scala AST Select node can't find members inherited from parent

问题

I'm writing a macro called assign whose job is to assign values from members of one instance to another with a particular prefix added to the name of the member. For example, I have an instance with members named my_prefix_data, my_prefix_rden, ... and I want to assign values to these members from another instance with corresponding members named data, rden, .... I've made a prototype version of the macro that just handles the my_prefix_data <- data assignment. The assignments are to be made using a special method :=, because this macro is ultimately going to be applied to Chisel code.

Unfortunately, it's not working. The macro implementation looks like this

package my_macros

import scala.language.experimental.macros
import scala.reflect.macros.blackbox


object Macro {
  def assign(foo: Any, prefix: String, bundle: Any): Unit = macro Impl.assign
}

class Impl(val c: blackbox.Context) {
  def assign(
    foo: c.Tree, // Foo
    prefix: c.Tree, // string
    bundle: c.Tree // bundle
  ): c.Tree = {
    import c.universe._
    val Literal(Constant(p: String)) = prefix
    Apply(
      Select(
        Select(
          foo,
          TermName(s"${p}_data")
        ),
        TermName(":=")
      ),
      List(
        Select(
          bundle,
          TermName("data")
        )
      )
    )
  }
}

I have a failing test case set up like this

package my_macros

import org.scalatest._

class MacroSpec extends FlatSpec {
  behavior of "Macro"
  it should "access parent methods" in {
    class Data(initial: Int) {
      var value: Int = initial
      def :=(other: Data): Unit = {
        value += other.value
      }
    }

    class UInt(initial: Int) extends Data(initial) {}

    class FooBundle {
      val my_prefix_data = new UInt(1)
    }

    class BarBundle {
      val data = new UInt(2)
    }

    val foo = new FooBundle
    val bar = new BarBundle

    Macro.assign(foo, "my_prefix", bar)

    assert(foo.my_prefix_data.value == bar.data.value)
  }
}

It's failing with error

[error] value := is not a member of UInt
[error]   Expression does not convert to assignment because receiver is not assignable.
[error]     Macro.assign(foo, "my_prefix", bar)
[error]                 ^

Why does the Select AST node fail to find the inherited := from UInt's parent class Data?

回答1:

Inheritance is irrelevant. For

class UInt(initial: Int) {
  var value: Int = initial
  def :=(other: UInt): Unit = {
    value += other.value
  }
}

behavior is the same.

Replace TermName(":=") with TermName("$colon$eq") or with TermName(":=").encodedName or replace manually built tree

val Literal(Constant(p: String)) = prefix
Apply(
  Select(
    Select(
      foo,
      TermName(s"${p}_data")
    ),
    TermName(":=")
  ),
  List(
    Select(
      bundle,
      TermName("data")
    )
  )
)

with quasiquote

val q"${p: String}" = prefix
val pdata = TermName(s"${p}_data")
q"$foo.$pdata.:=($bundle.data)"

Then the code compiles.

来源：https://stackoverflow.com/questions/61002619/scala-ast-select-node-cant-find-members-inherited-from-parent

标签

scala

scala-macros

scala-reflect