src/main/java/com/android/tools/r8/ir/desugar/itf/InterfaceProcessor.java

// 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.ClassAccessFlags;
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.DexProgramClass.ChecksumSupplier;
import com.android.tools.r8.graph.DexType;
import com.android.tools.r8.graph.DexTypeList;
import com.android.tools.r8.graph.DexValue.DexValueInt;
import com.android.tools.r8.graph.FieldAccessFlags;
import com.android.tools.r8.graph.GenericSignature.ClassSignature;
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.ParameterAnnotationsList;
import com.android.tools.r8.graph.ProgramMethod;
import com.android.tools.r8.origin.SynthesizedOrigin;
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.Collections;
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 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 InterfaceProcessorNestedGraphLens.Builder graphLensBuilder;

  // All created companion classes indexed by interface type.
  final Map<DexClass, DexProgramClass> syntheticClasses = new IdentityHashMap<>();

  InterfaceProcessor(AppView<?> appView, InterfaceMethodRewriter rewriter) {
    this.appView = appView;
    this.rewriter = rewriter;
    graphLensBuilder = InterfaceProcessorNestedGraphLens.builder();
  }

  @Override
  public boolean shouldProcess(DexProgramClass clazz) {
    return clazz.isInterface();
  }

  @Override
  public void process(DexProgramClass iface, ProgramMethodSet synthesizedMethods) {
    assert iface.isInterface();
    // The list of methods to be created in companion class.
    List<DexEncodedMethod> companionMethods = new ArrayList<>();

    ensureCompanionClassInitializesInterface(iface, companionMethods);

    // Process virtual interface methods first.
    processVirtualInterfaceMethods(iface, companionMethods, graphLensBuilder);

    // Process static and private methods, move them into companion class as well,
    // make private instance methods public static.
    processDirectInterfaceMethods(iface, companionMethods, graphLensBuilder);

    if (companionMethods.isEmpty()) {
      return; // No methods to create, companion class not needed.
    }

    ClassAccessFlags companionClassFlags = iface.accessFlags.copy();
    companionClassFlags.unsetAbstract();
    companionClassFlags.unsetInterface();
    companionClassFlags.unsetAnnotation();
    companionClassFlags.setFinal();
    companionClassFlags.setSynthetic();
    // Companion class must be public so moved methods can be called from anywhere.
    companionClassFlags.setPublic();

    // Create companion class.
    DexType companionClassType = rewriter.getCompanionClassType(iface.type);
    DexProgramClass companionClass =
        new DexProgramClass(
            companionClassType,
            null,
            new SynthesizedOrigin("interface desugaring", getClass()),
            companionClassFlags,
            rewriter.factory.objectType,
            DexTypeList.empty(),
            iface.sourceFile,
            null,
            Collections.emptyList(),
            null,
            Collections.emptyList(),
            ClassSignature.noSignature(),
            DexAnnotationSet.empty(),
            DexEncodedField.EMPTY_ARRAY,
            DexEncodedField.EMPTY_ARRAY,
            companionMethods.toArray(DexEncodedMethod.EMPTY_ARRAY),
            DexEncodedMethod.EMPTY_ARRAY,
            rewriter.factory.getSkipNameValidationForTesting(),
            getChecksumSupplier(iface));
    syntheticClasses.put(iface, companionClass);
    if (companionClass.hasClassInitializer()) {
      synthesizedMethods.add(companionClass.getProgramClassInitializer());
    }
  }

  private void ensureCompanionClassInitializesInterface(
      DexProgramClass iface, List<DexEncodedMethod> companionMethods) {
    if (!hasStaticMethodThatTriggersNonTrivialClassInitializer(iface)) {
      return;
    }
    DexEncodedField clinitField =
        findExistingStaticClinitFieldToTriggerInterfaceInitialization(iface);
    if (clinitField == null) {
      clinitField = createStaticClinitFieldToTriggerInterfaceInitialization(iface);
      iface.appendStaticField(clinitField);
    }
    companionMethods.add(createCompanionClassInitializer(iface, 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 DexEncodedMethod createCompanionClassInitializer(
      DexProgramClass iface, DexEncodedField clinitField) {
    DexType companionType = rewriter.getCompanionClassType(iface.getType());
    DexMethod clinitMethodReference = appView.dexItemFactory().createClinitMethod(companionType);
    CfCode code =
        new CfCode(
            companionType,
            1,
            0,
            ImmutableList.of(
                new CfFieldInstruction(
                    Opcodes.GETSTATIC, clinitField.getReference(), clinitField.getReference()),
                new CfStackInstruction(Opcode.Pop),
                new CfReturnVoid()),
            ImmutableList.of(),
            ImmutableList.of());
    return new DexEncodedMethod(
        clinitMethodReference,
        MethodAccessFlags.builder().setConstructor().setPackagePrivate().setStatic().build(),
        MethodTypeSignature.noSignature(),
        DexAnnotationSet.empty(),
        ParameterAnnotationsList.empty(),
        code,
        true,
        iface.getInitialClassFileVersion());
  }

  private void processVirtualInterfaceMethods(
      DexProgramClass iface,
      List<DexEncodedMethod> companionMethods,
      InterfaceProcessorNestedGraphLens.Builder graphLensBuilder) {
    List<DexEncodedMethod> newVirtualMethods = new ArrayList<>();
    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);
        DexEncodedMethod implMethod =
            new DexEncodedMethod(
                companionMethod,
                newFlags,
                virtual.getGenericSignature(),
                virtual.annotations(),
                virtual.parameterAnnotationsList,
                code,
                true);
        implMethod.copyMetadata(virtual);
        virtual.setDefaultInterfaceMethodImplementation(implMethod);
        companionMethods.add(implMethod);
        graphLensBuilder.recordCodeMovedToCompanionClass(
            method.getReference(), implMethod.getReference());
      }

      // 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));
    }
  }

  private void processDirectInterfaceMethods(
      DexProgramClass iface,
      List<DexEncodedMethod> companionMethods,
      InterfaceProcessorNestedGraphLens.Builder graphLensBuilder) {
    DexEncodedMethod clinit = null;
    for (ProgramMethod method : iface.directProgramMethods()) {
      DexEncodedMethod definition = method.getDefinition();
      if (definition.isClassInitializer()) {
        clinit = definition;
        continue;
      }
      if (definition.isInstanceInitializer()) {
        assert false
            : "Unexpected interface instance initializer: "
                + method.getReference().toSourceString();
        continue;
      }

      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);
        DexEncodedMethod implMethod =
            new DexEncodedMethod(
                companionMethod,
                newFlags,
                definition.getGenericSignature(),
                definition.annotations(),
                definition.parameterAnnotationsList,
                definition.getCode(),
                true);
        implMethod.copyMetadata(definition);
        companionMethods.add(implMethod);
        graphLensBuilder.move(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);
      DexEncodedMethod implMethod =
          new DexEncodedMethod(
              companionMethod,
              newFlags,
              definition.getGenericSignature(),
              definition.annotations(),
              definition.parameterAnnotationsList,
              code,
              true);
      implMethod.copyMetadata(definition);
      companionMethods.add(implMethod);
      graphLensBuilder.move(oldMethod, companionMethod);
    }

    MethodCollection methodCollection = iface.getMethodCollection();
    if (clinit != null) {
      methodCollection.setSingleDirectMethod(clinit);
    } else {
      methodCollection.clearDirectMethods();
    }
  }

  private ChecksumSupplier getChecksumSupplier(DexProgramClass iface) {
    if (!appView.options().encodeChecksums) {
      return DexProgramClass::invalidChecksumRequest;
    }
    long checksum = iface.getChecksum();
    return c -> 7 * checksum;
  }

  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()) {
      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());
  }

  @Override
  public void finalizeProcessing(Builder<?> builder, ProgramMethodSet synthesizedMethods) {
    InterfaceProcessorNestedGraphLens graphLens = graphLensBuilder.build(appView);
    if (appView.enableWholeProgramOptimizations() && graphLens != null) {
      appView.setGraphLens(graphLens);
    }
    syntheticClasses.forEach(
        (interfaceClass, synthesizedClass) -> {
          // Don't need to optimize synthesized class since all of its methods
          // are just moved from interfaces and don't need to be re-processed.
          builder.addSynthesizedClass(synthesizedClass);
          appView.appInfo().addSynthesizedClass(synthesizedClass, interfaceClass.asProgramClass());
        });
    new InterfaceMethodRewriterFixup(appView, graphLens).run();
  }

  // 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);
      }
    }
  }
}