Question

我有一个宏注释，用于将隐式类型类注入到伴随方法中。

@MyMacro case class MyClass[T](a: String, b: Int, t: T)

大多数情况下，它可以按预期运行，但是当我使用类型约束符号时，它会中断：

@MyMacro case class MyClass[T: TypeClass](a: String, b: Int, t: T)
// private[this] not allowed for case class parameters

此错误是described on SO和reported as a bug。

问题是：不再维护宏（v1），所以我不能指望它会得到解决。

所以我想知道的是：我可以自己在宏中修复此问题吗？是否以某种方式可以撤销AST的更改？我想尝试在宏中修复它，而不是强制所有用户将其代码重写为...(implicit tc: TypeClass[T])。

Answer 1

class AnnotationType() extends scala.annotation.StaticAnnotation {
  def macroTransform(annottees: Any*): Any = macro AnnotationTypeImpl.impl
}

class AnnotationTypeImpl(val c: blackbox.Context) {

  import c.universe._

  def impl(annottees: Tree*): Tree = {

    val tree = annottees.head.asInstanceOf[ClassDef]

    val newTree = tree match {
      case ClassDef(mods, name, tparams, impl@Template(parents, self, body)) =>
        val newBody = body.map {
          case ValDef(mods, name, tpt, rhs) =>
            // look here
            // the flag of `private[this]` is Flag.PRIVATE | Flag.LOCAL
            // the flag of `private` is Flag.PRIVATE
            // drop Flag.LOCAL in Modifiers.flags ,  it will change `private[this]` to `private`
            val newMods =
              if(mods.hasFlag(Flag.IMPLICIT))
                mods.asInstanceOf[scala.reflect.internal.Trees#Modifiers].&~(Flag.LOCAL.asInstanceOf[Long]).&~(Flag.CASEACCESSOR.asInstanceOf[Long]).asInstanceOf[Modifiers]
              else
                mods
            ValDef(newMods, name, tpt, rhs)

          case e => e
        }
        ClassDef(mods, name, tparams, Template(parents, self, newBody))
    }
    println(show(tree))
    println(show(newTree))

    q"..${newTree +: annottees.tail}"
  }
}

//测试

@AnnotationType()
case class AnnotationTypeTest[T: Option](a: T){
  def option = implicitly[Option[T]]
}

object AnnotationTypeTest {
  def main(args: Array[String]): Unit = {
    implicit val x = Option(1)

    println(AnnotationTypeTest(100))
    println(AnnotationTypeTest(100).option)
    println(AnnotationTypeTest(100).copy(a =2222))
    println(AnnotationTypeTest(100).copy(a =2222)(Some(999)).option)
  }

}

Scala宏注释错误的解决方法

1 个答案: