1 /*
  2  * Copyright (c) 2012, 2026, Oracle and/or its affiliates. All rights reserved.
  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  4  *
  5  * This code is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.  Oracle designates this
  8  * particular file as subject to the "Classpath" exception as provided
  9  * by Oracle in the LICENSE file that accompanied this code.
 10  *
 11  * This code is distributed in the hope that it will be useful, but WITHOUT
 12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 14  * version 2 for more details (a copy is included in the LICENSE file that
 15  * accompanied this code).
 16  *
 17  * You should have received a copy of the GNU General Public License version
 18  * 2 along with this work; if not, write to the Free Software Foundation,
 19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 20  *
 21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 22  * or visit www.oracle.com if you need additional information or have any
 23  * questions.
 24  */
 25 
 26 package java.lang.invoke;
 27 
 28 import jdk.internal.constant.ClassOrInterfaceDescImpl;
 29 import jdk.internal.misc.PreviewFeatures;
 30 import jdk.internal.misc.CDS;
 31 import jdk.internal.util.ClassFileDumper;
 32 import sun.invoke.util.VerifyAccess;
 33 
 34 import java.io.Serializable;
 35 import java.lang.classfile.ClassBuilder;
 36 import java.lang.classfile.ClassFile;
 37 import java.lang.classfile.CodeBuilder;
 38 import java.lang.classfile.MethodBuilder;
 39 import java.lang.classfile.Opcode;
 40 import java.lang.classfile.TypeKind;
 41 import java.lang.constant.ClassDesc;
 42 import java.lang.constant.MethodTypeDesc;
 43 import java.lang.reflect.ClassFileFormatVersion;
 44 import java.lang.reflect.Modifier;
 45 import java.util.LinkedHashSet;
 46 import java.util.List;
 47 import java.util.Set;
 48 import java.util.function.Consumer;
 49 
 50 import static java.lang.classfile.ClassFile.*;
 51 import java.lang.classfile.attribute.ExceptionsAttribute;
 52 import java.lang.classfile.constantpool.ClassEntry;
 53 import java.lang.classfile.constantpool.ConstantPoolBuilder;
 54 
 55 import static java.lang.constant.ConstantDescs.*;
 56 import static java.lang.invoke.MethodHandleNatives.Constants.NESTMATE_CLASS;
 57 import static java.lang.invoke.MethodHandleNatives.Constants.STRONG_LOADER_LINK;
 58 import jdk.internal.constant.ConstantUtils;
 59 import jdk.internal.constant.MethodTypeDescImpl;
 60 import jdk.internal.vm.annotation.Stable;
 61 import sun.invoke.util.Wrapper;
 62 
 63 /**
 64  * Lambda metafactory implementation which dynamically creates an
 65  * inner-class-like class per lambda callsite.
 66  *
 67  * @see LambdaMetafactory
 68  */
 69 /* package */ final class InnerClassLambdaMetafactory extends AbstractValidatingLambdaMetafactory {
 70     private static final String LAMBDA_INSTANCE_FIELD = "LAMBDA_INSTANCE$";
 71     private static final @Stable String[] ARG_NAME_CACHE = {"arg$1", "arg$2", "arg$3", "arg$4", "arg$5", "arg$6", "arg$7", "arg$8"};
 72     private static final ClassDesc[] EMPTY_CLASSDESC_ARRAY = ConstantUtils.EMPTY_CLASSDESC;
 73 
 74     // For dumping generated classes to disk, for debugging purposes
 75     private static final ClassFileDumper lambdaProxyClassFileDumper;
 76 
 77     private static final boolean disableEagerInitialization;
 78 
 79     static {
 80         // To dump the lambda proxy classes, set this system property:
 81         //    -Djdk.invoke.LambdaMetafactory.dumpProxyClassFiles
 82         // or -Djdk.invoke.LambdaMetafactory.dumpProxyClassFiles=true
 83         final String dumpProxyClassesKey = "jdk.invoke.LambdaMetafactory.dumpProxyClassFiles";
 84         lambdaProxyClassFileDumper = ClassFileDumper.getInstance(dumpProxyClassesKey, "DUMP_LAMBDA_PROXY_CLASS_FILES");
 85 
 86         final String disableEagerInitializationKey = "jdk.internal.lambda.disableEagerInitialization";
 87         disableEagerInitialization = Boolean.getBoolean(disableEagerInitializationKey);
 88     }
 89 
 90     // See context values in AbstractValidatingLambdaMetafactory
 91     private final ClassDesc implMethodClassDesc;     // Name of type containing implementation "CC"
 92     private final String implMethodName;             // Name of implementation method "impl"
 93     private final MethodTypeDesc implMethodDesc;     // Type descriptor for implementation methods "(I)Ljava/lang/String;"
 94     private final MethodType constructorType;        // Generated class constructor type "(CC)void"
 95     private final MethodTypeDesc constructorTypeDesc;// Type descriptor for the generated class constructor type "(CC)void"
 96     private final ClassDesc[] argDescs;              // Type descriptors for the constructor arguments
 97     private final String lambdaClassName;            // Generated name for the generated class "X$$Lambda$1"
 98     private final ConstantPoolBuilder pool = ConstantPoolBuilder.of();
 99     private final ClassEntry lambdaClassEntry;       // Class entry for the generated class "X$$Lambda$1"
100     private final boolean useImplMethodHandle;       // use MethodHandle invocation instead of symbolic bytecode invocation
101 
102     /**
103      * General meta-factory constructor, supporting both standard cases and
104      * allowing for uncommon options such as serialization or bridging.
105      *
106      * @param caller Stacked automatically by VM; represents a lookup context
107      *               with the accessibility privileges of the caller.
108      * @param factoryType Stacked automatically by VM; the signature of the
109      *                    invoked method, which includes the expected static
110      *                    type of the returned lambda object, and the static
111      *                    types of the captured arguments for the lambda.  In
112      *                    the event that the implementation method is an
113      *                    instance method, the first argument in the invocation
114      *                    signature will correspond to the receiver.
115      * @param interfaceMethodName Name of the method in the functional interface to
116      *                   which the lambda or method reference is being
117      *                   converted, represented as a String.
118      * @param interfaceMethodType Type of the method in the functional interface to
119      *                            which the lambda or method reference is being
120      *                            converted, represented as a MethodType.
121      * @param implementation The implementation method which should be called (with
122      *                       suitable adaptation of argument types, return types,
123      *                       and adjustment for captured arguments) when methods of
124      *                       the resulting functional interface instance are invoked.
125      * @param dynamicMethodType The signature of the primary functional
126      *                          interface method after type variables are
127      *                          substituted with their instantiation from
128      *                          the capture site
129      * @param isSerializable Should the lambda be made serializable?  If set,
130      *                       either the target type or one of the additional SAM
131      *                       types must extend {@code Serializable}.
132      * @param altInterfaces Additional interfaces which the lambda object
133      *                      should implement.
134      * @param altMethods Method types for additional signatures to be
135      *                   implemented by invoking the implementation method
136      * @throws LambdaConversionException If any of the meta-factory protocol
137      *         invariants are violated
138      */
139     public InnerClassLambdaMetafactory(MethodHandles.Lookup caller,
140                                        MethodType factoryType,
141                                        String interfaceMethodName,
142                                        MethodType interfaceMethodType,
143                                        MethodHandle implementation,
144                                        MethodType dynamicMethodType,
145                                        boolean isSerializable,
146                                        Class<?>[] altInterfaces,
147                                        MethodType[] altMethods)
148             throws LambdaConversionException {
149         super(caller, factoryType, interfaceMethodName, interfaceMethodType,
150               implementation, dynamicMethodType,
151               isSerializable, altInterfaces, altMethods);
152         implMethodClassDesc = implClassDesc(implClass);
153         implMethodName = implInfo.getName();
154         implMethodDesc = methodDesc(implInfo.getMethodType());
155         constructorType = factoryType.changeReturnType(Void.TYPE);
156         lambdaClassName = lambdaClassName(targetClass);
157         lambdaClassEntry = pool.classEntry(ConstantUtils.internalNameToDesc(lambdaClassName));
158         // If the target class invokes a protected method inherited from a
159         // superclass in a different package, or does 'invokespecial', the
160         // lambda class has no access to the resolved method, or does
161         // 'invokestatic' on a hidden class which cannot be resolved by name.
162         // Instead, we need to pass the live implementation method handle to
163         // the proxy class to invoke directly. (javac prefers to avoid this
164         // situation by generating bridges in the target class)
165         useImplMethodHandle = (Modifier.isProtected(implInfo.getModifiers()) &&
166                                !VerifyAccess.isSamePackage(targetClass, implInfo.getDeclaringClass())) ||
167                                implKind == MethodHandleInfo.REF_invokeSpecial ||
168                                implKind == MethodHandleInfo.REF_invokeStatic && implClass.isHidden();
169         int parameterCount = factoryType.parameterCount();
170         ClassDesc[] argDescs;
171         MethodTypeDesc constructorTypeDesc;
172         if (parameterCount > 0) {
173             argDescs = new ClassDesc[parameterCount];
174             for (int i = 0; i < parameterCount; i++) {
175                 argDescs[i] = classDesc(factoryType.parameterType(i));
176             }
177             constructorTypeDesc = MethodTypeDescImpl.ofValidated(CD_void, argDescs);
178         } else {
179             argDescs = EMPTY_CLASSDESC_ARRAY;
180             constructorTypeDesc = MTD_void;
181         }
182         this.argDescs = argDescs;
183         this.constructorTypeDesc = constructorTypeDesc;
184     }
185 
186     private static String argName(int i) {
187         return i < ARG_NAME_CACHE.length ? ARG_NAME_CACHE[i] :  "arg$" + (i + 1);
188     }
189 
190     private static String sanitizedTargetClassName(Class<?> targetClass) {
191         String name = targetClass.getName();
192         if (targetClass.isHidden()) {
193             // use the original class name
194             name = name.replace('/', '_');
195         }
196         return name.replace('.', '/');
197     }
198 
199     private static String lambdaClassName(Class<?> targetClass) {
200         return sanitizedTargetClassName(targetClass).concat("$$Lambda");
201     }
202 
203     /**
204      * Build the CallSite. Generate a class file which implements the functional
205      * interface, define the class, if there are no parameters create an instance
206      * of the class which the CallSite will return, otherwise, generate handles
207      * which will call the class' constructor.
208      *
209      * @return a CallSite, which, when invoked, will return an instance of the
210      * functional interface
211      * @throws LambdaConversionException If properly formed functional interface
212      * is not found
213      */
214     @Override
215     CallSite buildCallSite() throws LambdaConversionException {
216         final Class<?> innerClass = spinInnerClass();
217         if (factoryType.parameterCount() == 0 && disableEagerInitialization) {
218             try {
219                 return new ConstantCallSite(caller.findStaticGetter(innerClass, LAMBDA_INSTANCE_FIELD,
220                                                                     factoryType.returnType()));
221             } catch (ReflectiveOperationException e) {
222                 throw new LambdaConversionException(
223                         "Exception finding " + LAMBDA_INSTANCE_FIELD + " static field", e);
224             }
225         } else {
226             try {
227                 MethodHandle mh = caller.findConstructor(innerClass, constructorType);
228                 if (factoryType.parameterCount() == 0) {
229                     // In the case of a non-capturing lambda, we optimize linkage by pre-computing a single instance
230                     Object inst = mh.invokeBasic();
231                     return new ConstantCallSite(MethodHandles.constant(interfaceClass, inst));
232                 } else {
233                     return new ConstantCallSite(mh.asType(factoryType));
234                 }
235             } catch (ReflectiveOperationException e) {
236                 throw new LambdaConversionException("Exception finding constructor", e);
237             } catch (Throwable e) {
238                 throw new LambdaConversionException("Exception instantiating lambda object", e);
239             }
240         }
241     }
242 
243     /**
244      * Spins the lambda proxy class.
245      *
246      * This first checks if a lambda proxy class can be loaded from CDS archive.
247      * Otherwise, generate the lambda proxy class. If CDS dumping is enabled, it
248      * registers the lambda proxy class for including into the CDS archive.
249      */
250     private Class<?> spinInnerClass() throws LambdaConversionException {
251         // CDS does not handle disableEagerInitialization or useImplMethodHandle
252         if (!disableEagerInitialization && !useImplMethodHandle) {
253             if (CDS.isUsingArchive()) {
254                 // load from CDS archive if present
255                 Class<?> innerClass = LambdaProxyClassArchive.find(targetClass,
256                                                                    interfaceMethodName,
257                                                                    factoryType,
258                                                                    interfaceMethodType,
259                                                                    implementation,
260                                                                    dynamicMethodType,
261                                                                    isSerializable,
262                                                                    altInterfaces,
263                                                                    altMethods);
264                 if (innerClass != null) return innerClass;
265             }
266 
267             // include lambda proxy class in CDS archive at dump time
268             if (CDS.isDumpingArchive()) {
269                 Class<?> innerClass = generateInnerClass();
270                 LambdaProxyClassArchive.register(targetClass,
271                                                  interfaceMethodName,
272                                                  factoryType,
273                                                  interfaceMethodType,
274                                                  implementation,
275                                                  dynamicMethodType,
276                                                  isSerializable,
277                                                  altInterfaces,
278                                                  altMethods,
279                                                  innerClass);
280                 return innerClass;
281             }
282 
283         }
284         return generateInnerClass();
285     }
286 
287     /**
288      * Generate a class file which implements the functional
289      * interface, define and return the class.
290      *
291      * @return a Class which implements the functional interface
292      * @throws LambdaConversionException If properly formed functional interface
293      * is not found
294      */
295     private Class<?> generateInnerClass() throws LambdaConversionException {
296         List<ClassDesc> interfaces;
297         ClassDesc interfaceDesc = classDesc(interfaceClass);
298         boolean accidentallySerializable = !isSerializable && Serializable.class.isAssignableFrom(interfaceClass);
299         if (altInterfaces.length == 0) {
300             interfaces = List.of(interfaceDesc);
301         } else {
302             // Assure no duplicate interfaces (ClassFormatError)
303             Set<ClassDesc> itfs = LinkedHashSet.newLinkedHashSet(altInterfaces.length + 1);
304             itfs.add(interfaceDesc);
305             for (Class<?> i : altInterfaces) {
306                 itfs.add(classDesc(i));
307                 accidentallySerializable |= !isSerializable && Serializable.class.isAssignableFrom(i);
308             }
309             interfaces = List.copyOf(itfs);
310         }
311         final boolean finalAccidentallySerializable = accidentallySerializable;
312         final byte[] classBytes = ClassFile.of().build(lambdaClassEntry, pool, new Consumer<ClassBuilder>() {
313             @Override
314             public void accept(ClassBuilder clb) {
315                 clb.withVersion(ClassFileFormatVersion.latest().major(), (PreviewFeatures.isEnabled() ? ClassFile.PREVIEW_MINOR_VERSION : 0))
316                    .withFlags(ACC_SUPER | ACC_FINAL | ACC_SYNTHETIC)
317                    .withInterfaceSymbols(interfaces);
318                 // All Classes in the BSM argument method types are loaded; no need for LoadableDescriptors
319 
320                 // Generate final fields to be filled in by constructor
321                 for (int i = 0; i < argDescs.length; i++) {
322                     clb.withField(argName(i), argDescs[i], ACC_PRIVATE | ACC_FINAL);
323                 }
324 
325                 generateConstructor(clb);
326 
327                 if (factoryType.parameterCount() == 0 && disableEagerInitialization) {
328                     generateClassInitializer(clb);
329                 }
330 
331                 // Forward the SAM method
332                 clb.withMethodBody(interfaceMethodName,
333                         methodDesc(interfaceMethodType),
334                         ACC_PUBLIC,
335                         forwardingMethod(interfaceMethodType));
336 
337                 // Forward the bridges
338                 if (altMethods != null) {
339                     for (MethodType mt : altMethods) {
340                         clb.withMethodBody(interfaceMethodName,
341                                 methodDesc(mt),
342                                 ACC_PUBLIC | ACC_BRIDGE,
343                                 forwardingMethod(mt));
344                     }
345                 }
346 
347                 if (isSerializable)
348                     generateSerializationFriendlyMethods(clb);
349                 else if (finalAccidentallySerializable)
350                     generateSerializationHostileMethods(clb);
351             }
352         });
353 
354         // Define the generated class in this VM.
355 
356         try {
357             // this class is linked at the indy callsite; so define a hidden nestmate
358             var classdata = useImplMethodHandle? implementation : null;
359             return caller.makeHiddenClassDefiner(lambdaClassName, classBytes, lambdaProxyClassFileDumper, NESTMATE_CLASS | STRONG_LOADER_LINK)
360                          .defineClass(!disableEagerInitialization, classdata);
361 
362         } catch (Throwable t) {
363             throw new InternalError(t);
364         }
365     }
366 
367     /**
368      * Generate a static field and a static initializer that sets this field to an instance of the lambda
369      */
370     private void generateClassInitializer(ClassBuilder clb) {
371         ClassDesc lambdaTypeDescriptor = classDesc(factoryType.returnType());
372 
373         // Generate the static final field that holds the lambda singleton
374         clb.withField(LAMBDA_INSTANCE_FIELD, lambdaTypeDescriptor, ACC_PRIVATE | ACC_STATIC | ACC_FINAL);
375 
376         // Instantiate the lambda and store it to the static final field
377         clb.withMethodBody(CLASS_INIT_NAME, MTD_void, ACC_STATIC, new Consumer<>() {
378             @Override
379             public void accept(CodeBuilder cob) {
380                 assert factoryType.parameterCount() == 0;
381                 cob.new_(lambdaClassEntry)
382                    .dup()
383                    .invokespecial(pool.methodRefEntry(lambdaClassEntry, pool.nameAndTypeEntry(INIT_NAME, constructorTypeDesc)))
384                    .putstatic(pool.fieldRefEntry(lambdaClassEntry, pool.nameAndTypeEntry(LAMBDA_INSTANCE_FIELD, lambdaTypeDescriptor)))
385                    .return_();
386             }
387         });
388     }
389 
390     /**
391      * Generate the constructor for the class
392      */
393     private void generateConstructor(ClassBuilder clb) {
394         // Generate constructor
395         clb.withMethodBody(INIT_NAME, constructorTypeDesc, ACC_PRIVATE,
396                 new Consumer<>() {
397                     @Override
398                     public void accept(CodeBuilder cob) {
399                         int parameterCount = factoryType.parameterCount();
400                         for (int i = 0; i < parameterCount; i++) {
401                             cob.aload(0)
402                                .loadLocal(TypeKind.from(factoryType.parameterType(i)), cob.parameterSlot(i))
403                                .putfield(pool.fieldRefEntry(lambdaClassEntry, pool.nameAndTypeEntry(argName(i), argDescs[i])));
404                         }
405                         cob.aload(0)
406                            .invokespecial(CD_Object, INIT_NAME, MTD_void)
407                            .return_();
408                     }
409                 });
410     }
411 
412     private static class SerializationSupport {
413         // Serialization support
414         private static final ClassDesc CD_SerializedLambda = ClassOrInterfaceDescImpl.ofValidated("Ljava/lang/invoke/SerializedLambda;");
415         private static final ClassDesc CD_ObjectOutputStream = ClassOrInterfaceDescImpl.ofValidated("Ljava/io/ObjectOutputStream;");
416         private static final ClassDesc CD_ObjectInputStream = ClassOrInterfaceDescImpl.ofValidated("Ljava/io/ObjectInputStream;");
417         private static final MethodTypeDesc MTD_Object = MethodTypeDescImpl.ofValidated(CD_Object);
418         private static final MethodTypeDesc MTD_void_ObjectOutputStream = MethodTypeDescImpl.ofValidated(CD_void, CD_ObjectOutputStream);
419         private static final MethodTypeDesc MTD_void_ObjectInputStream = MethodTypeDescImpl.ofValidated(CD_void, CD_ObjectInputStream);
420 
421         private static final String NAME_METHOD_WRITE_REPLACE = "writeReplace";
422         private static final String NAME_METHOD_READ_OBJECT = "readObject";
423         private static final String NAME_METHOD_WRITE_OBJECT = "writeObject";
424 
425         static final ClassDesc CD_NotSerializableException = ClassOrInterfaceDescImpl.ofValidated("Ljava/io/NotSerializableException;");
426         static final MethodTypeDesc MTD_CTOR_NOT_SERIALIZABLE_EXCEPTION = MethodTypeDescImpl.ofValidated(CD_void, CD_String);
427         static final MethodTypeDesc MTD_CTOR_SERIALIZED_LAMBDA = MethodTypeDescImpl.ofValidated(CD_void,
428                 CD_Class, CD_String, CD_String, CD_String, CD_int, CD_String, CD_String, CD_String, CD_String, ConstantUtils.CD_Object_array);
429 
430     }
431 
432     /**
433      * Generate a writeReplace method that supports serialization
434      */
435     private void generateSerializationFriendlyMethods(ClassBuilder clb) {
436         clb.withMethodBody(SerializationSupport.NAME_METHOD_WRITE_REPLACE, SerializationSupport.MTD_Object, ACC_PRIVATE | ACC_FINAL,
437                 new Consumer<>() {
438                     @Override
439                     public void accept(CodeBuilder cob) {
440                         cob.new_(SerializationSupport.CD_SerializedLambda)
441                            .dup()
442                            .ldc(ClassDesc.ofInternalName(sanitizedTargetClassName(targetClass)))
443                            .ldc(factoryType.returnType().getName().replace('.', '/'))
444                            .ldc(interfaceMethodName)
445                            .ldc(interfaceMethodType.toMethodDescriptorString())
446                            .ldc(implInfo.getReferenceKind())
447                            .ldc(implInfo.getDeclaringClass().getName().replace('.', '/'))
448                            .ldc(implInfo.getName())
449                            .ldc(implInfo.getMethodType().toMethodDescriptorString())
450                            .ldc(dynamicMethodType.toMethodDescriptorString())
451                            .loadConstant(argDescs.length)
452                            .anewarray(CD_Object);
453                         for (int i = 0; i < argDescs.length; i++) {
454                             cob.dup()
455                                .loadConstant(i)
456                                .aload(0)
457                                .getfield(pool.fieldRefEntry(lambdaClassEntry, pool.nameAndTypeEntry(argName(i), argDescs[i])));
458                             TypeConvertingMethodAdapter.boxIfTypePrimitive(cob, TypeKind.from(argDescs[i]));
459                             cob.aastore();
460                         }
461                         cob.invokespecial(SerializationSupport.CD_SerializedLambda, INIT_NAME,
462                                           SerializationSupport.MTD_CTOR_SERIALIZED_LAMBDA)
463                            .areturn();
464                     }
465                 });
466     }
467 
468     /**
469      * Generate a readObject/writeObject method that is hostile to serialization
470      */
471     private void generateSerializationHostileMethods(ClassBuilder clb) {
472         var hostileMethod = new Consumer<MethodBuilder>() {
473             @Override
474             public void accept(MethodBuilder mb) {
475                 ConstantPoolBuilder cp = mb.constantPool();
476                 ClassEntry nseCE = cp.classEntry(SerializationSupport.CD_NotSerializableException);
477                 mb.with(ExceptionsAttribute.of(nseCE))
478                         .withCode(new Consumer<CodeBuilder>() {
479                             @Override
480                             public void accept(CodeBuilder cob) {
481                                 cob.new_(nseCE)
482                                         .dup()
483                                         .ldc("Non-serializable lambda")
484                                         .invokespecial(cp.methodRefEntry(nseCE, cp.nameAndTypeEntry(INIT_NAME,
485                                                 SerializationSupport.MTD_CTOR_NOT_SERIALIZABLE_EXCEPTION)))
486                                         .athrow();
487                             }
488                         });
489             }
490         };
491         clb.withMethod(SerializationSupport.NAME_METHOD_WRITE_OBJECT, SerializationSupport.MTD_void_ObjectOutputStream,
492                 ACC_PRIVATE + ACC_FINAL, hostileMethod);
493         clb.withMethod(SerializationSupport.NAME_METHOD_READ_OBJECT, SerializationSupport.MTD_void_ObjectInputStream,
494                 ACC_PRIVATE + ACC_FINAL, hostileMethod);
495     }
496 
497     /**
498      * This method generates a method body which calls the lambda implementation
499      * method, converting arguments, as needed.
500      */
501     Consumer<CodeBuilder> forwardingMethod(MethodType methodType) {
502         return new Consumer<>() {
503             @Override
504             public void accept(CodeBuilder cob) {
505                 if (implKind == MethodHandleInfo.REF_newInvokeSpecial) {
506                     cob.new_(implMethodClassDesc)
507                        .dup();
508                 }
509                 if (useImplMethodHandle) {
510                     ConstantPoolBuilder cp = cob.constantPool();
511                     cob.ldc(cp.constantDynamicEntry(cp.bsmEntry(cp.methodHandleEntry(BSM_CLASS_DATA), List.of()),
512                                                     cp.nameAndTypeEntry(DEFAULT_NAME, CD_MethodHandle)));
513                 }
514                 for (int i = 0; i < argDescs.length; i++) {
515                     cob.aload(0)
516                        .getfield(pool.fieldRefEntry(lambdaClassEntry, pool.nameAndTypeEntry(argName(i), argDescs[i])));
517                 }
518 
519                 convertArgumentTypes(cob, methodType);
520 
521                 if (useImplMethodHandle) {
522                     MethodType mtype = implInfo.getMethodType();
523                     if (implKind != MethodHandleInfo.REF_invokeStatic) {
524                         mtype = mtype.insertParameterTypes(0, implClass);
525                     }
526                     cob.invokevirtual(CD_MethodHandle, "invokeExact", methodDesc(mtype));
527                 } else {
528                     // Invoke the method we want to forward to
529                     cob.invoke(invocationOpcode(), implMethodClassDesc, implMethodName, implMethodDesc, implClass.isInterface());
530                 }
531                 // Convert the return value (if any) and return it
532                 // Note: if adapting from non-void to void, the 'return'
533                 // instruction will pop the unneeded result
534                 Class<?> implReturnClass = implMethodType.returnType();
535                 Class<?> samReturnClass = methodType.returnType();
536                 TypeConvertingMethodAdapter.convertType(cob, implReturnClass, samReturnClass, samReturnClass);
537                 cob.return_(TypeKind.from(samReturnClass));
538             }
539         };
540     }
541 
542     private void convertArgumentTypes(CodeBuilder cob, MethodType samType) {
543         int samParametersLength = samType.parameterCount();
544         int captureArity = factoryType.parameterCount();
545         for (int i = 0; i < samParametersLength; i++) {
546             Class<?> argType = samType.parameterType(i);
547             cob.loadLocal(TypeKind.from(argType), cob.parameterSlot(i));
548             TypeConvertingMethodAdapter.convertType(cob, argType, implMethodType.parameterType(captureArity + i), dynamicMethodType.parameterType(i));
549         }
550     }
551 
552     private Opcode invocationOpcode() throws InternalError {
553         return switch (implKind) {
554             case MethodHandleInfo.REF_invokeStatic     -> Opcode.INVOKESTATIC;
555             case MethodHandleInfo.REF_newInvokeSpecial -> Opcode.INVOKESPECIAL;
556             case MethodHandleInfo.REF_invokeVirtual    -> Opcode.INVOKEVIRTUAL;
557             case MethodHandleInfo.REF_invokeInterface  -> Opcode.INVOKEINTERFACE;
558             case MethodHandleInfo.REF_invokeSpecial    -> Opcode.INVOKESPECIAL;
559             default -> throw new InternalError("Unexpected invocation kind: " + implKind);
560         };
561     }
562 
563     static ClassDesc implClassDesc(Class<?> cls) {
564         return cls.isHidden() ? null : ConstantUtils.referenceClassDesc(cls.descriptorString());
565     }
566 
567     static ClassDesc classDesc(Class<?> cls) {
568         return cls.isPrimitive() ? Wrapper.forPrimitiveType(cls).basicClassDescriptor()
569                                  : ConstantUtils.referenceClassDesc(cls.descriptorString());
570     }
571 
572     static MethodTypeDesc methodDesc(MethodType mt) {
573         var params = new ClassDesc[mt.parameterCount()];
574         for (int i = 0; i < params.length; i++) {
575             params[i] = classDesc(mt.parameterType(i));
576         }
577         return MethodTypeDescImpl.ofValidated(classDesc(mt.returnType()), params);
578     }
579 }