stage2/lw: Fix crash when Minecraft and temp files are on separate drives

The way we used to pass extra jars which may contain mods to Forge, via
its `--mods` argument, only accepts relative paths, and on Windows it is
impossible to construct a relative path when the two paths are on
different drive letters.

This commit now instead uses our existing RelaunchTransformer to modify
the code in Forge which parses the `--mods` argument, to manually inject
the absolute paths to any such extra mods right after the regular
`--mods` parsing.

GitHub: #34

Author: Johni0702

stage2/launchwrapper/src/main/java/gg/essential/loader/stage2/Loader.java

@@ -117,10 +117,16 @@ private void relaunchViaNewerLoader(Path loaderJar) {
     }
 
     private void relaunch(List<JarInfo> jars) {
+        List<URL> loadedByForge = Launch.classLoader.getSources();
+
         RelaunchInfo relaunchInfo = new RelaunchInfo();
         relaunchInfo.loadedIds = jars.stream()
             .map(it -> it.id)
             .collect(Collectors.toSet());
+        relaunchInfo.extraMods = jars.stream()
+            .filter(it -> !loadedByForge.contains(it.url()))
+            .map(it -> it.path.toAbsolutePath().toString())
+            .collect(Collectors.toList());
         RelaunchInfo.put(relaunchInfo);
 
         Set<URL> priorityClassPath = new LinkedHashSet<>();
@@ -132,23 +138,7 @@ private void relaunch(List<JarInfo> jars) {
             priorityClassPath.add(jarInfo.url());
         }
 
-        List<URL> loadedByForge = Launch.classLoader.getSources();
-        String extraMods = jars.stream()
-            .filter(it -> !loadedByForge.contains(it.url()))
-            .map(it -> minecraftHome.relativize(it.path).toString())
-            .collect(Collectors.joining(","));
-
-        Consumer<List<String>> modifyArgsForExtraMods = extraMods.isEmpty() ? arg -> {} : args -> {
-            int index = args.indexOf("--mods");
-            if (index == -1) {
-                args.add("--mods");
-                args.add(extraMods);
-            } else {
-                args.set(index + 1, extraMods + "," + args.get(index + 1));
-            }
-        };
-
-        Relaunch.relaunch(priorityClassPath, modifyArgsForExtraMods);
+        Relaunch.relaunch(priorityClassPath);
         throw new AssertionError("relaunch should not return");
     }
 

stage2/launchwrapper/src/main/java/gg/essential/loader/stage2/RelaunchInfo.java

@@ -2,10 +2,12 @@
 
 import com.google.gson.Gson;
 
+import java.util.List;
 import java.util.Set;
 
 class RelaunchInfo {
     public Set<String> loadedIds;
+    public List<String> extraMods;
 
     private static String PROPERTY = "gg.essential.loader.stage2.relaunch-info";
 

stage2/launchwrapper/src/main/java/gg/essential/loader/stage2/RelaunchedLoader.java

@@ -24,6 +24,7 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Map;
 import java.util.jar.Attributes;
 import java.util.jar.JarFile;
 
@@ -188,6 +189,24 @@ private static void addMixinTransformerExclusionImpl(String name) {
         }
     }
 
+    @SuppressWarnings("unused") // called via ASM, see RelaunchTransformer
+    public static void injectExtraMods(Map<String, File> forgeExtraModsMap) {
+        RelaunchInfo relaunchInfo = RelaunchInfo.get();
+        assert(relaunchInfo != null);
+        for (String extraMod : relaunchInfo.extraMods) {
+            forgeExtraModsMap.put(extraMod, new File(extraMod));
+        }
+    }
+
+    @SuppressWarnings("unused") // called via ASM, see RelaunchTransformer
+    public static void injectExtraMods(List<File> forgeExtraModsList) {
+        RelaunchInfo relaunchInfo = RelaunchInfo.get();
+        assert(relaunchInfo != null);
+        for (String extraMod : relaunchInfo.extraMods) {
+            forgeExtraModsList.add(new File(extraMod));
+        }
+    }
+
     private static class SourceFile {
         final File file;
         final String tweaker;

stage2/launchwrapper/src/main/java/gg/essential/loader/stage2/relaunch/Relaunch.java

@@ -20,7 +20,6 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
-import java.util.function.Consumer;
 import java.util.jar.JarFile;
 import java.util.jar.Manifest;
 
@@ -32,7 +31,7 @@ public class Relaunch {
 
     private static final String HAPPENED_PROPERTY = "essential.loader.relaunched";
 
-    public static void relaunch(Set<URL> prioritizedUrls, Consumer<List<String>> modifyArgs) {
+    public static void relaunch(Set<URL> prioritizedUrls) {
         LOGGER.warn("");
         LOGGER.warn("");
         LOGGER.warn("");
@@ -79,7 +78,6 @@ public static void relaunch(Set<URL> prioritizedUrls, Consumer<List<String>> mod
             Launch.blackboard.put("gg.essential.loader.stage2.relaunchClassLoader", relaunchClassLoader);
 
             List<String> args = new ArrayList<>(LaunchArgs.guessLaunchArgs());
-            modifyArgs.accept(args);
             String main = args.remove(0);
 
             Class<?> innerLaunch = Class.forName(main, false, relaunchClassLoader);

stage2/launchwrapper/src/main/java/gg/essential/loader/stage2/relaunch/RelaunchTransformer.java

@@ -5,6 +5,7 @@
 import org.objectweb.asm.Opcodes;
 import org.objectweb.asm.tree.AbstractInsnNode;
 import org.objectweb.asm.tree.ClassNode;
+import org.objectweb.asm.tree.FieldInsnNode;
 import org.objectweb.asm.tree.InsnList;
 import org.objectweb.asm.tree.InsnNode;
 import org.objectweb.asm.tree.MethodInsnNode;
@@ -66,6 +67,51 @@ public byte[] apply(String name, byte[] bytes) {
             return classWriter.toByteArray();
         }
 
+        // Inject extra mods which EssentialLoader has discovered outside the mod directory (e.g. Loader extracts
+        // nested jars into the temporary files folder). If such jars contain mods/tweakers, Forge needs to explicitly
+        // be told about them so it can load those mods/tweakers.
+        // This should behave exactly like the `--mods` program argument which Forge adds (except that one is limited
+        // to paths relative to the game directory, and such relative paths cannot be created on Windows when temp files
+        // and game folder are on different drives).
+        // ModListHelper is used on 1.8.9 and older 1.12.2 versions
+        // LibraryManager is used on newer 1.12.2 versions
+        if (name.equals("net.minecraftforge.fml.relauncher.ModListHelper")) {
+            ClassNode classNode = new ClassNode(Opcodes.ASM5);
+            new ClassReader(bytes).accept(classNode, 0);
+            for (MethodNode method : classNode.methods) {
+                if ("parseModList".equals(method.name)) {
+                    InsnList instructions = method.instructions;
+                    AbstractInsnNode ret = instructions.getLast();
+                    while (ret.getOpcode() != Opcodes.RETURN) {
+                        ret = ret.getPrevious();
+                    }
+                    instructions.insertBefore(ret, new FieldInsnNode(Opcodes.GETSTATIC, classNode.name, "additionalMods", "Ljava/util/Map;"));
+                    instructions.insertBefore(ret, new MethodInsnNode(Opcodes.INVOKESTATIC, "gg/essential/loader/stage2/RelaunchedLoader", "injectExtraMods", "(Ljava/util/Map;)V", false));
+                }
+            }
+            ClassWriter classWriter = new ClassWriter(Opcodes.ASM5);
+            classNode.accept(classWriter);
+            return classWriter.toByteArray();
+        }
+        if (name.equals("net.minecraftforge.fml.relauncher.libraries.LibraryManager")) {
+            ClassNode classNode = new ClassNode(Opcodes.ASM5);
+            new ClassReader(bytes).accept(classNode, 0);
+            for (MethodNode method : classNode.methods) {
+                if ("gatherLegacyCanidates"/*sic*/.equals(method.name)) {
+                    InsnList instructions = method.instructions;
+                    AbstractInsnNode ret = instructions.getLast();
+                    while (ret.getOpcode() != Opcodes.ARETURN) {
+                        ret = ret.getPrevious();
+                    }
+                    instructions.insertBefore(ret, new InsnNode(Opcodes.DUP));
+                    instructions.insertBefore(ret, new MethodInsnNode(Opcodes.INVOKESTATIC, "gg/essential/loader/stage2/RelaunchedLoader", "injectExtraMods", "(Ljava/util/List;)V", false));
+                }
+            }
+            ClassWriter classWriter = new ClassWriter(Opcodes.ASM5);
+            classNode.accept(classWriter);
+            return classWriter.toByteArray();
+        }
+
         return bytes;
     }
 }