Support Legacy Forge versions for loom 1.2

build.gradle

@@ -84,6 +84,8 @@ dependencies {
 	implementation ('org.ow2.asm:asm-tree:9.5')
 	implementation ('org.ow2.asm:asm-util:9.5')
 	implementation ('me.tongfei:progressbar:0.9.0')
+	implementation 'com.github.jponge:lzma-java:1.3'
+	runtimeOnly 'dev.architectury.architectury-pack200:dev.architectury.architectury-pack200.gradle.plugin:0.1.3'
 
 	// game handling utils
 	implementation ('net.fabricmc:stitch:0.6.2') {

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

@@ -97,7 +97,7 @@ default List<Path> getMinecraftJars(MappingsNamespace mappingsNamespace) {
 		case INTERMEDIARY -> getIntermediaryMinecraftProvider().getMinecraftJarPaths();
 		case OFFICIAL -> getMinecraftProvider().getMinecraftJars();
 		case SRG -> {
-			ModPlatform.assertPlatform(this, ModPlatform.FORGE, () -> "SRG jars are only available on Forge.");
+			ModPlatform.assertPlatform(this, () -> "SRG jars are only available on Forge.", ModPlatform.FORGE);
 			yield getSrgMinecraftProvider().getMinecraftJarPaths();
 		}
 		};

src/main/java/net/fabricmc/loom/api/ForgeExtensionAPI.java

@@ -26,6 +26,8 @@
 
 import java.util.List;
 
+import net.fabricmc.loom.configuration.providers.forge.fg2.Pack200Provider;
+
 import org.gradle.api.Action;
 import org.gradle.api.file.ConfigurableFileCollection;
 import org.gradle.api.provider.Property;
@@ -134,6 +136,8 @@ default void mixinConfig(String... mixinConfigs) {
 	@Deprecated(forRemoval = true)
 	void dataGen(Action<DataGenConsumer> action);
 
+	Property<Pack200Provider> getPack200Provider();
+
 	/**
 	 * Data generation config.
 	 * @deprecated Removed in favor of configuring the data generator directly.

src/main/java/net/fabricmc/loom/api/LoomGradleExtensionAPI.java

@@ -232,10 +232,21 @@ default void splitMinecraftJar() {
 
 	Provider<ModPlatform> getPlatform();
 
+	/**
+	 * Most legacy forge functions work with this.
+	 */
 	default boolean isForge() {
+		return getPlatform().get() == ModPlatform.FORGE || getPlatform().get() == ModPlatform.LEGACY_FORGE;
+	}
+
+	default boolean isModernForge() {
 		return getPlatform().get() == ModPlatform.FORGE;
 	}
 
+	default boolean isLegacyForge() {
+		return getPlatform().get() == ModPlatform.LEGACY_FORGE;
+	}
+
 	default boolean isQuilt() {
 		return getPlatform().get() == ModPlatform.QUILT;
 	}

src/main/java/net/fabricmc/loom/configuration/CompileConfiguration.java

@@ -204,10 +204,12 @@ private synchronized void setupMinecraft(ConfigContext configContext) throws Exc
 
 		if (extension.isForge()) {
 			ForgeLibrariesProvider.provide(mappingConfiguration, project);
+			if (extension.isLegacyForge()) ((ForgeMinecraftProvider) minecraftProvider).getPatchedProvider().setMappingConfiguration(mappingConfiguration);
 			((ForgeMinecraftProvider) minecraftProvider).getPatchedProvider().provide();
 		}
 
-		mappingConfiguration.setupPost(project);
+		if (!extension.isLegacyForge())
+			mappingConfiguration.setupPost(project);
 		mappingConfiguration.applyToProject(getProject(), mappingsDep);
 
 		if (extension.isForge()) {
@@ -363,9 +365,9 @@ public static void setupDependencyProviders(Project project, LoomGradleExtension
 		}
 
 		if (extension.isForge()) {
+			dependencyProviders.addProvider(new ForgeUniversalProvider(project));
 			dependencyProviders.addProvider(new McpConfigProvider(project));
 			dependencyProviders.addProvider(new PatchProvider(project));
-			dependencyProviders.addProvider(new ForgeUniversalProvider(project));
 		}
 
 		dependencyProviders.handleDependencies(project);

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

@@ -168,6 +168,7 @@ public static void executeAt(Project project, Path input, Path output, AccessTra
 		args.add(output.toAbsolutePath().toString());
 
 		configuration.apply(args);
+		project.getLogger().info(args.toString());
 
 		ForgeToolExecutor.exec(project, spec -> {
 			spec.getMainClass().set("net.minecraftforge.accesstransformer.TransformerProcessor");

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

@@ -310,7 +310,7 @@ public void environmentVariable(String name, Object value) {
 	 * Add the {@code -XstartOnFirstThread} JVM argument when on OSX.
 	 */
 	public void startFirstThread() {
-		if (Platform.CURRENT.getOperatingSystem().isMacOS()) {
+		if (Platform.CURRENT.getOperatingSystem().isMacOS() && !extension.isLegacyForge()) {
 			vmArg("-XstartOnFirstThread");
 		}
 	}
@@ -355,7 +355,7 @@ public void server() {
 	 * <p>This method can only be used on Forge.
 	 */
 	public void data() {
-		ModPlatform.assertPlatform(getExtension(), ModPlatform.FORGE, () -> "RunConfigSettings.data() is only usable on Forge.");
+		ModPlatform.assertPlatform(getExtension(), () -> "RunConfigSettings.data() is only usable on Forge.", ModPlatform.FORGE);
 		environment("data");
 		forgeTemplate("data");
 	}
@@ -370,7 +370,7 @@ public void data() {
 	 * @since 1.0
 	 */
 	public void forgeTemplate(String templateName) {
-		ModPlatform.assertPlatform(getExtension(), ModPlatform.FORGE);
+		ModPlatform.assertPlatform(getExtension(), ModPlatform.FORGE, ModPlatform.LEGACY_FORGE);
 		defaultMainClass(Constants.Forge.UNDETERMINED_MAIN_CLASS);
 		// Evaluate later if Forge hasn't been resolved yet.
 		evaluateNowOrLater(() -> {

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

@@ -113,7 +113,7 @@ protected void manipulateMappings(Project project, Path mappingsJar) throws IOEx
 		if (extension.shouldGenerateSrgTiny()) {
 			if (Files.notExists(rawTinyMappingsWithSrg) || extension.refreshDeps()) {
 				// Merge tiny mappings with srg
-				SrgMerger.ExtraMappings extraMappings = SrgMerger.ExtraMappings.ofMojmapTsrg(getMojmapSrgFileIfPossible(project));
+				SrgMerger.ExtraMappings extraMappings = extension.isLegacyForge() ? null : SrgMerger.ExtraMappings.ofMojmapTsrg(getMojmapSrgFileIfPossible(project));
 				SrgMerger.mergeSrg(getRawSrgFile(project), rawTinyMappings, rawTinyMappingsWithSrg, extraMappings, true);
 			}
 		}

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

@@ -63,6 +63,9 @@ public static void provide(MappingConfiguration mappingConfiguration, Project pr
 
 		// Collect all dependencies with possible relocations, such as Mixin.
 		for (JsonElement lib : extension.getForgeUserdevProvider().getJson().get("libraries").getAsJsonArray()) {
+			if (extension.isLegacyForge()) {
+				lib = lib.getAsJsonObject().get("name");
+			}
 			String dep = null;
 
 			if (lib.getAsString().startsWith("org.spongepowered:mixin:")) {

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

@@ -64,12 +64,28 @@ public ForgeRunsProvider(Project project, JsonObject json) {
 	}
 
 	private void readTemplates() {
-		for (Map.Entry<String, JsonElement> entry : json.getAsJsonObject("runs").entrySet()) {
+		if (!extension.isLegacyForge()) {
+			configureRuns(json.getAsJsonObject("runs"));
+		} else {
+			configureRunsForLegacyForge();
+		}
+	}
+
+	private void configureRuns(JsonObject runs) {
+		for (Map.Entry<String, JsonElement> entry : runs.entrySet()) {
 			ForgeRunTemplate template = ForgeRunTemplate.fromJson(entry.getValue().getAsJsonObject());
 			templates.add(template);
 		}
 	}
 
+	private void configureRunsForLegacyForge() {
+		extension.getRunConfigs().configureEach(config -> {
+			//	if (Constants.Forge.LAUNCH_TESTING.equals(config.getDefaultMainClass())) {
+			config.setDefaultMainClass(Constants.LegacyForge.LAUNCH_WRAPPER);
+			//	}
+		});
+	}
+
 	public NamedDomainObjectSet<ForgeRunTemplate> getTemplates() {
 		return templates;
 	}

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

@@ -25,11 +25,13 @@
 package net.fabricmc.loom.configuration.providers.forge;
 
 import java.io.File;
+import java.io.IOException;
 import java.io.Reader;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
 import java.util.List;
+import java.util.Map;
 
 import com.google.gson.Gson;
 import com.google.gson.JsonObject;
@@ -40,11 +42,14 @@
 import net.fabricmc.loom.util.Constants;
 import net.fabricmc.loom.util.ZipUtils;
 
+import org.gradle.api.artifacts.repositories.IvyArtifactRepository;
+
 public class ForgeUserdevProvider extends DependencyProvider {
 	private File userdevJar;
 	private JsonObject json;
 	Path joinedPatches;
 	BinaryPatcherConfig binaryPatcherConfig;
+	private boolean isLegacyForge;
 
 	public ForgeUserdevProvider(Project project) {
 		super(project);
@@ -59,22 +64,80 @@ public void provide(DependencyInfo dependency) throws Exception {
 		if (!userdevJar.exists() || Files.notExists(configJson) || refreshDeps()) {
 			File resolved = dependency.resolveFile().orElseThrow(() -> new RuntimeException("Could not resolve Forge userdev"));
 			Files.copy(resolved.toPath(), userdevJar.toPath(), StandardCopyOption.REPLACE_EXISTING);
-			Files.write(configJson, ZipUtils.unpack(resolved.toPath(), "config.json"));
+			try {
+				Files.write(configJson, ZipUtils.unpack(resolved.toPath(), "config.json"));
+			} catch (IOException e) {
+				Files.write(configJson, ZipUtils.unpack(resolved.toPath(), "dev.json"));
+			}
 		}
 
 		try (Reader reader = Files.newBufferedReader(configJson)) {
 			json = new Gson().fromJson(reader, JsonObject.class);
 		}
 
-		addDependency(json.get("mcp").getAsString(), Constants.Configurations.MCP_CONFIG);
-		addDependency(json.get("mcp").getAsString(), Constants.Configurations.SRG);
-		addDependency(json.get("universal").getAsString(), Constants.Configurations.FORGE_UNIVERSAL);
-
-		if (Files.notExists(joinedPatches)) {
-			Files.write(joinedPatches, ZipUtils.unpack(userdevJar.toPath(), json.get("binpatches").getAsString()));
+		isLegacyForge = !json.has("mcp");
+
+		if (!isLegacyForge) {
+			addDependency(json.get("mcp").getAsString(), Constants.Configurations.MCP_CONFIG);
+			addDependency(json.get("mcp").getAsString(), Constants.Configurations.SRG);
+			addDependency(json.get("universal").getAsString(), Constants.Configurations.FORGE_UNIVERSAL);
+
+			binaryPatcherConfig = BinaryPatcherConfig.fromJson(json.getAsJsonObject("binpatcher"));
+
+			if (Files.notExists(joinedPatches)) {
+				Files.write(joinedPatches, ZipUtils.unpack(userdevJar.toPath(), json.get("binpatches").getAsString()));
+			}
+		} else {
+			Map<String, String> mcpDep = Map.of(
+					"group", "de.oceanlabs.mcp",
+					"name", "mcp",
+					"version", json.get("inheritsFrom").getAsString(),
+					"classifier", "srg",
+					"ext", "zip"
+			);
+			addDependency(mcpDep, Constants.Configurations.MCP_CONFIG);
+			addDependency(mcpDep, Constants.Configurations.SRG);
+			addDependency(dependency.getDepString() + ":universal", Constants.Configurations.FORGE_UNIVERSAL);
+			addLegacyMCPRepo();
+
+			binaryPatcherConfig = BinaryPatcherConfig.fromJson(new Gson().fromJson("""
+					{
+					  "version": "net.minecraftforge:binarypatcher:1.0.12:fatjar",
+					  "args": [
+					    "--clean",
+					    "{clean}",
+					    "--output",
+					    "{output}",
+					    "--apply",
+					    "{patch}"
+					  ]
+					}""", JsonObject.class));
+
+			if (Files.notExists(joinedPatches)) {
+				Files.write(joinedPatches, ZipUtils.unpack(userdevJar.toPath(), "devbinpatches.pack.lzma"));
+			}
 		}
+	}
+
+	private void addLegacyMCPRepo() {
+		getProject().getRepositories().ivy(repo -> {
+			// Old MCP data does not have POMs
+			repo.setName("LegacyMCP");
+			repo.setUrl("https://maven.minecraftforge.net/");
+			repo.patternLayout(layout -> {
+				layout.artifact("[orgPath]/[artifact]/[revision]/[artifact]-[revision](-[classifier])(.[ext])");
+				// also check the zip so people do not have to explicitly specify the extension for older versions
+				layout.artifact("[orgPath]/[artifact]/[revision]/[artifact]-[revision](-[classifier]).zip");
+			});
+			repo.content(descriptor -> {
+				descriptor.includeGroup("de.oceanlabs.mcp");
+			});
+			repo.metadataSources(IvyArtifactRepository.MetadataSources::artifact);
+		});
+	}
 
-		binaryPatcherConfig = BinaryPatcherConfig.fromJson(json.getAsJsonObject("binpatcher"));
+	public boolean isLegacyForge() {
+		return isLegacyForge;
 	}
 
 	public File getUserdevJar() {