annotation macro that rewrites and impls a trait, generics not processed correctly - scala-macros

Question

I am writing a macro that needs to create a class that rewrites a trait, having the same methods/args of the trait but different return type.
So say we got:
trait MyTrait[T]
{
def x(t1: T)(t2: T): T
}
#AnnProxy
class MyClass[T] extends MyTrait[T]
MyClass will be rewritten to:
class MyClass[T] {
def x(t1: T)(t2: T): R[T]
}
(so x will now return R[T] instead of T)
I wrote the macro and debugging it, it produces this code:
Expr[Any](class MyClass[T] extends scala.AnyRef {
def <init>() = {
super.<init>();
()
};
def x(t1: T)(t2: T): macrotests.R[T] = $qmark$qmark$qmark
})
#AnnProxy
As you see the signature seems ok. But when trying to use the macro, I get a compilation error:
val my = new MyClass[Int]
my.x(5)(6)
Error:(14, 7) type mismatch;
found : Int(5)
required: T
x.x(5)(6)
^
So it seems the method's generic T is not the same as the class [T]. Any ideas how to fix?
This is my macro so far. I am not any good with macros (coin'd this up with a lot of help from stackoverflow), but this is the current state:
#compileTimeOnly("enable macro paradise to expand macro annotations")
class AnnProxy extends StaticAnnotation
{
def macroTransform(annottees: Any*): Any = macro IdentityMacro.impl
}
trait R[T]
object IdentityMacro
{
private val SDKClasses = Set("java.lang.Object", "scala.Any")
def impl(c: whitebox.Context)(annottees: c.Expr[Any]*): c.Expr[Any] = {
import c.universe._
def showInfo(s: String) = c.info(c.enclosingPosition, s.split("\n").mkString("\n |---macro info---\n |", "\n |", ""), true)
val classDef = annottees.map(_.tree).head.asInstanceOf[ClassDef]
val clazz = c.typecheck(classDef).symbol.asClass
val tparams = clazz.typeParams
val baseClasses = clazz.baseClasses.tail.filter(clz => !SDKClasses(clz.fullName))
val methods = baseClasses.flatMap {
base =>
base.info.decls.filter(d => d.isMethod && d.isPublic).map { decl =>
val termName = decl.name.toTermName
val method = decl.asMethod
val params = method.paramLists.map(_.map {
s =>
val vd = internal.valDef(s)
val f = tparams.find(_.name == vd.tpt.symbol.name)
val sym = if (f.nonEmpty) f.get else vd.tpt.symbol
q"val ${vd.name} : $sym "
})
val paramVars = method.paramLists.flatMap(_.map(_.name))
q""" def $termName (...$params)(timeout:scala.concurrent.duration.FiniteDuration) : macrotests.R[${method.returnType}] = {
???
}"""
}
}
val cde = c.Expr[Any] {
q"""
class ${classDef.name} [..${classDef.tparams}] {
..$methods
}
"""
}
showInfo(show(cde))
cde
}
}
EDIT: I managed to work around by building the class as a string and then using c.parse to compile it. Feels like a hack but it works. There must be a better way by manipulating the tree.
package macrotests
import scala.annotation.{StaticAnnotation, compileTimeOnly}
import scala.language.experimental.macros
import scala.reflect.macros.whitebox
#compileTimeOnly("enable macro paradise to expand macro annotations")
class AnnProxy extends StaticAnnotation
{
def macroTransform(annottees: Any*): Any = macro AnnProxyMacro.impl
}
trait R[T]
trait Remote[T]
object AnnProxyMacro
{
private val SDKClasses = Set("java.lang.Object", "scala.Any")
def impl(c: whitebox.Context)(annottees: c.Expr[Any]*): c.Expr[Any] = {
import c.universe._
val classDef = annottees.map(_.tree).head.asInstanceOf[ClassDef]
val clazz = c.typecheck(classDef).symbol.asClass
val baseClasses = clazz.baseClasses.tail.filter(clz => !SDKClasses(clz.fullName))
val methods = baseClasses.flatMap {
base =>
base.info.decls.filter(d => d.isMethod && d.isPublic).map { decl =>
val termName = decl.name.toTermName
val method = decl.asMethod
val params = method.paramLists.map(_.map {
s =>
val vd = internal.valDef(s)
val tq = vd.tpt
s"${vd.name} : $tq"
})
val paramVars = method.paramLists.flatMap(_.map(_.name))
val paramVarsArray = paramVars.mkString("Array(", ",", ")")
val paramsStr = params.map(_.mkString("(", ",", ")")).mkString(" ")
val retTpe = method.returnType.typeArgs.mkString("-unexpected-")
s""" def $termName $paramsStr (timeout:scala.concurrent.duration.FiniteDuration) : macrotests.Remote[$retTpe] = {
println($paramVarsArray.toList)
new macrotests.Remote[$retTpe] {}
}"""
}
}
val tparams = clazz.typeParams.map(_.name)
val tparamsStr = if (tparams.isEmpty) "" else tparams.mkString("[", ",", "]")
val code =
s"""
|class ${classDef.name}$tparamsStr (x:Int) {
|${methods.mkString("\n")}
|}
""".stripMargin
// print(code)
val cde = c.Expr[Any](c.parse(code))
cde
}
}

Answer 1

the code is very long , you can look at the github: https://github.com/1178615156/scala-macro-example/blob/master/stackoverflow/src/main/scala/so/AnnotationWithTrait.scala
import scala.annotation.StaticAnnotation
import scala.language.experimental.macros
import scala.reflect.macros.blackbox.Context
/**
* Created by yu jie shui on 2015/12/2.
*/
class AnnotationWithTrait extends StaticAnnotation {
def macroTransform(annottees: Any*): Any = macro AnnotationWithTraitImpl.apply
}
class AnnotationWithTraitImpl(val c: Context) {
import c.universe._
val SDKClasses = Set("java.lang.Object", "scala.Any")
def showInfo(s: String) = c.info(c.enclosingPosition, s.split("\n").mkString("\n |---macro info---\n |", "\n |", ""), true)
def apply(annottees: c.Expr[Any]*) = {
val classDef = annottees.map(_.tree).head.asInstanceOf[ClassDef]
val superClassSymbol= c.typecheck(classDef).symbol.asClass.baseClasses.tail
.filterNot(e => SDKClasses.contains(e.fullName)).reverse
val superClassTree= classDef match {
case q"$mod class $name[..$t](..$params) extends ..$superClass { ..$body }" =>
(superClass: List[Tree]).filterNot(e =>
typeOf[Object].members.exists(_.name == e.children.head.toString())
)
}
showInfo(show(superClassSymbol))
showInfo(show(superClassTree))
val impl = q"private[this] object ${TermName("impl")} extends ..${superClassTree}"
//
//get super class all can call method
val methods = superClassSymbol.map(_.info.members
.filterNot(_.isConstructor)
.filterNot(e => typeOf[Object].members.exists(_.name == e.name)).map(_.asMethod)).toList
case class ReplaceTypeParams(from: String, to: String)
type ClassReplace = List[ReplaceTypeParams]
//trait a[A]
//class b[B] extends a[B]
//need replace type params A to B
val classReplaceList: List[ClassReplace] = superClassTree zip superClassSymbol map {
case (superClassTree, superClassSymbol) =>
superClassSymbol.asClass.typeParams.map(_.name) zip superClassTree.children.tail map
(e => ReplaceTypeParams(e._1.toString, e._2.toString()))
}
val out = classReplaceList zip methods map {
case (classReplace, func) =>
func map { e => {
val funcName = e.name
val funcTypeParams = e.typeParams.map(_.name.toString).map(name => {
TypeDef(Modifiers(Flag.PARAM), TypeName(name), List(), TypeBoundsTree(EmptyTree, EmptyTree))
})
val funcParams = e.paramLists.map(_.map(e => q"${e.name.toTermName}:${
TypeName(
classReplace.find(_.from == e.info.toString).map(_.to).getOrElse(e.info.toString)
)} "))
val funcResultType = TypeName(
classReplace.find(_.from == e.returnType.toString).map(_.to).getOrElse(e.info.toString)
)
q"""
def ${funcName}[..${funcTypeParams}](...$funcParams):${funcResultType}=
impl.${funcName}[..${funcTypeParams}](...$funcParams)
"""
}
}
}
showInfo(show(out))
q"""
class ${classDef.name}[..${classDef.tparams}]{
$impl
..${out.flatten}
}
"""
}
}
test
trait MyTrait[MT1] {
def x(t1: MT1)(t2: MT1): MT1 = t1
}
trait MyTrait2[MT2] {
def t(t2: MT2): MT2 = t2
}
#AnnotationWithTrait
class MyClass[MCT1, MCT2] extends MyTrait[MCT1] with MyTrait2[MCT2]
object AnnotationWithTraitUsing extends App {
assert(new MyClass[Int, String].x(1)(2) == 1)
assert(new MyClass[Int, String].t("aaa") == "aaa")
}