src/main/java/com/android/tools/r8/horizontalclassmerging/SyntheticArgumentClass.java

// Copyright (c) 2020, 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.horizontalclassmerging;

import com.android.tools.r8.dex.Constants;
import com.android.tools.r8.graph.AppView;
import com.android.tools.r8.graph.ClassAccessFlags;
import com.android.tools.r8.graph.DexAnnotationSet;
import com.android.tools.r8.graph.DexEncodedField;
import com.android.tools.r8.graph.DexEncodedMethod;
import com.android.tools.r8.graph.DexProgramClass;
import com.android.tools.r8.graph.DexType;
import com.android.tools.r8.graph.DexTypeList;
import com.android.tools.r8.graph.DirectMappedDexApplication;
import com.android.tools.r8.origin.SynthesizedOrigin;
import com.android.tools.r8.shaking.AppInfoWithLiveness;
import java.util.Collections;

/**
 * Lets assume we are merging a class A that looks like:
 *
 * <pre>
 *   class A {
 *     A() { ... }
 *     A(int) { ... }
 *   }
 * </pre>
 *
 * If {@code A::<init>()} is merged with other constructors, then we need to prevent a conflict with
 * {@code A::<init>(int)}. To do this we introduce a synthetic class so that the new signature for
 * the merged constructor is {@code A::<init>(SyntheticClass, int)}, as this is guaranteed to be
 * unique.
 *
 * <p>This class generates a synthetic class in the package of the first class to be merged.
 */
public class SyntheticArgumentClass {
  public static final String SYNTHETIC_CLASS_SUFFIX = "$r8$HorizontalClassMergingArgument";

  private final DexType syntheticClassType;

  private SyntheticArgumentClass(DexType syntheticClassType) {
    this.syntheticClassType = syntheticClassType;
  }

  public DexType getArgumentClass() {
    return syntheticClassType;
  }

  public static class Builder {

    public SyntheticArgumentClass build(
        AppView<AppInfoWithLiveness> appView,
        DirectMappedDexApplication.Builder appBuilder,
        Iterable<DexProgramClass> mergeClasses) {

      // Find a fresh name in an existing package.
      DexProgramClass context = mergeClasses.iterator().next();
      DexType syntheticClassType =
          context.type.addSuffix(SYNTHETIC_CLASS_SUFFIX, appView.dexItemFactory());

      boolean requiresMainDex = appView.appInfo().getMainDexClasses().containsAnyOf(mergeClasses);

      DexProgramClass clazz =
          new DexProgramClass(
              syntheticClassType,
              null,
              new SynthesizedOrigin("horizontal class merging", HorizontalClassMerger.class),
              ClassAccessFlags.fromCfAccessFlags(Constants.ACC_PUBLIC | Constants.ACC_SYNTHETIC),
              appView.dexItemFactory().objectType,
              DexTypeList.empty(),
              null,
              null,
              Collections.emptyList(),
              null,
              Collections.emptyList(),
              DexAnnotationSet.empty(),
              DexEncodedField.EMPTY_ARRAY,
              DexEncodedField.EMPTY_ARRAY,
              DexEncodedMethod.EMPTY_ARRAY,
              DexEncodedMethod.EMPTY_ARRAY,
              appView.dexItemFactory().getSkipNameValidationForTesting(),
              DexProgramClass::checksumFromType);

      appBuilder.addSynthesizedClass(clazz);
      appView.appInfo().addSynthesizedClass(clazz, requiresMainDex);

      return new SyntheticArgumentClass(clazz.type);
    }
  }
}