是否可以使用宏来修改结构类型实例调用的生成代码？

例如如下代码：

object Test extends App
{
    trait Class
    {
        val f1: Int
    }

    val c = new Class {
        val f1: Int = 1
        val f2: String = "Class"
    }

    println(c.f1)
    println(c.f2)
}

我使用反编译器查看字节码，并注意到编译生成了一个 java 接口“Test.Class”作为伪代码：

trait Class
{
    val f1: Int
}

和一个实现“Test.Class”的类“Test$$anon$1”，伪代码为：

class Test$$anon$1 extends Class
{
    val f1: Int = 1
    val f2: String = "Class"
}

然后编译器将变量“c”初始化为：

c = new Test$$anon$1()

然后像正常调用一样调用成员“f1”：

println(c.f1)

但它使用反射调用“f2”：

println(reflMethod(c, f2))

在这里，由于匿名类“Test$$anon$1”的定义在同一范围内可见，是否可以使用宏更改生成的代码以调用“f2”作为普通字段以避免反射？

我只想更改同一范围内的调用代码，不想跨范围更改反射代码，例如结构类型实例作为函数调用中的参数。所以我认为理论上是可能的。但我不熟悉 scala 宏，建议和代码示例表示赞赏。谢谢！

宏（更准确地说，宏注释 https://docs.scala-lang.org/overviews/macros/annotations.html因为定义宏 https://docs.scala-lang.org/overviews/macros/overview.html与此任务无关）还不够。您想要重写的不是类（特征、对象）或其参数或成员，而是本地表达式。你可以这样做编译器插件 https://docs.scala-lang.org/overviews/plugins/index.html (see also https://dotty.epfl.ch/docs/reference/changed-features/compiler-plugins.html) 在编译时或使用斯卡拉梅塔 https://scalameta.org/编译前生成代码。

如果你选择 Scalameta 那么实际上你想在语义上而不是在语法上重写你的表达式，因为你想从本地表达式开始new Class...到定义trait Class...并检查那里是否有合适的成员。所以你需要 Scalameta +语义数据库 https://scalameta.org/docs/semanticdb/guide.html。更方便的是使用Scalameta + SemanticDBScalafix https://scalacenter.github.io/scalafix/docs/developers/setup.html（另请参阅部分对于用户 https://scalacenter.github.io/scalafix/docs/users/installation.html).

您可以创建自己的重写规则。然后您可以使用它就地重写代码或生成代码（见下文）。

规则/src/main/scala/MyRule.scala

import scalafix.v1._
import scala.meta._

class MyRule extends SemanticRule("MyRule") {
  override def isRewrite: Boolean = true

  override def description: String = "My Rule"

  override def fix(implicit doc: SemanticDocument): Patch = {
    doc.tree.collect {
      case tree @ q"new { ..$stats } with ..$inits { $self => ..$stats1 }" =>
        val symbols = stats1.collect {
          case q"..$mods val ..${List(p"$name")}: $tpeopt = $expr" =>
            name.syntax
        }

        val symbols1 = inits.headOption.flatMap(_.symbol.info).flatMap(_.signature match {
          case ClassSignature(type_parameters, parents, self, declarations) =>
            Some(declarations.map(_.symbol.displayName))
          case _ => None
        })

        symbols1 match {
          case None => Patch.empty
          case Some(symbols1) if symbols.forall(symbols1.contains) => Patch.empty
          case _ =>
            val anon = Type.fresh("anon$meta$")
            val tree1 =
              q"""
                class $anon extends ${template"{ ..$stats } with ..$inits { $self => ..$stats1 }"}
                new ${init"$anon()"}
              """
            Patch.replaceTree(tree, tree1.syntax)
        }
    }.asPatch
  }
}

在/src/main/scala/Test.scala

object Test extends App
{
  trait Class
  {
    val f1: Int
  }

  val c = new Class {
    val f1: Int = 1
    val f2: String = "Class"
  }

  println(c.f1)
  println(c.f2)
}

out/target/scala-2.13/src_management/main/scala/Test.scala (after sbt out/compile)

object Test extends App
{
  trait Class
  {
    val f1: Int
  }

  val c = {
  class anon$meta$2 extends Class {
    val f1: Int = 1
    val f2: String = "Class"
  }
  new anon$meta$2()
}

  println(c.f1)
  println(c.f2)
}

构建.sbt

name := "scalafix-codegen-demo"

inThisBuild(
  List(
    scalaVersion := "2.13.2",
    addCompilerPlugin(scalafixSemanticdb),
    scalacOptions ++= List(
      "-Yrangepos"
    )
  )
)

lazy val rules = project
  .settings(
    libraryDependencies += "ch.epfl.scala" %% "scalafix-core" % "0.9.16"
  )

lazy val in = project

lazy val out = project
  .settings(
    sourceGenerators.in(Compile) += Def.taskDyn {
      val root = baseDirectory.in(ThisBuild).value.toURI.toString
      val from = sourceDirectory.in(in, Compile).value
      val to = sourceManaged.in(Compile).value
      val outFrom = from.toURI.toString.stripSuffix("/").stripPrefix(root)
      val outTo = to.toURI.toString.stripSuffix("/").stripPrefix(root)
      Def.task {
        scalafix
          .in(in, Compile)
//          .toTask(s" ProcedureSyntax --out-from=$outFrom --out-to=$outTo")
          .toTask(s" --rules=file:rules/src/main/scala/MyRule.scala --out-from=$outFrom --out-to=$outTo")
          .value
        (to ** "*.scala").get
      }
    }.taskValue
  )

项目/plugins.sbt

addSbtPlugin("ch.epfl.scala" % "sbt-scalafix" % "0.9.16")

其他例子：

https://github.com/olafurpg/scalafix-codegen https://github.com/olafurpg/scalafix-codegen

https://github.com/DmytroMitin/scalafix-codegen https://github.com/DmytroMitin/scalafix-codegen

https://github.com/DmytroMitin/scalameta-demo https://github.com/DmytroMitin/scalameta-demo

Scala 条件编译 https://stackoverflow.com/questions/61796570/scala-conditional-compilation

覆盖Scala函数toString的宏注释 https://stackoverflow.com/questions/35338239/macro-annotation-to-override-tostring-of-scala-function/

如何在scala中合并多个导入？ https://stackoverflow.com/questions/58562229/how-to-merge-multiple-imports-in-scala/