension> extensionClass);
 
-	void registerExtension(TweedExtension extension);
+	<E extends TweedExtension> Optional<E> extension(Class<E> extensionClass);
-
-	@Nullable
-	<E extends TweedExtension> E extension(Class<E> extensionClass);
 	Collection<TweedExtension> extensions();
 
 	void finishExtensionSetup();

tweed5-core/src/main/java/de/siphalor/tweed5/core/api/extension/TweedExtension.java

@@ -1,11 +1,18 @@
 package de.siphalor.tweed5.core.api.extension;
 
+import de.siphalor.tweed5.construct.api.TweedConstructFactory;
+import de.siphalor.tweed5.core.api.container.ConfigContainer;
 import de.siphalor.tweed5.core.api.entry.ConfigEntry;
 
 public interface TweedExtension {
+	TweedConstructFactory<TweedExtension> FACTORY = TweedConstructFactory.builder(TweedExtension.class)
+			.typedArg(ConfigContainer.class)
+			.typedArg(TweedExtensionSetupContext.class)
+			.build();
+
 	String getId();
 
-	default void setup(TweedExtensionSetupContext context) {
+	default void extensionsFinalized() {
 	}
 
 	default void initEntry(ConfigEntry<?> configEntry) {

tweed5-core/src/main/java/de/siphalor/tweed5/core/api/extension/TweedExtensionSetupContext.java

@@ -1,9 +1,6 @@
 package de.siphalor.tweed5.core.api.extension;
 
-import de.siphalor.tweed5.core.api.container.ConfigContainer;
-
 public interface TweedExtensionSetupContext {
-	ConfigContainer<?> configContainer();
 	<E> RegisteredExtensionData<EntryExtensionsData, E> registerEntryExtensionData(Class<E> dataClass);
-	void registerExtension(TweedExtension extension);
+	void registerExtension(Class<? extends TweedExtension> extensionClass);
 }

tweed5-core/src/main/java/de/siphalor/tweed5/core/impl/DefaultConfigContainer.java

@@ -3,7 +3,10 @@ package de.siphalor.tweed5.core.impl;
 import de.siphalor.tweed5.core.api.container.ConfigContainer;
 import de.siphalor.tweed5.core.api.container.ConfigContainerSetupPhase;
 import de.siphalor.tweed5.core.api.entry.ConfigEntry;
-import de.siphalor.tweed5.core.api.extension.*;
+import de.siphalor.tweed5.core.api.extension.EntryExtensionsData;
+import de.siphalor.tweed5.core.api.extension.RegisteredExtensionData;
+import de.siphalor.tweed5.core.api.extension.TweedExtension;
+import de.siphalor.tweed5.core.api.extension.TweedExtensionSetupContext;
 import de.siphalor.tweed5.patchwork.api.Patchwork;
 import de.siphalor.tweed5.patchwork.api.PatchworkClassCreator;
 import de.siphalor.tweed5.patchwork.impl.PatchworkClass;
@@ -12,56 +15,34 @@ import de.siphalor.tweed5.patchwork.impl.PatchworkClassPart;
 import de.siphalor.tweed5.utils.api.collection.InheritanceMap;
 import lombok.Getter;
 import lombok.Setter;
-import org.jspecify.annotations.NullUnmarked;
 import org.jspecify.annotations.Nullable;
 
 import java.lang.invoke.MethodHandle;
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
 import java.util.*;
 
-@NullUnmarked
 public class DefaultConfigContainer<T> implements ConfigContainer<T> {
 	@Getter
 	private ConfigContainerSetupPhase setupPhase = ConfigContainerSetupPhase.EXTENSIONS_SETUP;
+	private final Set<Class<? extends TweedExtension>> requestedExtensions = new HashSet<>();
 	private final InheritanceMap<TweedExtension> extensions = new InheritanceMap<>(TweedExtension.class);
-	private ConfigEntry<T> rootEntry;
+	private @Nullable ConfigEntry<T> rootEntry;
-	private PatchworkClass<EntryExtensionsData> entryExtensionsDataPatchworkClass;
+	private @Nullable PatchworkClass<EntryExtensionsData> entryExtensionsDataPatchworkClass;
-	private Map<Class<?>, RegisteredExtensionDataImpl<EntryExtensionsData, ?>> registeredEntryDataExtensions;
+	private final Map<Class<?>, RegisteredExtensionDataImpl<EntryExtensionsData, ?>> registeredEntryDataExtensions
+			= new HashMap<>();
 
 	@Override
-	public <E extends TweedExtension> @Nullable E extension(Class<E> extensionClass) {
+	public void registerExtension(Class<? extends TweedExtension> extensionClass) {
-		try {
-			return extensions.getSingleInstance(extensionClass);
-		} catch (InheritanceMap.NonUniqueResultException e) {
-			return null;
-		}
-	}
-
-	@Override
-	public Collection<TweedExtension> extensions() {
-		return Collections.unmodifiableCollection(extensions.values());
-	}
-
-	@Override
-	public void registerExtension(TweedExtension extension) {
 		requireSetupPhase(ConfigContainerSetupPhase.EXTENSIONS_SETUP);
-
+		requestedExtensions.add(extensionClass);
-		if (!extensions.putIfAbsent(extension)) {
-			throw new IllegalArgumentException("Extension " + extension.getClass().getName() + " is already registered");
-		}
 	}
 
 	@Override
 	public void finishExtensionSetup() {
 		requireSetupPhase(ConfigContainerSetupPhase.EXTENSIONS_SETUP);
-		registeredEntryDataExtensions = new HashMap<>();
 
-		Collection<TweedExtension> additionalExtensions = new ArrayList<>();
 		TweedExtensionSetupContext extensionSetupContext = new TweedExtensionSetupContext() {
-			@Override
-			public ConfigContainer<T> configContainer() {
-				return DefaultConfigContainer.this;
-			}
-
 			@Override
 			public <E> RegisteredExtensionData<EntryExtensionsData, E> registerEntryExtensionData(Class<E> dataClass) {
 				if (registeredEntryDataExtensions.containsKey(dataClass)) {
@@ -73,24 +54,31 @@ public class DefaultConfigContainer<T> implements ConfigContainer<T> {
 			}
 
 			@Override
-			public void registerExtension(TweedExtension extension) {
+			public void registerExtension(Class<? extends TweedExtension> extensionClass) {
-				if (!extensions.containsAnyInstanceForClass(extension.getClass())) {
+				if (!extensions.containsAnyInstanceForClass(extensionClass)) {
-					additionalExtensions.add(extension);
+					requestedExtensions.add(extensionClass);
 				}
 			}
 		};
 
-		Collection<TweedExtension> extensionsToSetup = extensions.values();
+		Set<Class<? extends TweedExtension>> abstractExtensionClasses = new HashSet<>();
-		while (!extensionsToSetup.isEmpty()) {
-			for (TweedExtension extension : extensionsToSetup) {
-				extension.setup(extensionSetupContext);
-			}
 
-			for (TweedExtension additionalExtension : additionalExtensions) {
+		while (true) {
-				extensions.putIfAbsent(additionalExtension);
+			if (!requestedExtensions.isEmpty()) {
+				Class<? extends TweedExtension> extensionClass = popFromIterable(requestedExtensions);
+				if (isAbstractClass(extensionClass)) {
+					abstractExtensionClasses.add(extensionClass);
+				} else {
+					extensions.put(instantiateExtension(extensionClass, extensionSetupContext));
+				}
+			} else if (!abstractExtensionClasses.isEmpty()) {
+				Class<? extends TweedExtension> extensionClass = popFromIterable(abstractExtensionClasses);
+				if (!extensions.containsAnyInstanceForClass(extensionClass)) {
+					extensions.put(instantiateAbstractExtension(extensionClass, extensionSetupContext));
+				}
+			} else {
+				break;
 			}
-			extensionsToSetup = new ArrayList<>(additionalExtensions);
-			additionalExtensions.clear();
 		}
 
 		PatchworkClassCreator<EntryExtensionsData> entryExtensionsDataGenerator = PatchworkClassCreator.<EntryExtensionsData>builder()
@@ -109,16 +97,135 @@ public class DefaultConfigContainer<T> implements ConfigContainer<T> {
 		}
 
 		setupPhase = ConfigContainerSetupPhase.TREE_SETUP;
+
+		extensions.values().forEach(TweedExtension::extensionsFinalized);
+	}
+
+	private static <T> T popFromIterable(Iterable<T> iterable) {
+		Iterator<T> iterator = iterable.iterator();
+		T value = iterator.next();
+		iterator.remove();
+		return value;
+	}
+
+	protected <E extends TweedExtension> E instantiateAbstractExtension(
+			Class<E> extensionClass,
+			TweedExtensionSetupContext setupContext
+	) {
+		try {
+			Field defaultField = extensionClass.getDeclaredField("DEFAULT");
+			if (defaultField.getType() != Class.class) {
+				throw new IllegalStateException(createAbstractExtensionInstantiationExceptionMessage(
+						extensionClass,
+						"DEFAULT field has incorrect class " + defaultField.getType().getName() + "."
+				));
+			}
+			if ((defaultField.getModifiers() & Modifier.STATIC) == 0) {
+				throw new IllegalStateException(createAbstractExtensionInstantiationExceptionMessage(
+						extensionClass,
+						"DEFAULT field is not static."
+				));
+			}
+			if ((defaultField.getModifiers() & Modifier.PUBLIC) == 0) {
+				throw new IllegalStateException(createAbstractExtensionInstantiationExceptionMessage(
+						extensionClass,
+						"DEFAULT field is not public."
+				));
+			}
+			Class<?> defaultClass = (Class<?>) defaultField.get(null);
+			if (!extensionClass.isAssignableFrom(defaultClass)) {
+				throw new IllegalStateException(createAbstractExtensionInstantiationExceptionMessage(
+						extensionClass,
+						"DEFAULT field contains class " + defaultClass.getName() + ", but that class "
+								+ "does not inherit from " + extensionClass.getName()
+				));
+			}
+			//noinspection unchecked
+			return instantiateExtension((Class<? extends E>) defaultClass, setupContext);
+		} catch (NoSuchFieldException ignored) {
+			throw new IllegalStateException(createAbstractExtensionInstantiationExceptionMessage(extensionClass, null));
+		} catch (IllegalAccessException e) {
+			throw new IllegalStateException(
+					createAbstractExtensionInstantiationExceptionMessage(
+							extensionClass,
+							"Couldn't access DEFAULT field."
+					),
+					e
+			);
+		}
+	}
+
+	private String createAbstractExtensionInstantiationExceptionMessage(
+			Class<?> extensionClass,
+			@Nullable String detail
+	) {
+		StringBuilder sb = new StringBuilder();
+		sb.append("Requested extension class ").append(extensionClass.getName()).append(" is ");
+		if (extensionClass.isInterface()) {
+			sb.append("an interface ");
+		} else {
+			sb.append("an abstract class ");
+		}
+		sb.append("and cannot be instantiated directly.\n");
+		sb.append("As the extension developer you can declare a public static DEFAULT field containing the class of ");
+		sb.append("a default implementation.\n");
+		sb.append("As a user you can try registering an implementation of the extension class directly.");
+		if (detail != null) {
+			sb.append("\n");
+			sb.append(detail);
+		}
+		return sb.toString();
+	}
+
+	protected  <E extends TweedExtension> E instantiateExtension(
+			Class<E> extensionClass,
+			TweedExtensionSetupContext setupContext
+	) {
+		if (isAbstractClass(extensionClass)) {
+			throw new IllegalStateException(
+					"Cannot instantiate extension class " + extensionClass.getName() + " as it is abstract"
+			);
+		}
+		return TweedExtension.FACTORY.construct(extensionClass)
+				.typedArg(TweedExtensionSetupContext.class, setupContext)
+				.typedArg(ConfigContainer.class, this)
+				.finish();
+	}
+
+	private boolean isAbstractClass(Class<?> clazz) {
+		return clazz.isInterface() || (clazz.getModifiers() & Modifier.ABSTRACT) != 0;
+	}
+
+	@Override
+	public <E extends TweedExtension> Optional<E> extension(Class<E> extensionClass) {
+		requireSetupPhase(
+				ConfigContainerSetupPhase.TREE_SETUP,
+				ConfigContainerSetupPhase.TREE_SEALED,
+				ConfigContainerSetupPhase.READY
+		);
+		try {
+			return Optional.ofNullable(extensions.getSingleInstance(extensionClass));
+		} catch (InheritanceMap.NonUniqueResultException e) {
+			throw new IllegalStateException("Multiple extensions registered for class " + extensionClass.getName(), e);
+		}
+	}
+
+	@Override
+	public Collection<TweedExtension> extensions() {
+		requireSetupPhase(
+				ConfigContainerSetupPhase.TREE_SETUP,
+				ConfigContainerSetupPhase.TREE_SEALED,
+				ConfigContainerSetupPhase.READY
+		);
+		return Collections.unmodifiableCollection(extensions.values());
 	}
 
 	@Override
 	public void attachAndSealTree(ConfigEntry<T> rootEntry) {
 		requireSetupPhase(ConfigContainerSetupPhase.TREE_SETUP);
-		this.rootEntry = rootEntry;
-		finishEntrySetup();
-	}
 
-	private void finishEntrySetup() {
+		this.rootEntry = rootEntry;
+
 		rootEntry.visitInOrder(entry -> {
 			if (!entry.sealed()) {
 				entry.seal(DefaultConfigContainer.this);
@@ -133,6 +240,7 @@ public class DefaultConfigContainer<T> implements ConfigContainer<T> {
 		requireSetupPhase(ConfigContainerSetupPhase.TREE_SETUP);
 
 		try {
+			assert entryExtensionsDataPatchworkClass != null;
 			return (EntryExtensionsData) entryExtensionsDataPatchworkClass.constructor().invoke();
 		} catch (Throwable e) {
 			throw new IllegalStateException("Failed to construct patchwork class for entry extensions' data", e);
@@ -141,7 +249,11 @@ public class DefaultConfigContainer<T> implements ConfigContainer<T> {
 
 	@Override
 	public Map<Class<?>, ? extends RegisteredExtensionData<EntryExtensionsData, ?>> entryDataExtensions() {
-		requireSetupPhase(ConfigContainerSetupPhase.TREE_SEALED);
+		requireSetupPhase(
+				ConfigContainerSetupPhase.TREE_SETUP,
+				ConfigContainerSetupPhase.TREE_SEALED,
+				ConfigContainerSetupPhase.READY
+		);
 		return registeredEntryDataExtensions;
 	}
 
@@ -149,6 +261,7 @@ public class DefaultConfigContainer<T> implements ConfigContainer<T> {
 	public void initialize() {
 		requireSetupPhase(ConfigContainerSetupPhase.TREE_SEALED);
 
+		assert rootEntry != null;
 		rootEntry.visitInOrder(entry -> {
 			for (TweedExtension extension : extensions()) {
 				extension.initEntry(entry);
@@ -160,12 +273,32 @@ public class DefaultConfigContainer<T> implements ConfigContainer<T> {
 
 	@Override
 	public ConfigEntry<T> rootEntry() {
+		requireSetupPhase(ConfigContainerSetupPhase.TREE_SEALED, ConfigContainerSetupPhase.READY);
+
+		assert rootEntry != null;
 		return rootEntry;
 	}
 
-	private void requireSetupPhase(ConfigContainerSetupPhase required) {
+	private void requireSetupPhase(ConfigContainerSetupPhase... allowedPhases) {
-		if (setupPhase != required) {
+		for (ConfigContainerSetupPhase allowedPhase : allowedPhases) {
-			throw new IllegalStateException("Config container is not in correct stage, expected " + required + ", but is in " + setupPhase);
+			if (allowedPhase == setupPhase) {
+				return;
+			}
+		}
+		if (allowedPhases.length == 1) {
+			throw new IllegalStateException(
+					"Config container is not in correct phase, expected "
+							+ allowedPhases[0]
+							+ ", but is in "
+							+ setupPhase
+			);
+		} else {
+			throw new IllegalStateException(
+					"Config container is not in correct phase, expected any of "
+							+ Arrays.toString(allowedPhases)
+							+ ", but is in "
+							+ setupPhase
+			);
 		}
 	}
 

tweed5-core/src/test/java/de/siphalor/tweed5/core/impl/DefaultConfigContainerTest.java

@@ -0,0 +1,247 @@
+package de.siphalor.tweed5.core.impl;
+
+import de.siphalor.tweed5.core.api.container.ConfigContainerSetupPhase;
+import de.siphalor.tweed5.core.api.entry.ConfigEntry;
+import de.siphalor.tweed5.core.api.extension.EntryExtensionsData;
+import de.siphalor.tweed5.core.api.extension.RegisteredExtensionData;
+import de.siphalor.tweed5.core.api.extension.TweedExtension;
+import de.siphalor.tweed5.core.api.extension.TweedExtensionSetupContext;
+import de.siphalor.tweed5.core.impl.entry.SimpleConfigEntryImpl;
+import de.siphalor.tweed5.core.impl.entry.StaticMapCompoundConfigEntryImpl;
+import lombok.Getter;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class DefaultConfigContainerTest {
+
+	@Test
+	void extensionSetup() {
+		var configContainer = new DefaultConfigContainer<>();
+		assertThat(configContainer.setupPhase()).isEqualTo(ConfigContainerSetupPhase.EXTENSIONS_SETUP);
+
+		configContainer.registerExtension(ExtensionA.class);
+		configContainer.finishExtensionSetup();
+
+		assertThat(configContainer.setupPhase()).isEqualTo(ConfigContainerSetupPhase.TREE_SETUP);
+		assertThat(configContainer.extensions())
+				.satisfiesExactlyInAnyOrder(
+						extension -> assertThat(extension).isInstanceOf(ExtensionA.class),
+						extension -> assertThat(extension).isInstanceOf(ExtensionBImpl.class)
+				);
+	}
+
+	@Test
+	void extensionSetupDefaultOverride() {
+		var configContainer = new DefaultConfigContainer<>();
+		assertThat(configContainer.setupPhase()).isEqualTo(ConfigContainerSetupPhase.EXTENSIONS_SETUP);
+
+		configContainer.registerExtensions(ExtensionA.class, ExtensionBNonDefaultImpl.class);
+		configContainer.finishExtensionSetup();
+
+		assertThat(configContainer.setupPhase()).isEqualTo(ConfigContainerSetupPhase.TREE_SETUP);
+		assertThat(configContainer.extensions())
+				.satisfiesExactlyInAnyOrder(
+						extension -> assertThat(extension).isInstanceOf(ExtensionA.class),
+						extension -> assertThat(extension).isInstanceOf(ExtensionBNonDefaultImpl.class)
+				);
+	}
+
+	@Test
+	void extensionSetupMissingDefault() {
+		var configContainer = new DefaultConfigContainer<>();
+		configContainer.registerExtension(ExtensionMissingDefault.class);
+		assertThatThrownBy(configContainer::finishExtensionSetup).hasMessageContaining("ExtensionMissingDefault");
+	}
+
+	@Test
+	void extensionSetupAbstractDefault() {
+		var configContainer = new DefaultConfigContainer<>();
+		configContainer.registerExtension(ExtensionSelfReferencingDefault.class);
+		assertThatThrownBy(configContainer::finishExtensionSetup).hasMessageContaining("ExtensionSelfReferencingDefault");
+	}
+
+	@Test
+	void extensionSetupWrongDefault() {
+		var configContainer = new DefaultConfigContainer<>();
+		configContainer.registerExtension(ExtensionWrongDefault.class);
+		assertThatThrownBy(configContainer::finishExtensionSetup)
+				.hasMessageContaining("ExtensionWrongDefault", "ExtensionBImpl");
+	}
+
+	@Test
+	void extensionSetupNonStaticDefault() {
+		var configContainer = new DefaultConfigContainer<>();
+		configContainer.registerExtension(ExtensionNonStaticDefault.class);
+		assertThatThrownBy(configContainer::finishExtensionSetup)
+				.hasMessageContaining("ExtensionNonStaticDefault", "static");
+	}
+
+	@Test
+	void extensionSetupNonPublicDefault() {
+		var configContainer = new DefaultConfigContainer<>();
+		configContainer.registerExtension(ExtensionNonPublicDefault.class);
+		assertThatThrownBy(configContainer::finishExtensionSetup)
+				.hasMessageContaining("ExtensionNonPublicDefault", "public");
+	}
+
+	@Test
+	void extension() {
+		var configContainer = new DefaultConfigContainer<>();
+		configContainer.registerExtensions(ExtensionA.class, ExtensionB.class);
+		configContainer.finishExtensionSetup();
+
+		assertThat(configContainer.extension(ExtensionA.class)).containsInstanceOf(ExtensionA.class);
+		assertThat(configContainer.extension(ExtensionB.class)).containsInstanceOf(ExtensionBImpl.class);
+		assertThat(configContainer.extension(ExtensionBImpl.class)).containsInstanceOf(ExtensionBImpl.class);
+		assertThat(configContainer.extension(ExtensionBNonDefaultImpl.class)).isEmpty();
+	}
+
+	@SuppressWarnings("unchecked")
+	@Test
+	void attachAndSealTree() {
+		var configContainer = new DefaultConfigContainer<Map<String, Object>>();
+		var compoundEntry = new StaticMapCompoundConfigEntryImpl<>(
+				(Class<Map<String, Object>>)(Class<?>) Map.class,
+				(capacity) -> new HashMap<>(capacity * 2, 0.5F)
+		);
+		var subEntry = new SimpleConfigEntryImpl<>(String.class);
+		compoundEntry.addSubEntry("test", subEntry);
+
+		configContainer.finishExtensionSetup();
+
+		assertThat(configContainer.setupPhase()).isEqualTo(ConfigContainerSetupPhase.TREE_SETUP);
+		configContainer.attachAndSealTree(compoundEntry);
+
+		assertThat(configContainer.setupPhase()).isEqualTo(ConfigContainerSetupPhase.TREE_SEALED);
+		assertThat(compoundEntry.sealed()).isTrue();
+		assertThat(subEntry.sealed()).isTrue();
+		assertThat(configContainer.rootEntry()).isSameAs(compoundEntry);
+	}
+
+	@Test
+	void createExtensionsData() {
+		var configContainer = new DefaultConfigContainer<>();
+		configContainer.registerExtension(ExtensionB.class);
+		configContainer.finishExtensionSetup();
+		var extensionData = configContainer.createExtensionsData();
+		assertThat(extensionData).isNotNull()
+				.satisfies(
+						data -> assertThat(data.isPatchworkPartDefined(ExtensionBData.class)).isTrue(),
+						data -> assertThat(data.isPatchworkPartDefined(String.class)).isFalse()
+				);
+	}
+
+	@Test
+	void entryDataExtensions() {
+		var configContainer = new DefaultConfigContainer<>();
+		configContainer.registerExtension(ExtensionB.class);
+		configContainer.finishExtensionSetup();
+
+		assertThat(configContainer.entryDataExtensions()).containsOnlyKeys(ExtensionBData.class);
+		//noinspection unchecked
+		var registeredExtension = (RegisteredExtensionData<EntryExtensionsData, ExtensionBData>)
+				configContainer.entryDataExtensions().get(ExtensionBData.class);
+
+		var extensionsData = configContainer.createExtensionsData();
+		registeredExtension.set(extensionsData, new ExtensionBDataImpl("blub"));
+
+		assertThat(((ExtensionBData) extensionsData).test()).isEqualTo("blub");
+	}
+
+	@Test
+	void initialize() {
+		var configContainer = new DefaultConfigContainer<Map<String, Object>>();
+		var compoundEntry = new StaticMapCompoundConfigEntryImpl<>(
+				(Class<Map<String, Object>>)(Class<?>) Map.class,
+				(capacity) -> new HashMap<>(capacity * 2, 0.5F)
+		);
+		var subEntry = new SimpleConfigEntryImpl<>(String.class);
+		compoundEntry.addSubEntry("test", subEntry);
+
+		configContainer.registerExtension(ExtensionInitTracker.class);
+		configContainer.finishExtensionSetup();
+		configContainer.attachAndSealTree(compoundEntry);
+
+		assertThat(configContainer.setupPhase()).isEqualTo(ConfigContainerSetupPhase.TREE_SEALED);
+		configContainer.initialize();
+		assertThat(configContainer.setupPhase()).isEqualTo(ConfigContainerSetupPhase.READY);
+
+		var initTracker = configContainer.extension(ExtensionInitTracker.class).orElseThrow();
+		assertThat(initTracker.initializedEntries()).containsExactlyInAnyOrder(compoundEntry, subEntry);
+	}
+
+	public static class ExtensionA implements TweedExtension {
+		public ExtensionA(TweedExtensionSetupContext context) {
+			context.registerExtension(ExtensionB.class);
+		}
+
+		@Override
+		public String getId() {
+			return "a";
+		}
+	}
+
+	public interface ExtensionB extends TweedExtension {
+		Class<? extends ExtensionB> DEFAULT = ExtensionBImpl.class;
+	}
+	public static class ExtensionBImpl implements ExtensionB {
+		public ExtensionBImpl(TweedExtensionSetupContext context) {
+			context.registerEntryExtensionData(ExtensionBData.class);
+		}
+
+		@Override
+		public String getId() {
+			return "b";
+		}
+	}
+	public static class ExtensionBNonDefaultImpl implements ExtensionB {
+		@Override
+		public String getId() {
+			return "b-non-default";
+		}
+	}
+	public interface ExtensionBData {
+		String test();
+	}
+	record ExtensionBDataImpl(String test) implements ExtensionBData { }
+
+	@Getter
+	public static class ExtensionInitTracker implements TweedExtension {
+		private final Collection<ConfigEntry<?>> initializedEntries = new ArrayList<>();
+
+		@Override
+		public String getId() {
+			return "init-tracker";
+		}
+
+		@Override
+		public void initEntry(ConfigEntry<?> configEntry) {
+			initializedEntries.add(configEntry);
+		}
+	}
+
+	public interface ExtensionMissingDefault extends TweedExtension {}
+
+	public interface ExtensionSelfReferencingDefault extends TweedExtension {
+		Class<ExtensionSelfReferencingDefault> DEFAULT = ExtensionSelfReferencingDefault.class;
+	}
+
+	public interface ExtensionWrongDefault extends TweedExtension {
+		Class<?> DEFAULT = ExtensionBImpl.class;
+	}
+
+	public static abstract class ExtensionNonStaticDefault implements TweedExtension {
+		public final Class<?> DEFAULT = ExtensionNonStaticDefault.class;
+	}
+
+	public static abstract class ExtensionNonPublicDefault implements TweedExtension {
+		protected static final Class<?> DEFAULT = ExtensionNonPublicDefault.class;
+	}
+}

tweed5-default-extensions/src/main/java/de/siphalor/tweed5/defaultextensions/comment/api/CommentExtension.java

@@ -2,8 +2,11 @@ package de.siphalor.tweed5.defaultextensions.comment.api;
 
 import de.siphalor.tweed5.core.api.entry.ConfigEntry;
 import de.siphalor.tweed5.core.api.extension.TweedExtension;
+import de.siphalor.tweed5.defaultextensions.comment.impl.CommentExtensionImpl;
 import org.jspecify.annotations.Nullable;
 
 public interface CommentExtension extends TweedExtension {
+	Class<? extends CommentExtension> DEFAULT = CommentExtensionImpl.class;
+
 	@Nullable String getFullComment(ConfigEntry<?> configEntry);
 }

tweed5-default-extensions/src/main/java/de/siphalor/tweed5/defaultextensions/comment/impl/CommentExtensionImpl.java

@@ -1,6 +1,7 @@
 package de.siphalor.tweed5.defaultextensions.comment.impl;
 
 import com.google.auto.service.AutoService;
+import de.siphalor.tweed5.core.api.container.ConfigContainer;
 import de.siphalor.tweed5.core.api.entry.ConfigEntry;
 import de.siphalor.tweed5.core.api.extension.EntryExtensionsData;
 import de.siphalor.tweed5.core.api.extension.RegisteredExtensionData;
@@ -14,15 +15,21 @@ import de.siphalor.tweed5.defaultextensions.comment.api.*;
 import lombok.Getter;
 import lombok.Value;
 import org.jspecify.annotations.NonNull;
-import org.jspecify.annotations.NullUnmarked;
 import org.jspecify.annotations.Nullable;
 
 @AutoService(CommentExtension.class)
-@NullUnmarked
 public class CommentExtensionImpl implements ReadWriteRelatedExtension, CommentExtension {
+	private final ConfigContainer<?> configContainer;
 	@Getter
-	private RegisteredExtensionData<EntryExtensionsData, InternalCommentEntryData> internalEntryDataExtension;
+	private final RegisteredExtensionData<EntryExtensionsData, InternalCommentEntryData> internalEntryDataExtension;
-	private DefaultMiddlewareContainer<CommentProducer> middlewareContainer;
+	private final DefaultMiddlewareContainer<CommentProducer> middlewareContainer;
+
+	public CommentExtensionImpl(ConfigContainer<?> configContainer, TweedExtensionSetupContext context) {
+		this.configContainer = configContainer;
+		this.internalEntryDataExtension = context.registerEntryExtensionData(InternalCommentEntryData.class);
+		context.registerEntryExtensionData(EntryComment.class);
+		this.middlewareContainer = new DefaultMiddlewareContainer<>();
+	}
 
 	@Override
 	public String getId() {
@@ -30,18 +37,12 @@ public class CommentExtensionImpl implements ReadWriteRelatedExtension, CommentE
 	}
 
 	@Override
-	public void setup(TweedExtensionSetupContext context) {
+	public void extensionsFinalized() {
-		internalEntryDataExtension = context.registerEntryExtensionData(InternalCommentEntryData.class);
+		for (TweedExtension extension : configContainer.extensions()) {
-		context.registerEntryExtensionData(EntryComment.class);
-
-		middlewareContainer = new DefaultMiddlewareContainer<>();
-
-		for (TweedExtension extension : context.configContainer().extensions()) {
 			if (extension instanceof CommentModifyingExtension) {
 				middlewareContainer.register(((CommentModifyingExtension) extension).commentMiddleware());
 			}
 		}
-
 		middlewareContainer.seal();
 	}
 

tweed5-default-extensions/src/main/java/de/siphalor/tweed5/defaultextensions/pather/api/PathTracking.java

@@ -32,8 +32,10 @@ public class PathTracking implements PatherData {
 	}
 
 	public void popPathPart() {
-		String poppedPart = pathParts.pop();
+		if (!pathParts.isEmpty()) {
-		pathBuilder.setLength(pathBuilder.length() - poppedPart.length() - 1);
+			String poppedPart = pathParts.pop();
+			pathBuilder.setLength(pathBuilder.length() - poppedPart.length() - 1);
+		}
 	}
 
 	public void pushListContext() {

tweed5-default-extensions/src/main/java/de/siphalor/tweed5/defaultextensions/pather/api/PatherExtension.java

@@ -1,6 +1,8 @@
 package de.siphalor.tweed5.defaultextensions.pather.api;
 
 import de.siphalor.tweed5.core.api.extension.TweedExtension;
+import de.siphalor.tweed5.defaultextensions.pather.impl.PatherExtensionImpl;
 
 public interface PatherExtension extends TweedExtension {
+	Class<? extends PatherExtension> DEFAULT = PatherExtensionImpl.class;
 }

tweed5-default-extensions/src/main/java/de/siphalor/tweed5/defaultextensions/pather/impl/PatherExtensionImpl.java

@@ -11,10 +11,7 @@ import de.siphalor.tweed5.data.extension.api.extension.ReadWriteExtensionSetupCo
 import de.siphalor.tweed5.data.extension.api.extension.ReadWriteRelatedExtension;
 import de.siphalor.tweed5.dataapi.api.TweedDataReader;
 import de.siphalor.tweed5.dataapi.api.TweedDataVisitor;
-import de.siphalor.tweed5.defaultextensions.pather.api.PathTracking;
+import de.siphalor.tweed5.defaultextensions.pather.api.*;
-import de.siphalor.tweed5.defaultextensions.pather.api.PathTrackingDataReader;
-import de.siphalor.tweed5.defaultextensions.pather.api.PathTrackingDataVisitor;
-import de.siphalor.tweed5.defaultextensions.pather.api.PatherExtension;
 import lombok.val;
 import org.jspecify.annotations.NonNull;
 import org.jspecify.annotations.NullUnmarked;
@@ -25,7 +22,7 @@ import org.jspecify.annotations.Nullable;
 public class PatherExtensionImpl implements PatherExtension, TweedExtension, ReadWriteRelatedExtension {
 	private static final String PATHER_ID = "pather";
 
-	private RegisteredExtensionData<ReadWriteContextExtensionsData, PathTracking> rwContextPathTrackingData;
+	private RegisteredExtensionData<ReadWriteContextExtensionsData, PatherData> rwContextPathTrackingData;
 	private Middleware<TweedEntryReader<?, ?>> entryReaderMiddleware;
 	private Middleware<TweedEntryWriter<?, ?>> entryWriterMiddleware;
 
@@ -36,7 +33,7 @@ public class PatherExtensionImpl implements PatherExtension, TweedExtension, Rea
 
 	@Override
 	public void setupReadWriteExtension(ReadWriteExtensionSetupContext context) {
-		rwContextPathTrackingData = context.registerReadWriteContextExtensionData(PathTracking.class);
+		rwContextPathTrackingData = context.registerReadWriteContextExtensionData(PatherData.class);
 
 		entryReaderMiddleware = createEntryReaderMiddleware();
 		entryWriterMiddleware = createEntryWriterMiddleware();
@@ -55,7 +52,7 @@ public class PatherExtensionImpl implements PatherExtension, TweedExtension, Rea
 				val castedInner = (TweedEntryReader<Object, @NonNull ConfigEntry<Object>>) inner;
 
 				return (TweedDataReader reader, ConfigEntry<Object> entry, TweedReadContext context) -> {
-					if (context.extensionsData().isPatchworkPartSet(PathTracking.class)) {
+					if (context.extensionsData().isPatchworkPartSet(PatherData.class)) {
 						return castedInner.read(reader, entry, context);
 					}
 
@@ -80,7 +77,7 @@ public class PatherExtensionImpl implements PatherExtension, TweedExtension, Rea
 				val castedInner = (TweedEntryWriter<Object, @NonNull ConfigEntry<Object>>) inner;
 
 				return (TweedDataVisitor writer, Object value, ConfigEntry<Object> entry, TweedWriteContext context) -> {
-					if (context.extensionsData().isPatchworkPartSet(PathTracking.class)) {
+					if (context.extensionsData().isPatchworkPartSet(PatherData.class)) {
 						castedInner.write(writer, value, entry, context);
 						return;
 					}

tweed5-default-extensions/src/main/java/de/siphalor/tweed5/defaultextensions/validation/api/ValidationExtension.java

@@ -3,8 +3,11 @@ package de.siphalor.tweed5.defaultextensions.validation.api;
 import de.siphalor.tweed5.core.api.entry.ConfigEntry;
 import de.siphalor.tweed5.core.api.extension.TweedExtension;
 import de.siphalor.tweed5.defaultextensions.validation.api.result.ValidationIssues;
+import de.siphalor.tweed5.defaultextensions.validation.impl.ValidationExtensionImpl;
 import org.jspecify.annotations.Nullable;
 
 public interface ValidationExtension extends TweedExtension {
+	Class<? extends ValidationExtension> DEFAULT = ValidationExtensionImpl.class;
+
 	<T extends @Nullable Object> ValidationIssues validate(ConfigEntry<T> entry, T value);
 }

tweed5-default-extensions/src/main/java/de/siphalor/tweed5/defaultextensions/validation/impl/ValidationExtensionImpl.java

@@ -1,6 +1,7 @@
 package de.siphalor.tweed5.defaultextensions.validation.impl;
 
 import com.google.auto.service.AutoService;
+import de.siphalor.tweed5.core.api.container.ConfigContainer;
 import de.siphalor.tweed5.core.api.entry.ConfigEntry;
 import de.siphalor.tweed5.core.api.entry.ConfigEntryValueVisitor;
 import de.siphalor.tweed5.core.api.extension.EntryExtensionsData;
@@ -22,26 +23,24 @@ import de.siphalor.tweed5.defaultextensions.comment.api.CommentProducer;
 import de.siphalor.tweed5.defaultextensions.pather.api.PathTracking;
 import de.siphalor.tweed5.defaultextensions.pather.api.PathTrackingConfigEntryValueVisitor;
 import de.siphalor.tweed5.defaultextensions.pather.api.PatherData;
-import de.siphalor.tweed5.defaultextensions.pather.impl.PatherExtensionImpl;
+import de.siphalor.tweed5.defaultextensions.pather.api.PatherExtension;
 import de.siphalor.tweed5.defaultextensions.validation.api.ConfigEntryValidator;
 import de.siphalor.tweed5.defaultextensions.validation.api.EntrySpecificValidation;
 import de.siphalor.tweed5.defaultextensions.validation.api.ValidationExtension;
 import de.siphalor.tweed5.defaultextensions.validation.api.ValidationProvidingExtension;
-import de.siphalor.tweed5.defaultextensions.validation.api.result.ValidationIssues;
 import de.siphalor.tweed5.defaultextensions.validation.api.result.ValidationIssue;
 import de.siphalor.tweed5.defaultextensions.validation.api.result.ValidationIssueLevel;
+import de.siphalor.tweed5.defaultextensions.validation.api.result.ValidationIssues;
 import de.siphalor.tweed5.defaultextensions.validation.api.result.ValidationResult;
 import lombok.Getter;
 import lombok.RequiredArgsConstructor;
 import lombok.Value;
 import org.jetbrains.annotations.NotNull;
-import org.jspecify.annotations.NullUnmarked;
 import org.jspecify.annotations.Nullable;
 
 import java.util.*;
 
 @AutoService(ValidationExtension.class)
-@NullUnmarked
 public class ValidationExtensionImpl implements ReadWriteRelatedExtension, ValidationExtension, CommentModifyingExtension {
 	private static final ValidationResult<?> PRIMITIVE_IS_NULL_RESULT = ValidationResult.withIssues(
 			null,
@@ -74,9 +73,19 @@ public class ValidationExtensionImpl implements ReadWriteRelatedExtension, Valid
 		}
 	};
 
-	private RegisteredExtensionData<EntryExtensionsData, InternalValidationEntryData> validationEntryDataExtension;
+	private final ConfigContainer<?> configContainer;
-	private MiddlewareContainer<ConfigEntryValidator> entryValidatorMiddlewareContainer;
+	private final RegisteredExtensionData<EntryExtensionsData, InternalValidationEntryData> validationEntryDataExtension;
-	private RegisteredExtensionData<ReadWriteContextExtensionsData, ValidationIssues> readContextValidationIssuesExtensionData;
+	private final MiddlewareContainer<ConfigEntryValidator> entryValidatorMiddlewareContainer
+			= new DefaultMiddlewareContainer<>();
+	private @Nullable RegisteredExtensionData<ReadWriteContextExtensionsData, ValidationIssues>
+			readContextValidationIssuesExtensionData;
+
+	public ValidationExtensionImpl(ConfigContainer<?> configContainer, TweedExtensionSetupContext context) {
+		this.configContainer = configContainer;
+		this.validationEntryDataExtension = context.registerEntryExtensionData(InternalValidationEntryData.class);
+		context.registerEntryExtensionData(EntrySpecificValidation.class);
+		context.registerExtension(PatherExtension.class);
+	}
 
 	@Override
 	public String getId() {
@@ -84,16 +93,12 @@ public class ValidationExtensionImpl implements ReadWriteRelatedExtension, Valid
 	}
 
 	@Override
-	public void setup(TweedExtensionSetupContext context) {
+	public void extensionsFinalized() {
-		context.registerExtension(new PatherExtensionImpl());
+		for (TweedExtension extension : configContainer.extensions()) {
-
-		validationEntryDataExtension = context.registerEntryExtensionData(InternalValidationEntryData.class);
-		context.registerEntryExtensionData(EntrySpecificValidation.class);
-
-		entryValidatorMiddlewareContainer = new DefaultMiddlewareContainer<>();
-		for (TweedExtension extension : context.configContainer().extensions()) {
 			if (extension instanceof ValidationProvidingExtension) {
-				entryValidatorMiddlewareContainer.register(((ValidationProvidingExtension) extension).validationMiddleware());
+				entryValidatorMiddlewareContainer.register(
+						((ValidationProvidingExtension) extension).validationMiddleware()
+				);
 			}
 		}
 		entryValidatorMiddlewareContainer.seal();

tweed5-default-extensions/src/main/java/de/siphalor/tweed5/defaultextensions/validationfallback/api/ValidationFallbackExtension.java

@@ -1,6 +1,8 @@
 package de.siphalor.tweed5.defaultextensions.validationfallback.api;
 
 import de.siphalor.tweed5.core.api.extension.TweedExtension;
+import de.siphalor.tweed5.defaultextensions.validationfallback.impl.ValidationFallbackExtensionImpl;
 
 public interface ValidationFallbackExtension extends TweedExtension {
+	Class<? extends ValidationFallbackExtension> DEFAULT = ValidationFallbackExtensionImpl.class;
 }

tweed5-default-extensions/src/main/java/de/siphalor/tweed5/defaultextensions/validationfallback/impl/ValidationFallbackExtensionImpl.java

@@ -20,14 +20,13 @@ import java.util.stream.Collectors;
 
 @AutoService(ValidationFallbackExtension.class)
 public class ValidationFallbackExtensionImpl implements ValidationFallbackExtension, ValidationProvidingExtension {
-	@Override
+	public ValidationFallbackExtensionImpl(TweedExtensionSetupContext context) {
-	public String getId() {
+		context.registerEntryExtensionData(ValidationFallbackValue.class);
-		return "validation-fallback";
 	}
 
 	@Override
-	public void setup(TweedExtensionSetupContext context) {
+	public String getId() {
-		context.registerEntryExtensionData(ValidationFallbackValue.class);
+		return "validation-fallback";
 	}
 
 	@Override

tweed5-default-extensions/src/test/java/de/siphalor/tweed5/defaultextensions/comment/impl/CommentExtensionImplTest.java

@@ -13,37 +13,40 @@ import de.siphalor.tweed5.data.extension.api.TweedEntryReader;
 import de.siphalor.tweed5.data.extension.api.TweedEntryWriter;
 import de.siphalor.tweed5.data.extension.api.readwrite.TweedEntryReaderWriter;
 import de.siphalor.tweed5.data.extension.api.readwrite.TweedEntryReaderWriters;
-import de.siphalor.tweed5.data.extension.impl.ReadWriteExtensionImpl;
 import de.siphalor.tweed5.data.hjson.HjsonCommentType;
 import de.siphalor.tweed5.data.hjson.HjsonWriter;
 import de.siphalor.tweed5.defaultextensions.comment.api.CommentExtension;
 import de.siphalor.tweed5.defaultextensions.comment.api.CommentModifyingExtension;
 import de.siphalor.tweed5.defaultextensions.comment.api.CommentProducer;
 import de.siphalor.tweed5.defaultextensions.comment.api.EntryComment;
+import lombok.NoArgsConstructor;
 import lombok.RequiredArgsConstructor;
 import lombok.Value;
+import org.jspecify.annotations.NullUnmarked;
 import org.junit.jupiter.api.Test;
 
 import java.io.StringWriter;
-import java.util.*;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.Map;
 
 import static org.junit.jupiter.api.Assertions.*;
 
+@NullUnmarked
 class CommentExtensionImplTest {
 
 	private DefaultConfigContainer<Map<String, Object>> configContainer;
-	private CommentExtension commentExtension;
 	private StaticMapCompoundConfigEntryImpl<Map<String, Object>> rootEntry;
 	private SimpleConfigEntryImpl<Integer> intEntry;
 	private SimpleConfigEntryImpl<String> stringEntry;
 	private SimpleConfigEntryImpl<Long> noCommentEntry;
 
-	void setupContainer(Collection<TweedExtension> extraExtensions) {
+	@SafeVarargs
+	final void setupContainer(Class<? extends TweedExtension>... extraExtensions) {
 		configContainer = new DefaultConfigContainer<>();
 
-		commentExtension = new CommentExtensionImpl();
+		configContainer.registerExtension(CommentExtension.DEFAULT);
-		configContainer.registerExtension(commentExtension);
+		configContainer.registerExtensions(extraExtensions);
-		extraExtensions.forEach(configContainer::registerExtension);
 		configContainer.finishExtensionSetup();
 
 		//noinspection unchecked
@@ -68,9 +71,10 @@ class CommentExtensionImplTest {
 
 	@Test
 	void simpleComments() {
-		setupContainer(Collections.emptyList());
+		setupContainer();
 		configContainer.initialize();
 
+		CommentExtension commentExtension = configContainer.extension(CommentExtension.class).orElseThrow();
 		assertEquals("It is an integer", commentExtension.getFullComment(intEntry));
 		assertEquals("It is a string", commentExtension.getFullComment(stringEntry));
 		assertNull(commentExtension.getFullComment(noCommentEntry));
@@ -78,9 +82,10 @@ class CommentExtensionImplTest {
 
 	@Test
 	void commentProvidingExtension() {
-		setupContainer(Collections.singletonList(new TestCommentModifyingExtension()));
+		setupContainer(TestCommentModifyingExtension.class);
 		configContainer.initialize();
 
+		CommentExtension commentExtension = configContainer.extension(CommentExtension.class).orElseThrow();
 		assertEquals("The comment is:\nIt is an integer\nEND", commentExtension.getFullComment(intEntry));
 		assertEquals("The comment is:\nIt is a string\nEND", commentExtension.getFullComment(stringEntry));
 		assertEquals("The comment is:\n\nEND", commentExtension.getFullComment(noCommentEntry));
@@ -88,8 +93,7 @@ class CommentExtensionImplTest {
 
 	@Test
 	void simpleCommentsInHjson() {
-		ReadWriteExtension readWriteExtension = new ReadWriteExtensionImpl();
+		setupContainer(ReadWriteExtension.DEFAULT);
-		setupContainer(Collections.singletonList(readWriteExtension));
 		setupReadWriteTypes();
 		configContainer.initialize();
 
@@ -98,6 +102,7 @@ class CommentExtensionImplTest {
 		value.put("string", "Hello World");
 		value.put("noComment", 567L);
 
+		ReadWriteExtension readWriteExtension = configContainer.extension(ReadWriteExtension.class).orElseThrow();
 		StringWriter output = new StringWriter();
 		assertDoesNotThrow(() -> readWriteExtension.write(
 				new HjsonWriter(output, new HjsonWriter.Options().multilineCommentType(HjsonCommentType.SLASHES)),
@@ -106,14 +111,23 @@ class CommentExtensionImplTest {
 				readWriteExtension.createReadWriteContextExtensionsData()
 		));
 
-		assertEquals("// This is the root value.\n// It is the topmost value in the tree.\n" +
+		assertEquals(
-				"{\n\t// It is an integer\n\tint: 123\n\t// It is a string\n" +
+				"""
-				"\tstring: Hello World\n\tnoComment: 567\n}\n", output.toString());
+				// This is the root value.
+				// It is the topmost value in the tree.
+				{
+				\t// It is an integer
+				\tint: 123
+				\t// It is a string
+				\tstring: Hello World
+				\tnoComment: 567
+				}
+				""", output.toString());
 	}
 
 	private void setupReadWriteTypes() {
 		//noinspection unchecked
-		RegisteredExtensionData<EntryExtensionsData, EntryReaderWriterDefinition> readerWriterData = (RegisteredExtensionData<EntryExtensionsData, EntryReaderWriterDefinition>) configContainer.entryDataExtensions().get(EntryReaderWriterDefinition.class);
+		var readerWriterData = (RegisteredExtensionData<EntryExtensionsData, EntryReaderWriterDefinition>) configContainer.entryDataExtensions().get(EntryReaderWriterDefinition.class);
 
 		readerWriterData.set(rootEntry.extensionsData(), new TrivialEntryReaderWriterDefinition(TweedEntryReaderWriters.compoundReaderWriter()));
 		readerWriterData.set(intEntry.extensionsData(), new TrivialEntryReaderWriterDefinition(TweedEntryReaderWriters.intReaderWriter()));
@@ -126,7 +140,8 @@ class CommentExtensionImplTest {
 		String comment;
 	}
 
-	private static class TestCommentModifyingExtension implements TweedExtension, CommentModifyingExtension {
+	@NoArgsConstructor
+	public static class TestCommentModifyingExtension implements TweedExtension, CommentModifyingExtension {
 		@Override
 		public String getId() {
 			return "test-extension";
@@ -162,4 +177,4 @@ class CommentExtensionImplTest {
 			return readerWriter;
 		}
 	}
-}
+}

tweed5-default-extensions/src/test/java/de/siphalor/tweed5/defaultextensions/validation/impl/ValidationExtensionImplTest.java

@@ -8,7 +8,6 @@ import de.siphalor.tweed5.core.impl.entry.SimpleConfigEntryImpl;
 import de.siphalor.tweed5.core.impl.entry.StaticMapCompoundConfigEntryImpl;
 import de.siphalor.tweed5.defaultextensions.comment.api.CommentExtension;
 import de.siphalor.tweed5.defaultextensions.comment.api.EntryComment;
-import de.siphalor.tweed5.defaultextensions.comment.impl.CommentExtensionImpl;
 import de.siphalor.tweed5.defaultextensions.validation.api.EntrySpecificValidation;
 import de.siphalor.tweed5.defaultextensions.validation.api.ValidationExtension;
 import de.siphalor.tweed5.defaultextensions.validation.api.result.ValidationIssue;
@@ -30,8 +29,6 @@ import static org.junit.jupiter.api.Assertions.*;
 
 class ValidationExtensionImplTest {
 	private DefaultConfigContainer<Map<String, Object>> configContainer;
-	private CommentExtension commentExtension;
-	private ValidationExtension validationExtension;
 	private StaticMapCompoundConfigEntryImpl<Map<String, Object>> rootEntry;
 	private SimpleConfigEntryImpl<Byte> byteEntry;
 	private SimpleConfigEntryImpl<Integer> intEntry;
@@ -41,10 +38,8 @@ class ValidationExtensionImplTest {
 	void setUp() {
 		configContainer = new DefaultConfigContainer<>();
 
-		commentExtension = new CommentExtensionImpl();
+		configContainer.registerExtension(CommentExtension.DEFAULT);
-		configContainer.registerExtension(commentExtension);
+		configContainer.registerExtension(ValidationExtension.DEFAULT);
-		validationExtension = new ValidationExtensionImpl();
-		configContainer.registerExtension(validationExtension);
 		configContainer.finishExtensionSetup();
 
 		//noinspection unchecked
@@ -90,6 +85,7 @@ class ValidationExtensionImplTest {
 		value.put("int", i);
 		value.put("double", d);
 
+		ValidationExtension validationExtension = configContainer.extension(ValidationExtension.class).orElseThrow();
 		ValidationIssues result = validationExtension.validate(rootEntry, value);
 		assertNotNull(result);
 		assertNotNull(result.issuesByPath());
@@ -103,6 +99,7 @@ class ValidationExtensionImplTest {
 		value.put("int", 124);
 		value.put("double", 0.2);
 
+		ValidationExtension validationExtension = configContainer.extension(ValidationExtension.class).orElseThrow();
 		ValidationIssues result = validationExtension.validate(rootEntry, value);
 		assertNotNull(result);
 		assertNotNull(result.issuesByPath());
@@ -127,4 +124,4 @@ class ValidationExtensionImplTest {
 		assertEquals(expectedIssue, entryIssues.issues().iterator().next(), "Issue must match");
 	}
 
-}
+}

tweed5-default-extensions/src/test/java/de/siphalor/tweed5/defaultextensions/validationfallback/impl/ValidationFallbackExtensionImplTest.java

@@ -10,13 +10,11 @@ import de.siphalor.tweed5.data.extension.api.ReadWriteExtension;
 import de.siphalor.tweed5.data.extension.api.TweedEntryReader;
 import de.siphalor.tweed5.data.extension.api.TweedEntryWriter;
 import de.siphalor.tweed5.data.extension.api.readwrite.TweedEntryReaderWriters;
-import de.siphalor.tweed5.data.extension.impl.ReadWriteExtensionImpl;
 import de.siphalor.tweed5.data.hjson.HjsonCommentType;
 import de.siphalor.tweed5.data.hjson.HjsonLexer;
 import de.siphalor.tweed5.data.hjson.HjsonReader;
 import de.siphalor.tweed5.data.hjson.HjsonWriter;
 import de.siphalor.tweed5.defaultextensions.comment.api.CommentExtension;
-import de.siphalor.tweed5.defaultextensions.comment.impl.CommentExtensionImpl;
 import de.siphalor.tweed5.defaultextensions.validation.api.ConfigEntryValidator;
 import de.siphalor.tweed5.defaultextensions.validation.api.EntrySpecificValidation;
 import de.siphalor.tweed5.defaultextensions.validation.api.ValidationExtension;
@@ -24,10 +22,10 @@ import de.siphalor.tweed5.defaultextensions.validation.api.result.ValidationIssu
 import de.siphalor.tweed5.defaultextensions.validation.api.result.ValidationIssueLevel;
 import de.siphalor.tweed5.defaultextensions.validation.api.result.ValidationResult;
 import de.siphalor.tweed5.defaultextensions.validation.api.validators.SimpleValidatorMiddleware;
-import de.siphalor.tweed5.defaultextensions.validation.impl.ValidationExtensionImpl;
 import de.siphalor.tweed5.defaultextensions.validationfallback.api.ValidationFallbackExtension;
 import de.siphalor.tweed5.defaultextensions.validationfallback.api.ValidationFallbackValue;
 import org.jetbrains.annotations.NotNull;
+import org.jspecify.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -44,24 +42,16 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class ValidationFallbackExtensionImplTest {
 	private DefaultConfigContainer<Integer> configContainer;
-	private CommentExtension commentExtension;
-	private ValidationExtension validationExtension;
-	private ValidationFallbackExtension validationFallbackExtension;
-	private ReadWriteExtension readWriteExtension;
 	private SimpleConfigEntryImpl<Integer> intEntry;
 
 	@SuppressWarnings("unchecked")
 	@BeforeEach
 	void setUp() {
 		configContainer = new DefaultConfigContainer<>();
-		commentExtension = new CommentExtensionImpl();
+		configContainer.registerExtension(CommentExtension.DEFAULT);
-		configContainer.registerExtension(commentExtension);
+		configContainer.registerExtension(ValidationExtension.DEFAULT);
-		validationExtension = new ValidationExtensionImpl();
+		configContainer.registerExtension(ValidationFallbackExtension.DEFAULT);
-		configContainer.registerExtension(validationExtension);
+		configContainer.registerExtension(ReadWriteExtension.DEFAULT);
-		validationFallbackExtension = new ValidationFallbackExtensionImpl();
-		configContainer.registerExtension(validationFallbackExtension);
-		readWriteExtension = new ReadWriteExtensionImpl();
-		configContainer.registerExtension(readWriteExtension);
 
 		configContainer.finishExtensionSetup();
 
@@ -73,7 +63,7 @@ class ValidationFallbackExtensionImplTest {
 		entrySpecificValidation.set(intEntry.extensionsData(), () -> Arrays.asList(
 				new SimpleValidatorMiddleware("non-null", new ConfigEntryValidator() {
 					@Override
-					public <T> ValidationResult<T> validate(ConfigEntry<T> configEntry, T value) {
+					public <T> ValidationResult<T> validate(ConfigEntry<T> configEntry, @Nullable T value) {
 						if (value == null) {
 							return ValidationResult.withIssues(null, Collections.singleton(
 									new ValidationIssue("Value must not be null", ValidationIssueLevel.ERROR)
@@ -89,7 +79,7 @@ class ValidationFallbackExtensionImplTest {
 				}),
 				new SimpleValidatorMiddleware("range", new ConfigEntryValidator() {
 					@Override
-					public <T> ValidationResult<T> validate(ConfigEntry<T> configEntry, T value) {
+					public <T> ValidationResult<T> validate(ConfigEntry<T> configEntry, @Nullable T value) {
 						Integer intValue = (Integer) value;
 						if (intValue < 1) {
 							return ValidationResult.withIssues(value, Collections.singleton(new ValidationIssue("Must be greater or equal to 1", ValidationIssueLevel.ERROR)));
@@ -134,6 +124,7 @@ class ValidationFallbackExtensionImplTest {
 	@ParameterizedTest
 	@ValueSource(strings = {"0", "7", "123", "null"})
 	void fallbackTriggers(String input) {
+		ReadWriteExtension readWriteExtension = configContainer.extension(ReadWriteExtension.class).orElseThrow();
 		Integer result = assertDoesNotThrow(() -> readWriteExtension.read(
 				new HjsonReader(new HjsonLexer(new StringReader(input))),
 				intEntry,
@@ -144,6 +135,7 @@ class ValidationFallbackExtensionImplTest {
 
 	@Test
 	void description() {
+		ReadWriteExtension readWriteExtension = configContainer.extension(ReadWriteExtension.class).orElseThrow();
 		StringWriter stringWriter = new StringWriter();
 		assertDoesNotThrow(() -> readWriteExtension.write(
 				new HjsonWriter(stringWriter, new HjsonWriter.Options().multilineCommentType(HjsonCommentType.SLASHES)),
@@ -152,6 +144,13 @@ class ValidationFallbackExtensionImplTest {
 				readWriteExtension.createReadWriteContextExtensionsData()
 		));
 
-		assertEquals("// Must not be null.\n// Must be between 1 and 6\n// \n// Default/Fallback value: 3\n5\n", stringWriter.toString());
+		assertEquals(
+				"""
+				// Must not be null.
+				// Must be between 1 and 6
+				//\s
+				// Default/Fallback value: 3
+				5
+				""", stringWriter.toString());
 	}
-}
+}

tweed5-patchwork/src/main/java/de/siphalor/tweed5/patchwork/impl/PatchworkClassGenerator.java

@@ -22,9 +22,6 @@ public class PatchworkClassGenerator {
 	 * Class version to use (Java 8)
 	 */
 	private static final int CLASS_VERSION = Opcodes.V1_8;
-	private static final String TARGET_PACKAGE = "de.siphalor.tweed5.core.generated.contextextensions";
-	private static final List<Type> DEFAULT_PATHWORK_INTERFACES
-			= Collections.singletonList(Type.getType(Patchwork.class));
 
 	private static final String INNER_EQUALS_METHOD_NAME = "patchwork$innerEquals";
 
@@ -609,6 +606,11 @@ public class PatchworkClassGenerator {
 			super("Invalid patchwork part class " + partClass.getName() + ": " + message);
 			this.partClass = partClass;
 		}
+
+		@Override
+		public String toString() {
+			return super.toString();
+		}
 	}
 
 	@Value
@@ -636,6 +638,11 @@ public class PatchworkClassGenerator {
 			stringBuilder.append("\n");
 			return stringBuilder.toString();
 		}
+
+		@Override
+		public String toString() {
+			return super.toString();
+		}
 	}
 
 	public static class GenerationException extends Exception {

tweed5-serde-extension/src/main/java/de/siphalor/tweed5/data/extension/api/ReadWriteExtension.java

@@ -3,11 +3,14 @@ package de.siphalor.tweed5.data.extension.api;
 import de.siphalor.tweed5.core.api.entry.ConfigEntry;
 import de.siphalor.tweed5.core.api.extension.TweedExtension;
 import de.siphalor.tweed5.data.extension.api.extension.ReadWriteContextExtensionsData;
+import de.siphalor.tweed5.data.extension.impl.ReadWriteExtensionImpl;
 import de.siphalor.tweed5.dataapi.api.TweedDataReader;
 import de.siphalor.tweed5.dataapi.api.TweedDataVisitor;
 import org.jspecify.annotations.Nullable;
 
 public interface ReadWriteExtension extends TweedExtension {
+	Class<? extends ReadWriteExtension> DEFAULT = ReadWriteExtensionImpl.class;
+
 	void setEntryReaderWriterDefinition(ConfigEntry<?> entry, EntryReaderWriterDefinition readerWriterDefinition);
 
 	ReadWriteContextExtensionsData createReadWriteContextExtensionsData();

tweed5-serde-extension/src/main/java/de/siphalor/tweed5/data/extension/impl/ReadWriteExtensionImpl.java

@@ -1,6 +1,7 @@
 package de.siphalor.tweed5.data.extension.impl;
 
 import com.google.auto.service.AutoService;
+import de.siphalor.tweed5.core.api.container.ConfigContainer;
 import de.siphalor.tweed5.core.api.entry.ConfigEntry;
 import de.siphalor.tweed5.core.api.extension.EntryExtensionsData;
 import de.siphalor.tweed5.core.api.extension.RegisteredExtensionData;
@@ -24,7 +25,6 @@ import lombok.Setter;
 import lombok.Value;
 import lombok.val;
 import org.jspecify.annotations.NonNull;
-import org.jspecify.annotations.NullUnmarked;
 import org.jspecify.annotations.Nullable;
 
 import java.lang.invoke.MethodHandle;
@@ -33,16 +33,27 @@ import java.util.HashMap;
 import java.util.Map;
 
 @AutoService(ReadWriteExtension.class)
-@NullUnmarked
 public class ReadWriteExtensionImpl implements ReadWriteExtension {
+	private final ConfigContainer<?> configContainer;
+	private final RegisteredExtensionData<EntryExtensionsData, EntryReaderWriterDefinition>
+			readerWriterDefinitionExtension;
+	private final RegisteredExtensionData<EntryExtensionsData, ReadWriteEntryDataExtension> readWriteEntryDataExtension;
+	private DefaultMiddlewareContainer<TweedEntryReader<?, ?>>
+			entryReaderMiddlewareContainer
+			= new DefaultMiddlewareContainer<>();
+	private DefaultMiddlewareContainer<TweedEntryWriter<?, ?>>
+			entryWriterMiddlewareContainer
+			= new DefaultMiddlewareContainer<>();
+	private final Map<Class<?>, RegisteredExtensionDataImpl<ReadWriteContextExtensionsData, ?>>
+			readWriteContextExtensionsDataClasses
+			= new HashMap<>();
+	private @Nullable PatchworkClass<@NonNull ReadWriteContextExtensionsData> readWriteContextExtensionsDataPatchwork;
 
-	private RegisteredExtensionData<EntryExtensionsData, EntryReaderWriterDefinition> readerWriterDefinitionExtension;
+	public ReadWriteExtensionImpl(ConfigContainer<?> configContainer, TweedExtensionSetupContext context) {
-	private RegisteredExtensionData<EntryExtensionsData, ReadWriteEntryDataExtension> readWriteEntryDataExtension;
+		this.configContainer = configContainer;
-	private DefaultMiddlewareContainer<TweedEntryReader<?, ?>> entryReaderMiddlewareContainer;
+		this.readerWriterDefinitionExtension = context.registerEntryExtensionData(EntryReaderWriterDefinition.class);
-	private DefaultMiddlewareContainer<TweedEntryWriter<?, ?>> entryWriterMiddlewareContainer;
+		this.readWriteEntryDataExtension = context.registerEntryExtensionData(ReadWriteEntryDataExtension.class);
-	private Map<Class<?>, RegisteredExtensionDataImpl<ReadWriteContextExtensionsData, ?>>
+	}
-			readWriteContextExtensionsDataClasses;
-	private PatchworkClass<@NonNull ReadWriteContextExtensionsData> readWriteContextExtensionsDataPatchwork;
 
 	@Override
 	public String getId() {
@@ -50,13 +61,8 @@ public class ReadWriteExtensionImpl implements ReadWriteExtension {
 	}
 
 	@Override
-	public void setup(TweedExtensionSetupContext context) {
+	public void extensionsFinalized() {
-		readerWriterDefinitionExtension = context.registerEntryExtensionData(EntryReaderWriterDefinition.class);
+		Collection<TweedExtension> extensions = configContainer.extensions();
-		readWriteEntryDataExtension = context.registerEntryExtensionData(ReadWriteEntryDataExtension.class);
-
-		Collection<TweedExtension> extensions = context.configContainer().extensions();
-
-		readWriteContextExtensionsDataClasses = new HashMap<>(extensions.size());
 
 		ReadWriteExtensionSetupContext setupContext = new ReadWriteExtensionSetupContext() {
 			@Override
@@ -154,6 +160,7 @@ public class ReadWriteExtensionImpl implements ReadWriteExtension {
 	@Override
 	public ReadWriteContextExtensionsData createReadWriteContextExtensionsData() {
 		try {
+			assert readWriteContextExtensionsDataPatchwork != null;
 			return (ReadWriteContextExtensionsData) readWriteContextExtensionsDataPatchwork.constructor().invoke();
 		} catch (Throwable e) {
 			throw new IllegalStateException("Failed to instantiate read write context extensions' data", e);
@@ -161,7 +168,7 @@ public class ReadWriteExtensionImpl implements ReadWriteExtension {
 	}
 
 	@Override
-	public <T> T read(
+	public <T extends @Nullable Object> T read(
 			@NonNull TweedDataReader reader,
 			@NonNull ConfigEntry<T> entry,
 			@NonNull ReadWriteContextExtensionsData contextExtensionsData
@@ -174,7 +181,7 @@ public class ReadWriteExtensionImpl implements ReadWriteExtension {
 	}
 
 	@Override
-	public <T> void write(
+	public <T extends @Nullable Object> void write(
 			@NonNull TweedDataVisitor writer,
 			@Nullable T value,
 			@NonNull ConfigEntry<T> entry,

tweed5-serde-extension/src/test/java/de/siphalor/tweed5/data/extension/impl/ReadWriteExtensionImplTest.java

@@ -27,21 +27,19 @@ import java.io.Writer;
 import java.util.*;
 import java.util.function.Function;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class ReadWriteExtensionImplTest {
-	private StringWriter stringWriter;
+	private final StringWriter stringWriter = new StringWriter();
+	private final ConfigContainer<Map<String, Object>> configContainer = new DefaultConfigContainer<>();
 	private StaticMapCompoundConfigEntryImpl<Map<String, Object>> rootEntry;
-	private ReadWriteExtension readWriteExtension;
 
 	@SuppressWarnings("unchecked")
 	@BeforeEach
 	void setUp() {
-		ConfigContainer<Map<String, Object>> configContainer = new DefaultConfigContainer<>();
+		configContainer.registerExtension(ReadWriteExtension.DEFAULT);
-
-		readWriteExtension = new ReadWriteExtensionImpl();
-		configContainer.registerExtension(readWriteExtension);
 		configContainer.finishExtensionSetup();
 
 		rootEntry = new StaticMapCompoundConfigEntryImpl<>(((Class<Map<String, Object>>) (Class<?>) Map.class), LinkedHashMap::new);
@@ -73,6 +71,7 @@ class ReadWriteExtensionImplTest {
 		value.put("int", 123);
 		value.put("list", Arrays.asList(true, false, true));
 
+		ReadWriteExtension readWriteExtension = configContainer.extension(ReadWriteExtension.class).orElseThrow();
 		assertDoesNotThrow(() -> readWriteExtension.write(
 				setupWriter(writer -> new HjsonWriter(writer, new HjsonWriter.Options())),
 				value,
@@ -80,13 +79,33 @@ class ReadWriteExtensionImplTest {
 				readWriteExtension.createReadWriteContextExtensionsData()
 		));
 
-		assertEquals("{\n\tint: 123\n\tlist: [\n\t\ttrue\n\t\tfalse\n\t\ttrue\n\t]\n}\n", stringWriter.toString());
+		assertThat(stringWriter.toString()).isEqualTo("""
+				{
+				\tint: 123
+				\tlist: [
+				\t\ttrue
+				\t\tfalse
+				\t\ttrue
+				\t]
+				}
+				"""
+		);
 	}
 
 	@Test
 	void read() {
+		ReadWriteExtension readWriteExtension = configContainer.extension(ReadWriteExtension.class).orElseThrow();
 		Map<String, Object> result = assertDoesNotThrow(() -> readWriteExtension.read(
-				new HjsonReader(new HjsonLexer(new StringReader("{\n\tint: 123\n\tlist: [\n\t\ttrue\n\t\tfalse\n\t\ttrue\n\t]\n}\n"))),
+				new HjsonReader(new HjsonLexer(new StringReader("""
+						{
+						\tint: 123
+						\tlist: [
+						\t\ttrue
+						\t\tfalse
+						\t\ttrue
+						\t]
+						}
+						"""))),
 				rootEntry,
 				readWriteExtension.createReadWriteContextExtensionsData()
 		));
@@ -97,7 +116,6 @@ class ReadWriteExtensionImplTest {
 	}
 
 	private TweedDataVisitor setupWriter(Function<Writer, TweedDataVisitor> writerFactory) {
-		stringWriter = new StringWriter();
 		return writerFactory.apply(stringWriter);
 	}
 

tweed5-weaver-pojo-serde-extension/src/main/java/de/siphalor/tweed5/weaver/pojoext/serde/api/ReadWritePojoPostProcessor.java

@@ -68,7 +68,7 @@ public class ReadWritePojoPostProcessor implements TweedPojoWeavingPostProcessor
 			return;
 		}
 
-		ReadWriteExtension readWriteExtension = context.configContainer().extension(ReadWriteExtension.class);
+		ReadWriteExtension readWriteExtension = context.configContainer().extension(ReadWriteExtension.class).orElse(null);
 		if (readWriteExtension == null) {
 			log.error("You must not use {} without the {}", this.getClass().getSimpleName(), ReadWriteExtension.class.getSimpleName());
 			return;

tweed5-weaver-pojo-serde-extension/src/test/java/de/siphalor/tweed5/weaver/pojoext/serde/WeaverPojoSerdeExtensionTest.java

@@ -32,8 +32,7 @@ class WeaverPojoSerdeExtensionTest {
 		ConfigContainer<AnnotatedConfig> configContainer = weaverBootstrapper.weave();
 		configContainer.initialize();
 
-		ReadWriteExtension readWriteExtension = configContainer.extension(ReadWriteExtension.class);
+		ReadWriteExtension readWriteExtension = configContainer.extension(ReadWriteExtension.class).orElseThrow();
-		assertThat(readWriteExtension).isNotNull();
 
 		AnnotatedConfig config = new AnnotatedConfig(123, "test", new TestClass(987));
 

tweed5-weaver-pojo/src/main/java/de/siphalor/tweed5/weaver/pojo/impl/weaving/TweedPojoWeaverBootstrapper.java

@@ -3,7 +3,6 @@ package de.siphalor.tweed5.weaver.pojo.impl.weaving;
 import de.siphalor.tweed5.core.api.container.ConfigContainer;
 import de.siphalor.tweed5.core.api.entry.ConfigEntry;
 import de.siphalor.tweed5.core.api.extension.RegisteredExtensionData;
-import de.siphalor.tweed5.core.api.extension.TweedExtension;
 import de.siphalor.tweed5.patchwork.api.PatchworkClassCreator;
 import de.siphalor.tweed5.patchwork.impl.PatchworkClass;
 import de.siphalor.tweed5.patchwork.impl.PatchworkClassGenerator;
@@ -15,7 +14,6 @@ import de.siphalor.tweed5.weaver.pojo.api.weaving.WeavingContext;
 import de.siphalor.tweed5.weaver.pojo.api.weaving.postprocess.TweedPojoWeavingPostProcessor;
 import lombok.*;
 import lombok.extern.slf4j.Slf4j;
-import org.jspecify.annotations.Nullable;
 
 import java.lang.annotation.Annotation;
 import java.lang.invoke.MethodHandle;
@@ -44,21 +42,12 @@ public class TweedPojoWeaverBootstrapper<T> {
 		Collection<TweedPojoWeaver> weavers = loadWeavers(Arrays.asList(rootWeavingConfig.weavers()));
 		Collection<TweedPojoWeavingPostProcessor> postProcessors = loadPostProcessors(Arrays.asList(rootWeavingConfig.postProcessors()));
 
-		Collection<TweedExtension> extensions = loadExtensions(Arrays.asList(rootWeavingConfig.extensions()));
+		configContainer.registerExtensions(rootWeavingConfig.extensions());
-		configContainer.registerExtensions(extensions.toArray(new TweedExtension[0]));
 		configContainer.finishExtensionSetup();
 
 		return new TweedPojoWeaverBootstrapper<>(pojoClass, configContainer, weavers, postProcessors);
 	}
 
-	private static Collection<TweedExtension> loadExtensions(Collection<Class<? extends TweedExtension>> extensionClasses) {
-		try {
-			return loadSingleServices(extensionClasses);
-		} catch (Exception e) {
-			throw new PojoWeavingException("Failed to load Tweed extensions", e);
-		}
-	}
-
 	private static Collection<TweedPojoWeaver> loadWeavers(Collection<Class<? extends TweedPojoWeaver>> weaverClasses) {
 		return weaverClasses.stream()
 				.map(weaverClass -> TweedPojoWeaver.FACTORY.construct(weaverClass).finish())
@@ -79,60 +68,6 @@ public class TweedPojoWeaverBootstrapper<T> {
 		}
 	}
 
-
-	private static <S> Collection<S> loadSingleServices(Collection<Class<? extends S>> serviceClasses) {
-		Collection<S> services = new ArrayList<>(serviceClasses.size());
-		for (Class<? extends S> serviceClass : serviceClasses) {
-			try {
-				services.add(loadSingleService(serviceClass));
-			} catch (Exception e) {
-				throw new PojoWeavingException("Failed to instantiate single service " + serviceClass.getName(), e);
-			}
-		}
-		return services;
-	}
-
-	private static <S> S loadSingleService(Class<S> serviceClass) {
-		try {
-			ServiceLoader<S> loader = ServiceLoader.load(serviceClass);
-			Iterator<S> iterator = loader.iterator();
-			if (!iterator.hasNext()) {
-				throw new PojoWeavingException("Could not find any service for class " + serviceClass.getName());
-			}
-			S service = iterator.next();
-
-			if (iterator.hasNext()) {
-				throw new PojoWeavingException(
-						"Found multiple services for class " + serviceClass.getName() + ": " +
-								createInstanceDebugStringFromIterator(loader.iterator())
-				);
-			}
-
-			return service;
-		} catch (ServiceConfigurationError e) {
-			throw new PojoWeavingException("Failed to load service " + serviceClass.getName(), e);
-		}
-	}
-
-	private static String createInstanceDebugStringFromIterator(Iterator<?> iterator) {
-		StringBuilder stringBuilder = new StringBuilder();
-		stringBuilder.append("[ ");
-		while (iterator.hasNext()) {
-			stringBuilder.append(createInstanceDebugDescriptor(iterator.next()));
-			stringBuilder.append(", ");
-		}
-		stringBuilder.append(" ]");
-		return stringBuilder.toString();
-	}
-
-	private static String createInstanceDebugDescriptor(@Nullable Object object) {
-		if (object == null) {
-			return "null";
-		} else {
-			return object.getClass().getName() + "@" + System.identityHashCode(object);
-		}
-	}
-
 	private static <A extends Annotation> A expectAnnotation(Class<?> clazz, Class<A> annotationClass) {
 		A annotation = clazz.getAnnotation(annotationClass);
 		if (annotation == null) {

tweed5-weaver-pojo/src/test/java/de/siphalor/tweed5/weaver/pojo/api/weaving/CompoundPojoWeaverTest.java

@@ -4,6 +4,7 @@ import de.siphalor.tweed5.core.api.container.ConfigContainer;
 import de.siphalor.tweed5.core.api.entry.ConfigEntry;
 import de.siphalor.tweed5.core.api.entry.SimpleConfigEntry;
 import de.siphalor.tweed5.core.api.extension.RegisteredExtensionData;
+import de.siphalor.tweed5.core.impl.entry.SimpleConfigEntryImpl;
 import de.siphalor.tweed5.namingformat.api.NamingFormat;
 import de.siphalor.tweed5.weaver.pojo.api.annotation.CompoundWeaving;
 import de.siphalor.tweed5.weaver.pojo.api.entry.WeavableCompoundConfigEntry;
@@ -12,6 +13,7 @@ import de.siphalor.tweed5.weaver.pojo.impl.weaving.compound.CompoundWeavingConfi
 import lombok.AllArgsConstructor;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
+import org.jspecify.annotations.NullUnmarked;
 import org.junit.jupiter.api.Test;
 
 import static de.siphalor.tweed5.weaver.pojo.test.ConfigEntryAssertions.isCompoundEntryForClassWith;
@@ -20,6 +22,7 @@ import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.Mockito.*;
 
 @SuppressWarnings("unused")
+@NullUnmarked
 class CompoundPojoWeaverTest {
 
 	@Test
@@ -39,10 +42,7 @@ class CompoundPojoWeaverTest {
 						if (entry != null) {
 							return entry;
 						} else {
-							//noinspection unchecked
+							return new SimpleConfigEntryImpl<>(valueType.declaredType());
-							ConfigEntry<T> configEntry = mock((Class<SimpleConfigEntry<T>>) (Class<?>) SimpleConfigEntry.class);
-							when(configEntry.valueClass()).thenReturn(valueType.declaredType());
-							return configEntry;
 						}
 					}
 				}, mock(ConfigContainer.class))