Make legacy Forge discover and load coremods from the classpath

2 files changed, 253 insertions, 0 deletions

diff --git a/src/main/java/net/fabricmc/loom/configuration/providers/forge/fg2/MinecraftLegacyPatchedProvider.java b/src/main/java/net/fabricmc/loom/configuration/providers/forge/fg2/MinecraftLegacyPatchedProvider.java
index 3e931862..49dd48f0 100644
--- a/src/main/java/net/fabricmc/loom/configuration/providers/forge/fg2/MinecraftLegacyPatchedProvider.java
+++ b/src/main/java/net/fabricmc/loom/configuration/providers/forge/fg2/MinecraftLegacyPatchedProvider.java
@@ -64,9 +64,11 @@ import net.fabricmc.loom.configuration.providers.MinecraftProviderImpl;
 import net.fabricmc.loom.configuration.providers.forge.MinecraftPatchedProvider;
 import net.fabricmc.loom.configuration.providers.forge.PatchProvider;
 import net.fabricmc.loom.util.FileSystemUtil;
+import net.fabricmc.loom.util.Pair;
 import net.fabricmc.loom.util.ThreadingUtils;
 import net.fabricmc.loom.util.TinyRemapperHelper;
 import net.fabricmc.loom.util.ZipUtils;
+import net.fabricmc.loom.util.legacyforge.CoreModManagerTransformer;
 import net.fabricmc.loom.util.srg.AccessTransformSetMapper;
 import net.fabricmc.lorenztiny.TinyMappingsReader;
 import net.fabricmc.mappingio.tree.MappingTree;
@@ -186,6 +188,19 @@ public class MinecraftLegacyPatchedProvider extends MinecraftPatchedProvider {
 			walkFileSystems(log4jBeta9.toFile(), forgeJar, isHelper, this::copyReplacing);
 		}
 
+		// While Forge will discover mods on the classpath, it won't do the same for ATs, coremods or tweakers.
+		// ForgeGradle "solves" this problem using a huge, gross hack (GradleForgeHacks and related classes), and only
+		// for ATs and coremods, not tweakers.
+		// No clue why FG went the hack route when it's the same project and they could have just added first-party
+		// support for loading both from the classpath right into Forge (it's even really simply to do).
+		// We'll have none of those hacks and instead patch first-party support into Forge.
+		ZipUtils.transform(forgeJar.toPath(), Stream.of(new Pair<>(CoreModManagerTransformer.FILE, original -> {
+			ClassReader reader = new ClassReader(original);
+			ClassWriter writer = new ClassWriter(reader, 0);
+			reader.accept(new CoreModManagerTransformer(writer), 0);
+			return writer.toByteArray();
+		})));
+
 		logger.lifecycle(":patched forge in " + stopwatch.stop());
 	}
 
diff --git a/src/main/java/net/fabricmc/loom/util/legacyforge/CoreModManagerTransformer.java b/src/main/java/net/fabricmc/loom/util/legacyforge/CoreModManagerTransformer.java
new file mode 100644
index 00000000..e3ee932a
--- /dev/null
+++ b/src/main/java/net/fabricmc/loom/util/legacyforge/CoreModManagerTransformer.java
@@ -0,0 +1,238 @@
+package net.fabricmc.loom.util.legacyforge;
+
+import static org.objectweb.asm.Opcodes.ACC_PRIVATE;
+import static org.objectweb.asm.Opcodes.ACC_STATIC;
+import static org.objectweb.asm.Opcodes.ALOAD;
+import static org.objectweb.asm.Opcodes.ASTORE;
+import static org.objectweb.asm.Opcodes.BIPUSH;
+import static org.objectweb.asm.Opcodes.CHECKCAST;
+import static org.objectweb.asm.Opcodes.DUP;
+import static org.objectweb.asm.Opcodes.GOTO;
+import static org.objectweb.asm.Opcodes.ICONST_0;
+import static org.objectweb.asm.Opcodes.IFEQ;
+import static org.objectweb.asm.Opcodes.IFNONNULL;
+import static org.objectweb.asm.Opcodes.INVOKEINTERFACE;
+import static org.objectweb.asm.Opcodes.INVOKESPECIAL;
+import static org.objectweb.asm.Opcodes.INVOKESTATIC;
+import static org.objectweb.asm.Opcodes.INVOKEVIRTUAL;
+import static org.objectweb.asm.Opcodes.NEW;
+import static org.objectweb.asm.Opcodes.POP;
+import static org.objectweb.asm.Opcodes.RETURN;
+
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.Label;
+import org.objectweb.asm.MethodVisitor;
+import org.objectweb.asm.Opcodes;
+
+/**
+ * Transforms Forge's CoreModManager class to search the classpath for coremods.
+ * For motivation, see comments at usage site.
+ */
+public class CoreModManagerTransformer extends ClassVisitor {
+	private static final String CLASS = "net/minecraftforge/fml/relauncher/CoreModManager";
+	public static final String FILE = CLASS + ".class";
+
+	private static final String TARGET_METHOD = "discoverCoreMods";
+	private static final String OUR_METHOD_NAME = "loom$injectCoremodsFromClasspath";
+	private static final String OUR_METHOD_DESCRIPTOR = "(Lnet/minecraft/launchwrapper/LaunchClassLoader;)V";
+
+	public CoreModManagerTransformer(ClassVisitor classVisitor) {
+		super(Opcodes.ASM9, classVisitor);
+	}
+
+	@Override
+	public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
+		MethodVisitor methodVisitor = super.visitMethod(access, name, descriptor, signature, exceptions);
+
+		// We inject a call to our method, which will discover and load coremods from the classpath, at the very start of the
+		// regular discovery method.
+		if (name.equals(TARGET_METHOD)) {
+			methodVisitor = new InjectCallAtHead(methodVisitor);
+		}
+
+		return methodVisitor;
+	}
+
+	@Override
+	public void visitEnd() {
+		// We add the following method, which will find all coremods on the classpath, and load them.
+		//
+		//     private static void loom$injectCoremodsFromClasspath(LaunchClassLoader classLoader) throws Exception {
+		//         Enumeration<URL> urls = classLoader.getResources("META-INF/MANIFEST.MF");
+		//         while (urls.hasMoreElements()) {
+		//             URL url = urls.nextElement();
+		//             InputStream stream = url.openStream();
+		//             Manifest manifest = new Manifest(stream);
+		//             stream.close();
+		//             String coreModClass = manifest.getMainAttributes().getValue("FMLCorePlugin");
+		//             if (coreModClass == null) continue;
+		//             File file;
+		//             if ("jar".equals(url.getProtocol())) {
+		//                 file = new File(new URL(url.getPath()).toURI());
+		//             } else if ("file".equals(url.getProtocol())) {
+		//                 file = new File(url.toURI()).getParentFile().getParentFile();
+		//             } else {
+		//                 continue;
+		//             }
+		//             loadCoreMod(classLoader, coreModClass, file);
+		//         }
+		//     }
+		//
+		// Converted to ASM via the "ASM Bytecode Viewer" IntelliJ plugin:
+		{
+			MethodVisitor methodVisitor = super.visitMethod(ACC_PRIVATE | ACC_STATIC, OUR_METHOD_NAME, OUR_METHOD_DESCRIPTOR, null, null);
+			methodVisitor.visitCode();
+			Label label0 = new Label();
+			methodVisitor.visitLabel(label0);
+			methodVisitor.visitLineNumber(25, label0);
+			methodVisitor.visitVarInsn(ALOAD, 0);
+			methodVisitor.visitLdcInsn("META-INF/MANIFEST.MF");
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "net/minecraft/launchwrapper/LaunchClassLoader", "getResources", "(Ljava/lang/String;)Ljava/util/Enumeration;", false);
+			methodVisitor.visitVarInsn(ASTORE, 1);
+			Label label1 = new Label();
+			methodVisitor.visitLabel(label1);
+			methodVisitor.visitLineNumber(26, label1);
+			methodVisitor.visitFrame(Opcodes.F_APPEND, 1, new Object[]{"java/util/Enumeration"}, 0, null);
+			methodVisitor.visitVarInsn(ALOAD, 1);
+			methodVisitor.visitMethodInsn(INVOKEINTERFACE, "java/util/Enumeration", "hasMoreElements", "()Z", true);
+			Label label2 = new Label();
+			methodVisitor.visitJumpInsn(IFEQ, label2);
+			Label label3 = new Label();
+			methodVisitor.visitLabel(label3);
+			methodVisitor.visitLineNumber(27, label3);
+			methodVisitor.visitVarInsn(ALOAD, 1);
+			methodVisitor.visitMethodInsn(INVOKEINTERFACE, "java/util/Enumeration", "nextElement", "()Ljava/lang/Object;", true);
+			methodVisitor.visitTypeInsn(CHECKCAST, "java/net/URL");
+			methodVisitor.visitVarInsn(ASTORE, 2);
+			Label label4 = new Label();
+			methodVisitor.visitLabel(label4);
+			methodVisitor.visitLineNumber(28, label4);
+			methodVisitor.visitVarInsn(ALOAD, 2);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/net/URL", "openStream", "()Ljava/io/InputStream;", false);
+			methodVisitor.visitVarInsn(ASTORE, 3);
+			Label label5 = new Label();
+			methodVisitor.visitLabel(label5);
+			methodVisitor.visitLineNumber(29, label5);
+			methodVisitor.visitTypeInsn(NEW, "java/util/jar/Manifest");
+			methodVisitor.visitInsn(DUP);
+			methodVisitor.visitVarInsn(ALOAD, 3);
+			methodVisitor.visitMethodInsn(INVOKESPECIAL, "java/util/jar/Manifest", "<init>", "(Ljava/io/InputStream;)V", false);
+			methodVisitor.visitVarInsn(ASTORE, 4);
+			Label label6 = new Label();
+			methodVisitor.visitLabel(label6);
+			methodVisitor.visitLineNumber(30, label6);
+			methodVisitor.visitVarInsn(ALOAD, 3);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/io/InputStream", "close", "()V", false);
+			Label label7 = new Label();
+			methodVisitor.visitLabel(label7);
+			methodVisitor.visitLineNumber(31, label7);
+			methodVisitor.visitVarInsn(ALOAD, 4);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/util/jar/Manifest", "getMainAttributes", "()Ljava/util/jar/Attributes;", false);
+			methodVisitor.visitLdcInsn("FMLCorePlugin");
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/util/jar/Attributes", "getValue", "(Ljava/lang/String;)Ljava/lang/String;", false);
+			methodVisitor.visitVarInsn(ASTORE, 5);
+			Label label8 = new Label();
+			methodVisitor.visitLabel(label8);
+			methodVisitor.visitLineNumber(32, label8);
+			methodVisitor.visitVarInsn(ALOAD, 5);
+			Label label9 = new Label();
+			methodVisitor.visitJumpInsn(IFNONNULL, label9);
+			methodVisitor.visitJumpInsn(GOTO, label1);
+			methodVisitor.visitLabel(label9);
+			methodVisitor.visitLineNumber(34, label9);
+			methodVisitor.visitFrame(Opcodes.F_FULL, 6, new Object[]{"net/minecraft/launchwrapper/LaunchClassLoader", "java/util/Enumeration", "java/net/URL", "java/io/InputStream", "java/util/jar/Manifest", "java/lang/String"}, 0, new Object[]{});
+			methodVisitor.visitLdcInsn("jar");
+			methodVisitor.visitVarInsn(ALOAD, 2);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/net/URL", "getProtocol", "()Ljava/lang/String;", false);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/lang/String", "equals", "(Ljava/lang/Object;)Z", false);
+			Label label10 = new Label();
+			methodVisitor.visitJumpInsn(IFEQ, label10);
+			Label label11 = new Label();
+			methodVisitor.visitLabel(label11);
+			methodVisitor.visitLineNumber(35, label11);
+			methodVisitor.visitTypeInsn(NEW, "java/io/File");
+			methodVisitor.visitInsn(DUP);
+			methodVisitor.visitTypeInsn(NEW, "java/net/URL");
+			methodVisitor.visitInsn(DUP);
+			methodVisitor.visitVarInsn(ALOAD, 2);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/net/URL", "getPath", "()Ljava/lang/String;", false);
+			methodVisitor.visitInsn(ICONST_0);
+			methodVisitor.visitVarInsn(ALOAD, 2);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/net/URL", "getPath", "()Ljava/lang/String;", false);
+			methodVisitor.visitIntInsn(BIPUSH, 33);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/lang/String", "lastIndexOf", "(I)I", false);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/lang/String", "substring", "(II)Ljava/lang/String;", false);
+			methodVisitor.visitMethodInsn(INVOKESPECIAL, "java/net/URL", "<init>", "(Ljava/lang/String;)V", false);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/net/URL", "toURI", "()Ljava/net/URI;", false);
+			methodVisitor.visitMethodInsn(INVOKESPECIAL, "java/io/File", "<init>", "(Ljava/net/URI;)V", false);
+			methodVisitor.visitVarInsn(ASTORE, 6);
+			Label label12 = new Label();
+			methodVisitor.visitLabel(label12);
+			Label label13 = new Label();
+			methodVisitor.visitJumpInsn(GOTO, label13);
+			methodVisitor.visitLabel(label10);
+			methodVisitor.visitLineNumber(36, label10);
+			methodVisitor.visitFrame(Opcodes.F_SAME, 0, null, 0, null);
+			methodVisitor.visitLdcInsn("file");
+			methodVisitor.visitVarInsn(ALOAD, 2);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/net/URL", "getProtocol", "()Ljava/lang/String;", false);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/lang/String", "equals", "(Ljava/lang/Object;)Z", false);
+			methodVisitor.visitJumpInsn(IFEQ, label1);
+			Label label14 = new Label();
+			methodVisitor.visitLabel(label14);
+			methodVisitor.visitLineNumber(37, label14);
+			methodVisitor.visitTypeInsn(NEW, "java/io/File");
+			methodVisitor.visitInsn(DUP);
+			methodVisitor.visitVarInsn(ALOAD, 2);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/net/URL", "toURI", "()Ljava/net/URI;", false);
+			methodVisitor.visitMethodInsn(INVOKESPECIAL, "java/io/File", "<init>", "(Ljava/net/URI;)V", false);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/io/File", "getParentFile", "()Ljava/io/File;", false);
+			methodVisitor.visitMethodInsn(INVOKEVIRTUAL, "java/io/File", "getParentFile", "()Ljava/io/File;", false);
+			methodVisitor.visitVarInsn(ASTORE, 6);
+			methodVisitor.visitLabel(label13);
+			methodVisitor.visitLineNumber(41, label13);
+			methodVisitor.visitFrame(Opcodes.F_APPEND, 1, new Object[]{"java/io/File"}, 0, null);
+			methodVisitor.visitVarInsn(ALOAD, 0);
+			methodVisitor.visitVarInsn(ALOAD, 5);
+			methodVisitor.visitVarInsn(ALOAD, 6);
+			methodVisitor.visitMethodInsn(INVOKESTATIC, "net/minecraftforge/fml/relauncher/CoreModManager", "loadCoreMod", "(Lnet/minecraft/launchwrapper/LaunchClassLoader;Ljava/lang/String;Ljava/io/File;)Lnet/minecraftforge/fml/relauncher/CoreModManager$FMLPluginWrapper;", false);
+			methodVisitor.visitInsn(POP);
+			Label label15 = new Label();
+			methodVisitor.visitLabel(label15);
+			methodVisitor.visitLineNumber(42, label15);
+			methodVisitor.visitJumpInsn(GOTO, label1);
+			methodVisitor.visitLabel(label2);
+			methodVisitor.visitLineNumber(43, label2);
+			methodVisitor.visitFrame(Opcodes.F_FULL, 2, new Object[]{"net/minecraft/launchwrapper/LaunchClassLoader", "java/util/Enumeration"}, 0, new Object[]{});
+			methodVisitor.visitInsn(RETURN);
+			Label label16 = new Label();
+			methodVisitor.visitLabel(label16);
+			methodVisitor.visitLocalVariable("file", "Ljava/io/File;", null, label12, label10, 6);
+			methodVisitor.visitLocalVariable("url", "Ljava/net/URL;", null, label4, label15, 2);
+			methodVisitor.visitLocalVariable("stream", "Ljava/io/InputStream;", null, label5, label15, 3);
+			methodVisitor.visitLocalVariable("manifest", "Ljava/util/jar/Manifest;", null, label6, label15, 4);
+			methodVisitor.visitLocalVariable("coreModClass", "Ljava/lang/String;", null, label8, label15, 5);
+			methodVisitor.visitLocalVariable("file", "Ljava/io/File;", null, label13, label15, 6);
+			methodVisitor.visitLocalVariable("classLoader", "Lnet/minecraft/launchwrapper/LaunchClassLoader;", null, label0, label16, 0);
+			methodVisitor.visitLocalVariable("urls", "Ljava/util/Enumeration;", "Ljava/util/Enumeration<Ljava/net/URL;>;", label1, label16, 1);
+			methodVisitor.visitMaxs(8, 7);
+			methodVisitor.visitEnd();
+		}
+
+		super.visitEnd();
+	}
+
+	private static class InjectCallAtHead extends MethodVisitor {
+		private InjectCallAtHead(MethodVisitor methodVisitor) {
+			super(Opcodes.ASM9, methodVisitor);
+		}
+
+		@Override
+		public void visitCode() {
+			super.visitCode();
+
+			super.visitVarInsn(Opcodes.ALOAD, 1);
+			super.visitMethodInsn(Opcodes.INVOKESTATIC, CLASS, OUR_METHOD_NAME, OUR_METHOD_DESCRIPTOR, false);
+		}
+	}
+}