Add an auto discovery plugin for mixins

build.gradle.kts

@@ -107,7 +107,7 @@ tasks.processResources {
     inputs.property("version", project.version)
     inputs.property("mcversion", mcVersion)
     inputs.property("modid", modid)
-    inputs.property("mixinGroup", mixinGroup)
+    inputs.property("basePackage", baseGroup)
 
     filesMatching(listOf("mcmod.info", "mixins.$modid.json")) {
         expand(inputs.properties)

src/main/java/com/example/init/AutoDiscoveryMixinPlugin.java

@@ -0,0 +1,188 @@
+package com.example.init;
+
+import org.spongepowered.asm.lib.tree.ClassNode;
+import org.spongepowered.asm.mixin.extensibility.IMixinConfigPlugin;
+import org.spongepowered.asm.mixin.extensibility.IMixinInfo;
+
+import java.io.IOException;
+import java.net.MalformedURLException;
+import java.net.URISyntaxException;
+import java.net.URL;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Stream;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipInputStream;
+
+/**
+ * A mixin plugin to automatically discover all mixins in the current JAR.
+ * <p>
+ * This mixin plugin automatically scans your entire JAR (or class directory, in case of an in-IDE launch) for classes inside of your
+ * mixin package and registers those. It does this recursively for sub packages of the mixin package as well. This means you will need
+ * to only have mixin classes inside of your mixin package, which is good style anyway.
+ *
+ * @author Linnea Gräf
+ */
+public class AutoDiscoveryMixinPlugin implements IMixinConfigPlugin {
+    private static final List<AutoDiscoveryMixinPlugin> mixinPlugins = new ArrayList<>();
+
+    public static List<AutoDiscoveryMixinPlugin> getMixinPlugins() {
+        return mixinPlugins;
+    }
+
+    private String mixinPackage;
+
+    @Override
+    public void onLoad(String mixinPackage) {
+        this.mixinPackage = mixinPackage;
+        mixinPlugins.add(this);
+    }
+
+    /**
+     * Resolves the base class root for a given class URL. This resolves either the JAR root, or the class file root.
+     * In either case the return value of this + the class name will resolve back to the original class url, or to other
+     * class urls for other classes.
+     */
+    public URL getBaseUrlForClassUrl(URL classUrl) {
+        String string = classUrl.toString();
+        if (classUrl.getProtocol().equals("jar")) {
+            try {
+                return new URL(string.substring(4).split("!")[0]);
+            } catch (MalformedURLException e) {
+                throw new RuntimeException(e);
+            }
+        }
+        if (string.endsWith(".class")) {
+            try {
+                return new URL(string.replace("\\", "/")
+                        .replace(getClass().getCanonicalName()
+                                .replace(".", "/") + ".class", ""));
+            } catch (MalformedURLException e) {
+                throw new RuntimeException(e);
+            }
+        }
+        return classUrl;
+    }
+
+    /**
+     * Get the package that contains all the mixins. This value is set by mixin itself using {@link #onLoad}.
+     */
+    public String getMixinPackage() {
+        return mixinPackage;
+    }
+
+    /**
+     * Get the path inside the class root to the mixin package
+     */
+    public String getMixinBaseDir() {
+        return mixinPackage.replace(".", "/");
+    }
+
+    /**
+     * A list of all discovered mixins.
+     */
+    private List<String> mixins = null;
+
+    /**
+     * Try to add mixin class ot the mixins based on the filepath inside of the class root.
+     * Removes the {@code .class} file suffix, as well as the base mixin package.
+     * <p><b>This method cannot be called after mixin initialization.</p>
+     *
+     * @param className the name or path of a class to be registered as a mixin.
+     */
+    public void tryAddMixinClass(String className) {
+        String norm = (className.endsWith(".class") ? className.substring(0, className.length() - ".class".length()) : className)
+                .replace("\\", "/")
+                .replace("/", ".");
+        if (norm.startsWith(getMixinPackage() + ".") && !norm.endsWith(".")) {
+            mixins.add(norm.substring(getMixinPackage().length() + 1));
+        }
+    }
+
+    /**
+     * Search through the JAR or class directory to find mixins contained in {@link #getMixinPackage()}
+     */
+    @Override
+    public List<String> getMixins() {
+        if (mixins != null) return mixins;
+        System.out.println("Trying to discover mixins");
+        mixins = new ArrayList<>();
+        URL classUrl = getClass().getProtectionDomain().getCodeSource().getLocation();
+        System.out.println("Found classes at " + classUrl);
+        Path file;
+        try {
+            file = Paths.get(getBaseUrlForClassUrl(classUrl).toURI());
+        } catch (URISyntaxException e) {
+            throw new RuntimeException(e);
+        }
+        System.out.println("Base directory found at " + file);
+        if (Files.isDirectory(file)) {
+            walkDir(file);
+        } else {
+            walkJar(file);
+        }
+        System.out.println("Found mixins: " + mixins);
+
+        return mixins;
+    }
+
+    /**
+     * Search through directory for mixin classes based on {@link #getMixinBaseDir}.
+     *
+     * @param classRoot The root directory in which classes are stored for the default package.
+     */
+    private void walkDir(Path classRoot) {
+        System.out.println("Trying to find mixins from directory");
+        try (Stream<Path> classes = Files.walk(classRoot.resolve(getMixinBaseDir()))) {
+            classes.map(it -> classRoot.relativize(it).toString())
+                    .forEach(this::tryAddMixinClass);
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    /**
+     * Read through a JAR file, trying to find all mixins inside.
+     */
+    private void walkJar(Path file) {
+        System.out.println("Trying to find mixins from jar file");
+        try (ZipInputStream zis = new ZipInputStream(Files.newInputStream(file))) {
+            ZipEntry next;
+            while ((next = zis.getNextEntry()) != null) {
+                tryAddMixinClass(next.getName());
+                zis.closeEntry();
+            }
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @Override
+    public void preApply(String targetClassName, ClassNode targetClass, String mixinClassName, IMixinInfo mixinInfo) {
+
+    }
+
+    @Override
+    public void postApply(String targetClassName, ClassNode targetClass, String mixinClassName, IMixinInfo mixinInfo) {
+
+    }
+
+    @Override
+    public String getRefMapperConfig() {
+        return null;
+    }
+
+    @Override
+    public boolean shouldApplyMixin(String targetClassName, String mixinClassName) {
+        return true;
+    }
+
+    @Override
+    public void acceptTargets(Set<String> myTargets, Set<String> otherTargets) {
+
+    }
+}

src/main/resources/mixins.examplemod.json

@@ -1,11 +1,8 @@
 {
-  "package": "${mixinGroup}",
+  "package": "${basePackage}.mixin",
+  "plugin": "${basePackage}.init.AutoDiscoveryMixinPlugin",
   "refmap": "mixins.${modid}.refmap.json",
   "minVersion": "0.7",
   "compatibilityLevel": "JAVA_8",
-  "mixins": [
-  ],
-  "client": [
-	"MixinGuiMainMenu"
-  ]
+  "__comment": "You do not need to manually register mixins in this template. Check the auto discovery mixin plugin for more info."
 }