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package scala.tools.reflect
package quasiquotes
import scala.collection.{immutable, mutable}
import scala.reflect.internal.Flags._
import scala.reflect.macros.TypecheckException
class Cardinality private[Cardinality](val value: Int) extends AnyVal {
def pred = { assert(value - 1 >= 0); new Cardinality(value - 1) }
def succ = new Cardinality(value + 1)
override def toString = if (value == 0) "no dots" else "." * (value + 1)
}
object Cardinality {
val NoDot = new Cardinality(0)
val DotDot = new Cardinality(1)
val DotDotDot = new Cardinality(2)
object Dot { def unapply(card: Cardinality) = card != NoDot }
def parseDots(part: String) = {
if (part.endsWith("...")) (part.stripSuffix("..."), DotDotDot)
else if (part.endsWith("..")) (part.stripSuffix(".."), DotDot)
else (part, NoDot)
}
}
/** Defines abstractions that provide support for splicing into Scala syntax.
*/
trait Holes { self: Quasiquotes =>
import global._
import Cardinality._
import definitions._
import universeTypes._
protected lazy val IterableTParam = IterableClass.typeParams(0).asType.toType
protected def inferParamImplicit(tfun: Type, targ: Type) = c.inferImplicitValue(appliedType(tfun, List(targ)), silent = true)
protected def inferLiftable(tpe: Type): Tree = inferParamImplicit(liftableType, tpe)
protected def inferUnliftable(tpe: Type): Tree = inferParamImplicit(unliftableType, tpe)
protected def isLiftableType(tpe: Type) = inferLiftable(tpe) != EmptyTree
protected def isNativeType(tpe: Type) =
(tpe <:< treeType) || (tpe <:< nameType) || (tpe <:< modsType) ||
(tpe <:< flagsType) || (tpe <:< symbolType)
protected def isBottomType(tpe: Type) =
tpe <:< NothingClass.tpe || tpe <:< NullClass.tpe
protected def extractIterableTParam(tpe: Type) =
IterableTParam.asSeenFrom(tpe, IterableClass)
protected def stripIterable(tpe: Type, limit: Option[Cardinality] = None): (Cardinality, Type) =
if (limit.map { _ == NoDot }.getOrElse { false }) (NoDot, tpe)
else if (tpe != null && !isIterableType(tpe)) (NoDot, tpe)
else if (isBottomType(tpe)) (NoDot, tpe)
else {
val targ = extractIterableTParam(tpe)
val (card, innerTpe) = stripIterable(targ, limit.map { _.pred })
(card.succ, innerTpe)
}
protected def iterableTypeFromCard(n: Cardinality, tpe: Type): Type = {
if (n == NoDot) tpe
else appliedType(IterableClass.toType, List(iterableTypeFromCard(n.pred, tpe)))
}
/** Hole encapsulates information about splices in quasiquotes.
* It packs together a cardinality of a splice, pre-reified tree
* representation (possibly preprocessed) and position.
*/
abstract class Hole {
val tree: Tree
val pos: Position
val cardinality: Cardinality
}
object Hole {
def apply(card: Cardinality, tree: Tree): Hole =
if (method != nme.unapply) new ApplyHole(card, tree)
else new UnapplyHole(card, tree)
def unapply(hole: Hole): Some[(Tree, Cardinality)] = Some((hole.tree, hole.cardinality))
}
class ApplyHole(card: Cardinality, splicee: Tree) extends Hole {
val (strippedTpe, tpe): (Type, Type) = {
val (strippedCard, strippedTpe) = stripIterable(splicee.tpe, limit = Some(card))
if (isBottomType(strippedTpe)) cantSplice()
else if (isNativeType(strippedTpe)) (strippedTpe, iterableTypeFromCard(card, strippedTpe))
else if (isLiftableType(strippedTpe)) (strippedTpe, iterableTypeFromCard(card, treeType))
else cantSplice()
}
val tree = {
def inner(itpe: Type)(tree: Tree) =
if (isNativeType(itpe)) tree
else if (isLiftableType(itpe)) lifted(itpe)(tree)
else global.abort("unreachable")
if (card == NoDot) inner(strippedTpe)(splicee)
else iterated(card, splicee, splicee.tpe)
}
val pos = splicee.pos
val cardinality = stripIterable(tpe)._1
protected def cantSplice(): Nothing = {
val (iterableCard, iterableType) = stripIterable(splicee.tpe)
val holeCardMsg = if (card != NoDot) s" with $card" else ""
val action = "splice " + splicee.tpe + holeCardMsg
val suggestCard = card != iterableCard || card != NoDot
val spliceeCardMsg = if (card != iterableCard && iterableCard != NoDot) s"using $iterableCard" else "omitting the dots"
val cardSuggestion = if (suggestCard) spliceeCardMsg else ""
val suggestLifting = (card == NoDot || iterableCard != NoDot) && !(iterableType <:< treeType) && !isLiftableType(iterableType)
val liftedTpe = if (card != NoDot) iterableType else splicee.tpe
val liftSuggestion = if (suggestLifting) s"providing an implicit instance of Liftable[$liftedTpe]" else ""
val advice =
if (isBottomType(iterableType)) "bottom type values often indicate programmer mistake"
else "consider " + List(cardSuggestion, liftSuggestion).filter(_ != "").mkString(" or ")
c.abort(splicee.pos, s"Can't $action, $advice")
}
protected def lifted(tpe: Type)(tree: Tree): Tree = {
val lifter = inferLiftable(tpe)
assert(lifter != EmptyTree, s"couldnt find a liftable for $tpe")
val lifted = Apply(lifter, List(tree))
atPos(tree.pos)(lifted)
}
protected def toStats(tree: Tree): Tree =
// q"$u.build.toStats($tree)"
Apply(Select(Select(u, nme.build), nme.toStats), tree :: Nil)
protected def toList(tree: Tree, tpe: Type): Tree =
if (isListType(tpe)) tree
else Select(tree, nme.toList)
protected def mapF(tree: Tree, f: Tree => Tree): Tree =
if (f(Ident(TermName("x"))) equalsStructure Ident(TermName("x"))) tree
else {
val x: TermName = c.freshName()
// q"$tree.map { $x => ${f(Ident(x))} }"
Apply(Select(tree, nme.map),
Function(ValDef(Modifiers(PARAM), x, TypeTree(), EmptyTree) :: Nil,
f(Ident(x))) :: Nil)
}
protected object IterableType {
def unapply(tpe: Type): Option[Type] =
if (isIterableType(tpe)) Some(extractIterableTParam(tpe)) else None
}
protected object LiftedType {
def unapply(tpe: Type): Option[Tree => Tree] =
if (tpe <:< treeType) Some(t => t)
else if (isLiftableType(tpe)) Some(lifted(tpe)(_))
else None
}
/** Map high-cardinality splice onto an expression that eveluates as a list of given cardinality.
*
* All possible combinations of representations are given in the table below:
*
* input output for T <: Tree output for T: Liftable
*
* ..${x: List[T]} x x.map(lift)
* ..${x: Iterable[T]} x.toList x.toList.map(lift)
* ..${x: T} toStats(x) toStats(lift(x))
*
* ...${x: List[List[T]]} x x.map { _.map(lift) } }
* ...${x: List[Iterable[T]} x.map { _.toList } x.map { _.toList.map(lift) } }
* ...${x: List[T]} x.map { toStats(_) } x.map { toStats(lift(_)) }
* ...${x: Iterable[List[T]]} x.toList x.toList.map { _.map(lift) }
* ...${x: Iterable[Iterable[T]]} x.toList { _.toList } x.toList.map { _.toList.map(lift) }
* ...${x: Iterable[T]} x.toList.map { toStats(_) } x.toList.map { toStats(lift(_)) }
* ...${x: T} toStats(x).map { toStats(_) } toStats(lift(x)).map(toStats)
*
* As you can see table is quite repetetive. Middle column is equivalent to the right one with
* lift function equal to identity. Cases with List are equivalent to Iterated ones (due to
* the fact that toList method call is just an identity we can omit it altogether.)
*/
protected def iterated(card: Cardinality, tree: Tree, tpe: Type): Tree = (card, tpe) match {
case (DotDot, tpe @ IterableType(LiftedType(lift))) => mapF(toList(tree, tpe), lift)
case (DotDot, LiftedType(lift)) => toStats(lift(tree))
case (DotDotDot, tpe @ IterableType(inner)) => mapF(toList(tree, tpe), t => iterated(DotDot, t, inner))
case (DotDotDot, LiftedType(lift)) => mapF(toStats(lift(tree)), toStats)
case _ => global.abort("unreachable")
}
}
class UnapplyHole(val cardinality: Cardinality, pat: Tree) extends Hole {
val (placeholderName, pos, tptopt) = pat match {
case Bind(pname, inner @ Bind(_, Typed(Ident(nme.WILDCARD), tpt))) => (pname, inner.pos, Some(tpt))
case Bind(pname, inner @ Typed(Ident(nme.WILDCARD), tpt)) => (pname, inner.pos, Some(tpt))
case Bind(pname, inner) => (pname, inner.pos, None)
}
val treeNoUnlift = Bind(placeholderName, Ident(nme.WILDCARD))
lazy val tree =
tptopt.map { tpt =>
val TypeDef(_, _, _, typedTpt) =
try c.typeCheck(TypeDef(NoMods, TypeName("T"), Nil, tpt))
catch { case TypecheckException(pos, msg) => c.abort(pos.asInstanceOf[c.Position], msg) }
val tpe = typedTpt.tpe
val (iterableCard, _) = stripIterable(tpe)
if (iterableCard.value < cardinality.value)
c.abort(pat.pos, s"Can't extract $tpe with $cardinality, consider using $iterableCard")
val (_, strippedTpe) = stripIterable(tpe, limit = Some(cardinality))
if (strippedTpe <:< treeType) treeNoUnlift
else
unlifters.spawn(strippedTpe, cardinality).map {
Apply(_, treeNoUnlift :: Nil)
}.getOrElse {
c.abort(pat.pos, s"Can't find $unliftableType[$strippedTpe], consider providing it")
}
}.getOrElse { treeNoUnlift }
}
/** Full support for unliftable implies that it's possible to interleave
* deconstruction with higher cardinality and unlifting of the values.
* In particular extraction of List[Tree] as List[T: Unliftable] requires
* helper extractors that would do the job: UnliftListElementwise[T]. Similarly
* List[List[Tree]] needs UnliftListOfListsElementwise[T].
*
* See also "unlift list" tests in UnapplyProps.scala
*/
object unlifters {
private var records = List.empty[(Type, Cardinality)]
// Materialize unlift helper that does elementwise
// unlifting for corresponding cardinality and type.
def spawn(tpe: Type, card: Cardinality): Option[Tree] = {
val unlifter = inferUnliftable(tpe)
if (unlifter == EmptyTree) None
else if (card == NoDot) Some(unlifter)
else {
val idx = records.indexWhere { p => p._1 =:= tpe && p._2 == card }
val resIdx = if (idx != -1) idx else { records +:= (tpe, card); records.length - 1}
Some(Ident(TermName(nme.QUASIQUOTE_UNLIFT_HELPER + resIdx)))
}
}
// Returns a list of vals that will defined required unlifters
def preamble(): List[Tree] =
records.zipWithIndex.map { case ((tpe, card), idx) =>
val name = TermName(nme.QUASIQUOTE_UNLIFT_HELPER + idx)
val helperName = card match {
case DotDot => nme.UnliftListElementwise
case DotDotDot => nme.UnliftListOfListsElementwise
}
val lifter = inferUnliftable(tpe)
assert(helperName.isTermName)
// q"val $name: $u.build.${helperName.toTypeName} = $u.build.$helperName($lifter)"
ValDef(NoMods, name,
AppliedTypeTree(Select(Select(u, nme.build), helperName.toTypeName), List(TypeTree(tpe))),
Apply(Select(Select(u, nme.build), helperName), lifter :: Nil))
}
}
}
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