Generate a class with Kotlin IR.

IrClass.kt

package com.squareup.anvil.compiler

import org.jetbrains.kotlin.backend.common.IrElementTransformerVoidWithContext
import org.jetbrains.kotlin.backend.common.extensions.IrGenerationExtension
import org.jetbrains.kotlin.backend.common.extensions.IrPluginContext
import org.jetbrains.kotlin.backend.common.ir.addChild
import org.jetbrains.kotlin.backend.common.ir.addSimpleDelegatingConstructor
import org.jetbrains.kotlin.backend.common.ir.createImplicitParameterDeclarationWithWrappedDescriptor
import org.jetbrains.kotlin.cli.common.messages.CompilerMessageSeverity.WARNING
import org.jetbrains.kotlin.cli.common.messages.MessageCollector
import org.jetbrains.kotlin.descriptors.ClassKind.CLASS
import org.jetbrains.kotlin.ir.IrElement
import org.jetbrains.kotlin.ir.builders.declarations.buildClass
import org.jetbrains.kotlin.ir.declarations.IrClass
import org.jetbrains.kotlin.ir.declarations.IrModuleFragment
import org.jetbrains.kotlin.ir.declarations.IrPackageFragment
import org.jetbrains.kotlin.ir.util.constructors
import org.jetbrains.kotlin.ir.util.getPackageFragment
import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
import org.jetbrains.kotlin.name.Name

class FullDiExtension(
  private val messageCollector: MessageCollector
) : IrGenerationExtension {

  override fun generate(
    moduleFragment: IrModuleFragment,
    pluginContext: IrPluginContext
  ) {
    val classes = mutableListOf<IrClass>()

    moduleFragment.acceptChildren(object : IrElementVisitor<Unit, MutableList<IrClass>> {
      override fun visitElement(
        element: IrElement,
        data: MutableList<IrClass>
      ) {
        element.acceptChildren(this, data)
      }

      override fun visitClass(
        declaration: IrClass,
        data: MutableList<IrClass>
      ) {
        if (declaration.name.asString() == "AppComponentImpl") {
          data += declaration
        } else {
          super.visitClass(declaration, data)
        }
      }
    }, classes)

    moduleFragment.transformChildrenVoid(object : IrElementTransformerVoidWithContext() {
      override fun visitPackageFragment(declaration: IrPackageFragment): IrPackageFragment {
        classes
          .filter { it.getPackageFragment() == declaration }
          .forEach {
            messageCollector.report(WARNING, "Hello ${it.name}")

            val irClass = pluginContext.irFactory
              .buildClass {
                name = Name.identifier("AppComponentImplAbc")
                kind = CLASS
              }
              .apply {
                this.parent = declaration
                createImplicitParameterDeclarationWithWrappedDescriptor()

                val constructorOfAny = pluginContext.irBuiltIns.anyClass.owner.constructors.first()
                addSimpleDelegatingConstructor(
                  constructorOfAny,
                  pluginContext.irBuiltIns,
                  isPrimary = true
                )
              }

            declaration.addChild(irClass)
          }

        return declaration
      }
    })
  }
}