stage2/ml9: Fix crash with SinytraConnector

The "Sinytra Connector" mod uses a custom `SecureJar` implementation,
which prior to this commit resulted in us doing an out of bounds memory
read (returning what looks like a String, resulting in a class cast
exception) because we were using the same unsafe getter that we were
using for ML's `Jar` implementation.

This commit fixes the issue by using a separate getter for each
implementation class.
This change alone is sufficient to fix the issue because we'll then get
an explicit `NoSuchFieldException`, which we catch. However, to avoid
unnessecary log spam, this commit additionally special cases the dummy
class to silently return `null`. It also changes our `getVersion` method
to still try the fallback paths (which do work!) instead of returning
early on `null` since that is now a legitimate case.

GitHub: #25

Author: Johni0702

stage2/modlauncher9/src/main/java/gg/essential/loader/stage2/util/SortedJarOrPathList.java

@@ -14,6 +14,7 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Comparator;
+import java.util.HashMap;
 import java.util.IdentityHashMap;
 import java.util.List;
 import java.util.Map;
@@ -30,7 +31,7 @@ public class SortedJarOrPathList extends ArrayList<Object> {
     private static final Logger LOGGER = LogManager.getLogger();
     private static final ArtifactVersion FALLBACK_VERSION = new DefaultArtifactVersion("1");
     private static Function<Object, SecureJar> jarGetter;
-    private Function<SecureJar, JarMetadata> metadataGetter;
+    private final Map<Class<?>, Function<SecureJar, JarMetadata>> metadataGetters = new HashMap<>();
     private BiFunction<NamedPath, SecureJar, Object> pathOrJarConstructor;
 
     private final Map<Object, ArtifactVersion> versionCache = new IdentityHashMap<>();
@@ -53,9 +54,13 @@ public SortedJarOrPathList(CompatibilityLayer compatibilityLayer, Function<Secur
     private ArtifactVersion getVersion(Object pathOrJar) {
         SecureJar jar = getJar(pathOrJar);
         if (jar == null) return FALLBACK_VERSION;
+
+        String version = null;
+
         JarMetadata metadata = getMetadata(jar);
-        if (metadata == null) return FALLBACK_VERSION;
-        String version = metadata.version();
+        if (metadata != null) {
+            version = metadata.version();
+        }
 
         // Some revisions of ModLauncher have a bug where they simply call `toString` on `Optional<String>`, resulting
         // in versions being reported as the string "Optional.empty" or "Optional[1.2.3]" instead of `null` or "1.2.3".
@@ -119,13 +124,24 @@ public static SecureJar getJar(Object pathOrJar) {
     }
 
     private JarMetadata getMetadata(SecureJar jar) {
+        Class<? extends SecureJar> implClass = jar.getClass();
+        Function<SecureJar, JarMetadata> metadataGetter = metadataGetters.get(implClass);
         if (metadataGetter == null) {
             try {
-                metadataGetter = UnsafeHacks.makeGetter(jar.getClass().getDeclaredField("metadata"));
+                String implName = implClass.getName();
+                switch (implName) {
+                    case "org.sinytra.connector.service.DummyVirtualJar":
+                        // Used for the dummy fabric-loader mod as well as for code generated by ManninghamMills
+                        metadataGetter = __ -> null;
+                        break;
+                    default: // probably the main ModLauncher-internal impl
+                        metadataGetter = UnsafeHacks.makeGetter(implClass.getDeclaredField("metadata"));
+                }
             } catch (Throwable t) {
-                LOGGER.error("Failed to get metadata from " + jar.getClass() + ":", t);
+                LOGGER.error("Failed to get metadata from " + implClass + ":", t);
                 metadataGetter = __ -> null;
             }
+            metadataGetters.put(implClass, metadataGetter);
         }
         return metadataGetter.apply(jar);
     }