PaperMC/patches/server/0022-Remap-reflection-calls-in-plugins-using-internals.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Nassim Jahnke <nassim@njahnke.dev>
Date: Sun, 30 Oct 2022 23:47:26 +0100
Subject: [PATCH] Remap reflection calls in plugins using internals

Co-authored-by: Jason Penilla <11360596+jpenilla@users.noreply.github.com>

diff --git a/build.gradle.kts b/build.gradle.kts
index 5f94206910467c3302da5a995da5f74961a3365a..b995ea46b0fabdab6d398aa1980f9d801460b772 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -34,7 +34,6 @@ dependencies {
     implementation("org.ow2.asm:asm-commons:9.7")
     implementation("org.spongepowered:configurate-yaml:4.2.0-SNAPSHOT") // Paper - config files
     implementation("commons-lang:commons-lang:2.6")
-    implementation("net.fabricmc:mapping-io:0.5.0") // Paper - needed to read mappings for stacktrace deobfuscation
     runtimeOnly("com.lmax:disruptor:3.4.4") // Paper
 
     runtimeOnly("org.apache.maven:maven-resolver-provider:3.9.6")
@@ -48,6 +47,12 @@ dependencies {
     testImplementation("org.junit-pioneer:junit-pioneer:2.2.0") // Paper - CartesianTest
     implementation("net.neoforged:AutoRenamingTool:2.0.3") // Paper - remap plugins
     implementation("net.neoforged:srgutils:1.0.9") // Paper - remap plugins - bump transitive of ART
+    // Paper start - Remap reflection
+    val reflectionRewriterVersion = "0.0.1"
+    implementation("io.papermc:reflection-rewriter:$reflectionRewriterVersion")
+    implementation("io.papermc:reflection-rewriter-runtime:$reflectionRewriterVersion")
+    implementation("io.papermc:reflection-rewriter-proxy-generator:$reflectionRewriterVersion")
+    // Paper end - Remap reflection
 }
 
 paperweight {
diff --git a/src/main/java/io/papermc/paper/configuration/serializer/PacketClassSerializer.java b/src/main/java/io/papermc/paper/configuration/serializer/PacketClassSerializer.java
index 893ad5e7c2d32ccd64962d95d146bbd317c28ab8..3d73ea0e63c97b2b08e719b7be7af3894fb2d4e8 100644
--- a/src/main/java/io/papermc/paper/configuration/serializer/PacketClassSerializer.java
+++ b/src/main/java/io/papermc/paper/configuration/serializer/PacketClassSerializer.java
@@ -5,6 +5,7 @@ import com.google.common.collect.ImmutableBiMap;
 import com.mojang.logging.LogUtils;
 import io.leangen.geantyref.TypeToken;
 import io.papermc.paper.configuration.serializer.collections.MapSerializer;
+import io.papermc.paper.util.MappingEnvironment;
 import io.papermc.paper.util.ObfHelper;
 import net.minecraft.network.protocol.Packet;
 import org.checkerframework.checker.nullness.qual.Nullable;
@@ -69,7 +70,7 @@ public final class PacketClassSerializer extends ScalarSerializer<Class<? extend
     @Override
     protected @Nullable Object serialize(final Class<? extends Packet<?>> packetClass, final Predicate<Class<?>> typeSupported) {
         final String name = packetClass.getName();
-        @Nullable String mojName = ObfHelper.INSTANCE.mappingsByMojangName() == null ? name : MOJANG_TO_OBF.inverse().get(name); // if the mappings are null, running on moj-mapped server
+        @Nullable String mojName = ObfHelper.INSTANCE.mappingsByMojangName() == null || !MappingEnvironment.reobf() ? name : MOJANG_TO_OBF.inverse().get(name); // if the mappings are null, running on moj-mapped server
         if (mojName == null && MOJANG_TO_OBF.containsKey(name)) {
             mojName = name;
         }
diff --git a/src/main/java/io/papermc/paper/plugin/entrypoint/classloader/PaperClassloaderBytecodeModifier.java b/src/main/java/io/papermc/paper/plugin/entrypoint/classloader/PaperClassloaderBytecodeModifier.java
index f9a2c55a354c877749db3f92956de802ae575788..39182cdd17473da0123dc7172dce507eab29fedc 100644
--- a/src/main/java/io/papermc/paper/plugin/entrypoint/classloader/PaperClassloaderBytecodeModifier.java
+++ b/src/main/java/io/papermc/paper/plugin/entrypoint/classloader/PaperClassloaderBytecodeModifier.java
@@ -1,12 +1,17 @@
 package io.papermc.paper.plugin.entrypoint.classloader;
 
 import io.papermc.paper.plugin.configuration.PluginMeta;
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassWriter;
 
 // Stub, implement in future.
 public class PaperClassloaderBytecodeModifier implements ClassloaderBytecodeModifier {
 
     @Override
     public byte[] modify(PluginMeta configuration, byte[] bytecode) {
-        return bytecode;
+        ClassReader classReader = new ClassReader(bytecode);
+        ClassWriter classWriter = new ClassWriter(classReader, 0);
+        classReader.accept(io.papermc.paper.pluginremap.reflect.ReflectionRemapper.visitor(classWriter), 0);
+        return classWriter.toByteArray();
     }
 }
diff --git a/src/main/java/io/papermc/paper/pluginremap/reflect/PaperReflection.java b/src/main/java/io/papermc/paper/pluginremap/reflect/PaperReflection.java
new file mode 100644
index 0000000000000000000000000000000000000000..c653d1f5af8b407cfba715e6027dbb695046892a
--- /dev/null
+++ b/src/main/java/io/papermc/paper/pluginremap/reflect/PaperReflection.java
@@ -0,0 +1,212 @@
+package io.papermc.paper.pluginremap.reflect;
+
+import com.mojang.logging.LogUtils;
+import io.papermc.paper.util.MappingEnvironment;
+import io.papermc.paper.util.ObfHelper;
+import io.papermc.reflectionrewriter.runtime.AbstractDefaultRulesReflectionProxy;
+import io.papermc.reflectionrewriter.runtime.DefineClassReflectionProxy;
+import java.lang.invoke.MethodHandles;
+import java.nio.ByteBuffer;
+import java.security.CodeSource;
+import java.security.ProtectionDomain;
+import java.util.Map;
+import java.util.Objects;
+import java.util.stream.Collectors;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.framework.qual.DefaultQualifier;
+import org.objectweb.asm.ClassReader;
+import org.objectweb.asm.ClassWriter;
+import org.slf4j.Logger;
+
+// todo proper inheritance handling
+@SuppressWarnings("unused")
+@DefaultQualifier(NonNull.class)
+public final class PaperReflection extends AbstractDefaultRulesReflectionProxy implements DefineClassReflectionProxy {
+    // concat to avoid being rewritten by shadow
+    private static final Logger LOGGER = LogUtils.getLogger();
+    private static final String CB_PACKAGE_PREFIX = "org.bukkit.".concat("craftbukkit.");
+    private static final String LEGACY_CB_PACKAGE_PREFIX = "org.bukkit.".concat("craftbukkit.") + MappingEnvironment.LEGACY_CB_VERSION + ".";
+
+    private final DefineClassReflectionProxy defineClassProxy;
+    private final Map<String, ObfHelper.ClassMapping> mappingsByMojangName;
+    private final Map<String, ObfHelper.ClassMapping> mappingsByObfName;
+    // Reflection does not care about method return values, so this map removes the return value descriptor from the key
+    private final Map<String, Map<String, String>> strippedMethodMappings;
+
+    PaperReflection() {
+        this.defineClassProxy = DefineClassReflectionProxy.create(PaperReflection::processClass);
+        if (!MappingEnvironment.hasMappings()) {
+            this.mappingsByMojangName = Map.of();
+            this.mappingsByObfName = Map.of();
+            this.strippedMethodMappings = Map.of();
+            return;
+        }
+        final ObfHelper obfHelper = ObfHelper.INSTANCE;
+        this.mappingsByMojangName = Objects.requireNonNull(obfHelper.mappingsByMojangName(), "mappingsByMojangName");
+        this.mappingsByObfName = Objects.requireNonNull(obfHelper.mappingsByObfName(), "mappingsByObfName");
+        this.strippedMethodMappings = this.mappingsByMojangName.entrySet().stream().collect(Collectors.toUnmodifiableMap(
+            Map.Entry::getKey,
+            entry -> entry.getValue().strippedMethods()
+        ));
+    }
+
+    @Override
+    protected String mapClassName(final String name) {
+        final ObfHelper.@Nullable ClassMapping mapping = this.mappingsByObfName.get(name);
+        return mapping != null ? mapping.mojangName() : removeCraftBukkitRelocation(name);
+    }
+
+    @Override
+    protected String mapDeclaredMethodName(final Class<?> clazz, final String name, final Class<?>... parameterTypes) {
+        final @Nullable Map<String, String> mapping = this.strippedMethodMappings.get(clazz.getName());
+        if (mapping == null) {
+            return name;
+        }
+        return mapping.getOrDefault(strippedMethodKey(name, parameterTypes), name);
+    }
+
+    @Override
+    protected String mapMethodName(final Class<?> clazz, final String name, final Class<?>... parameterTypes) {
+        final @Nullable String mapped = this.findMappedMethodName(clazz, name, parameterTypes);
+        return mapped != null ? mapped : name;
+    }
+
+    @Override
+    protected String mapDeclaredFieldName(final Class<?> clazz, final String name) {
+        final ObfHelper.@Nullable ClassMapping mapping = this.mappingsByMojangName.get(clazz.getName());
+        if (mapping == null) {
+            return name;
+        }
+        return mapping.fieldsByObf().getOrDefault(name, name);
+    }
+
+    @Override
+    protected String mapFieldName(final Class<?> clazz, final String name) {
+        final @Nullable String mapped = this.findMappedFieldName(clazz, name);
+        return mapped != null ? mapped : name;
+    }
+
+    private @Nullable String findMappedMethodName(final Class<?> clazz, final String name, final Class<?>... parameterTypes) {
+        final Map<String, String> map = this.strippedMethodMappings.get(clazz.getName());
+        @Nullable String mapped = null;
+        if (map != null) {
+            mapped = map.get(strippedMethodKey(name, parameterTypes));
+            if (mapped != null) {
+                return mapped;
+            }
+        }
+        // JVM checks super before interfaces
+        final Class<?> superClass = clazz.getSuperclass();
+        if (superClass != null) {
+            mapped = this.findMappedMethodName(superClass, name, parameterTypes);
+        }
+        if (mapped == null) {
+            for (final Class<?> i : clazz.getInterfaces()) {
+                mapped = this.findMappedMethodName(i, name, parameterTypes);
+                if (mapped != null) {
+                    break;
+                }
+            }
+        }
+        return mapped;
+    }
+
+    private @Nullable String findMappedFieldName(final Class<?> clazz, final String name) {
+        final ObfHelper.ClassMapping mapping = this.mappingsByMojangName.get(clazz.getName());
+        @Nullable String mapped = null;
+        if (mapping != null) {
+            mapped = mapping.fieldsByObf().get(name);
+            if (mapped != null) {
+                return mapped;
+            }
+        }
+        // The JVM checks super before interfaces
+        final Class<?> superClass = clazz.getSuperclass();
+        if (superClass != null) {
+            mapped = this.findMappedFieldName(superClass, name);
+        }
+        if (mapped == null) {
+            for (final Class<?> i : clazz.getInterfaces()) {
+                mapped = this.findMappedFieldName(i, name);
+                if (mapped != null) {
+                    break;
+                }
+            }
+        }
+        return mapped;
+    }
+
+    private static String strippedMethodKey(final String methodName, final Class<?>... parameterTypes) {
+        return methodName + parameterDescriptor(parameterTypes);
+    }
+
+    private static String parameterDescriptor(final Class<?>... parameterTypes) {
+        final StringBuilder builder = new StringBuilder();
+        builder.append('(');
+        for (final Class<?> parameterType : parameterTypes) {
+            builder.append(parameterType.descriptorString());
+        }
+        builder.append(')');
+        return builder.toString();
+    }
+
+    private static String removeCraftBukkitRelocation(final String name) {
+        if (MappingEnvironment.hasMappings()) {
+            // Relocation is applied in reobf, and when mappings are present they handle the relocation
+            return name;
+        }
+        if (name.startsWith(LEGACY_CB_PACKAGE_PREFIX)) {
+            return CB_PACKAGE_PREFIX + name.substring(LEGACY_CB_PACKAGE_PREFIX.length());
+        }
+        return name;
+    }
+
+    @Override
+    public Class<?> defineClass(final Object loader, final byte[] b, final int off, final int len) throws ClassFormatError {
+        return this.defineClassProxy.defineClass(loader, b, off, len);
+    }
+
+    @Override
+    public Class<?> defineClass(final Object loader, final String name, final byte[] b, final int off, final int len) throws ClassFormatError {
+        return this.defineClassProxy.defineClass(loader, name, b, off, len);
+    }
+
+    @Override
+    public Class<?> defineClass(final Object loader, final @Nullable String name, final byte[] b, final int off, final int len, final @Nullable ProtectionDomain protectionDomain) throws ClassFormatError {
+        return this.defineClassProxy.defineClass(loader, name, b, off, len, protectionDomain);
+    }
+
+    @Override
+    public Class<?> defineClass(final Object loader, final String name, final ByteBuffer b, final ProtectionDomain protectionDomain) throws ClassFormatError {
+        return this.defineClassProxy.defineClass(loader, name, b, protectionDomain);
+    }
+
+    @Override
+    public Class<?> defineClass(final Object secureLoader, final String name, final byte[] b, final int off, final int len, final CodeSource cs) {
+        return this.defineClassProxy.defineClass(secureLoader, name, b, off, len, cs);
+    }
+
+    @Override
+    public Class<?> defineClass(final Object secureLoader, final String name, final ByteBuffer b, final CodeSource cs) {
+        return this.defineClassProxy.defineClass(secureLoader, name, b, cs);
+    }
+
+    @Override
+    public Class<?> defineClass(final MethodHandles.Lookup lookup, final byte[] bytes) throws IllegalAccessException {
+        return this.defineClassProxy.defineClass(lookup, bytes);
+    }
+
+    // todo apply bytecode remap here as well
+    private static byte[] processClass(final byte[] bytes) {
+        try {
+            final ClassReader reader = new ClassReader(bytes);
+            final ClassWriter writer = new ClassWriter(reader, 0);
+            reader.accept(ReflectionRemapper.visitor(writer), 0);
+            return writer.toByteArray();
+        } catch (final Exception ex) {
+            LOGGER.warn("Failed to process class bytes", ex);
+            return bytes;
+        }
+    }
+}
diff --git a/src/main/java/io/papermc/paper/pluginremap/reflect/ReflectionRemapper.java b/src/main/java/io/papermc/paper/pluginremap/reflect/ReflectionRemapper.java
new file mode 100644
index 0000000000000000000000000000000000000000..5fa5868e82d1f00498d0c5771369e1718b2df4ee
--- /dev/null
+++ b/src/main/java/io/papermc/paper/pluginremap/reflect/ReflectionRemapper.java
@@ -0,0 +1,54 @@
+package io.papermc.paper.pluginremap.reflect;
+
+import io.papermc.asm.ClassInfoProvider;
+import io.papermc.asm.RewriteRuleVisitorFactory;
+import io.papermc.paper.util.MappingEnvironment;
+import io.papermc.reflectionrewriter.BaseReflectionRules;
+import io.papermc.reflectionrewriter.DefineClassRule;
+import io.papermc.reflectionrewriter.proxygenerator.ProxyGenerator;
+import java.lang.invoke.MethodHandles;
+import java.lang.reflect.Method;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+import org.objectweb.asm.ClassVisitor;
+import org.objectweb.asm.Opcodes;
+
+@DefaultQualifier(NonNull.class)
+public final class ReflectionRemapper {
+    private static final String PAPER_REFLECTION_HOLDER = "io.papermc.paper.pluginremap.reflect.PaperReflectionHolder";
+    private static final String PAPER_REFLECTION_HOLDER_DESC = PAPER_REFLECTION_HOLDER.replace('.', '/');
+    private static final RewriteRuleVisitorFactory VISITOR_FACTORY = RewriteRuleVisitorFactory.create(
+        Opcodes.ASM9,
+        chain -> chain.then(new BaseReflectionRules(PAPER_REFLECTION_HOLDER).rules())
+            .then(DefineClassRule.create(PAPER_REFLECTION_HOLDER_DESC, true)),
+        ClassInfoProvider.basic()
+    );
+
+    static {
+        if (!MappingEnvironment.reobf()) {
+            setupProxy();
+        }
+    }
+
+    private ReflectionRemapper() {
+    }
+
+    public static ClassVisitor visitor(final ClassVisitor parent) {
+        if (MappingEnvironment.reobf()) {
+            return parent;
+        }
+        return VISITOR_FACTORY.createVisitor(parent);
+    }
+
+    private static void setupProxy() {
+        try {
+            final byte[] bytes = ProxyGenerator.generateProxy(PaperReflection.class, PAPER_REFLECTION_HOLDER_DESC);
+            final MethodHandles.Lookup lookup = MethodHandles.lookup();
+            final Class<?> generated = lookup.defineClass(bytes);
+            final Method init = generated.getDeclaredMethod("init", PaperReflection.class);
+            init.invoke(null, new PaperReflection());
+        } catch (final ReflectiveOperationException ex) {
+            throw new RuntimeException(ex);
+        }
+    }
+}
diff --git a/src/main/java/io/papermc/paper/util/MappingEnvironment.java b/src/main/java/io/papermc/paper/util/MappingEnvironment.java
index 8e4229634d41a42b3d93948eebb77def7c0c72b1..38745299ea49f253a410e77557100903ecb472b0 100644
--- a/src/main/java/io/papermc/paper/util/MappingEnvironment.java
+++ b/src/main/java/io/papermc/paper/util/MappingEnvironment.java
@@ -10,6 +10,7 @@ import org.checkerframework.framework.qual.DefaultQualifier;
 
 @DefaultQualifier(NonNull.class)
 public final class MappingEnvironment {
+    public static final String LEGACY_CB_VERSION = "v1_20_R4";
     private static final @Nullable String MAPPINGS_HASH = readMappingsHash();
     private static final boolean REOBF = checkReobf();
 
diff --git a/src/main/java/io/papermc/paper/util/ObfHelper.java b/src/main/java/io/papermc/paper/util/ObfHelper.java
index 3f03d5efcd95e3adb76dc4292b3d2c420fdc58af..9eecb96cb7ec6d6a157ed2c5637e05138c3f55b9 100644
--- a/src/main/java/io/papermc/paper/util/ObfHelper.java
+++ b/src/main/java/io/papermc/paper/util/ObfHelper.java
@@ -2,19 +2,13 @@ package io.papermc.paper.util;
 
 import java.io.IOException;
 import java.io.InputStream;
-import java.io.InputStreamReader;
-import java.nio.charset.StandardCharsets;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
-import java.util.function.Function;
 import java.util.stream.Collectors;
-import net.fabricmc.mappingio.MappingReader;
-import net.fabricmc.mappingio.format.MappingFormat;
-import net.fabricmc.mappingio.tree.MappingTree;
-import net.fabricmc.mappingio.tree.MemoryMappingTree;
+import net.neoforged.srgutils.IMappingFile;
 import org.checkerframework.checker.nullness.qual.NonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.checkerframework.framework.qual.DefaultQualifier;
@@ -23,9 +17,6 @@ import org.checkerframework.framework.qual.DefaultQualifier;
 public enum ObfHelper {
     INSTANCE;
 
-    public static final String MOJANG_PLUS_YARN_NAMESPACE = "mojang+yarn";
-    public static final String SPIGOT_NAMESPACE = "spigot";
-
     private final @Nullable Map<String, ClassMapping> mappingsByObfName;
     private final @Nullable Map<String, ClassMapping> mappingsByMojangName;
 
@@ -93,55 +84,73 @@ public enum ObfHelper {
             return null;
         }
         try (final InputStream mappingsInputStream = MappingEnvironment.mappingsStream()) {
-            final MemoryMappingTree tree = new MemoryMappingTree();
-            MappingReader.read(new InputStreamReader(mappingsInputStream, StandardCharsets.UTF_8), MappingFormat.TINY_2_FILE, tree);
+            final IMappingFile mappings = IMappingFile.load(mappingsInputStream); // Mappings are mojang->spigot
             final Set<ClassMapping> classes = new HashSet<>();
 
             final StringPool pool = new StringPool();
-            for (final MappingTree.ClassMapping cls : tree.getClasses()) {
+            for (final IMappingFile.IClass cls : mappings.getClasses()) {
                 final Map<String, String> methods = new HashMap<>();
+                final Map<String, String> fields = new HashMap<>();
+                final Map<String, String> strippedMethods = new HashMap<>();
 
-                for (final MappingTree.MethodMapping methodMapping : cls.getMethods()) {
+                for (final IMappingFile.IMethod methodMapping : cls.getMethods()) {
                     methods.put(
                         pool.string(methodKey(
-                            Objects.requireNonNull(methodMapping.getName(SPIGOT_NAMESPACE)),
-                            Objects.requireNonNull(methodMapping.getDesc(SPIGOT_NAMESPACE))
+                            Objects.requireNonNull(methodMapping.getMapped()),
+                            Objects.requireNonNull(methodMapping.getMappedDescriptor())
                         )),
-                        pool.string(Objects.requireNonNull(methodMapping.getName(MOJANG_PLUS_YARN_NAMESPACE)))
+                        pool.string(Objects.requireNonNull(methodMapping.getOriginal()))
+                    );
+
+                    strippedMethods.put(
+                        pool.string(pool.string(strippedMethodKey(
+                            methodMapping.getMapped(),
+                            methodMapping.getDescriptor()
+                        ))),
+                        pool.string(methodMapping.getOriginal())
+                    );
+                }
+                for (final IMappingFile.IField field : cls.getFields()) {
+                    fields.put(
+                        pool.string(field.getMapped()),
+                        pool.string(field.getOriginal())
                     );
                 }
 
                 final ClassMapping map = new ClassMapping(
-                    Objects.requireNonNull(cls.getName(SPIGOT_NAMESPACE)).replace('/', '.'),
-                    Objects.requireNonNull(cls.getName(MOJANG_PLUS_YARN_NAMESPACE)).replace('/', '.'),
-                    Map.copyOf(methods)
+                    Objects.requireNonNull(cls.getMapped()).replace('/', '.'),
+                    Objects.requireNonNull(cls.getOriginal()).replace('/', '.'),
+                    Map.copyOf(methods),
+                    Map.copyOf(fields),
+                    Map.copyOf(strippedMethods)
                 );
                 classes.add(map);
             }
 
             return Set.copyOf(classes);
         } catch (final IOException ex) {
-            System.err.println("Failed to load mappings for stacktrace deobfuscation.");
+            System.err.println("Failed to load mappings.");
             ex.printStackTrace();
             return null;
         }
     }
 
-    public static String methodKey(final String obfName, final String obfDescriptor) {
-        return obfName + obfDescriptor;
+    public static String strippedMethodKey(final String methodName, final String methodDescriptor) {
+        final String methodKey = methodKey(methodName, methodDescriptor);
+        final int returnDescriptorEnd = methodKey.indexOf(')');
+        return methodKey.substring(0, returnDescriptorEnd + 1);
     }
 
-    private static final class StringPool {
-        private final Map<String, String> pool = new HashMap<>();
-
-        public String string(final String string) {
-            return this.pool.computeIfAbsent(string, Function.identity());
-        }
+    public static String methodKey(final String methodName, final String methodDescriptor) {
+        return methodName + methodDescriptor;
     }
 
     public record ClassMapping(
         String obfName,
         String mojangName,
-        Map<String, String> methodsByObf
+        Map<String, String> methodsByObf,
+        Map<String, String> fieldsByObf,
+        // obf name with mapped desc to mapped name. return value is excluded from desc as reflection doesn't use it
+        Map<String, String> strippedMethods
     ) {}
 }
diff --git a/src/main/java/io/papermc/paper/util/StacktraceDeobfuscator.java b/src/main/java/io/papermc/paper/util/StacktraceDeobfuscator.java
index eb910d4abf91488fa7cf1f5d47e0ee916c47f512..0b65fdf53124f3dd042b2363b1b8df8e1ca7de00 100644
--- a/src/main/java/io/papermc/paper/util/StacktraceDeobfuscator.java
+++ b/src/main/java/io/papermc/paper/util/StacktraceDeobfuscator.java
@@ -1,12 +1,11 @@
 package io.papermc.paper.util;
 
 import io.papermc.paper.configuration.GlobalConfiguration;
-import it.unimi.dsi.fastutil.ints.IntArrayList;
-import it.unimi.dsi.fastutil.ints.IntList;
+import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
+import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.Map;
 import org.checkerframework.checker.nullness.qual.NonNull;
@@ -22,14 +21,17 @@ import org.objectweb.asm.Opcodes;
 public enum StacktraceDeobfuscator {
     INSTANCE;
 
-    private final Map<Class<?>, Map<String, IntList>> lineMapCache = Collections.synchronizedMap(new LinkedHashMap<>(128, 0.75f, true) {
+    private final Map<Class<?>, Int2ObjectMap<String>> lineMapCache = Collections.synchronizedMap(new LinkedHashMap<>(128, 0.75f, true) {
         @Override
-        protected boolean removeEldestEntry(final Map.Entry<Class<?>, Map<String, IntList>> eldest) {
+        protected boolean removeEldestEntry(final Map.Entry<Class<?>, Int2ObjectMap<String>> eldest) {
             return this.size() > 127;
         }
     });
 
     public void deobfuscateThrowable(final Throwable throwable) {
+        if (!MappingEnvironment.reobf()) {
+            return;
+        }
         if (GlobalConfiguration.get() != null && !GlobalConfiguration.get().logging.deobfuscateStacktraces) { // handle null as true
             return;
         }
@@ -45,6 +47,9 @@ public enum StacktraceDeobfuscator {
     }
 
     public StackTraceElement[] deobfuscateStacktrace(final StackTraceElement[] traceElements) {
+        if (!MappingEnvironment.reobf()) {
+            return traceElements;
+        }
         if (GlobalConfiguration.get() != null && !GlobalConfiguration.get().logging.deobfuscateStacktraces) { // handle null as true
             return traceElements;
         }
@@ -89,18 +94,7 @@ public enum StacktraceDeobfuscator {
     }
 
     private @Nullable String determineMethodForLine(final Class<?> clazz, final int lineNumber) {
-        final Map<String, IntList> lineMap = this.lineMapCache.computeIfAbsent(clazz, StacktraceDeobfuscator::buildLineMap);
-        for (final var entry : lineMap.entrySet()) {
-            final String methodKey = entry.getKey();
-            final IntList lines = entry.getValue();
-            for (int i = 0, linesSize = lines.size(); i < linesSize; i++) {
-                final int num = lines.getInt(i);
-                if (num == lineNumber) {
-                    return methodKey;
-                }
-            }
-        }
-        return null;
+        return this.lineMapCache.computeIfAbsent(clazz, StacktraceDeobfuscator::buildLineMap).get(lineNumber);
     }
 
     private static String sourceFileName(final String fullClassName) {
@@ -112,34 +106,27 @@ public enum StacktraceDeobfuscator {
         return rootClassName + ".java";
     }
 
-    private static Map<String, IntList> buildLineMap(final Class<?> key) {
-        final Map<String, IntList> lineMap = new HashMap<>();
+    private static Int2ObjectMap<String> buildLineMap(final Class<?> key) {
+        final StringPool pool = new StringPool();
+        final Int2ObjectMap<String> lineMap = new Int2ObjectOpenHashMap<>();
         final class LineCollectingMethodVisitor extends MethodVisitor {
-            private final IntList lines = new IntArrayList();
             private final String name;
             private final String descriptor;
 
-            LineCollectingMethodVisitor(String name, String descriptor) {
+            LineCollectingMethodVisitor(final String name, final String descriptor) {
                 super(Opcodes.ASM9);
                 this.name = name;
                 this.descriptor = descriptor;
             }
 
             @Override
-            public void visitLineNumber(int line, Label start) {
-                super.visitLineNumber(line, start);
-                this.lines.add(line);
-            }
-
-            @Override
-            public void visitEnd() {
-                super.visitEnd();
-                lineMap.put(ObfHelper.methodKey(this.name, this.descriptor), this.lines);
+            public void visitLineNumber(final int line, final Label start) {
+                lineMap.put(line, pool.string(ObfHelper.methodKey(this.name, this.descriptor)));
             }
         }
         final ClassVisitor classVisitor = new ClassVisitor(Opcodes.ASM9) {
             @Override
-            public MethodVisitor visitMethod(int access, String name, String descriptor, String signature, String[] exceptions) {
+            public MethodVisitor visitMethod(final int access, final String name, final String descriptor, final String signature, final String[] exceptions) {
                 return new LineCollectingMethodVisitor(name, descriptor);
             }
         };
diff --git a/src/main/java/io/papermc/paper/util/StringPool.java b/src/main/java/io/papermc/paper/util/StringPool.java
new file mode 100644
index 0000000000000000000000000000000000000000..c0a486cb46ff30353c3ff09567891cd36238eeb4
--- /dev/null
+++ b/src/main/java/io/papermc/paper/util/StringPool.java
@@ -0,0 +1,34 @@
+package io.papermc.paper.util;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.function.Function;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+/**
+ * De-duplicates {@link String} instances without using {@link String#intern()}.
+ *
+ * <p>Interning may not be desired as we may want to use the heap for our pool,
+ * so it can be garbage collected as normal, etc.</p>
+ *
+ * <p>Additionally, interning can be slow due to the potentially large size of the
+ * pool (as it is shared for the entire JVM), and because most JVMs implement
+ * it using JNI.</p>
+ */
+@DefaultQualifier(NonNull.class)
+public final class StringPool {
+    private final Map<String, String> pool;
+
+    public StringPool() {
+        this(new HashMap<>());
+    }
+
+    public StringPool(final Map<String, String> map) {
+        this.pool = map;
+    }
+
+    public String string(final String string) {
+        return this.pool.computeIfAbsent(string, Function.identity());
+    }
+}
diff --git a/src/main/java/net/minecraft/world/level/redstone/CollectingNeighborUpdater.java b/src/main/java/net/minecraft/world/level/redstone/CollectingNeighborUpdater.java
index 457a963ee6ebd3cf5c3831f6660e3850335af49f..61744d8fde3ba98585cf261fc09f0acc042b67b8 100644
--- a/src/main/java/net/minecraft/world/level/redstone/CollectingNeighborUpdater.java
+++ b/src/main/java/net/minecraft/world/level/redstone/CollectingNeighborUpdater.java
@@ -128,7 +128,7 @@ public class CollectingNeighborUpdater implements NeighborUpdater {
         }
     }
 
-    interface NeighborUpdates {
+    public interface NeighborUpdates { // Paper - TODO make package-private again (it is just made public for testing LambdaMetafactory remapping)
         boolean runNext(Level world);
     }
 
diff --git a/src/main/java/org/bukkit/craftbukkit/util/Commodore.java b/src/main/java/org/bukkit/craftbukkit/util/Commodore.java
index 8420a53672cfb0f060d9c85c445d200b6701f521..fc04bfcb8b5dfa6d093c8d75b2f20c502ef94a63 100644
--- a/src/main/java/org/bukkit/craftbukkit/util/Commodore.java
+++ b/src/main/java/org/bukkit/craftbukkit/util/Commodore.java
@@ -76,36 +76,26 @@ public class Commodore {
     private static final Map<String, RerouteMethodData> FIELD_RENAME_METHOD_REROUTE = Commodore.createReroutes(FieldRename.class);
 
     // Paper start - Plugin rewrites
-    private static final Map<String, String> SEARCH_AND_REMOVE = initReplacementsMap();
-    private static Map<String, String> initReplacementsMap() {
-        Map<String, String> getAndRemove = new HashMap<>();
-        // Be wary of maven shade's relocations
-
-        final java.util.jar.Manifest manifest = io.papermc.paper.util.JarManifests.manifest(Commodore.class);
-        if (Boolean.getBoolean( "debug.rewriteForIde") && manifest != null)
-        {
-            // unversion incoming calls for pre-relocate debug work
-            final String NMS_REVISION_PACKAGE = "v" + manifest.getMainAttributes().getValue("CraftBukkit-Package-Version") + "/";
-
-            getAndRemove.put("org/bukkit/".concat("craftbukkit/" + NMS_REVISION_PACKAGE), NMS_REVISION_PACKAGE);
+    private static final String CB_PACKAGE_PREFIX = "org/bukkit/".concat("craftbukkit/");
+    private static final String LEGACY_CB_PACKAGE_PREFIX = CB_PACKAGE_PREFIX + io.papermc.paper.util.MappingEnvironment.LEGACY_CB_VERSION + "/";
+    private static String runtimeCbPkgPrefix() {
+        if (io.papermc.paper.util.MappingEnvironment.reobf()) {
+            return LEGACY_CB_PACKAGE_PREFIX;
         }
-
-        return getAndRemove;
+        return CB_PACKAGE_PREFIX;
     }
 
     @Nonnull
     private static String getOriginalOrRewrite(@Nonnull String original)
     {
-        String rewrite = null;
-        for ( Map.Entry<String, String> entry : SEARCH_AND_REMOVE.entrySet() )
-        {
-            if ( original.contains( entry.getKey() ) )
-            {
-                rewrite = original.replace( entry.getValue(), "" );
+        // Relocation is applied in reobf, and when mappings are present they handle the relocation
+        if (!io.papermc.paper.util.MappingEnvironment.reobf() && !io.papermc.paper.util.MappingEnvironment.hasMappings()) {
+            if (original.contains(LEGACY_CB_PACKAGE_PREFIX)) {
+                original = original.replace(LEGACY_CB_PACKAGE_PREFIX, CB_PACKAGE_PREFIX);
             }
         }
 
-        return rewrite != null ? rewrite : original;
+        return original;
     }
     // Paper end - Plugin rewrites
 
@@ -176,7 +166,7 @@ public class Commodore {
         ClassReader cr = new ClassReader(b);
         ClassWriter cw = new ClassWriter(cr, 0);
 
-        cr.accept(new ClassRemapper(new ClassVisitor(Opcodes.ASM9, cw) {
+        cr.accept(new ClassRemapper(new ClassVisitor(Opcodes.ASM9, io.papermc.paper.pluginremap.reflect.ReflectionRemapper.visitor(cw)) { // Paper
             final Set<RerouteMethodData> rerouteMethodData = new HashSet<>();
             String className;
             boolean isInterface;