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package magnolia
import scala.reflect._, macros._
import macrocompat.bundle
import scala.util.Try
import language.existentials
import language.higherKinds
abstract class Transformation[C <: whitebox.Context](val c: C) {
def typeclassBody(genericType: c.Type, implementation: c.Tree): c.Tree
def coproductReduction(left: c.Tree, right: c.Tree): c.Tree
}
abstract class MagnoliaMacro(val c: whitebox.Context) {
import c.universe._
import CompileTimeState._
protected def transformation(c: whitebox.Context): Transformation[c.type]
private def findType(key: c.universe.Type): Option[c.TermName] =
recursionStack(c.enclosingPosition).frames.find(_.genericType == key).map(_.termName(c))
private def recurse[T](path: TypePath, key: c.universe.Type, value: c.TermName)(fn: => T):
Option[T] = {
recursionStack = recursionStack.updated(
c.enclosingPosition,
recursionStack.get(c.enclosingPosition).map(_.push(path, key, value)).getOrElse(
Stack(List(Frame(path, key, value)), Nil))
)
try Some(fn) catch { case e: Exception => None } finally {
val currentStack = recursionStack(c.enclosingPosition)
recursionStack = recursionStack.updated(c.enclosingPosition,
currentStack.pop())
}
}
private val removeLazy: Transformer = new Transformer {
override def transform(tree: Tree): Tree = tree match {
case q"magnolia.Lazy.apply[$returnType](${Literal(Constant(method: String))})" =>
q"${TermName(method)}"
case _ =>
super.transform(tree)
}
}
private def getImplicit(paramName: Option[String],
genericType: c.universe.Type,
typeConstructor: c.universe.Type,
assignedName: c.TermName,
dereferencerImplicit: c.Tree): c.Tree = {
findType(genericType).map { methodName =>
val methodAsString = methodName.encodedName.toString
val searchType = appliedType(typeConstructor, genericType)
q"_root_.magnolia.Lazy[$searchType]($methodAsString)"
}.orElse {
val searchType = appliedType(typeConstructor, genericType)
findType(genericType).map { _ =>
directInferImplicit(genericType, typeConstructor, dereferencerImplicit)
}.getOrElse {
scala.util.Try {
val genericTypeName: String = genericType.typeSymbol.name.encodedName.toString.toLowerCase
val assignedName: TermName = TermName(c.freshName(s"${genericTypeName}Typeclass"))
recurse(RecursiveCall(genericType.toString), genericType, assignedName) {
val inferredImplicit = c.inferImplicitValue(searchType, false, false)
q"""{
def $assignedName: $searchType = $inferredImplicit
$assignedName
}"""
}.get
}.toOption.orElse(directInferImplicit(genericType, typeConstructor, dereferencerImplicit))
}
}.getOrElse {
val currentStack: Stack = recursionStack(c.enclosingPosition)
val error = ImplicitNotFound(genericType.toString,
recursionStack(c.enclosingPosition).frames.map(_.path))
val updatedStack = currentStack.copy(errors = error :: currentStack.errors)
recursionStack = recursionStack.updated(c.enclosingPosition, updatedStack)
c.abort(c.enclosingPosition, s"Could not find type class for type $genericType")
}
}
private def directInferImplicit(genericType: c.universe.Type,
typeConstructor: c.universe.Type,
dereferencerImplicit: c.Tree): Option[c.Tree] = {
val genericTypeName: String = genericType.typeSymbol.name.encodedName.toString.toLowerCase
val assignedName: TermName = TermName(c.freshName(s"${genericTypeName}Typeclass"))
val typeSymbol = genericType.typeSymbol
val classType = if(typeSymbol.isClass) Some(typeSymbol.asClass) else None
val isCaseClass = classType.map(_.isCaseClass).getOrElse(false)
val isSealedTrait = classType.map(_.isSealed).getOrElse(false)
val isValueClass = genericType <:< typeOf[AnyVal]
val resultType = appliedType(typeConstructor, genericType)
val construct = if(isCaseClass) {
val implicits = genericType.decls.collect {
case m: MethodSymbol if m.isCaseAccessor => m.asMethod
}.map { param =>
val paramName = param.name.encodedName.toString
val derivedImplicit = recurse(ProductType(paramName, genericType.toString), genericType, assignedName) {
getImplicit(Some(paramName), param.returnType, typeConstructor, assignedName, dereferencerImplicit)
}.getOrElse {
c.abort(c.enclosingPosition, s"failed to get implicit for type $genericType")
}
val dereferencedValue = q"$dereferencerImplicit.dereference(src, ${param.name.toString})"
val result = q"$dereferencerImplicit.delegate($derivedImplicit, $dereferencedValue)"
println(result+"\n\n")
result
}
Some(q"new $genericType(..$implicits)")
} else if(isSealedTrait) {
val subtypes = classType.get.knownDirectSubclasses.to[List]
Some {
val reduction = subtypes.map(_.asType.toType).map { searchType =>
recurse(CoproductType(genericType.toString), genericType, assignedName) {
getImplicit(None, searchType, typeConstructor, assignedName, dereferencerImplicit)
}.getOrElse {
c.abort(c.enclosingPosition, s"failed to get implicit for type $searchType")
}
}.reduce(transformation(c).coproductReduction)
q"$dereferencerImplicit.delegate($reduction, src)"
}
} else None
construct.map { const =>
val bodyImplementation = transformation(c).typeclassBody(genericType, const)
q"""{
def $assignedName: $resultType = new $resultType { $bodyImplementation }
$assignedName
}"""
}
}
def magnolia[T: c.WeakTypeTag, Typeclass: c.WeakTypeTag]: c.Tree = {
import c.universe._
val genericType: Type = weakTypeOf[T]
val currentStack: List[Frame] = recursionStack.get(c.enclosingPosition).map(_.frames).getOrElse(List())
val directlyReentrant = Some(genericType) == currentStack.headOption.map(_.genericType)
val typeConstructor: Type = weakTypeOf[Typeclass].typeConstructor
val dereferencerTypeclass = weakTypeOf[Dereferencer[_]].typeConstructor
val dereferencerType = appliedType(dereferencerTypeclass, typeConstructor)
val dereferencerImplicit = c.untypecheck(c.inferImplicitValue(dereferencerType, false, false))
if(directlyReentrant) throw DirectlyReentrantException()
val result: Option[c.Tree] = if(!recursionStack.isEmpty) {
findType(genericType) match {
case None =>
directInferImplicit(genericType, typeConstructor, dereferencerImplicit)
case Some(enclosingRef) =>
val methodAsString = enclosingRef.toString
val searchType = appliedType(typeConstructor, genericType)
Some(q"_root_.magnolia.Lazy[$searchType]($methodAsString)")
}
} else {
val typeConstructor: Type = weakTypeOf[Typeclass].typeConstructor
directInferImplicit(genericType, typeConstructor, dereferencerImplicit)
}
result.map { tree =>
if(currentStack.isEmpty) c.untypecheck(removeLazy.transform(tree)) else tree
}.getOrElse {
if(currentStack.isEmpty) println("Foo")
c.abort(c.enclosingPosition, "could not infer typeclass for type $genericType")
}
}
}
private[magnolia] case class DirectlyReentrantException() extends
Exception("attempt to recurse directly")
private[magnolia] object Lazy { def apply[T](method: String): T = ??? }
private[magnolia] object CompileTimeState {
sealed trait TypePath
case class CoproductType(typeName: String) extends TypePath {
override def toString = s"coproduct type $typeName"
}
case class ProductType(paramName: String, typeName: String) extends TypePath {
override def toString = s"parameter '$paramName' of product type $typeName"
}
case class RecursiveCall(typeName: String) extends TypePath {
override def toString = s"recursive implicit of type $typeName"
}
case class ImplicitNotFound(genericType: String, path: List[TypePath])
case class Stack(frames: List[Frame], errors: List[ImplicitNotFound]) {
def push(path: TypePath, key: whitebox.Context#Type,
value: whitebox.Context#TermName): Stack =
Stack(Frame(path, key, value) :: frames, errors)
def pop(): Stack = Stack(frames.tail, errors)
}
case class Frame(path: TypePath, genericType: whitebox.Context#Type,
term: whitebox.Context#TermName) {
def termName(c: whitebox.Context): c.TermName = term.asInstanceOf[c.TermName]
}
private[magnolia] var recursionStack: Map[api.Position, Stack] =
Map()
}
@bundle
class Macros(val context: whitebox.Context) extends MagnoliaMacro(context) {
protected def transformation(c: whitebox.Context): Transformation[c.type] =
new Transformation[c.type](c) {
import c.universe._
def typeclassBody(genericType: c.Type, implementation: c.Tree): c.Tree =
q"""def extract(src: _root_.magnolia.Thing): $genericType = $implementation"""
def coproductReduction(left: c.Tree, right: c.Tree): c.Tree = q"$left.orElse($right)"
}
}
trait Dereferencer[Typeclass[_]] {
type Value
def dereference(value: Value, param: String): Value
def delegate[T](typeclass: Typeclass[T], value: Value): T
}
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