package magnolia
import scala.reflect._, macros._
import scala.collection.immutable.ListMap
import language.existentials
import language.higherKinds
import language.experimental.macros
trait Subclass[Tc[_], T] {
type S <: T
def typeclass: Tc[S]
def label: String
def cast: PartialFunction[T, S]
}
trait Param[Tc[_], T] {
type S
def typeclass: Tc[S]
def label: String
def dereference(param: T): S
}
trait JoinContext[Tc[_], T] {
def construct[R](param: ((Param[Tc, T]) => Any)): T
def typeName: String
def parameters: List[Param[Tc, T]]
def isObject: Boolean
}
object Magnolia {
import CompileTimeState._
def generic[T: c.WeakTypeTag](c: whitebox.Context): c.Tree = {
import c.universe._
import scala.util.{Try, Success, Failure}
val typeConstructor: c.Type =
c.prefix.tree.tpe.member(TypeName("Typeclass")).asType.toType.typeConstructor
def findType(key: Type): Option[TermName] =
recursionStack(c.enclosingPosition).frames.find(_.genericType == key).map(_.termName(c))
def recurse[T](path: TypePath, key: Type, value: TermName)(fn: => T):
Option[T] = {
recursionStack = recursionStack.updated(
c.enclosingPosition,
recursionStack.get(c.enclosingPosition).map(_.push(path, key, value)).getOrElse(
Stack(Map(), 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())
}
}
val removeDeferred: Transformer = new Transformer {
override def transform(tree: Tree): Tree = tree match {
case q"_root_.magnolia.Deferred.apply[$returnType](${Literal(Constant(method: String))})" =>
q"${TermName(method)}"
case _ =>
super.transform(tree)
}
}
def implicitTree(paramName: Option[String],
genericType: Type,
typeConstructor: Type,
assignedName: TermName): Tree = {
val searchType = appliedType(typeConstructor, genericType)
findType(genericType).map { methodName =>
val methodAsString = methodName.encodedName.toString
q"_root_.magnolia.Deferred.apply[$searchType]($methodAsString)"
}.orElse {
val (inferredImplicit, newStack) = recursionStack(c.enclosingPosition).lookup(c)(searchType) {
scala.util.Try {
val genericTypeName: String = genericType.typeSymbol.name.encodedName.toString.toLowerCase
val assignedName: TermName = TermName(c.freshName(s"${genericTypeName}Typeclass"))
recurse(ChainedImplicit(genericType.toString), genericType, assignedName) {
c.inferImplicitValue(searchType, false, false)
}.get
}.toOption.orElse(directInferImplicit(genericType, typeConstructor))
}
recursionStack = recursionStack.updated(c.enclosingPosition, newStack)
inferredImplicit
}.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)
val stack = recursionStack(c.enclosingPosition).frames.map(_.path).mkString(" in ", "\n in ", "\n")
c.abort(c.enclosingPosition, s"magnolia: could not find typeclass for type $genericType\n$stack")
}
}
def directInferImplicit(genericType: c.Type,
typeConstructor: Type): 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 isCaseObject = classType.map(_.isModuleClass).getOrElse(false)
val isSealedTrait = classType.map(_.isSealed).getOrElse(false)
val isValueClass = genericType <:< typeOf[AnyVal]
val resultType = appliedType(typeConstructor, genericType)
// FIXME: Handle AnyVals
val result = if(isCaseObject) {
val termSym = genericType.typeSymbol.companionSymbol
val obj = termSym.asTerm
val className = obj.name.toString
val impl = q"""
${c.prefix}.join(new _root_.magnolia.JoinContext[$typeConstructor, $genericType] {
def construct[R](fn: ((Param[${typeConstructor}, $genericType]) => Any)): $genericType = $obj
def typeName: _root_.java.lang.String = $className
def parameters: _root_.scala.List[Param[$typeConstructor, $genericType]] = _root_.scala.List()
def isObject = true
})
"""
Some(impl)
} else if(isCaseClass) {
val caseClassParameters = genericType.decls.collect {
case m: MethodSymbol if m.isCaseAccessor => m.asMethod
}
val className = genericType.toString
val implicits: List[(c.universe.MethodSymbol, c.Tree, c.Type)] = caseClassParameters.map { param =>
val paramName = param.name.encodedName.toString
val paramType = param.returnType.substituteTypes(genericType.etaExpand.typeParams, genericType.typeArgs)
val derivedImplicit = recurse(ProductType(paramName, genericType.toString), genericType,
assignedName) {
implicitTree(Some(paramName), paramType, typeConstructor, assignedName)
}.getOrElse {
c.abort(c.enclosingPosition, s"failed to get implicit for type $genericType")
}
(param, derivedImplicit, paramType)
}.to[List]
Some {
val callables = implicits.map { case (param, imp, paramType) =>
val label = param.name.toString
q"""new _root_.magnolia.Param[$typeConstructor, ${genericType}] {
type S = ${paramType}
def typeclass: ${appliedType(typeConstructor, paramType)} = $imp
def label: _root_.java.lang.String = $label
def dereference(param: ${genericType}): ${paramType} = param.${TermName(label)}
}"""
}
val constructor = q"""new $genericType(..${callables.zip(implicits).map { case (call, imp) =>
q"fn($call).asInstanceOf[${imp._3}]"
} })"""
q"""
${c.prefix}.join(new _root_.magnolia.JoinContext[$typeConstructor, $genericType] {
def construct[R](fn: ((Param[${typeConstructor}, $genericType]) => Any)): $genericType = $constructor
def typeName: _root_.java.lang.String = $className
def parameters: _root_.scala.List[Param[$typeConstructor, $genericType]] =
_root_.scala.List(..$callables)
def isObject = false
})
"""
}
} else if(isSealedTrait) {
val genericSubtypes = classType.get.knownDirectSubclasses.to[List]
val subtypes = genericSubtypes.map { sub =>
val mapping = sub.asType.typeSignature.baseType(genericType.typeSymbol).typeArgs.zip(genericType.typeArgs).toMap
val newTypeParams = sub.asType.toType.typeArgs.map(mapping(_))
appliedType(sub.asType.toType.typeConstructor, newTypeParams)
}
if(subtypes.isEmpty) {
c.info(c.enclosingPosition,
s"magnolia: could not find any direct subtypes of $typeSymbol", true)
c.abort(c.enclosingPosition, "")
}
Some {
val subclasses = subtypes.map { searchType =>
recurse(CoproductType(genericType.toString), genericType, assignedName) {
(searchType, implicitTree(None, searchType, typeConstructor, assignedName))
}.getOrElse {
c.abort(c.enclosingPosition, s"failed to get implicit for type $searchType")
}
}.map { case (typ, typeclass) =>
val caseClause = cq"(t: $typ) => t"
val pf = q"""new _root_.scala.PartialFunction[$genericType, $typ] {
def isDefinedAt(t: $genericType): Boolean = t.isInstanceOf[$typ]
def apply(t: $genericType): $typ = t.asInstanceOf[$typ]
}"""
q"""new _root_.magnolia.Subclass[$typeConstructor, $genericType] {
type S = $typ
def label: _root_.java.lang.String = ${typ.typeSymbol.name.toString}
def typeclass: ${appliedType(typeConstructor, typ)} = $typeclass
def cast: _root_.scala.PartialFunction[$genericType, $typ] = $pf
}"""
}
q"""{
${c.prefix}.split(_root_.scala.collection.immutable.List[_root_.magnolia.Subclass[$typeConstructor, $genericType]](..$subclasses))
}"""
}
} else None
result.map { r =>
q"""{
def $assignedName: $resultType = $r
$assignedName
}"""
}
}
val genericType: Type = weakTypeOf[T]
val currentStack: Stack =
recursionStack.get(c.enclosingPosition).getOrElse(Stack(Map(), List(), List()))
val directlyReentrant = Some(genericType) == currentStack.frames.headOption.map(_.genericType)
if(directlyReentrant) throw DirectlyReentrantException()
currentStack.errors.foreach { error =>
if(!emittedErrors.contains(error)) {
emittedErrors += error
val trace = error.path.mkString("\n in ", "\n in ", "\n \n")
val msg = s"magnolia: could not derive ${typeConstructor} instance for type "+
s"${error.genericType}"
c.info(c.enclosingPosition, msg+trace, true)
}
}
val result: Option[Tree] = if(!currentStack.frames.isEmpty) {
findType(genericType) match {
case None =>
directInferImplicit(genericType, typeConstructor)
case Some(enclosingRef) =>
val methodAsString = enclosingRef.toString
val searchType = appliedType(typeConstructor, genericType)
Some(q"_root_.magnolia.Deferred[$searchType]($methodAsString)")
}
} else directInferImplicit(genericType, typeConstructor)
if(currentStack.frames.isEmpty) recursionStack = ListMap()
result.map { tree =>
if(currentStack.frames.isEmpty) {
val out = c.untypecheck(removeDeferred.transform(tree))
//println(out)
out
} else tree
}.getOrElse {
c.abort(c.enclosingPosition, s"magnolia: could not infer typeclass for type $genericType")
}
}
}
private[magnolia] case class DirectlyReentrantException() extends
Exception("attempt to recurse directly")
private[magnolia] object Deferred { def apply[T](method: String): T = ??? }
private[magnolia] object CompileTimeState {
sealed class TypePath(path: String) { override def toString = path }
case class CoproductType(typeName: String) extends
TypePath(s"coproduct type $typeName")
case class ProductType(paramName: String, typeName: String) extends
TypePath(s"parameter '$paramName' of product type $typeName")
case class ChainedImplicit(typeName: String) extends
TypePath(s"chained implicit of type $typeName")
case class ImplicitNotFound(genericType: String, path: List[TypePath])
case class Stack(cache: Map[whitebox.Context#Type, Option[whitebox.Context#Tree]], frames: List[Frame], errors: List[ImplicitNotFound]) {
def lookup(c: whitebox.Context)(t: c.Type)(orElse: => Option[c.Tree]): (Option[c.Tree], Stack) =
if(cache.contains(t)) {
(cache(t).asInstanceOf[Option[c.Tree]], this)
} else {
val value = orElse
(value, copy(cache.updated(t, value)))
}
def push(path: TypePath, key: whitebox.Context#Type,
value: whitebox.Context#TermName): Stack =
Stack(cache, Frame(path, key, value) :: frames, errors)
def pop(): Stack = Stack(cache, 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]
}
var recursionStack: ListMap[api.Position, Stack] = ListMap()
var emittedErrors: Set[ImplicitNotFound] = Set()
}