src/main/java/com/android/tools/r8/ir/optimize/lambda/kstyle/KStyleLambdaGroup.java

// Copyright (c) 2018, 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.optimize.lambda.kstyle;

import com.android.tools.r8.graph.AppInfoWithSubtyping;
import com.android.tools.r8.graph.DexClass;
import com.android.tools.r8.graph.DexField;
import com.android.tools.r8.graph.DexItemFactory;
import com.android.tools.r8.graph.DexProto;
import com.android.tools.r8.graph.DexType;
import com.android.tools.r8.ir.optimize.lambda.CaptureSignature;
import com.android.tools.r8.ir.optimize.lambda.CodeProcessor.Strategy;
import com.android.tools.r8.ir.optimize.lambda.LambdaGroup;
import com.android.tools.r8.ir.optimize.lambda.LambdaGroupClassBuilder;
import com.android.tools.r8.kotlin.Kotlin;
import com.android.tools.r8.utils.ThrowingConsumer;

// Represents a k-style lambda group created to combine several lambda classes
// generated by kotlin compiler for regular kotlin lambda expressions, like:
//
//      -----------------------------------------------------------------------
//      fun foo(m: String, v: Int): () -> String {
//        val lambda: (String, Int) -> String = { s, i -> s.substring(i) }
//        return { "$m: $v" }
//      }
//      -----------------------------------------------------------------------
//
// Regular stateless k-style lambda class structure looks like below:
//
// -----------------------------------------------------------------------------------------------
// // signature Lkotlin/jvm/internal/Lambda;Lkotlin/jvm/functions/Function2<
//                          Ljava/lang/String;Ljava/lang/Integer;Ljava/lang/String;>;
// final class lambdas/LambdasKt$foo$lambda1$1
//                  extends kotlin/jvm/internal/Lambda
//                  implements kotlin/jvm/functions/Function2  {
//
//    public synthetic bridge invoke(Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
//
//     public final invoke(Ljava/lang/String;I)Ljava/lang/String;
//       @Lorg/jetbrains/annotations/NotNull;() // invisible
//         @Lorg/jetbrains/annotations/NotNull;() // invisible, parameter 0
//
//     <init>()V
//
//     public final static Llambdas/LambdasKt$foo$lambda1$1; INSTANCE
//
//     static <clinit>()V
//
//     OUTERCLASS lambdas/LambdasKt foo (Ljava/lang/String;I)Lkotlin/jvm/functions/Function0;
//     final static INNERCLASS lambdas/LambdasKt$foo$lambda1$1 null null
// }
// -----------------------------------------------------------------------------------------------
//
// Regular stateful k-style lambda class structure looks like below:
//
// -----------------------------------------------------------------------------------------------
// // signature Lkotlin/jvm/internal/Lambda;Lkotlin/jvm/functions/Function0<Ljava/lang/String;>;
// final class lambdas/LambdasKt$foo$1
//                  extends kotlin/jvm/internal/Lambda
//                  implements kotlin/jvm/functions/Function0  {
//
//     public synthetic bridge invoke()Ljava/lang/Object;
//
//     public final invoke()Ljava/lang/String;
//       @Lorg/jetbrains/annotations/NotNull;() // invisible
//
//     <init>(Ljava/lang/String;I)V
//
//     final synthetic Ljava/lang/String; $m
//     final synthetic I $v
//
//     OUTERCLASS lambdas/LambdasKt foo (Ljava/lang/String;I)Lkotlin/jvm/functions/Function0;
//     final static INNERCLASS lambdas/LambdasKt$foo$1 null null
// }
// -----------------------------------------------------------------------------------------------
//
// Key k-style lambda class details:
//   - extends kotlin.jvm.internal.Lambda
//   - implements one of kotlin.jvm.functions.Function0..Function22, or FunctionN
//     see: https://github.com/JetBrains/kotlin/blob/master/libraries/
//                  stdlib/jvm/runtime/kotlin/jvm/functions/Functions.kt
//     and: https://github.com/JetBrains/kotlin/blob/master/spec-docs/function-types.md
//   - lambda class is created as an anonymous inner class
//   - lambda class carries generic signature and kotlin metadata attribute
//   - class instance fields represent captured values and have an instance constructor
//     with matching parameters initializing them (see the second class above)
//   - stateless lambda is implemented as a singleton with a static field storing the only
//     instance and initialized in static class constructor (see the first class above)
//   - main lambda method usually matches an exact lambda signature and may have
//     generic signature attribute and nullability parameter annotations
//   - optional bridge method created to satisfy interface implementation and
//     forwarding call to lambda main method
//
final class KStyleLambdaGroup extends LambdaGroup {
  private final Strategy strategy = new KStyleLambdaGroupCodeStrategy(this);

  KStyleLambdaGroup(KStyleLambdaGroupId id) {
    super(id);
  }

  final KStyleLambdaGroupId id() {
    return (KStyleLambdaGroupId) id;
  }

  final boolean isStateless() {
    return id().capture.isEmpty();
  }

  // Field referencing singleton instance for a lambda with specified id.
  final DexField getSingletonInstanceField(DexItemFactory factory, int id) {
    return factory.createField(this.getGroupClassType(),
        this.getGroupClassType(), factory.createString("INSTANCE$" + id));
  }

  @Override
  protected String getTypePackage() {
    String pkg = id().pkg;
    return pkg.isEmpty() ? "" : (pkg + "/");
  }

  final DexProto createConstructorProto(DexItemFactory factory) {
    String capture = id().capture;
    DexType[] newParameters = new DexType[capture.length() + 1];
    newParameters[0] = factory.intType; // Lambda id.
    for (int i = 0; i < capture.length(); i++) {
      newParameters[i + 1] = CaptureSignature.fieldType(factory, capture, i);
    }
    return factory.createProto(factory.voidType, newParameters);
  }

  final DexField getLambdaIdField(DexItemFactory factory) {
    return factory.createField(this.getGroupClassType(), factory.intType, "$id$");
  }

  final int mapFieldIntoCaptureIndex(DexType lambda, DexField field) {
    return CaptureSignature.mapFieldIntoCaptureIndex(
        id().capture, lambdaCaptureFields(lambda), field);
  }

  final DexField getCaptureField(DexItemFactory factory, int index) {
    assert index >= 0 && index < id().capture.length();
    return factory.createField(this.getGroupClassType(),
        CaptureSignature.fieldType(factory, id().capture, index), "$capture$" + index);
  }

  @Override
  protected LambdaGroupClassBuilder getBuilder(DexItemFactory factory) {
    return new KStyleLambdaGroupClassBuilder(factory, this, "kotlin-style lambda group");
  }

  @Override
  public Strategy getCodeStrategy() {
    return strategy;
  }

  @Override
  public ThrowingConsumer<DexClass, LambdaStructureError> lambdaClassValidator(
      Kotlin kotlin, AppInfoWithSubtyping appInfo) {
    return new KStyleLambdaClassValidator(kotlin, this, appInfo);
  }
}