package magnolia
import scala.reflect._, macros._
import scala.collection.immutable.ListMap
import language.existentials
import language.higherKinds
/** the object which defines the Magnolia macro */
object Magnolia {
import CompileTimeState._
/** derives a generic typeclass instance for the type `T`
*
* This is a macro definition method which should be bound to a method defined inside a Magnolia
* generic derivation object, that is, one which defines the methods `combine`, `dispatch` and
* the type constructor, `Typeclass[_]`. This will typically look like,
* <pre>
* object Derivation {
* // other definitions
* implicit def gen[T]: Typeclass[T] = Magnolia.gen[T]
* }
* </pre>
* which would support automatic derivation of typeclass instances by calling
* `Derivation.gen[T]` or with `implicitly[Typeclass[T]]`, if the implicit method is imported
* into the current scope.
*
* The definition expects a type constructor called `Typeclass`, taking one *-kinded type
* parameter to be defined on the same object as a means of determining how the typeclass should
* be genericized. While this may be obvious for typeclasses like `Show[T]` which take only a
* single type parameter, Magnolia can also derive typeclass instances for types such as
* `Decoder[Format, Type]` which would typically fix the `Format` parameter while varying the
* `Type` parameter.
*
* While there is no "interface" for a derivation, in the object-oriented sense, the Magnolia
* macro expects to be able to call certain methods on the object within which it is bound to a
* method.
*
* Specifically, for deriving case classes (product types), the macro will attempt to call the
* `combine` method with an instance of [[CaseClass]], like so,
* <pre>
* <derivation>.combine(<caseClass>): Typeclass[T]
* </pre>
* That is to say, the macro expects there to exist a method called `combine` on the derivation
* object, which may be called with the code above, and for it to return a type which conforms
* to the type `Typeclass[T]`. The implementation of `combine` will therefore typically look
* like this,
* <pre>
* def combine[T](caseClass: CaseClass[Typeclass, T]): Typeclass[T] = ...
* </pre>
* however, there is the flexibility to provide additional type parameters or additional
* implicit parameters to the definition, provided these do not affect its ability to be invoked
* as described above.
*
* Likewise, for deriving sealed traits (coproduct or sum types), the macro will attempt to call
* the `dispatch` method with an instance of [[SealedTrait]], like so,
* <pre>
* <derivation>.dispatch(<sealedTrait>): Typeclass[T]
* </pre>
* so a definition such as,
* <pre>
* def dispatch[T](sealedTrait: SealedTrait[Typeclass, T]): Typeclass[T] = ...
* </pre>
* will suffice, however the qualifications regarding additional type parameters and implicit
* parameters apply equally to `dispatch` as to `combine`.
* */
def gen[T: c.WeakTypeTag](c: whitebox.Context): c.Tree = {
import c.universe._
import scala.util.{Try, Success, Failure}
val magnoliaPkg = q"_root_.magnolia"
val magnoliaObj = q"$magnoliaPkg.Magnolia"
val arrayCls = tq"_root_.scala.Array"
val prefixType = c.prefix.tree.tpe
val typeDefs = prefixType.baseClasses.flatMap { cls =>
cls.asType.toType.decls.filter(_.isType).find(_.name.toString == "Typeclass").map { tpe =>
tpe.asType.toType.asSeenFrom(prefixType, cls)
}
}
val typeConstructorOpt =
typeDefs.headOption.map(_.typeConstructor)
val typeConstructor = typeConstructorOpt.getOrElse {
c.abort(c.enclosingPosition,
"magnolia: the derivation object does not define the Typeclass type constructor")
}
def findType(key: Type): Option[TermName] =
recursionStack(c.enclosingPosition).frames.find(_.genericType == key).map(_.termName(c))
case class Typeclass(typ: c.Type, tree: c.Tree)
def recurse[T](path: TypePath, key: Type, value: TermName)(fn: => T): Option[T] = {
val oldRecursionStack = recursionStack.get(c.enclosingPosition)
recursionStack = recursionStack.updated(
c.enclosingPosition,
oldRecursionStack.map(_.push(path, key, value)).getOrElse {
Stack(Map(), List(Frame(path, key, value)), Nil)
}
)
try Some(fn)
catch { case e: Exception => None } finally {
val currentStack = recursionStack(c.enclosingPosition)
recursionStack = recursionStack.updated(c.enclosingPosition, currentStack.pop())
}
}
val removeDeferred: Transformer = new Transformer {
override def transform(tree: Tree): Tree = tree match {
case q"$magnoliaPkg.Deferred.apply[$returnType](${Literal(Constant(method: String))})" =>
q"${TermName(method)}"
case _ =>
super.transform(tree)
}
}
def typeclassTree(paramName: Option[String],
genericType: Type,
typeConstructor: Type,
assignedName: TermName): Tree = {
val searchType = appliedType(typeConstructor, genericType)
val deferredRef = findType(genericType).map { methodName =>
val methodAsString = methodName.decodedName.toString
q"$magnoliaPkg.Deferred.apply[$searchType]($methodAsString)"
}
val foundImplicit = deferredRef.orElse {
val (inferredImplicit, newStack) =
recursionStack(c.enclosingPosition).lookup(c)(searchType) {
val implicitSearchTry = scala.util.Try {
val genericTypeName: String =
genericType.typeSymbol.name.decodedName.toString.toLowerCase
val assignedName: TermName = TermName(c.freshName(s"${genericTypeName}Typeclass"))
recurse(ChainedImplicit(genericType.toString), genericType, assignedName) {
c.inferImplicitValue(searchType, false, false)
}.get
}
implicitSearchTry.toOption.orElse(
directInferImplicit(genericType, typeConstructor).map(_.tree)
)
}
recursionStack = recursionStack.updated(c.enclosingPosition, newStack)
inferredImplicit
}
foundImplicit.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 stackPaths = recursionStack(c.enclosingPosition).frames.map(_.path)
val stack = stackPaths.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[Typeclass] = {
val genericTypeName: String = genericType.typeSymbol.name.decodedName.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 primitives = Set(typeOf[Double], typeOf[Float], typeOf[Short], typeOf[Byte],
typeOf[Int], typeOf[Long], typeOf[Char], typeOf[Boolean])
val isValueClass = genericType <:< typeOf[AnyVal] && !primitives.exists(_ =:= genericType)
val resultType = appliedType(typeConstructor, genericType)
// FIXME: Handle AnyVals
val result = if (isCaseObject) {
// FIXME: look for an alternative which isn't deprecated on Scala 2.12+
val obj = genericType.typeSymbol.companionSymbol.asTerm
val className = obj.name.decodedName.toString
val impl = q"""
${c.prefix}.combine($magnoliaObj.caseClass[$typeConstructor, $genericType](
$className, true, false, new $arrayCls(0), _ => $obj)
)
"""
Some(Typeclass(genericType, impl))
} else if (isCaseClass || isValueClass) {
val caseClassParameters = genericType.decls.collect {
case m: MethodSymbol if m.isCaseAccessor || (isValueClass && m.isParamAccessor) =>
m.asMethod
}
val className = genericType.typeSymbol.name.decodedName.toString
case class CaseParam(sym: c.universe.MethodSymbol,
typeclass: c.Tree,
paramType: c.Type,
ref: c.TermName)
val caseParamsReversed: List[CaseParam] = caseClassParameters.foldLeft(List[CaseParam]()) {
case (acc, param) =>
val paramName = param.name.decodedName.toString
val paramType = param.returnType.substituteTypes(genericType.etaExpand.typeParams,
genericType.typeArgs)
val predefinedRef = acc.find(_.paramType == paramType)
val caseParamOpt = predefinedRef.map { backRef =>
CaseParam(param, q"()", paramType, backRef.ref) :: acc
}
caseParamOpt.getOrElse {
val derivedImplicit =
recurse(ProductType(paramName, genericType.toString), genericType, assignedName) {
typeclassTree(Some(paramName), paramType, typeConstructor, assignedName)
}.getOrElse(
c.abort(c.enclosingPosition, s"failed to get implicit for type $genericType")
)
val ref = TermName(c.freshName("paramTypeclass"))
val assigned = q"""val $ref = $derivedImplicit"""
CaseParam(param, assigned, paramType, ref) :: acc
}
}
val caseParams = caseParamsReversed.reverse
val paramsVal: TermName = TermName(c.freshName("parameters"))
val fnVal: TermName = TermName(c.freshName("fn"))
val preAssignments = caseParams.map(_.typeclass)
val defaults = if(!isValueClass) {
val caseClassCompanion = genericType.companion
val constructorMethod = caseClassCompanion.decl(TermName("apply")).asMethod
val indexedConstructorParams = constructorMethod.paramLists.head.map(_.asTerm).zipWithIndex
indexedConstructorParams.map {
case (p, idx) =>
if (p.isParamWithDefault) {
val method = TermName("apply$default$" + (idx + 1))
q"_root_.scala.Some(${genericType.typeSymbol.companionSymbol.asTerm}.$method)"
} else q"_root_.scala.None"
}
} else List(q"_root_.scala.None")
val assignments = caseParams.zip(defaults).zipWithIndex.map {
case ((CaseParam(param, typeclass, paramType, ref), defaultVal), idx) =>
q"""$paramsVal($idx) = $magnoliaObj.param[$typeConstructor, $genericType,
$paramType](
${param.name.decodedName.toString}, $ref, $defaultVal, _.${param.name}
)"""
}
Some(
Typeclass(
genericType,
q"""{
..$preAssignments
val $paramsVal: $arrayCls[Param[$typeConstructor, $genericType]] =
new $arrayCls(${assignments.length})
..$assignments
${c.prefix}.combine($magnoliaObj.caseClass[$typeConstructor, $genericType](
$className,
false,
$isValueClass,
$paramsVal,
($fnVal: Param[$typeConstructor, $genericType] => Any) =>
new $genericType(..${caseParams.zipWithIndex.map {
case (typeclass, idx) =>
q"$fnVal($paramsVal($idx)).asInstanceOf[${typeclass.paramType}]"
}})
))
}"""
)
)
} else if (isSealedTrait) {
val genericSubtypes = classType.get.knownDirectSubclasses.to[List]
val subtypes = genericSubtypes.map { sub =>
val typeArgs = sub.asType.typeSignature.baseType(genericType.typeSymbol).typeArgs
val mapping = 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, "")
}
val subtypesVal: TermName = TermName(c.freshName("subtypes"))
val typeclasses = subtypes.map { searchType =>
recurse(CoproductType(genericType.toString), genericType, assignedName) {
(searchType, typeclassTree(None, searchType, typeConstructor, assignedName))
}.getOrElse {
c.abort(c.enclosingPosition, s"failed to get implicit for type $searchType")
}
}
val assignments = typeclasses.zipWithIndex.map {
case ((typ, typeclass), idx) =>
q"""$subtypesVal($idx) = $magnoliaObj.subtype[$typeConstructor, $genericType, $typ](
${typ.typeSymbol.fullName.toString},
$typeclass,
(t: $genericType) => t.isInstanceOf[$typ],
(t: $genericType) => t.asInstanceOf[$typ]
)"""
}
Some {
Typeclass(
genericType,
q"""{
val $subtypesVal: $arrayCls[_root_.magnolia.Subtype[$typeConstructor, $genericType]] =
new $arrayCls(${assignments.size})
..$assignments
${c.prefix}.dispatch(new _root_.magnolia.SealedTrait(
$genericTypeName,
$subtypesVal: $arrayCls[_root_.magnolia.Subtype[$typeConstructor, $genericType]])
): $resultType
}"""
)
}
} else None
result.map {
case Typeclass(t, r) =>
Typeclass(t, 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).map(_.tree)
case Some(enclosingRef) =>
val methodAsString = enclosingRef.toString
val searchType = appliedType(typeConstructor, genericType)
Some(q"_root_.magnolia.Deferred[$searchType]($methodAsString)")
}
} else directInferImplicit(genericType, typeConstructor).map(_.tree)
if (currentStack.frames.isEmpty) recursionStack = ListMap()
val dereferencedResult = result.map { tree =>
if (currentStack.frames.isEmpty) c.untypecheck(removeDeferred.transform(tree)) else tree
}
dereferencedResult.getOrElse {
c.abort(c.enclosingPosition, s"magnolia: could not infer typeclass for type $genericType")
}
}
/** constructs a new [[Subtype]] instance
*
* This method is intended to be called only from code generated by the Magnolia macro, and
* should not be called directly from users' code. */
def subtype[Tc[_], T, S <: T](name: String, tc: => Tc[S], isType: T => Boolean, asType: T => S) =
new Subtype[Tc, T] {
type SType = S
def label: String = name
def typeclass: Tc[SType] = tc
def cast: PartialFunction[T, SType] = new PartialFunction[T, S] {
def isDefinedAt(t: T) = isType(t)
def apply(t: T): SType = asType(t)
}
}
/** constructs a new [[Param]] instance
*
* This method is intended to be called only from code generated by the Magnolia macro, and
* should not be called directly from users' code. */
def param[Tc[_], T, P](name: String,
typeclassParam: Tc[P],
defaultVal: => Option[P],
deref: T => P) = new Param[Tc, T] {
type PType = P
def label: String = name
def default: Option[PType] = defaultVal
def typeclass: Tc[PType] = typeclassParam
def dereference(t: T): PType = deref(t)
}
/** constructs a new [[CaseClass]] instance
*
* This method is intended to be called only from code generated by the Magnolia macro, and
* should not be called directly from users' code. */
def caseClass[Tc[_], T](name: String,
obj: Boolean,
valClass: Boolean,
params: Array[Param[Tc, T]],
constructor: (Param[Tc, T] => Any) => T) =
new CaseClass[Tc, T](name, obj, valClass, params) {
def construct[R](param: Param[Tc, T] => R): T = constructor(param)
}
}
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()
}