// Copyright (c) 2021, the R8 project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

package com.android.tools.r8.ir.desugar.itf;


import com.android.tools.r8.cf.code.CfFieldInstruction;
import com.android.tools.r8.cf.code.CfInstruction;
import com.android.tools.r8.cf.code.CfInvoke;
import com.android.tools.r8.cf.code.CfReturnVoid;
import com.android.tools.r8.cf.code.CfStackInstruction;
import com.android.tools.r8.cf.code.CfStackInstruction.Opcode;
import com.android.tools.r8.code.Instruction;
import com.android.tools.r8.code.InvokeSuper;
import com.android.tools.r8.errors.CompilationError;
import com.android.tools.r8.errors.Unimplemented;
import com.android.tools.r8.graph.AppView;
import com.android.tools.r8.graph.CfCode;
import com.android.tools.r8.graph.Code;
import com.android.tools.r8.graph.DexAnnotationSet;
import com.android.tools.r8.graph.DexApplication.Builder;
import com.android.tools.r8.graph.DexClass;
import com.android.tools.r8.graph.DexEncodedField;
import com.android.tools.r8.graph.DexEncodedMethod;
import com.android.tools.r8.graph.DexField;
import com.android.tools.r8.graph.DexItemFactory;
import com.android.tools.r8.graph.DexMethod;
import com.android.tools.r8.graph.DexProgramClass;
import com.android.tools.r8.graph.DexType;
import com.android.tools.r8.graph.DexValue.DexValueInt;
import com.android.tools.r8.graph.FieldAccessFlags;
import com.android.tools.r8.graph.GenericSignature.ClassTypeSignature;
import com.android.tools.r8.graph.GenericSignature.FieldTypeSignature;
import com.android.tools.r8.graph.GenericSignature.MethodTypeSignature;
import com.android.tools.r8.graph.GraphLens;
import com.android.tools.r8.graph.MethodAccessFlags;
import com.android.tools.r8.graph.MethodCollection;
import com.android.tools.r8.graph.NestedGraphLens;
import com.android.tools.r8.graph.ProgramMethod;
import com.android.tools.r8.synthesis.SyntheticMethodBuilder;
import com.android.tools.r8.synthesis.SyntheticNaming;
import com.android.tools.r8.synthesis.SyntheticProgramClassBuilder;
import com.android.tools.r8.utils.Pair;
import com.android.tools.r8.utils.collections.BidirectionalManyToManyRepresentativeMap;
import com.android.tools.r8.utils.collections.BidirectionalManyToOneRepresentativeMap;
import com.android.tools.r8.utils.collections.BidirectionalOneToOneHashMap;
import com.android.tools.r8.utils.collections.BidirectionalOneToOneMap;
import com.android.tools.r8.utils.collections.MutableBidirectionalOneToOneMap;
import com.android.tools.r8.utils.collections.ProgramMethodSet;
import com.google.common.collect.ImmutableList;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.HashSet;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import org.objectweb.asm.Opcodes;

// Default and static method interface desugaring processor for interfaces.
//
// Makes default interface methods abstract, moves their implementation to
// a companion class. Removes bridge default methods.
//
// Also moves static interface methods into a companion class.
public final class InterfaceProcessor implements InterfaceDesugaringProcessor {

  private final AppView<?> appView;
  private final InterfaceMethodRewriter rewriter;
  private final Map<DexProgramClass, PostProcessingInterfaceInfo> postProcessingInterfaceInfos =
      new ConcurrentHashMap<>();
  private final ClassTypeSignature objectTypeSignature;

  InterfaceProcessor(AppView<?> appView, InterfaceMethodRewriter rewriter) {
    this.appView = appView;
    this.rewriter = rewriter;
    this.objectTypeSignature = new ClassTypeSignature(appView.dexItemFactory().objectType);
  }

  @Override
  public void process(DexProgramClass iface, ProgramMethodSet synthesizedMethods) {
    if (!iface.isInterface()) {
      return;
    }
    analyzeBridges(iface);
    if (needsCompanionClass(iface)) {
      ensureCompanionClass(iface, synthesizedMethods);
    }
  }

  private void analyzeBridges(DexProgramClass iface) {
    for (ProgramMethod method : iface.virtualProgramMethods()) {
      DexEncodedMethod virtual = method.getDefinition();
      if (!interfaceMethodRemovalChangesApi(virtual, iface)) {
        getPostProcessingInterfaceInfo(iface).setHasBridgesToRemove();
        return;
      }
    }
  }

  private boolean needsCompanionClass(DexProgramClass iface) {
    if (hasStaticMethodThatTriggersNonTrivialClassInitializer(iface)) {
      return true;
    }
    for (ProgramMethod method : iface.virtualProgramMethods()) {
      DexEncodedMethod virtual = method.getDefinition();
      if (rewriter.isDefaultMethod(virtual)) {
        return true;
      }
    }
    for (ProgramMethod method : iface.directProgramMethods()) {
      DexEncodedMethod definition = method.getDefinition();
      if (!definition.isInitializer()) {
        return true;
      }
    }
    return false;
  }

  private DexProgramClass ensureCompanionClass(
      DexProgramClass iface, ProgramMethodSet synthesizedMethods) {

    DexProgramClass companionClass =
        appView
            .getSyntheticItems()
            .ensureFixedClass(
                SyntheticNaming.SyntheticKind.COMPANION_CLASS,
                iface,
                appView,
                builder -> {
                  builder.setSourceFile(iface.sourceFile);
                  builder.setGenericSignature(
                      iface.getClassSignature().toObjectBoundWithSameFormals(objectTypeSignature));
                  ensureCompanionClassInitializesInterface(iface, builder);
                  processVirtualInterfaceMethods(iface, builder);
                  processDirectInterfaceMethods(iface, builder);
                });
    assert companionClass.getType() == rewriter.getCompanionClassType(iface.type);
    assert companionClass.hasMethods();

    // D8 and R8 don't need to optimize the methods since they are just moved from interfaces and
    // don't need to be re-processed, besides the clinit, which has just been inserted.
    if (companionClass.hasClassInitializer()) {
      synthesizedMethods.add(companionClass.getProgramClassInitializer());
    }

    return companionClass;
  }

  private void ensureCompanionClassInitializesInterface(
      DexProgramClass iface, SyntheticProgramClassBuilder builder) {
    if (!hasStaticMethodThatTriggersNonTrivialClassInitializer(iface)) {
      return;
    }
    DexEncodedField clinitField = ensureStaticClinitFieldToTriggerinterfaceInitialization(iface);
    builder.addMethod(
        methodBuilder -> createCompanionClassInitializer(iface, clinitField, methodBuilder));
  }

  private DexEncodedField ensureStaticClinitFieldToTriggerinterfaceInitialization(
      DexProgramClass iface) {
    DexEncodedField clinitField =
        findExistingStaticClinitFieldToTriggerInterfaceInitialization(iface);
    if (clinitField == null) {
      clinitField = createStaticClinitFieldToTriggerInterfaceInitialization(iface);
      iface.appendStaticField(clinitField);
    }
    return clinitField;
  }

  private boolean hasStaticMethodThatTriggersNonTrivialClassInitializer(DexProgramClass iface) {
    return iface.hasClassInitializer()
        && iface
            .getMethodCollection()
            .hasDirectMethods(method -> method.isStatic() && !method.isClassInitializer());
  }

  private DexEncodedField findExistingStaticClinitFieldToTriggerInterfaceInitialization(
      DexProgramClass iface) {
    // Don't select a field that has been marked dead, since we'll assert later that these fields
    // have been dead code eliminated.
    for (DexEncodedField field :
        iface.staticFields(field -> !field.isPrivate() && !field.getOptimizationInfo().isDead())) {
      return field;
    }
    return null;
  }

  private DexEncodedField createStaticClinitFieldToTriggerInterfaceInitialization(
      DexProgramClass iface) {
    DexItemFactory dexItemFactory = appView.dexItemFactory();
    DexField clinitFieldTemplateReference =
        dexItemFactory.createField(iface.getType(), dexItemFactory.intType, "$desugar$clinit");
    DexField clinitFieldReference =
        dexItemFactory.createFreshFieldName(
            clinitFieldTemplateReference, candidate -> iface.lookupField(candidate) == null);
    return new DexEncodedField(
        clinitFieldReference,
        FieldAccessFlags.builder().setPackagePrivate().setStatic().setSynthetic().build(),
        FieldTypeSignature.noSignature(),
        DexAnnotationSet.empty(),
        DexValueInt.DEFAULT);
  }

  private void createCompanionClassInitializer(
      DexProgramClass iface, DexEncodedField clinitField, SyntheticMethodBuilder methodBuilder) {
    SyntheticMethodBuilder.SyntheticCodeGenerator codeGenerator =
        method ->
            new CfCode(
                method.holder,
                clinitField.getType().isWideType() ? 2 : 1,
                0,
                ImmutableList.of(
                    new CfFieldInstruction(
                        Opcodes.GETSTATIC, clinitField.getReference(), clinitField.getReference()),
                    clinitField.getType().isWideType()
                        ? new CfStackInstruction(Opcode.Pop2)
                        : new CfStackInstruction(Opcode.Pop),
                    new CfReturnVoid()),
                ImmutableList.of(),
                ImmutableList.of());
    methodBuilder
        .setName(appView.dexItemFactory().classConstructorMethodName)
        .setProto(appView.dexItemFactory().createProto(appView.dexItemFactory().voidType))
        .setAccessFlags(
            MethodAccessFlags.builder().setConstructor().setPackagePrivate().setStatic().build())
        .setCode(codeGenerator)
        .setClassFileVersion(iface.getInitialClassFileVersion());
  }

  private void processVirtualInterfaceMethods(
      DexProgramClass iface, SyntheticProgramClassBuilder builder) {
    for (ProgramMethod method : iface.virtualProgramMethods()) {
      DexEncodedMethod virtual = method.getDefinition();
      if (rewriter.isDefaultMethod(virtual)) {
        if (!canMoveToCompanionClass(virtual)) {
          throw new CompilationError(
              "One or more instruction is preventing default interface "
                  + "method from being desugared: "
                  + method.toSourceString(),
              iface.origin);
        }

        // Create a new method in a companion class to represent default method implementation.
        DexMethod companionMethod = rewriter.defaultAsMethodOfCompanionClass(method);

        Code code = virtual.getCode();
        if (code == null) {
          throw new CompilationError(
              "Code is missing for default " + "interface method: " + method.toSourceString(),
              iface.origin);
        }

        MethodAccessFlags newFlags = method.getAccessFlags().copy();
        newFlags.promoteToStatic();
        DexEncodedMethod.setDebugInfoWithFakeThisParameter(
            code, companionMethod.getArity(), appView);

        builder.addMethod(
            methodBuilder ->
                methodBuilder
                    .setName(companionMethod.getName())
                    .setProto(companionMethod.getProto())
                    .setAccessFlags(newFlags)
                    .setGenericSignature(MethodTypeSignature.noSignature())
                    .setAnnotations(virtual.annotations())
                    .setParameterAnnotationsList(virtual.getParameterAnnotations())
                    .setCode(ignored -> virtual.getCode())
                    .setOnBuildConsumer(
                        implMethod -> {
                          implMethod.copyMetadata(virtual);
                          getPostProcessingInterfaceInfo(iface)
                              .mapDefaultMethodToCompanionMethod(virtual, implMethod);
                        }));
      }
    }
  }

  private void processDirectInterfaceMethods(
      DexProgramClass iface, SyntheticProgramClassBuilder builder) {
    for (ProgramMethod method : iface.directProgramMethods()) {
      DexEncodedMethod definition = method.getDefinition();
      if (definition.isClassInitializer()) {
        continue;
      }
      if (definition.isInstanceInitializer()) {
        assert false
            : "Unexpected interface instance initializer: "
                + method.getReference().toSourceString();
        continue;
      }

      getPostProcessingInterfaceInfo(iface).setHasNonClinitDirectMethods();

      MethodAccessFlags originalFlags = method.getAccessFlags();
      MethodAccessFlags newFlags = originalFlags.copy();
      if (originalFlags.isPrivate()) {
        newFlags.promoteToPublic();
      }

      DexMethod oldMethod = method.getReference();
      if (isStaticMethod(definition)) {
        assert originalFlags.isPrivate() || originalFlags.isPublic()
            : "Static interface method "
                + method.toSourceString()
                + " is expected to "
                + "either be public or private in "
                + iface.origin;
        DexMethod companionMethod = rewriter.staticAsMethodOfCompanionClass(method);

        builder.addMethod(
            methodBuilder ->
                methodBuilder
                    .setName(companionMethod.getName())
                    .setProto(companionMethod.getProto())
                    .setAccessFlags(newFlags)
                    .setGenericSignature(definition.getGenericSignature())
                    .setAnnotations(definition.annotations())
                    .setParameterAnnotationsList(definition.getParameterAnnotations())
                    .setCode(ignored -> definition.getCode())
                    .setOnBuildConsumer(
                        implMethod -> {
                          implMethod.copyMetadata(definition);
                        }));

        getPostProcessingInterfaceInfo(iface).moveMethod(oldMethod, companionMethod);
        continue;
      }

      assert originalFlags.isPrivate();

      newFlags.promoteToStatic();

      DexMethod companionMethod =
          InterfaceMethodRewriter.privateAsMethodOfCompanionClass(
              oldMethod, appView.dexItemFactory());

      Code code = definition.getCode();
      if (code == null) {
        throw new CompilationError(
            "Code is missing for private instance "
                + "interface method: "
                + oldMethod.toSourceString(),
            iface.origin);
      }

      DexEncodedMethod.setDebugInfoWithFakeThisParameter(code, companionMethod.getArity(), appView);

      builder.addMethod(
          methodBuilder ->
              methodBuilder
                  .setName(companionMethod.getName())
                  .setProto(companionMethod.getProto())
                  .setAccessFlags(newFlags)
                  .setGenericSignature(definition.getGenericSignature())
                  .setAnnotations(definition.annotations())
                  .setParameterAnnotationsList(definition.getParameterAnnotations())
                  .setCode(ignored -> definition.getCode())
                  .setOnBuildConsumer(
                      implMethod -> {
                        implMethod.copyMetadata(definition);
                        getPostProcessingInterfaceInfo(iface)
                            .moveMethod(oldMethod, companionMethod);
                      }));
    }
  }

  private void clearDirectMethods(DexProgramClass iface) {
    DexEncodedMethod clinit = iface.getClassInitializer();
    MethodCollection methodCollection = iface.getMethodCollection();
    if (clinit != null) {
      methodCollection.setSingleDirectMethod(clinit);
    } else {
      methodCollection.clearDirectMethods();
    }
  }

  private boolean canMoveToCompanionClass(DexEncodedMethod method) {
    Code code = method.getCode();
    assert code != null;
    if (code.isDexCode()) {
      for (Instruction insn : code.asDexCode().instructions) {
        if (insn instanceof InvokeSuper) {
          return false;
        }
      }
    } else {
      assert code.isCfCode();
      for (CfInstruction insn : code.asCfCode().getInstructions()) {
        if (insn instanceof CfInvoke && ((CfInvoke) insn).isInvokeSuper(method.getHolderType())) {
          return false;
        }
      }
    }
    return true;
  }

  private DexClass definitionForDependency(DexType dependency, DexClass dependent) {
    return dependent.isProgramClass()
        ? appView.appInfo().definitionForDesugarDependency(dependent.asProgramClass(), dependency)
        : appView.definitionFor(dependency);
  }

  // Returns true if the given interface method must be kept on [iface] after moving its
  // implementation to the companion class of [iface]. This is always the case for non-bridge
  // methods. Bridge methods that does not override an implementation in a super-interface must
  // also be kept (such a situation can happen if the vertical class merger merges two interfaces).
  private boolean interfaceMethodRemovalChangesApi(DexEncodedMethod method, DexClass iface) {
    if (appView.enableWholeProgramOptimizations()) {
      if (appView.appInfo().withLiveness().isPinned(method.getReference())) {
        return true;
      }
    }
    if (method.accessFlags.isBridge()) {
      if (appView.options().cfToCfDesugar) {
        // TODO(b/187176895): Find the compilation causing this to not be removed.
        return false;
      }
      Deque<Pair<DexClass, DexType>> worklist = new ArrayDeque<>();
      Set<DexType> seenBefore = new HashSet<>();
      addSuperTypes(iface, worklist);
      while (!worklist.isEmpty()) {
        Pair<DexClass, DexType> item = worklist.pop();
        DexClass clazz = definitionForDependency(item.getSecond(), item.getFirst());
        if (clazz == null || !seenBefore.add(clazz.type)) {
          continue;
        }
        if (clazz.lookupVirtualMethod(method.getReference()) != null) {
          return false;
        }
        addSuperTypes(clazz, worklist);
      }
    }
    return true;
  }

  private static void addSuperTypes(DexClass clazz, Deque<Pair<DexClass, DexType>> worklist) {
    if (clazz.superType != null) {
      worklist.add(new Pair<>(clazz, clazz.superType));
    }
    for (DexType iface : clazz.interfaces.values) {
      worklist.add(new Pair<>(clazz, iface));
    }
  }

  private boolean isStaticMethod(DexEncodedMethod method) {
    if (method.accessFlags.isNative()) {
      throw new Unimplemented("Native interface methods are not yet supported.");
    }
    return method.accessFlags.isStatic()
        && !rewriter.factory.isClassConstructor(method.getReference());
  }

  private InterfaceProcessorNestedGraphLens postProcessInterfaces() {
    InterfaceProcessorNestedGraphLens.Builder graphLensBuilder =
        InterfaceProcessorNestedGraphLens.builder();
    postProcessingInterfaceInfos.forEach(
        (iface, info) -> {
          if (info.hasNonClinitDirectMethods()) {
            clearDirectMethods(iface);
          }
          if (info.hasDefaultMethodsToImplementationMap()) {
            info.getDefaultMethodsToImplementation()
                .forEach(
                    (defaultMethod, companionMethod) -> {
                      defaultMethod.setDefaultInterfaceMethodImplementation(companionMethod);
                      graphLensBuilder.recordCodeMovedToCompanionClass(
                          defaultMethod.getReference(), companionMethod.getReference());
                    });
          }
          if (info.hasMethodsToMove()) {
            info.getMethodsToMove().forEach(graphLensBuilder::move);
          }
          if (info.hasBridgesToRemove()) {
            removeBridges(iface);
          }
        });
    return graphLensBuilder.build(appView);
  }

  private void removeBridges(DexProgramClass iface) {
    List<DexEncodedMethod> newVirtualMethods = new ArrayList<>();
    for (ProgramMethod method : iface.virtualProgramMethods()) {
      DexEncodedMethod virtual = method.getDefinition();
      // Remove bridge methods.
      if (interfaceMethodRemovalChangesApi(virtual, iface)) {
        newVirtualMethods.add(virtual);
      }
    }

    // If at least one bridge method was removed then update the table.
    if (newVirtualMethods.size() < iface.getMethodCollection().numberOfVirtualMethods()) {
      iface.setVirtualMethods(newVirtualMethods.toArray(DexEncodedMethod.EMPTY_ARRAY));
    } else {
      assert false
          : "Interface "
              + iface
              + " was analysed as having bridges to remove, but no bridges were found.";
    }
  }

  @Override
  public void finalizeProcessing(Builder<?> builder, ProgramMethodSet synthesizedMethods) {
    InterfaceProcessorNestedGraphLens graphLens = postProcessInterfaces();
    if (appView.enableWholeProgramOptimizations() && graphLens != null) {
      appView.setGraphLens(graphLens);
    }
    new InterfaceMethodRewriterFixup(appView, graphLens).run();
  }

  private PostProcessingInterfaceInfo getPostProcessingInterfaceInfo(DexProgramClass iface) {
    return postProcessingInterfaceInfos.computeIfAbsent(
        iface, ignored -> new PostProcessingInterfaceInfo());
  }

  static class PostProcessingInterfaceInfo {
    private Map<DexEncodedMethod, DexEncodedMethod> defaultMethodsToImplementation;
    private Map<DexMethod, DexMethod> methodsToMove;
    private boolean hasNonClinitDirectMethods;
    private boolean hasBridgesToRemove;

    public void mapDefaultMethodToCompanionMethod(
        DexEncodedMethod defaultMethod, DexEncodedMethod companionMethod) {
      if (defaultMethodsToImplementation == null) {
        defaultMethodsToImplementation = new IdentityHashMap<>();
      }
      defaultMethodsToImplementation.put(defaultMethod, companionMethod);
    }

    public Map<DexEncodedMethod, DexEncodedMethod> getDefaultMethodsToImplementation() {
      return defaultMethodsToImplementation;
    }

    boolean hasDefaultMethodsToImplementationMap() {
      return defaultMethodsToImplementation != null;
    }

    public void moveMethod(DexMethod ifaceMethod, DexMethod companionMethod) {
      if (methodsToMove == null) {
        methodsToMove = new IdentityHashMap<>();
      }
      methodsToMove.put(ifaceMethod, companionMethod);
    }

    public Map<DexMethod, DexMethod> getMethodsToMove() {
      return methodsToMove;
    }

    public boolean hasMethodsToMove() {
      return methodsToMove != null;
    }

    boolean hasNonClinitDirectMethods() {
      return hasNonClinitDirectMethods;
    }

    void setHasNonClinitDirectMethods() {
      hasNonClinitDirectMethods = true;
    }

    boolean hasBridgesToRemove() {
      return hasBridgesToRemove;
    }

    void setHasBridgesToRemove() {
      hasBridgesToRemove = true;
    }
  }

  // Specific lens which remaps invocation types to static since all rewrites performed here
  // are to static companion methods.
  public static class InterfaceProcessorNestedGraphLens extends NestedGraphLens {

    private BidirectionalManyToManyRepresentativeMap<DexMethod, DexMethod> extraNewMethodSignatures;

    public InterfaceProcessorNestedGraphLens(
        AppView<?> appView,
        BidirectionalManyToOneRepresentativeMap<DexField, DexField> fieldMap,
        BidirectionalManyToOneRepresentativeMap<DexMethod, DexMethod> methodMap,
        Map<DexType, DexType> typeMap,
        BidirectionalOneToOneMap<DexMethod, DexMethod> extraNewMethodSignatures) {
      super(appView, fieldMap, methodMap, typeMap);
      this.extraNewMethodSignatures = extraNewMethodSignatures;
    }

    public static InterfaceProcessorNestedGraphLens find(GraphLens lens) {
      if (lens.isInterfaceProcessorLens()) {
        return lens.asInterfaceProcessorLens();
      }
      if (lens.isIdentityLens()) {
        return null;
      }
      if (lens.isNonIdentityLens()) {
        return find(lens.asNonIdentityLens().getPrevious());
      }
      assert false;
      return null;
    }

    public void toggleMappingToExtraMethods() {
      BidirectionalManyToManyRepresentativeMap<DexMethod, DexMethod> tmp = newMethodSignatures;
      this.newMethodSignatures = extraNewMethodSignatures;
      this.extraNewMethodSignatures = tmp;
    }

    public BidirectionalManyToManyRepresentativeMap<DexMethod, DexMethod>
        getExtraNewMethodSignatures() {
      return extraNewMethodSignatures;
    }

    @Override
    public boolean isInterfaceProcessorLens() {
      return true;
    }

    @Override
    public InterfaceProcessorNestedGraphLens asInterfaceProcessorLens() {
      return this;
    }

    @Override
    public boolean isLegitimateToHaveEmptyMappings() {
      return true;
    }

    @Override
    protected DexMethod internalGetPreviousMethodSignature(DexMethod method) {
      return extraNewMethodSignatures.getRepresentativeKeyOrDefault(
          method, newMethodSignatures.getRepresentativeKeyOrDefault(method, method));
    }

    @Override
    protected DexMethod internalGetNextMethodSignature(DexMethod method) {
      return newMethodSignatures.getRepresentativeValueOrDefault(
          method, extraNewMethodSignatures.getRepresentativeValueOrDefault(method, method));
    }

    public static Builder builder() {
      return new Builder();
    }

    public static class Builder extends GraphLens.Builder {

      private final MutableBidirectionalOneToOneMap<DexMethod, DexMethod> extraNewMethodSignatures =
          new BidirectionalOneToOneHashMap<>();

      public void recordCodeMovedToCompanionClass(DexMethod from, DexMethod to) {
        assert from != to;
        methodMap.put(from, from);
        extraNewMethodSignatures.put(from, to);
      }

      @Override
      public InterfaceProcessorNestedGraphLens build(AppView<?> appView) {
        if (fieldMap.isEmpty() && methodMap.isEmpty() && extraNewMethodSignatures.isEmpty()) {
          return null;
        }
        return new InterfaceProcessorNestedGraphLens(
            appView, fieldMap, methodMap, typeMap, extraNewMethodSignatures);
      }
    }
  }
}