Merge remote-tracking branch 'origin/dev/1.4' into dev/1.5

# Conflicts:
#	gradle/libs.versions.toml

build.gradle

@@ -186,6 +186,7 @@ dependencies {
 	implementation libs.opencsv
 	implementation libs.forge.diffpatch
 	implementation libs.datafixerupper
+	implementation libs.at
 
 	// Forge mods.toml parsing
 	implementation libs.night.config.toml

gradle/libs.versions.toml

@@ -28,6 +28,7 @@ opencsv = "5.4"
 forge-diffpatch = "2.0.7"
 night-config = "3.6.6"
 datafixerupper = "6.0.8"
+at = "1.0.1"
 
 [libraries]
 # Loom compile libraries
@@ -60,6 +61,7 @@ opencsv = { module = "com.opencsv:opencsv", version.ref = "opencsv" }
 forge-diffpatch = { module = "net.minecraftforge:DiffPatch", version.ref = "forge-diffpatch" }
 night-config-toml = { module = "com.electronwill.night-config:toml", version.ref = "night-config" }
 datafixerupper = { module = "com.mojang:datafixerupper", version.ref = "datafixerupper" }
+at = { module = "dev.architectury:at", version.ref = "at" }
 
 [plugins]
 kotlin = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }

gradle/runtime.libs.versions.toml

@@ -18,6 +18,7 @@ access-transformers = "3.0.1"
 access-transformers-new = "8.0.5"
 unprotect = "1.2.0"
 asm = "9.3"
+union-relauncher = "1.0.0"
 
 [libraries]
 # Decompilers
@@ -41,3 +42,4 @@ access-transformers = { module = "net.minecraftforge:accesstransformers", versio
 access-transformers-new = { module = "net.minecraftforge:accesstransformers", version.ref = "access-transformers-new" }
 unprotect = { module = "io.github.juuxel:unprotect", version.ref = "unprotect" }
 asm = { module = "org.ow2.asm:asm", version.ref = "asm" }
+union-relauncher = { module = "io.github.juuxel:union-relauncher", version.ref = "union-relauncher" }

src/main/java/dev/architectury/loom/extensions/ModBuildExtensions.java

@@ -16,9 +16,8 @@ import java.util.jar.Attributes;
 import java.util.jar.JarFile;
 import java.util.jar.Manifest;
 
-import org.cadixdev.at.AccessTransformSet;
-import org.cadixdev.at.io.AccessTransformFormats;
-import org.cadixdev.lorenz.MappingSet;
+import dev.architectury.at.AccessTransformSet;
+import dev.architectury.at.io.AccessTransformFormats;
 import org.gradle.api.provider.Property;
 import org.gradle.api.provider.SetProperty;
 import org.jetbrains.annotations.Nullable;
@@ -29,7 +28,6 @@ import net.fabricmc.loom.util.FileSystemUtil;
 import net.fabricmc.loom.util.LfWriter;
 import net.fabricmc.loom.util.aw2at.Aw2At;
 import net.fabricmc.loom.util.service.UnsafeWorkQueueHelper;
-import net.fabricmc.lorenztiny.TinyMappingsReader;
 
 public final class ModBuildExtensions {
 	public static Set<String> readMixinConfigsFromManifest(File jarFile) {
@@ -87,11 +85,7 @@ public final class ModBuildExtensions {
 			}
 
 			MappingsService service = UnsafeWorkQueueHelper.get(mappingBuildServiceUuid, MappingsService.class);
-
-			try (TinyMappingsReader reader = new TinyMappingsReader(service.getMemoryMappingTree(), service.getFromNamespace(), service.getToNamespace())) {
-				MappingSet mappingSet = reader.read();
-				at = at.remap(mappingSet);
-			}
+			at = at.remap(service.getMemoryMappingTree(), service.getFromNamespace(), service.getToNamespace());
 
 			try (Writer writer = new LfWriter(Files.newBufferedWriter(atPath))) {
 				AccessTransformFormats.FML.write(writer, at);

src/main/java/dev/architectury/loom/metadata/ArchitecturyCommonJson.java

@@ -18,6 +18,7 @@ import org.jetbrains.annotations.Nullable;
 
 import net.fabricmc.loom.LoomGradlePlugin;
 import net.fabricmc.loom.configuration.ifaceinject.InterfaceInjectionProcessor;
+import net.fabricmc.loom.util.ModPlatform;
 
 public final class ArchitecturyCommonJson implements JsonBackedModMetadataFile, SingleIdModMetadataFile {
 	public static final String FILE_NAME = "architectury.common.json";
@@ -68,6 +69,11 @@ public final class ArchitecturyCommonJson implements JsonBackedModMetadataFile,
 		}
 	}
 
+	@Override
+	public Set<String> getAccessTransformers(ModPlatform platform) {
+		return Set.of();
+	}
+
 	@Override
 	public List<InterfaceInjectionProcessor.InjectedInterface> getInjectedInterfaces(@Nullable String modId) {
 		if (modId == null) {

src/main/java/dev/architectury/loom/metadata/ErroringModMetadataFile.java

@@ -7,6 +7,7 @@ import org.jetbrains.annotations.Nullable;
 import org.jetbrains.annotations.VisibleForTesting;
 
 import net.fabricmc.loom.configuration.ifaceinject.InterfaceInjectionProcessor;
+import net.fabricmc.loom.util.ModPlatform;
 
 /**
  * A fallback mod metadata file that represents a non-fatal format error
@@ -31,6 +32,11 @@ public final class ErroringModMetadataFile implements ModMetadataFile {
 		return Set.of();
 	}
 
+	@Override
+	public Set<String> getAccessTransformers(ModPlatform platform) {
+		return Set.of();
+	}
+
 	@Override
 	public List<InterfaceInjectionProcessor.InjectedInterface> getInjectedInterfaces(@Nullable String modId) {
 		return List.of();

src/main/java/dev/architectury/loom/metadata/ModMetadataFile.java

@@ -6,6 +6,7 @@ import java.util.Set;
 import org.jetbrains.annotations.Nullable;
 
 import net.fabricmc.loom.configuration.ifaceinject.InterfaceInjectionProcessor;
+import net.fabricmc.loom.util.ModPlatform;
 import net.fabricmc.loom.util.function.CollectionUtil;
 
 /**
@@ -32,6 +33,13 @@ public interface ModMetadataFile {
 	 */
 	Set<String> getAccessWideners();
 
+	/**
+	 * {@return the paths to the access transformer files of this mod, or an empty set if absent}.
+	 *
+	 * @param platform the platform to run the query on
+	 */
+	Set<String> getAccessTransformers(ModPlatform platform);
+
 	/**
 	 * {@return the injected interface data in this mod metadata file}.
 	 *

src/main/java/dev/architectury/loom/metadata/ModsToml.java

@@ -6,6 +6,7 @@ import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Objects;
 import java.util.Optional;
@@ -19,6 +20,7 @@ import org.jetbrains.annotations.Nullable;
 
 import net.fabricmc.loom.configuration.ifaceinject.InterfaceInjectionProcessor;
 import net.fabricmc.loom.util.ExceptionUtil;
+import net.fabricmc.loom.util.ModPlatform;
 
 public final class ModsToml implements ModMetadataFile {
 	public static final String FILE_PATH = "META-INF/mods.toml";
@@ -72,6 +74,26 @@ public final class ModsToml implements ModMetadataFile {
 		return Set.of();
 	}
 
+	@Override
+	public Set<String> getAccessTransformers(ModPlatform platform) {
+		if (platform == ModPlatform.NEOFORGE) {
+			final List<? extends Config> ats = config.get("accessTransformers");
+
+			if (ats != null) {
+				final Set<String> result = new HashSet<>();
+
+				for (Config atEntry : ats) {
+					final String file = atEntry.get("file");
+					if (file != null) result.add(file);
+				}
+
+				return result;
+			}
+		}
+
+		return Set.of();
+	}
+
 	@Override
 	public List<InterfaceInjectionProcessor.InjectedInterface> getInjectedInterfaces(@Nullable String modId) {
 		return List.of();

src/main/java/dev/architectury/loom/metadata/QuiltModJson.java

@@ -20,6 +20,7 @@ import org.slf4j.LoggerFactory;
 
 import net.fabricmc.loom.LoomGradlePlugin;
 import net.fabricmc.loom.configuration.ifaceinject.InterfaceInjectionProcessor;
+import net.fabricmc.loom.util.ModPlatform;
 import net.fabricmc.loom.util.function.CollectionUtil;
 
 public final class QuiltModJson implements JsonBackedModMetadataFile, SingleIdModMetadataFile {
@@ -84,6 +85,11 @@ public final class QuiltModJson implements JsonBackedModMetadataFile, SingleIdMo
 		}
 	}
 
+	@Override
+	public Set<String> getAccessTransformers(ModPlatform platform) {
+		return Set.of();
+	}
+
 	@Override
 	public List<InterfaceInjectionProcessor.InjectedInterface> getInjectedInterfaces(@Nullable String modId) {
 		try {

src/main/java/dev/architectury/loom/neoforge/NeoForgeModDependencies.java

@@ -0,0 +1,43 @@
+package dev.architectury.loom.neoforge;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Set;
+
+import dev.architectury.at.AccessTransformSet;
+import dev.architectury.at.io.AccessTransformFormats;
+import dev.architectury.loom.metadata.ModMetadataFile;
+import dev.architectury.loom.metadata.ModMetadataFiles;
+
+import net.fabricmc.loom.util.Constants;
+import net.fabricmc.loom.util.FileSystemUtil;
+import net.fabricmc.loom.util.ModPlatform;
+import net.fabricmc.mappingio.tree.MappingTreeView;
+
+public final class NeoForgeModDependencies {
+	public static void remapAts(Path jar, MappingTreeView mappings, String from, String to) throws IOException {
+		final ModMetadataFile modMetadata = ModMetadataFiles.fromJar(jar);
+		Set<String> atPaths = Set.of(Constants.Forge.ACCESS_TRANSFORMER_PATH);
+
+		if (modMetadata != null) {
+			final Set<String> modsTomlAts = modMetadata.getAccessTransformers(ModPlatform.NEOFORGE);
+
+			if (!modsTomlAts.isEmpty()) {
+				atPaths = modsTomlAts;
+			}
+		}
+
+		try (FileSystemUtil.Delegate fs = FileSystemUtil.getJarFileSystem(jar)) {
+			for (String atPathStr : atPaths) {
+				final Path atPath = fs.getPath(atPathStr);
+
+				if (Files.exists(atPath)) {
+					AccessTransformSet ats = AccessTransformFormats.FML.read(atPath);
+					ats = ats.remap(mappings, from, to);
+					AccessTransformFormats.FML.write(atPath, ats);
+				}
+			}
+		}
+	}
+}

src/main/java/net/fabricmc/loom/LoomGradlePlugin.java

@@ -49,6 +49,7 @@ import net.fabricmc.loom.extension.LoomFiles;
 import net.fabricmc.loom.extension.LoomGradleExtensionImpl;
 import net.fabricmc.loom.task.LoomTasks;
 import net.fabricmc.loom.task.RemapTaskConfiguration;
+import net.fabricmc.loom.util.Constants;
 import net.fabricmc.loom.util.LibraryLocationLogger;
 
 public class LoomGradlePlugin implements BootstrappedPlugin {
@@ -85,7 +86,11 @@ public class LoomGradlePlugin implements BootstrappedPlugin {
 			loggedVersions.add(LOOM_VERSION);
 			System.setProperty("loom.printed.logged", String.join(",", loggedVersions));
 			project.getLogger().lifecycle("Architectury Loom: " + LOOM_VERSION);
-			project.getLogger().lifecycle("This version of Architectury Loom is in beta! Please report any issues you encounter: https://github.com/architectury/architectury-loom/issues");
+			if (Constants.PLUGIN_BETA) {
+				project.getLogger().lifecycle("This version of Architectury Loom is in beta! Please report any issues you encounter: https://github.com/architectury/architectury-loom/issues");
+			} else if (Constants.PLUGIN_DEPRECATED) {
+				project.getLogger().lifecycle("You are using an outdated version of Architectury Loom! This version will not receive any support, please consider updating!");
+			}
 		}
 
 		LibraryLocationLogger.logLibraryVersions();

src/main/java/net/fabricmc/loom/configuration/accesstransformer/AccessTransformerJarProcessor.java

@@ -40,9 +40,9 @@ import javax.inject.Inject;
 
 import com.google.common.hash.Hashing;
 import com.google.common.io.MoreFiles;
+import dev.architectury.at.AccessTransformSet;
+import dev.architectury.at.io.AccessTransformFormats;
 import dev.architectury.loom.util.TempFiles;
-import org.cadixdev.at.AccessTransformSet;
-import org.cadixdev.at.io.AccessTransformFormats;
 import org.gradle.api.Project;
 import org.gradle.api.file.FileCollection;
 import org.gradle.api.logging.Logger;
@@ -61,7 +61,6 @@ import net.fabricmc.loom.util.ExceptionUtil;
 import net.fabricmc.loom.util.ForgeToolExecutor;
 import net.fabricmc.loom.util.LoomVersions;
 import net.fabricmc.loom.util.fmj.FabricModJson;
-import net.fabricmc.lorenztiny.TinyMappingsReader;
 
 public class AccessTransformerJarProcessor implements MinecraftJarProcessor<AccessTransformerJarProcessor.Spec> {
 	private static final Logger LOGGER = Logging.getLogger(AccessTransformerJarProcessor.class);
@@ -139,7 +138,7 @@ public class AccessTransformerJarProcessor implements MinecraftJarProcessor<Acce
 			}
 		}
 
-		accessTransformSet = accessTransformSet.remap(new TinyMappingsReader(context.getMappings(), IntermediaryNamespaces.intermediary(project), MappingsNamespace.NAMED.toString()).read());
+		accessTransformSet = accessTransformSet.remap(context.getMappings(), IntermediaryNamespaces.intermediary(project), MappingsNamespace.NAMED.toString());
 
 		final Path accessTransformerPath = tempFiles.file("accesstransformer-merged", ".cfg");
 

src/main/java/net/fabricmc/loom/configuration/mods/AccessWidenerUtils.java

@@ -37,6 +37,7 @@ import net.fabricmc.loom.api.mappings.layered.MappingsNamespace;
 import net.fabricmc.loom.util.ModPlatform;
 import net.fabricmc.loom.util.fmj.FabricModJson;
 import net.fabricmc.loom.util.fmj.FabricModJsonFactory;
+import net.fabricmc.loom.util.fmj.ModMetadataFabricModJson;
 
 public class AccessWidenerUtils {
 	/**
@@ -63,6 +64,13 @@ public class AccessWidenerUtils {
 		}
 
 		final FabricModJson fabricModJson = FabricModJsonFactory.createFromZip(inputJar);
+
+		if (platform.isForgeLike() && !(fabricModJson instanceof ModMetadataFabricModJson)) {
+			// Ignore actual fabric.mod.json files on NeoForge and Forge.
+			// See https://github.com/architectury/architectury-loom/issues/165.
+			return null;
+		}
+
 		final List<String> classTweakers = List.copyOf(fabricModJson.getClassTweakers().keySet());
 
 		if (classTweakers.isEmpty()) {

src/main/java/net/fabricmc/loom/configuration/mods/ArtifactMetadata.java

@@ -93,6 +93,12 @@ public record ArtifactMetadata(boolean isFabricMod, RemapRequirements remapRequi
 				if (loomVersion != null && refmapRemapType != MixinRemapType.STATIC) {
 					validateLoomVersion(loomVersion, currentLoomVersion);
 				}
+
+				// Check to see if the jar was built with a newer version of loom.
+				// This version of loom does not support the remap type value so throw an exception.
+				if (mainAttributes.getValue("Fabric-Loom-Mixin-Remap-Type") != null) {
+					throw new IllegalStateException("This version of loom does not support the mixin remap type value. Please update to the latest version of loom.");
+				}
 			}
 
 			final String installerFile = platform == ModPlatform.QUILT ? QUILT_INSTALLER_PATH : INSTALLER_PATH;

src/main/java/net/fabricmc/loom/configuration/mods/ModProcessor.java

@@ -43,6 +43,7 @@ import java.util.regex.Pattern;
 
 import com.google.common.base.Stopwatch;
 import com.google.gson.JsonObject;
+import dev.architectury.loom.neoforge.NeoForgeModDependencies;
 import dev.architectury.loom.util.MappingOption;
 import org.gradle.api.Project;
 import org.gradle.api.artifacts.Configuration;
@@ -64,7 +65,7 @@ import net.fabricmc.loom.util.ZipUtils;
 import net.fabricmc.loom.util.kotlin.KotlinClasspathService;
 import net.fabricmc.loom.util.kotlin.KotlinRemapperClassloader;
 import net.fabricmc.loom.util.service.SharedServiceManager;
-import net.fabricmc.loom.util.srg.AtRemapper;
+import net.fabricmc.loom.util.srg.AtClassRemapper;
 import net.fabricmc.loom.util.srg.CoreModClassRemapper;
 import net.fabricmc.mappingio.tree.MemoryMappingTree;
 import net.fabricmc.tinyremapper.InputTag;
@@ -285,7 +286,14 @@ public class ModProcessor {
 			remapJarManifestEntries(output);
 
 			if (extension.isForgeLike()) {
-				AtRemapper.remap(project, output, mappings);
+				if (extension.isNeoForge()) {
+					// NeoForge: Fully map ATs
+					NeoForgeModDependencies.remapAts(output, mappings, fromM, toM);
+				} else {
+					// Forge: only map class names, the rest are mapped srg -> named at runtime
+					AtClassRemapper.remap(project, output, mappings);
+				}
+
 				CoreModClassRemapper.remapJar(project, extension.getPlatform().get(), output, mappings);
 			}
 

src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeProvider.java

@@ -32,6 +32,7 @@ import org.gradle.api.Project;
 import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.configuration.DependencyInfo;
 import net.fabricmc.loom.util.Constants;
+import net.fabricmc.loom.util.LoomVersions;
 import net.fabricmc.loom.util.ModPlatform;
 
 public class ForgeProvider extends DependencyProvider {
@@ -49,6 +50,10 @@ public class ForgeProvider extends DependencyProvider {
 		version = new ForgeVersion(dependency.getResolvedVersion());
 		addDependency(dependency.getDepString() + ":userdev", Constants.Configurations.FORGE_USERDEV);
 		addDependency(dependency.getDepString() + ":installer", Constants.Configurations.FORGE_INSTALLER);
+
+		if (getExtension().isForge() && version.getMajorVersion() >= Constants.Forge.MIN_UNION_RELAUNCHER_VERSION) {
+			addDependency(LoomVersions.UNION_RELAUNCHER.mavenNotation(), Constants.Configurations.FORGE_EXTRA);
+		}
 	}
 
 	public ForgeVersion getVersion() {
@@ -86,6 +91,7 @@ public class ForgeProvider extends DependencyProvider {
 		private final String combined;
 		private final String minecraftVersion;
 		private final String forgeVersion;
+		private final int majorVersion;
 
 		public ForgeVersion(String combined) {
 			this.combined = combined;
@@ -93,6 +99,7 @@ public class ForgeProvider extends DependencyProvider {
 			if (combined == null) {
 				this.minecraftVersion = "NO_VERSION";
 				this.forgeVersion = "NO_VERSION";
+				this.majorVersion = -1;
 				return;
 			}
 
@@ -105,6 +112,21 @@ public class ForgeProvider extends DependencyProvider {
 				this.minecraftVersion = "NO_VERSION";
 				this.forgeVersion = combined;
 			}
+
+			int dotIndex = forgeVersion.indexOf('.');
+			int major;
+
+			try {
+				if (dotIndex >= 0) {
+					major = Integer.parseInt(forgeVersion.substring(0, dotIndex));
+				} else {
+					major = Integer.parseInt(forgeVersion);
+				}
+			} catch (NumberFormatException e) {
+				major = -1;
+			}
+
+			this.majorVersion = major;
 		}
 
 		public String getCombined() {
@@ -118,5 +140,9 @@ public class ForgeProvider extends DependencyProvider {
 		public String getForgeVersion() {
 			return forgeVersion;
 		}
+
+		public int getMajorVersion() {
+			return majorVersion;
+		}
 	}
 }

src/main/java/net/fabricmc/loom/configuration/providers/forge/ForgeRunTemplate.java

@@ -109,5 +109,12 @@ public record ForgeRunTemplate(
 
 		// Add MOD_CLASSES, this is something that ForgeGradle does
 		settings.getEnvironmentVariables().computeIfAbsent("MOD_CLASSES", $ -> ConfigValue.of("{source_roots}").resolve(configValueResolver));
+
+		final ForgeProvider forgeProvider = settings.getExtension().getForgeProvider();
+
+		if (settings.getExtension().isForge() && forgeProvider.getVersion().getMajorVersion() >= Constants.Forge.MIN_UNION_RELAUNCHER_VERSION) {
+			settings.defaultMainClass(Constants.Forge.UNION_RELAUNCHER_MAIN_CLASS);
+			settings.property(Constants.Forge.UNION_RELAUNCHER_MAIN_CLASS_PROPERTY, main);
+		}
 	}
 }

src/main/java/net/fabricmc/loom/configuration/providers/forge/mcpconfig/McpConfigData.java

@@ -35,6 +35,7 @@ import com.google.gson.JsonObject;
 /**
  * Data extracted from the MCPConfig JSON file.
  *
+ * @param version      the Minecraft version - the value of the {@code version} property
  * @param data         the value of the {@code data} property
  * @param mappingsPath the path to srg mappings inside the MCP zip
  * @param official     the value of the {@code official} property
@@ -42,6 +43,7 @@ import com.google.gson.JsonObject;
  * @param functions    the MCP function definitions by name
  */
 public record McpConfigData(
+		String version,
 		JsonObject data,
 		String mappingsPath,
 		boolean official,
@@ -49,6 +51,7 @@ public record McpConfigData(
 		Map<String, McpConfigFunction> functions
 ) {
 	public static McpConfigData fromJson(JsonObject json) {
+		String version = json.get("version").getAsString();
 		JsonObject data = json.getAsJsonObject("data");
 		String mappingsPath = data.get("mappings").getAsString();
 		boolean official = json.has("official") && json.getAsJsonPrimitive("official").getAsBoolean();
@@ -73,6 +76,6 @@ public record McpConfigData(
 			functionsBuilder.put(key, McpConfigFunction.fromJson(functionsJson.getAsJsonObject(key)));
 		}
 
-		return new McpConfigData(data, mappingsPath, official, stepsBuilder.build(), functionsBuilder.build());
+		return new McpConfigData(version, data, mappingsPath, official, stepsBuilder.build(), functionsBuilder.build());
 	}
 }

src/main/java/net/fabricmc/loom/configuration/providers/forge/mcpconfig/McpExecutor.java

@@ -55,6 +55,7 @@ import org.jetbrains.annotations.Nullable;
 
 import net.fabricmc.loom.LoomGradleExtension;
 import net.fabricmc.loom.configuration.providers.forge.ConfigValue;
+import net.fabricmc.loom.configuration.providers.forge.ForgeProvider;
 import net.fabricmc.loom.configuration.providers.forge.mcpconfig.steplogic.ConstantLogic;
 import net.fabricmc.loom.configuration.providers.forge.mcpconfig.steplogic.DownloadManifestFileLogic;
 import net.fabricmc.loom.configuration.providers.forge.mcpconfig.steplogic.FunctionLogic;
@@ -69,6 +70,7 @@ import net.fabricmc.loom.util.Constants;
 import net.fabricmc.loom.util.ForgeToolExecutor;
 import net.fabricmc.loom.util.download.DownloadBuilder;
 import net.fabricmc.loom.util.function.CollectionUtil;
+import net.fabricmc.loom.util.gradle.GradleUtils;
 
 public final class McpExecutor {
 	private static final LogLevel STEP_LOG_LEVEL = LogLevel.LIFECYCLE;
@@ -92,9 +94,35 @@ public final class McpExecutor {
 		this.dependencySet.skip(step -> getStepLogic(step.name(), step.type()) instanceof NoOpLogic);
 		this.dependencySet.setIgnoreDependenciesFilter(step -> getStepLogic(step.name(), step.type()).hasNoContext());
 
+		checkMinecraftVersion(provider);
 		addDefaultFiles(provider, environment);
 	}
 
+	private void checkMinecraftVersion(McpConfigProvider provider) {
+		final String expected = provider.getData().version();
+		final String actual = minecraftProvider.minecraftVersion();
+
+		if (!expected.equals(actual)) {
+			final LoomGradleExtension extension = LoomGradleExtension.get(project);
+			final ForgeProvider forgeProvider = extension.getForgeProvider();
+			final String message = "%s %s is not for Minecraft %s (expected: %s)."
+					.formatted(
+							extension.getPlatform().get().displayName(),
+							forgeProvider.getVersion().getCombined(),
+							actual,
+							expected
+					);
+
+			if (GradleUtils.getBooleanProperty(project, Constants.Properties.ALLOW_MISMATCHED_PLATFORM_VERSION)) {
+				project.getLogger().warn(message);
+			} else {
+				final String fullMessage = "%s\nYou can suppress this error by adding '%s = true' to gradle.properties."
+						.formatted(message, Constants.Properties.ALLOW_MISMATCHED_PLATFORM_VERSION);
+				throw new UnsupportedOperationException(fullMessage);
+			}
+		}
+	}
+
 	private void addDefaultFiles(McpConfigProvider provider, String environment) {
 		for (Map.Entry<String, JsonElement> entry : provider.getData().data().entrySet()) {
 			if (entry.getValue().isJsonPrimitive()) {

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

@@ -28,6 +28,8 @@ import org.objectweb.asm.Opcodes;
 
 public class Constants {
 	public static final String PLUGIN_ID = "dev.architectury.loom";
+	public static final boolean PLUGIN_BETA = false;
+	public static final boolean PLUGIN_DEPRECATED = false;
 	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://piston-meta.mojang.com/mc/game/version_manifest_v2.json";
@@ -148,6 +150,7 @@ public class Constants {
 		public static final String DISABLE_REMAPPED_VARIANTS = "fabric.loom.disableRemappedVariants";
 		public static final String DISABLE_PROJECT_DEPENDENT_MODS = "fabric.loom.disableProjectDependentMods";
 		public static final String LIBRARY_PROCESSORS = "fabric.loom.libraryProcessors";
+		public static final String ALLOW_MISMATCHED_PLATFORM_VERSION = "loom.allowMismatchedPlatformVersion";
 	}
 
 	public static final class Manifest {
@@ -175,6 +178,13 @@ public class Constants {
 		public static final String ACCESS_TRANSFORMER_PATH = "META-INF/accesstransformer.cfg";
 		public static final String MIXIN_CONFIGS_MANIFEST_KEY = "MixinConfigs";
 
+		/**
+		 * The minimum Forge version that needs Union Relauncher to use {@code MOD_CLASSES}.
+		 */
+		public static final int MIN_UNION_RELAUNCHER_VERSION = 49;
+		public static final String UNION_RELAUNCHER_MAIN_CLASS = "juuxel.unionrelauncher.UnionRelauncher";
+		public static final String UNION_RELAUNCHER_MAIN_CLASS_PROPERTY = "unionRelauncher.mainClass";
+
 		private Forge() {
 		}
 	}

src/main/java/net/fabricmc/loom/util/aw2at/Aw2At.java

@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2021 FabricMC
+ * Copyright (c) 2021-2023 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
@@ -29,10 +29,10 @@ import java.io.File;
 import java.io.IOException;
 import java.nio.file.Path;
 
-import org.cadixdev.at.AccessChange;
-import org.cadixdev.at.AccessTransform;
-import org.cadixdev.at.AccessTransformSet;
-import org.cadixdev.at.ModifierChange;
+import dev.architectury.at.AccessChange;
+import dev.architectury.at.AccessTransform;
+import dev.architectury.at.AccessTransformSet;
+import dev.architectury.at.ModifierChange;
 import org.cadixdev.bombe.type.signature.MethodSignature;
 import org.gradle.api.Project;
 import org.gradle.api.tasks.SourceSet;

src/main/java/net/fabricmc/loom/util/srg/AtClassRemapper.java

@@ -48,7 +48,7 @@ import net.fabricmc.mappingio.tree.MappingTree;
  *
  * @author Juuz
  */
-public final class AtRemapper {
+public final class AtClassRemapper {
 	public static void remap(Project project, Path jar, MappingTree mappings) throws IOException {
 		final Logger logger = project.getLogger();
 		final String sourceNamespace = IntermediaryNamespaces.intermediary(project);

src/test/groovy/net/fabricmc/loom/test/unit/forge/Aw2AtTest.groovy

@@ -1,7 +1,7 @@
 /*
  * This file is part of fabric-loom, licensed under the MIT License (MIT).
  *
- * Copyright (c) 2022 FabricMC
+ * Copyright (c) 2022-2023 FabricMC
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -24,8 +24,8 @@
 
 package net.fabricmc.loom.test.unit.forge
 
-import org.cadixdev.at.AccessChange
-import org.cadixdev.at.ModifierChange
+import dev.architectury.at.AccessChange
+import dev.architectury.at.ModifierChange
 import spock.lang.Specification
 
 import net.fabricmc.accesswidener.AccessWidenerReader