src/main/java/com/android/tools/r8/ir/desugar/ClassProcessor.java

// Copyright (c) 2017, 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;

import com.android.tools.r8.errors.CompilationError;
import com.android.tools.r8.graph.AppView;
import com.android.tools.r8.graph.DexClass;
import com.android.tools.r8.graph.DexEncodedMethod;
import com.android.tools.r8.graph.DexItemFactory;
import com.android.tools.r8.graph.DexMethod;
import com.android.tools.r8.graph.DexType;
import com.android.tools.r8.graph.MethodAccessFlags;
import com.android.tools.r8.ir.code.Invoke;
import com.android.tools.r8.ir.synthetic.ForwardMethodSourceCode;
import com.android.tools.r8.ir.synthetic.SynthesizedCode;
import com.google.common.collect.Sets;
import java.util.ArrayList;
import java.util.Collections;
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;

// Default and static method interface desugaring processor for classes.
// Adds default interface methods into the class when needed.
final class ClassProcessor {

  private final AppView<?> appView;
  private final DexItemFactory dexItemFactory;
  private final InterfaceMethodRewriter rewriter;
  // Set of already processed classes.
  private final Set<DexClass> processedClasses = Sets.newIdentityHashSet();
  // Maps already created methods into default methods they were generated based on.
  private final Map<DexEncodedMethod, DexEncodedMethod> createdMethods = new IdentityHashMap<>();

  ClassProcessor(AppView<?> appView, InterfaceMethodRewriter rewriter) {
    this.appView = appView;
    this.dexItemFactory = appView.dexItemFactory();
    this.rewriter = rewriter;
  }

  final Set<DexEncodedMethod> getForwardMethods() {
    return createdMethods.keySet();
  }

  final void process(DexClass clazz) {
    assert !clazz.isInterface();
    if (clazz.isNotProgramClass()) {
      // We assume that library classes don't need to be processed, since they
      // are provided by a runtime not supporting default interface methods.
      // We also skip classpath classes, which results in sub-optimal behavior
      // in case classpath superclass when processed adds a default method which
      // could have been reused in this class otherwise.
      return;
    }
    if (!processedClasses.add(clazz)) {
      return; // Has already been processed.
    }

    // Ensure superclasses are processed first. We need it since we use information
    // about methods added to superclasses when we decide if we want to add a default
    // method to class `clazz`.
    DexType superType = clazz.superType;
    // If superClass definition is missing, just skip this part and let real processing of its
    // subclasses report the error if it is required.
    DexClass superClass = superType == null ? null : appView.definitionFor(superType);
    if (superClass != null && superType != dexItemFactory.objectType) {
      if (superClass.isInterface()) {
        throw new CompilationError("Interface `" + superClass.toSourceString()
            + "` used as super class of `" + clazz.toSourceString() + "`.");
      }
      process(superClass);
    }

    // When inheriting from a library class, the library class may implement interfaces to
    // desugar. We therefore need to look the interfaces of the library classes.
    boolean desugaredLibraryLookup =
        superClass != null
            && superClass.isLibraryClass()
            && appView.options().emulateLibraryInterface.size() > 0;

    if (clazz.interfaces.isEmpty() && !desugaredLibraryLookup) {
      // Since superclass has already been processed and it has all missing methods
      // added, these methods will be inherited by `clazz`, and only need to be revised
      // in case this class has *additional* interfaces implemented, which may change
      // the entire picture of the default method selection in runtime.
      return;
    }

    // Collect the default interface methods to be added to this class.
    List<DexEncodedMethod> methodsToImplement =
        collectMethodsToImplement(clazz, desugaredLibraryLookup);
    if (methodsToImplement.isEmpty()) {
      return;
    }

    // Add the methods.
    List<DexEncodedMethod> newForwardingMethods = new ArrayList<>(methodsToImplement.size());
    for (DexEncodedMethod method : methodsToImplement) {
      assert method.accessFlags.isPublic() && !method.accessFlags.isAbstract();
      DexEncodedMethod newMethod = addForwardingMethod(method, clazz);
      newForwardingMethods.add(newMethod);
      createdMethods.put(newMethod, method);
    }
    clazz.appendVirtualMethods(newForwardingMethods);
  }

  private DexEncodedMethod addForwardingMethod(DexEncodedMethod defaultMethod, DexClass clazz) {
    DexMethod method = defaultMethod.method;
    DexClass target = appView.definitionFor(method.holder);
    // NOTE: Never add a forwarding method to methods of classes unknown or coming from android.jar
    // even if this results in invalid code, these classes are never desugared.
    assert target != null && !rewriter.isNonDesugaredLibraryClass(target);
    // New method will have the same name, proto, and also all the flags of the
    // default method, including bridge flag.
    DexMethod newMethod = dexItemFactory.createMethod(clazz.type, method.proto, method.name);
    MethodAccessFlags newFlags = defaultMethod.accessFlags.copy();
    // Some debuggers (like IntelliJ) automatically skip synthetic methods on single step.
    newFlags.setSynthetic();
    ForwardMethodSourceCode.Builder forwardSourceCodeBuilder =
        ForwardMethodSourceCode.builder(newMethod);
    forwardSourceCodeBuilder
        .setReceiver(clazz.type)
        .setTarget(rewriter.defaultAsMethodOfCompanionClass(method))
        .setInvokeType(Invoke.Type.STATIC)
        .setIsInterface(target.isInterface());
    return new DexEncodedMethod(
        newMethod,
        newFlags,
        defaultMethod.annotations,
        defaultMethod.parameterAnnotationsList,
        new SynthesizedCode(forwardSourceCodeBuilder::build));
  }

  // For a given class `clazz` inspects all interfaces it implements directly or
  // indirectly and collect a set of all default methods to be implemented
  // in this class.
  private List<DexEncodedMethod> collectMethodsToImplement(
      DexClass clazz, boolean desugaredLibraryLookup) {
    DefaultMethodsHelper helper = new DefaultMethodsHelper();
    DexClass current = clazz;
    List<DexEncodedMethod> accumulatedVirtualMethods = new ArrayList<>();
    // Collect candidate default methods by inspecting interfaces implemented
    // by this class as well as its superclasses.
    //
    // We assume here that interfaces implemented by java.lang.Object don't
    // have default methods to desugar since they are library interfaces. And we assume object
    // methods don't hide any default interface methods. Default interface method matching Object's
    // methods is supposed to fail with a compilation error.
    // Note that this last assumption will be broken if Object API is augmented with a new method in
    // the future.
    while (current.type != dexItemFactory.objectType) {
      for (DexType type : current.interfaces.values) {
        helper.merge(rewriter.getOrCreateInterfaceInfo(clazz, current, type));
      }

      // TODO(anyone): Using clazz here instead of current looks suspicious, should this be hoisted
      // out of the loop or changed to current?
      accumulatedVirtualMethods.addAll(clazz.virtualMethods());

      List<DexEncodedMethod> defaultMethodsInDirectInterface = helper.createFullList();

      List<DexEncodedMethod> toBeImplementedFromDirectInterface =
          new ArrayList<>(defaultMethodsInDirectInterface.size());
      hideCandidates(accumulatedVirtualMethods,
          defaultMethodsInDirectInterface,
          toBeImplementedFromDirectInterface);
      // toBeImplementedFromDirectInterface are those that we know for sure we need to implement by
      // looking at the already desugared super classes.
      // Remaining methods in defaultMethodsInDirectInterface are those methods we need to look at
      // the hierarchy to know how they should be handled.
      if (toBeImplementedFromDirectInterface.isEmpty()
          && defaultMethodsInDirectInterface.isEmpty()
          && !desugaredLibraryLookup) {
        // No interface with default in direct hierarchy, nothing to do: super already has all that
        // is needed.
        return Collections.emptyList();
      }

      if (current.superType == null) {
        // TODO(anyone): Can this ever happen? It seems the loop stops on Object.
        break;
      } else {
        DexClass superClass = appView.definitionFor(current.superType);
        if (superClass != null) {
          current = superClass;
        } else {
          String message = "Default method desugaring of `" + clazz.toSourceString() + "` failed";
          if (current == clazz) {
            message += " because its super class `" +
                clazz.superType.toSourceString() + "` is missing";
          } else {
            message +=
                " because it's hierarchy is incomplete. The class `"
                    + current.superType.toSourceString()
                    + "` is missing and it is the declared super class of `"
                    + current.toSourceString() + "`";
          }
          throw new CompilationError(message);
        }
      }
    }

    List<DexEncodedMethod> candidates = helper.createCandidatesList();
    if (candidates.isEmpty()) {
      return candidates;
    }

    // Remove from candidates methods defined in class or any of its superclasses.
    List<DexEncodedMethod> toBeImplemented = new ArrayList<>(candidates.size());
    current = clazz;
    while (true) {
      // In desugared library look-up, methods from library classes cannot hide methods from
      // emulated interfaces (the method being desugared implied the implementation is not
      // present in the library class).
      if (desugaredLibraryLookup && current.isLibraryClass()) {
        Iterator<DexEncodedMethod> iterator = candidates.iterator();
        while (iterator.hasNext()) {
          DexEncodedMethod candidate = iterator.next();
          if (rewriter.isEmulatedInterface(candidate.method.holder)) {
            toBeImplemented.add(candidate);
            iterator.remove();
          }
        }
      }
      // Hide candidates by virtual method of the class.
      hideCandidates(current.virtualMethods(), candidates, toBeImplemented);
      if (candidates.isEmpty()) {
        return toBeImplemented;
      }

      DexType superType = current.superType;
      DexClass superClass = null;
      if (superType != null) {
        superClass = appView.definitionFor(superType);
        // It's available or we would have failed while analyzing the hierarchy for interfaces.
        assert superClass != null;
      }
      if (superClass == null || superType == dexItemFactory.objectType) {
        // Note that default interface methods must never have same
        // name/signature as any method in java.lang.Object (JLS §9.4.1.2).

        // Everything still in candidate list is not hidden.
        toBeImplemented.addAll(candidates);

        return toBeImplemented;
      }
      current = superClass;
    }
  }

  private void hideCandidates(List<DexEncodedMethod> virtualMethods,
      List<DexEncodedMethod> candidates, List<DexEncodedMethod> toBeImplemented) {
    Iterator<DexEncodedMethod> it = candidates.iterator();
    while (it.hasNext()) {
      DexEncodedMethod candidate = it.next();
      for (DexEncodedMethod encoded : virtualMethods) {
        if (candidate.method.match(encoded)) {
          // Found a methods hiding the candidate.
          DexEncodedMethod basedOnCandidate = createdMethods.get(encoded);
          if (basedOnCandidate != null) {
            // The method we found is a method we have generated for a default interface
            // method in a superclass. If the method is based on the same candidate we don't
            // need to re-generate this method again since it is going to be inherited.
            if (basedOnCandidate != candidate) {
              // Need to re-generate since the inherited version is
              // based on a different candidate.
              toBeImplemented.add(candidate);
            }
          }

          // Done with this candidate.
          it.remove();
          break;
        }
      }
    }
  }
}