Scala Compiler Plugin - 确定方法是否被覆盖

Question

我正在编写一个带有组件的 Scala 编译器插件，该组件在需要知道方法被覆盖的“jvm”阶段之后执行。这是我正在处理的一个测试用例的提炼版本：

abstract class GenericController[T] {

    def getPath():String

    def save(entity:T):String = "parent"
}

class StatusController extends GenericController[String] {

    override def getPath():String = "/statuses"

    override def save(entity:String):String = "child"
}

在遍历 AST 时，我会遍历类和方法，确保只处理未被覆盖的方法。应用于StatusController.getPath 方法的符号的scala.reflect.internal.Symbols.MethodSymbol.overrides() 方法将包括GenericController.getPath 的方法。

但是，MethodSymbol.overrides() 无法为 StatusController.save 符号返回 GenericController.save 方法。似乎泛型类型使这种行为复杂化，是否应该在另一个编译器阶段之后完成？

Answer 1

让我们定义测试编译器插件。

core/src/main/scala/Main.scala

abstract class GenericController[T] {
  def getPath():String
  def save(entity:T):String = "parent"
}

class StatusController extends GenericController[String] {
  override def getPath():String = "/statuses"
  override def save(entity:String):String = "child"
}

plugin/src/main/resources/scalac-plugin.xml

<plugin>
    <name>MyCompilerPlugin</name>
    <classname>compilerPlugin.MyCompilerPlugin</classname>
</plugin>

plugin/src/main/scala/compilerPlugin/MyCompilerPlugin.scala

package compilerPlugin

import scala.tools.nsc.{Global, Phase}
import scala.tools.nsc.plugins.{Plugin, PluginComponent}

class MyCompilerPlugin(val global: Global) extends Plugin {
  import global._

  val name = "MyCompilerPlugin"
  val description = "My compiler plugin"
  val components: List[PluginComponent] = List[PluginComponent](MyComponent)

  private object MyComponent extends PluginComponent {
    val global: MyCompilerPlugin.this.global.type = MyCompilerPlugin.this.global
    val runsAfter: List[String] = List[String](/*"typer"*/"jvm")
    val phaseName: String = MyCompilerPlugin.this.name
    def newPhase(_prev: Phase) = new MyPhase(_prev)

    class MyPhase(prev: Phase) extends StdPhase(prev) {
      override def name: String = MyCompilerPlugin.this.name

      def apply(unit: CompilationUnit): Unit = {
        for (tree@q"$mods def $tname[..$tparams](...$paramss): $tpt = $expr" <- unit.body) {
          println(s"tree=$tree, symbol=${tree.symbol.fullName}, symbol.overrides=${tree.symbol.overrides.map(_.fullName)}")
        }
      }
    }
  }
}

build.sbt

ThisBuild / name := "compiler-plugin-demo"

lazy val commonSettings = Seq(
  scalaVersion := "2.13.3",
  version := "1.0",
)

lazy val plugin = project
  .settings(
    commonSettings,
    libraryDependencies ++= Seq(
      scalaOrganization.value % "scala-reflect" % scalaVersion.value,
      scalaOrganization.value % "scala-compiler" % scalaVersion.value,
    )
  )

lazy val core = project
  .settings(
    commonSettings,
    scalacOptions ++= Seq(
      "-Xplugin:plugin/target/scala-2.13/plugin_2.13-1.0.jar",
      "-Xplugin-require:MyCompilerPlugin"
    )
  )

如果你在typer 阶段之后运行（sbt reload; clean; plugin/package; core/compile）这个编译器插件，它会打印出来

tree=def <init>(): GenericController[T] = {
  GenericController.super.<init>();
  ()
}, symbol=GenericController.<init>, symbol.overrides=List()
tree=def getPath(): String, symbol=GenericController.getPath, symbol.overrides=List()
tree=def save(entity: T): String = "parent", symbol=GenericController.save, symbol.overrides=List()
tree=def <init>(): StatusController = {
  StatusController.super.<init>();
  ()
}, symbol=StatusController.<init>, symbol.overrides=List()
tree=override def getPath(): String = "/statuses", symbol=StatusController.getPath, symbol.overrides=List(GenericController.getPath)
tree=override def save(entity: String): String = "child", symbol=StatusController.save, symbol.overrides=List(GenericController.save)

但如果你在jvm 阶段之后运行它，它会打印出来

tree=def getPath(): String, symbol=GenericController.getPath, symbol.overrides=List()
tree=def save(entity: Object): String = "parent", symbol=GenericController.save, symbol.overrides=List()
tree=def <init>(): GenericController = {
  GenericController.super.<init>();
  ()
}, symbol=GenericController.<init>, symbol.overrides=List()
tree=override def getPath(): String = "/statuses", symbol=StatusController.getPath, symbol.overrides=List(GenericController.getPath)
tree=override def save(entity: String): String = "child", symbol=StatusController.save, symbol.overrides=List()
tree=override <bridge> <artifact> def save(entity: Object): String = StatusController.this.save(entity.$asInstanceOf[String]()), symbol=StatusController.save, symbol.overrides=List(GenericController.save)
tree=def <init>(): StatusController = {
  StatusController.super.<init>();
  ()
}, symbol=StatusController.<init>, symbol.overrides=List()

如您所见，在typer 阶段之后，方法符号StatusController.getPath 覆盖方法符号GenericController.getPath 和StatusController.save 覆盖GenericController.save。在jvm 阶段之后StatusController.getPath 再次覆盖GenericController.getPath 但它是桥StatusController.save 而不是普通的StatusController.save 覆盖GenericController.save。所以我猜你把桥方法的符号和普通方法的符号混淆了。