Force unique module name for libraries

Fixes #2293

Author: Su5eD

transformer/src/main/java/org/sinytra/connector/transformer/jar/JarTransformInstance.java

@@ -136,6 +136,7 @@ public AuditTrail transformJar(File input, Path output, FabricModFileMetadata me
 
     private static void processGeneratedJar(File input, Path output, Stopwatch stopwatch) throws IOException {
         Files.copy(input.toPath(), output);
+        JarSignatureStripper.processJarInPlace(output);
         stopwatch.stop();
         LOGGER.debug(JarTransformer.TRANSFORM_MARKER, "Skipping transformation of jar {} after {} ms as it contains generated metadata, assuming it's a java library", input.getName(), stopwatch.elapsed(TimeUnit.MILLISECONDS));
     }

transformer/src/main/java/org/sinytra/connector/transformer/transform/JarSignatureStripper.java

@@ -1,11 +1,19 @@
 package org.sinytra.connector.transformer.transform;
 
+import com.mojang.logging.LogUtils;
 import net.minecraftforge.fart.api.Transformer;
+import org.slf4j.Logger;
 
 import java.io.*;
+import java.nio.file.FileSystem;
+import java.nio.file.FileSystems;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.jar.Attributes;
 import java.util.jar.Manifest;
 
 public class JarSignatureStripper implements Transformer {
+    private static final Logger LOGGER = LogUtils.getLogger();
 
     @Override
     public ResourceEntry process(ResourceEntry entry) {
@@ -18,12 +26,38 @@ public ManifestEntry process(ManifestEntry entry) {
         Manifest manifest = new Manifest();
         try (InputStream is = new ByteArrayInputStream(entry.getData())) {
             manifest.read(is);
-            manifest.getEntries().clear();
+            processManifest(manifest);
             ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
             manifest.write(byteStream);
             return ManifestEntry.create(entry.getTime(), byteStream.toByteArray());
         } catch (IOException e) {
             throw new UncheckedIOException("Error writing manifest", e);
         }
     }
+
+    // Remove Automatic Module Name from libraries to force giving them a unique module name
+    // and avoid FML silently ignoring those with duplicate names
+    public static void processJarInPlace(Path path) {
+        try(FileSystem fs = FileSystems.newFileSystem(path)) {
+            Path mfPath = fs.getPath("META-INF/MANIFEST.MF");
+            if (!Files.exists(mfPath)) return;
+
+            Manifest manifest = new Manifest();
+            try (InputStream ins = Files.newInputStream(mfPath)) {
+                manifest.read(ins);
+            }
+            processManifest(manifest);
+
+            try (OutputStream os = Files.newOutputStream(mfPath)) {
+                manifest.write(os);
+            }
+        } catch (Exception e) {
+            LOGGER.error("Error stripping jar signature from {}", path, e);
+        }
+    }
+
+    private static void processManifest(Manifest manifest) {
+        manifest.getEntries().clear();
+        manifest.getMainAttributes().remove(new Attributes.Name("Automatic-Module-Name"));
+    }
 }