Custom file handler (Also workaround for issue with mixin paths in mixin configs)

src/main/java/io/github/pacifistmc/forgix/Forgix.java

@@ -3,6 +3,8 @@
 import io.github.pacifistmc.forgix.core.Multiversion;
 import io.github.pacifistmc.forgix.core.RelocationConfig;
 import io.github.pacifistmc.forgix.core.Relocator;
+import io.github.pacifistmc.forgix.core.filehandlers.CustomFileHandler;
+import io.github.pacifistmc.forgix.plugin.configurations.ForgixConfiguration;
 import io.github.pacifistmc.forgix.utils.JAR;
 
 import java.io.File;
@@ -17,7 +19,9 @@ public class Forgix {
     private static final String MANIFEST_VERSION_KEY = "Forgix-Version";
     private static final String MANIFEST_MAPPINGS_KEY = "Forgix-Mappings";
 
-    public static void mergeLoaders(Map<File, String> jarsAndLoadersMap, File outputFile, boolean silence = false) {
+    public static void mergeLoaders(Map<File, String> jarsAndLoadersMap, File outputFile,
+                                    Map<String, CustomFileHandler> customFileHandlers = new HashMap(),
+                                    boolean silence = false) {
         if (!silence) {
             """
             Thank you for using Forgix!
@@ -27,7 +31,7 @@ public static void mergeLoaders(Map<File, String> jarsAndLoadersMap, File output
 
         List<RelocationConfig> configs = new ArrayList<>();
         jarsAndLoadersMap.forEach((jar, loader) -> configs.add(new RelocationConfig(new JarFile(jar), loader)));
-        Relocator.relocate(configs);
+        Relocator.relocate(configs, customFileHandlers);
 
         Map<File, String> tinyFiles = configs.stream()
                 .map(RelocationConfig::getTinyFile)

src/main/java/io/github/pacifistmc/forgix/core/Multiversion.java

@@ -48,7 +48,7 @@ private static String generateMultiversionUUID() {
 
             var relocationConfig = new RelocationConfig(jarFile, uuid);
             relocationConfig.setMappings(renameMap);
-            Relocator.relocate(List.of(relocationConfig));
+            Relocator.relocate(List.of(relocationConfig), Map.of());
         }
 
         JAR.removeFiles(multiversionJar, List.of(

src/main/java/io/github/pacifistmc/forgix/core/RelocationConfig.java

@@ -1,5 +1,7 @@
 package io.github.pacifistmc.forgix.core;
 
+import io.github.pacifistmc.forgix.plugin.configurations.ForgixConfiguration;
+
 import java.io.File;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;

src/main/java/io/github/pacifistmc/forgix/core/filehandlers/CustomFileHandler.java

@@ -0,0 +1,8 @@
+package io.github.pacifistmc.forgix.core.filehandlers;
+
+import java.util.Map;
+
+@FunctionalInterface
+public interface CustomFileHandler {
+    String handle(String fileName, String fileContent, Map<String, String> replacementPaths);
+}

src/main/java/io/github/pacifistmc/forgix/core/filehandlers/MixinFileHandler.java

@@ -0,0 +1,41 @@
+package io.github.pacifistmc.forgix.core.filehandlers;
+
+import com.google.gson.*;
+
+import java.util.Map;
+
+public class MixinFileHandler implements CustomFileHandler {
+    @Override
+    public String handle(String fileName, String fileContent, Map<String, String> replacementPaths) {
+        Gson gson = new GsonBuilder().setPrettyPrinting().create();
+        JsonObject mixinJson = gson.fromJson(fileContent, JsonObject.class);
+        String packagePath = mixinJson.get("package").getAsString();
+
+        JsonArray commonMixinPaths = mixinJson.getAsJsonArray("mixins");
+        JsonArray newCommonMixinPaths = new JsonArray();
+        for (JsonElement mixinPath : commonMixinPaths) {
+            String fullPath = packagePath + "." + mixinPath.getAsString();
+            if (replacementPaths.containsKey(fullPath))
+                newCommonMixinPaths.add(replacementPaths.get(fullPath).substring(packagePath.length() + 1));
+            else
+                newCommonMixinPaths.add(mixinPath);
+        }
+        mixinJson.add("mixins", newCommonMixinPaths);
+
+        JsonArray clientMixinPaths = mixinJson.getAsJsonArray("client");
+        JsonArray newClientMixinPaths = new JsonArray();
+        for (JsonElement mixinPath : clientMixinPaths) {
+            String fullPath = packagePath + "." + mixinPath.getAsString();
+            if (replacementPaths.containsKey(fullPath))
+                newClientMixinPaths.add(replacementPaths.get(fullPath).substring(packagePath.length() + 1));
+            else
+                newClientMixinPaths.add(mixinPath);
+        }
+        mixinJson.add("client", newClientMixinPaths);
+
+        JsonPrimitive mixinPlugin = mixinJson.getAsJsonPrimitive("plugin");
+        JsonPrimitive mixinRef = mixinJson.getAsJsonPrimitive("refmap");
+
+        return gson.toJson(mixinJson);
+    }
+}

src/main/java/io/github/pacifistmc/forgix/plugin/configurations/ForgixConfiguration.java

@@ -1,5 +1,8 @@
 package io.github.pacifistmc.forgix.plugin.configurations;
 
+import com.google.gson.*;
+import io.github.pacifistmc.forgix.core.filehandlers.CustomFileHandler;
+import io.github.pacifistmc.forgix.core.filehandlers.MixinFileHandler;
 import org.gradle.api.Action;
 import org.gradle.api.Project;
 import org.gradle.api.file.Directory;
@@ -22,6 +25,7 @@ public class ForgixConfiguration {
     private final Property<Directory> destinationDirectory;
     private final Map<String, MergeLoaderConfiguration> mergeConfigurations = new HashMap<>();
     public MultiversionConfiguration multiversionConfiguration;
+    private final Map<String, CustomFileHandler> customFileHandlers = new HashMap<>();
 
     private final Map<String, Consumer<ForgixConfiguration>> LOADER_DEFAULT_METHOD_MAP = new HashMap<>();
     private final Project rootProject;
@@ -327,6 +331,20 @@ public Property<FileCollection> getInputJars() {
         }
     }
 
+    // Custom file handling stuff
+
+    public void mixin(String mixinPathPattern) {
+        fileHandler(mixinPathPattern, new MixinFileHandler());
+    }
+
+    public void fileHandler(String fileNamePattern, CustomFileHandler handler) {
+        customFileHandlers.put(fileNamePattern, handler);
+    }
+
+    public Map<String, CustomFileHandler> getCustomFileHandlers() {
+        return customFileHandlers;
+    }
+
     // Internal Gradle stuff
 
     @Inject

src/main/java/io/github/pacifistmc/forgix/plugin/tasks/MergeJarsTask.java

@@ -74,7 +74,7 @@ void mergeJars() {
         }
 
         // Perform the merge operation
-        Forgix.mergeLoaders(jarMap, outputFile, silence.get());
+        Forgix.mergeLoaders(jarMap, outputFile, settings.customFileHandlers, silence.get());
     }
 
     @Override

src/test/java/io/github/pacifistmc/forgix/tests/CoreTest.java

@@ -3,8 +3,11 @@
 import io.github.pacifistmc.forgix.Forgix;
 import io.github.pacifistmc.forgix.core.Multiversion;
 import io.github.pacifistmc.forgix.core.Relocator;
+import io.github.pacifistmc.forgix.core.filehandlers.MixinFileHandler;
 import io.github.pacifistmc.forgix.utils.JAR;
 import io.github.pacifistmc.forgix.utils.TinyClassWriter;
+import org.apache.commons.io.IOUtils;
+import org.gradle.internal.impldep.org.junit.Assert;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -13,13 +16,16 @@
 import java.io.File;
 import java.io.FileOutputStream;
 import java.io.IOException;
+import java.io.InputStream;
 import java.net.URISyntaxException;
 import java.net.URL;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Path;
 import java.util.*;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.jar.JarEntry;
 import java.util.jar.JarFile;
+import java.util.zip.ZipEntry;
 
 import org.apache.commons.io.FileUtils;
 
@@ -184,7 +190,7 @@ void testRelocation() throws IOException {
                     new RelocationConfig(differentJarA, "diffA"),
                     new RelocationConfig(differentJarB, "diffB")
             ));
-            Relocator.relocate(files);
+            Relocator.relocate(files, Map.of());
             var differentJarA1 = new JarFile(differentJarACopy);
             var differentJarB1 = new JarFile(differentJarBCopy);
 
@@ -242,7 +248,7 @@ void testMerge() throws IOException {
                     new RelocationConfig(mergeJarA, "diffA"),
                     new RelocationConfig(mergeJarB, "diffB")
             ));
-            Relocator.relocate(files);
+            Relocator.relocate(files, Map.of());
             try (var baos = JAR.combineJars(List.of(mergeJarACopy, mergeJarBCopy))) {
                 try (var fos = new FileOutputStream(mergedJar)) {
                     baos.writeTo(fos);
@@ -307,6 +313,106 @@ void testMergeCLI() throws IOException {
         }
     }
 
+    @Test
+    void testCustomFileHandling() throws IOException {
+        File differentJarACopy = tempDir.resolve("conflict-a.jar").toFile();
+        File differentJarBCopy = tempDir.resolve("conflict-b.jar").toFile();
+        FileUtils.copyFile(differentJarA, differentJarACopy);
+        FileUtils.copyFile(differentJarB, differentJarBCopy);
+
+        // Relocate & merge
+        try(JarFile differentJarA = new JarFile(differentJarACopy);
+            JarFile differentJarB = new JarFile(differentJarBCopy)) {
+
+            List<RelocationConfig> files = new ArrayList<>(List.of(
+                    new RelocationConfig(differentJarA, "diffA"),
+                    new RelocationConfig(differentJarB, "diffB")
+            ));
+            Relocator.relocate(files, Map.of("**.mixins.json", new MixinFileHandler()));
+        }
+
+        // Verify the merged JAR mixins
+        try (JarFile differentJarA = new JarFile(differentJarACopy);
+             JarFile differentJarB = new JarFile(differentJarBCopy)) {
+            ZipEntry mixinEntryA = differentJarA.getEntry("DistantHorizons.fabric.mixins_diffA.json");
+            try (InputStream is = differentJarA.getInputStream(mixinEntryA)) {
+                String content = IOUtils.toString(is, StandardCharsets.UTF_8);
+                if (debug) {
+                    content.println();
+                }
+                Assert.assertEquals(content, """
+                        {
+                          "required": true,
+                          "minVersion": "0.8",
+                          "package": "com.seibel.distanthorizons.fabric.mixins",
+                          "mixins": [
+                            "server.MixinChunkGenerator_diffA",
+                            "server.MixinChunkMap_diffA",
+                            "server.MixinEntity_diffA",
+                            "server.MixinServerPlayer_diffA",
+                            "server.MixinTracingExecutor_diffA",
+                            "server.MixinUtilBackgroundThread_diffA"
+                          ],
+                          "client": [
+                            "client.MixinClientLevel_diffA",
+                            "client.MixinClientPacketListener_diffA",
+                            "client.MixinDebugScreenOverlay_diffA",
+                            "client.MixinFogRenderer_diffA",
+                            "client.MixinLevelRenderer_diffA",
+                            "client.MixinLightTexture_diffA",
+                            "client.MixinMinecraft_diffA",
+                            "client.MixinOptionsScreen_diffA",
+                            "client.MixinTextureUtil_diffA"
+                          ],
+                          "server": [],
+                          "injectors": {
+                            "defaultRequire": 1
+                          },
+                          "plugin": "com.seibel.distanthorizons.fabric.mixins.FabricMixinPlugin",
+                          "refmap": "DistantHorizons-fabric-refmap.json"
+                        }""".stripIndent());
+            }
+
+            ZipEntry mixinEntryB = differentJarB.getEntry("DistantHorizons.fabric.mixins_diffB.json");
+            try (InputStream is = differentJarB.getInputStream(mixinEntryB)) {
+                String content = IOUtils.toString(is, StandardCharsets.UTF_8);
+                if (debug) {
+                    content.println();
+                }
+                Assert.assertEquals(content, """
+                        {
+                          "required": true,
+                          "minVersion": "0.8",
+                          "package": "com.seibel.distanthorizons.fabric.mixins",
+                          "mixins": [
+                            "server.MixinChunkGenerator_diffB",
+                            "server.MixinChunkMap_diffB",
+                            "server.MixinEntity_diffB",
+                            "server.MixinServerPlayer_diffB",
+                            "server.MixinTracingExecutor_diffB",
+                            "server.MixinUtilBackgroundThread_diffB"
+                          ],
+                          "client": [
+                            "client.MixinClientLevel_diffB",
+                            "client.MixinClientPacketListener_diffB",
+                            "client.MixinDebugScreenOverlay_diffB",
+                            "client.MixinFogRenderer_diffB",
+                            "client.MixinLevelRenderer_diffB",
+                            "client.MixinLightTexture_diffB",
+                            "client.MixinMinecraft_diffB",
+                            "client.MixinOptionsScreen_diffB",
+                            "client.MixinTextureUtil_diffB"
+                          ],
+                          "injectors": {
+                            "defaultRequire": 1
+                          },
+                          "plugin": "com.seibel.distanthorizons.fabric.mixins.FabricMixinPlugin",
+                          "refmap": "DistantHorizons-fabric-refmap.json"
+                        }""".stripIndent());
+            }
+        }
+    }
+
     @Test
     void testMultiversion() throws IOException {
         // Copy version jars into the temp directory