Convert Coremods from JS to Java

coremods/build.gradle

@@ -0,0 +1,46 @@
+plugins {
+    id 'java-library'
+    id 'com.diffplug.spotless'
+    id 'net.neoforged.licenser'
+    id 'neoforge.formatting-conventions'
+}
+
+repositories {
+    maven { url = 'https://maven.neoforged.net/releases' }
+    maven {
+        name 'Mojang'
+        url 'https://libraries.minecraft.net'
+    }
+    mavenCentral()
+}
+
+jar {
+    manifest {
+        attributes(
+                "Automatic-Module-Name": "neoforge.coremods",
+                FMLModType: "LIBRARY",
+        )
+    }
+}
+
+java {
+    toolchain {
+        languageVersion.set(JavaLanguageVersion.of(project.java_version))
+    }
+}
+
+dependencies {
+    compileOnly "org.jetbrains:annotations:${project.jetbrains_annotations_version}"
+    compileOnly "com.google.code.gson:gson:${gson_version}"
+    compileOnly "org.slf4j:slf4j-api:${slf4j_api_version}"
+    compileOnly "net.neoforged.fancymodloader:loader:${project.fancy_mod_loader_version}"
+}
+
+license {
+    header = rootProject.file('codeformat/HEADER.txt')
+    include '**/*.java'
+}
+
+tasks.withType(JavaCompile).configureEach {
+    options.encoding = 'UTF-8'
+}

coremods/src/main/java/net/neoforged/neoforge/coremods/CoremodUtils.java

@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) NeoForged and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.neoforged.neoforge.coremods;
+
+import com.google.gson.Gson;
+import com.google.gson.reflect.TypeToken;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.nio.charset.StandardCharsets;
+import java.util.Objects;
+import org.jetbrains.annotations.Nullable;
+import org.objectweb.asm.tree.ClassNode;
+import org.objectweb.asm.tree.FieldNode;
+import org.objectweb.asm.tree.MethodNode;
+
+final class CoremodUtils {
+    private static final Gson GSON = new Gson();
+
+    CoremodUtils() {}
+
+    static <T> T loadResource(String filename, TypeToken<T> type) {
+        var stream = NeoForgeCoreMod.class.getResourceAsStream(filename);
+        if (stream == null) {
+            throw new IllegalStateException("Missing resource: " + filename);
+        }
+        try (var reader = new InputStreamReader(stream, StandardCharsets.UTF_8)) {
+            return GSON.fromJson(reader, type);
+        } catch (IOException e) {
+            throw new IllegalStateException("Failed to read JSON resource " + filename);
+        }
+    }
+
+    static <T> T loadResource(String filename, Class<T> type) {
+        return loadResource(filename, TypeToken.get(type));
+    }
+
+    static FieldNode getFieldByName(ClassNode classNode, String fieldName) {
+        FieldNode foundField = null;
+        for (var fieldNode : classNode.fields) {
+            if (Objects.equals(fieldNode.name, fieldName)) {
+                if (foundField == null) {
+                    foundField = fieldNode;
+                } else {
+                    throw new IllegalStateException("Found multiple fields with name " + fieldName + " in " + classNode.name);
+                }
+            }
+        }
+        if (foundField == null) {
+            throw new IllegalStateException("No field with name " + fieldName + " found in class " + classNode.name);
+        }
+        return foundField;
+    }
+
+    static MethodNode getMethodByDescriptor(ClassNode classNode, @Nullable String methodName, String methodSignature) {
+        MethodNode foundMethod = null;
+        for (var methodNode : classNode.methods) {
+            if (Objects.equals(methodNode.desc, methodSignature)
+                    && (methodName == null || Objects.equals(methodNode.name, methodName))) {
+                if (foundMethod == null) {
+                    foundMethod = methodNode;
+                } else {
+                    throw new IllegalStateException("Found duplicate method with signature " + methodSignature + " in " + classNode.name);
+                }
+            }
+        }
+
+        if (foundMethod == null) {
+            if (methodName != null) {
+                throw new IllegalStateException("Unable to find method " + methodSignature + " with name " + methodName + " in " + classNode.name);
+            } else {
+                throw new IllegalStateException("Unable to find method " + methodSignature + " in " + classNode.name);
+            }
+        }
+        return foundMethod;
+    }
+}

coremods/src/main/java/net/neoforged/neoforge/coremods/MethodRedirector.java

@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) NeoForged and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.neoforged.neoforge.coremods;
+
+import cpw.mods.modlauncher.api.ITransformer;
+import cpw.mods.modlauncher.api.ITransformerVotingContext;
+import cpw.mods.modlauncher.api.TargetType;
+import cpw.mods.modlauncher.api.TransformerVoteResult;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Function;
+import org.objectweb.asm.Opcodes;
+import org.objectweb.asm.tree.ClassNode;
+import org.objectweb.asm.tree.MethodInsnNode;
+
+/**
+ * Redirect calls to one method to another.
+ */
+public class MethodRedirector implements ITransformer<ClassNode> {
+    private final Map<String, List<MethodRedirection>> redirectionsByClass = new HashMap<>();
+    private final Set<Target<ClassNode>> targets = new HashSet<>();
+
+    private static final List<MethodRedirection> REDIRECTIONS = List.of(
+            new MethodRedirection(
+                    Opcodes.INVOKEVIRTUAL,
+                    "finalizeSpawn",
+                    "(Lnet/minecraft/world/level/ServerLevelAccessor;Lnet/minecraft/world/DifficultyInstance;Lnet/minecraft/world/entity/MobSpawnType;Lnet/minecraft/world/entity/SpawnGroupData;)Lnet/minecraft/world/entity/SpawnGroupData;",
+                    "finalize_spawn_targets.json",
+                    methodInsnNode -> new MethodInsnNode(
+                            Opcodes.INVOKESTATIC,
+                            "net/neoforged/neoforge/event/EventHooks",
+                            "finalizeMobSpawn",
+                            "(Lnet/minecraft/world/entity/Mob;Lnet/minecraft/world/level/ServerLevelAccessor;Lnet/minecraft/world/DifficultyInstance;Lnet/minecraft/world/entity/MobSpawnType;Lnet/minecraft/world/entity/SpawnGroupData;)Lnet/minecraft/world/entity/SpawnGroupData;",
+                            false)));
+
+    public MethodRedirector() {
+        for (var redirection : REDIRECTIONS) {
+            var targetClassNames = CoremodUtils.loadResource(redirection.targetClassListFile, String[].class);
+            for (var targetClassName : targetClassNames) {
+                targets.add(Target.targetClass(targetClassName));
+                var redirections = redirectionsByClass.computeIfAbsent(targetClassName, s -> new ArrayList<>());
+                redirections.add(redirection);
+            }
+        }
+    }
+
+    @Override
+    public TargetType<ClassNode> getTargetType() {
+        return TargetType.CLASS;
+    }
+
+    @Override
+    public Set<Target<ClassNode>> targets() {
+        return targets;
+    }
+
+    @Override
+    public ClassNode transform(ClassNode classNode, ITransformerVotingContext votingContext) {
+        var redirections = redirectionsByClass.getOrDefault(classNode.name, Collections.emptyList());
+
+        var methods = classNode.methods;
+        for (var method : methods) {
+            var instr = method.instructions;
+            for (var i = 0; i < instr.size(); i++) {
+                var node = instr.get(i);
+                if (node instanceof MethodInsnNode methodInsnNode) {
+                    for (var redirection : redirections) {
+                        if (redirection.invokeOpCode == methodInsnNode.getOpcode()
+                                && redirection.methodName.equals(methodInsnNode.name)
+                                && redirection.methodDescriptor.equals(methodInsnNode.desc)) {
+                            // Found a match for the target method
+                            instr.set(
+                                    methodInsnNode,
+                                    redirection.redirector.apply(methodInsnNode));
+                        }
+                    }
+                }
+            }
+        }
+        return classNode;
+    }
+
+    @Override
+    public TransformerVoteResult castVote(ITransformerVotingContext context) {
+        return TransformerVoteResult.YES;
+    }
+
+    private record MethodRedirection(
+            int invokeOpCode,
+            String methodName,
+            String methodDescriptor,
+            String targetClassListFile,
+            Function<MethodInsnNode, MethodInsnNode> redirector) {}
+}

coremods/src/main/java/net/neoforged/neoforge/coremods/NeoForgeCoreMod.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) NeoForged and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.neoforged.neoforge.coremods;
+
+import cpw.mods.modlauncher.api.ITransformer;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import net.neoforged.neoforgespi.coremod.ICoreMod;
+
+public class NeoForgeCoreMod implements ICoreMod {
+    @Override
+    public Iterable<? extends ITransformer<?>> getTransformers() {
+        List<ITransformer<?>> transformers = new ArrayList<>();
+        transformers.add(new ReplaceFieldWithGetterAccess("net.minecraft.world.level.biome.Biome", Map.of(
+                "climateSettings", "getModifiedClimateSettings",
+                "specialEffects", "getModifiedSpecialEffects")));
+        transformers.add(new ReplaceFieldWithGetterAccess("net.minecraft.world.level.levelgen.structure.Structure", Map.of(
+                "settings", "getModifiedStructureSettings")));
+        transformers.add(new ReplaceFieldWithGetterAccess("net.minecraft.world.level.block.FlowerPotBlock", Map.of(
+                "potted", "getPotted")));
+
+        transformers.add(new MethodRedirector());
+
+        return transformers;
+    }
+}

coremods/src/main/java/net/neoforged/neoforge/coremods/ReplaceFieldComparisonWithInstanceOf.java

@@ -0,0 +1,88 @@
+/*
+ * Copyright (c) NeoForged and contributors
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+
+package net.neoforged.neoforge.coremods;
+
+import cpw.mods.modlauncher.api.ITransformer;
+import cpw.mods.modlauncher.api.ITransformerVotingContext;
+import cpw.mods.modlauncher.api.TargetType;
+import cpw.mods.modlauncher.api.TransformerVoteResult;
+import java.util.List;
+import java.util.Set;
+import org.objectweb.asm.Opcodes;
+import org.objectweb.asm.tree.FieldInsnNode;
+import org.objectweb.asm.tree.JumpInsnNode;
+import org.objectweb.asm.tree.MethodNode;
+import org.objectweb.asm.tree.TypeInsnNode;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Replaces code such as {@code itemstack.getItem() == Items.CROSSBOW} with instanceof checks such
+ * as {@code itemstack.getItem() instanceof CrossbowItem}.
+ * This transformer targets a set of methods to replace the occurrence of a single field-comparison.
+ */
+public class ReplaceFieldComparisonWithInstanceOf implements ITransformer<MethodNode> {
+    private static final Logger LOG = LoggerFactory.getLogger(ReplaceFieldComparisonWithInstanceOf.class);
+
+    private final Set<Target<MethodNode>> targets;
+    private final String fieldOwner;
+    private final String fieldName;
+    private final String replacementClassName;
+
+    /**
+     * @param fieldOwner           The class that owns {@code fieldName}
+     * @param fieldName            The name of a field in {@code fieldOwner}
+     * @param replacementClassName Reference comparisons against {@code fieldName} in {@code fieldOwner} are replaced
+     *                             by instanceof checks against this class.
+     * @param methodsToScan        The methods to scan
+     */
+    public ReplaceFieldComparisonWithInstanceOf(String fieldOwner,
+            String fieldName,
+            String replacementClassName,
+            List<Target<MethodNode>> methodsToScan) {
+        this.targets = Set.copyOf(methodsToScan);
+
+        this.fieldOwner = fieldOwner;
+        this.fieldName = fieldName;
+        this.replacementClassName = replacementClassName;
+    }
+
+    @Override
+    public TargetType<MethodNode> getTargetType() {
+        return TargetType.METHOD;
+    }
+
+    @Override
+    public Set<Target<MethodNode>> targets() {
+        return targets;
+    }
+
+    @Override
+    public MethodNode transform(MethodNode methodNode, ITransformerVotingContext votingContext) {
+        var count = 0;
+        for (var node = methodNode.instructions.getFirst(); node != null; node = node.getNext()) {
+            if (node instanceof JumpInsnNode jumpNode && (jumpNode.getOpcode() == Opcodes.IF_ACMPEQ || jumpNode.getOpcode() == Opcodes.IF_ACMPNE)) {
+                if (node.getPrevious() instanceof FieldInsnNode fieldAccessNode && (fieldAccessNode.getOpcode() == Opcodes.GETSTATIC || fieldAccessNode.getOpcode() == Opcodes.GETFIELD)) {
+                    if (fieldAccessNode.owner.equals(fieldOwner) && fieldAccessNode.name.equals(fieldName)) {
+                        methodNode.instructions.set(fieldAccessNode, new TypeInsnNode(Opcodes.INSTANCEOF, replacementClassName));
+                        methodNode.instructions.set(jumpNode, new JumpInsnNode(jumpNode.getOpcode() == Opcodes.IF_ACMPEQ ? Opcodes.IFNE : Opcodes.IFEQ, jumpNode.label));
+                        count++;
+                    }
+                }
+            }
+        }
+
+        LOG.trace("Transforming: {}.", methodNode.name);
+        LOG.trace("field_to_instance: Replaced {} checks", count);
+
+        return methodNode;
+    }
+
+    @Override
+    public TransformerVoteResult castVote(ITransformerVotingContext context) {
+        return TransformerVoteResult.YES;
+    }
+}