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/* NSC -- new Scala compiler
* Copyright 2005-2012 LAMP/EPFL
* @author Paul Phillips
*/
package scala.tools.nsc
package typechecker
import scala.collection.{ mutable, immutable }
import scala.collection.mutable.ListBuffer
import scala.util.control.ControlThrowable
import symtab.Flags._
import scala.annotation.tailrec
import Checkability._
/** On pattern matcher checkability:
*
* Consider a pattern match of this form: (x: X) match { case _: P => }
*
* There are four possibilities to consider:
* [P1] X will always conform to P
* [P2] x will never conform to P
* [P3] X <: P if some runtime test is true
* [P4] X cannot be checked against P
*
* The first two cases correspond to those when there is enough static
* information to say X <: P or that !(X <: P) for all X and P.
* The fourth case includes unknown abstract types or structural
* refinements appearing within a pattern.
*
* The third case is the interesting one. We designate another type, XR,
* which is essentially the intersection of X and |P|, where |P| is
* the erasure of P. If XR <: P, then no warning is emitted.
*
* Examples of how this info is put to use:
* sealed trait A[T] ; class B[T] extends A[T]
* def f(x: B[Int]) = x match { case _: A[Int] if true => }
* def g(x: A[Int]) = x match { case _: B[Int] => }
*
* `f` requires no warning because X=B[Int], P=A[Int], and B[Int] <:< A[Int].
* `g` requires no warning because X=A[Int], P=B[Int], XR=B[Int], and B[Int] <:< B[Int].
* XR=B[Int] because a value of type A[Int] which is tested to be a B can
* only be a B[Int], due to the definition of B (B[T] extends A[T].)
*
* This is something like asSeenFrom, only rather than asking what a type looks
* like from the point of view of one of its base classes, we ask what it looks
* like from the point of view of one of its subclasses.
*/
trait Checkable {
self: Analyzer =>
import global._
import definitions._
/** The applied type of class 'to' after inferring anything
* possible from the knowledge that 'to' must also be of the
* type given in 'from'.
*/
def propagateKnownTypes(from: Type, to: Symbol): Type = {
def tparams = to.typeParams
val tvars = tparams map (p => TypeVar(p))
val tvarType = appliedType(to, tvars: _*)
val bases = from.baseClasses filter (to.baseClasses contains _)
bases foreach { bc =>
val tps1 = (from baseType bc).typeArgs
val tps2 = (tvarType baseType bc).typeArgs
(tps1, tps2).zipped foreach (_ =:= _)
}
val resArgs = tparams zip tvars map {
case (_, tvar) if tvar.instValid => tvar.constr.inst
case (tparam, _) => tparam.tpe
}
appliedType(to, resArgs: _*)
}
private def isUnwarnableTypeArgSymbol(sym: Symbol) = (
sym.isTypeParameterOrSkolem // dummy
|| (sym.name.toTermName == nme.WILDCARD) // _
|| nme.isVariableName(sym.name) // type variable
|| (sym == NonLocalReturnControlClass) // synthetic
)
private def isUnwarnableTypeArg(arg: Type) = (
isUnwarnableTypeArgSymbol(arg.typeSymbolDirect) // has to be direct: see pos/t1439
|| (arg hasAnnotation UncheckedClass) // @unchecked T
)
private def typeArgsInTopLevelType(tp: Type): List[Type] = {
val tps = tp match {
case RefinedType(parents, _) => parents flatMap typeArgsInTopLevelType
case TypeRef(_, ArrayClass, arg :: Nil) => typeArgsInTopLevelType(arg)
case TypeRef(pre, sym, args) => typeArgsInTopLevelType(pre) ++ args
case ExistentialType(tparams, underlying) => tparams.map(_.tpe) ++ typeArgsInTopLevelType(underlying)
case _ => Nil
}
tps filterNot isUnwarnableTypeArg
}
private def isReifiableArray(tp: Type): Boolean = tp match {
case TypeRef(_, ArrayClass, arg :: Nil) => isReifiableArray(arg)
case TypeRef(_, sym, args) => isUnwarnableTypeArg(tp) || (!sym.isAbstractType && args.isEmpty)
case _ => false
}
private class CheckabilityChecker(val X: Type, val P: Type) {
def Xsym = X.typeSymbol
def Psym = P.typeSymbol
def XR = propagateKnownTypes(X, Psym)
def P1 = X matchesPattern P
def P2 = CheckabilityChecker.isNeverSubType(X, P)
def P3 = Psym.isClass && ((XR matchesPattern P) || isReifiableArray(P) || P.typeArgs.forall(isUnwarnableTypeArg))
def P4 = !(P1 || P2 || P3)
def summaryString = f"""
|Checking checkability of (x: $X) against pattern $P
|[P1] $P1%-6s X <: P // $X <: $P
|[P2] $P2%-6s X !<: P // $X !<: $P for all X, P
|[P3] $P3%-6s XR <: P // $XR <: $P
|[P4] $P4%-6s None of the above // !(P1 || P2 || P3)
""".stripMargin.trim
val result = (
if (X.isErroneous || P.isErroneous) CheckabilityError
else if (P1) StaticallyTrue
else if (P2) StaticallyFalse
else if (P3) RuntimeCheckable
else if (uncheckableType == NoType) {
// Avoid warning (except ourselves) if we can't pinpoint the uncheckable type
debugwarn("Checkability checker says 'Uncheckable', but uncheckable type cannot be found:\n" + summaryString)
CheckabilityError
}
else Uncheckable
)
lazy val uncheckableType = if (Psym.isAbstractType) P else {
val possibles = typeArgsInTopLevelType(P).toSet
val opt = possibles find { targ =>
// Create a derived type with every possibly uncheckable type replaced
// with a WildcardType, except for 'targ'. If !(XR <: derived) then
// 'targ' is uncheckable.
val derived = P map (tp => if (possibles(tp) && !(tp =:= targ)) WildcardType else tp)
!(XR <:< derived)
}
opt getOrElse NoType
}
def isUncheckable = result == Uncheckable
def uncheckableMessage = uncheckableType match {
case NoType => "something"
case tp @ RefinedType(_, _) => "refinement " + tp
case TypeRef(_, sym, _) if sym.isAbstractType => "abstract type " + sym.name
case tp => "non-variable type argument " + tp
}
}
/** X, P, [P1], etc. are all explained at the top of the file.
*/
private object CheckabilityChecker {
private def isNeverSubClass(sym1: Symbol, sym2: Symbol) = (
sym1.isClass
&& sym2.isClass
&& sym1.isEffectivelyFinal
&& !(sym1 isSubClass sym2)
)
private def isNeverSubArgs(tps1: List[Type], tps2: List[Type], tparams: List[Symbol]): Boolean = {
def isNeverSubArg(t1: Type, t2: Type, variance: Int) = {
if (variance > 0) isNeverSubType(t2, t1)
else if (variance < 0) isNeverSubType(t1, t2)
else isNeverSameType(t1, t2)
}
exists3(tps1, tps2, tparams map (_.variance))(isNeverSubArg)
}
private def isNeverSameType(tp1: Type, tp2: Type): Boolean = (tp1, tp2) match {
case (TypeRef(_, sym1, args1), TypeRef(_, sym2, args2)) =>
sym1.isClass && sym2.isClass && (sym1 ne sym2) && (sym1.isEffectivelyFinal || sym2.isEffectivelyFinal)
case _ =>
false
}
private def isNeverSubType(tp1: Type, tp2: Type): Boolean = (tp1, tp2) match {
case (TypeRef(_, sym1, args1), TypeRef(_, sym2, args2)) =>
isNeverSubClass(sym1, sym2) || {
(sym1 isSubClass sym2) && {
val tp1seen = tp1 baseType sym2
isNeverSubArgs(tp1seen.typeArgs, args2, sym2.typeParams)
}
}
case _ => false
}
}
trait InferCheckable {
self: Inferencer =>
/** TODO: much better error positions.
* Kind of stuck right now because they just pass us the one tree.
* TODO: Eliminate inPattern, canRemedy, which have no place here.
*/
def checkCheckable(tree: Tree, P0: Type, X: Type, inPattern: Boolean, canRemedy: Boolean = false) {
// singleton types not considered here
val P = P0.widen
P match {
// Prohibit top-level type tests for these, but they are ok nested (e.g. case Foldable[Nothing] => ... )
case TypeRef(_, NothingClass | NullClass | AnyValClass, _) =>
InferErrorGen.TypePatternOrIsInstanceTestError(tree, P)
// If top-level abstract types can be checked using a classtag extractor, don't warn about them
case TypeRef(_, sym, _) if sym.isAbstractType && canRemedy =>
;
case _ =>
val checker = new CheckabilityChecker(X.widen, P)
log(checker.summaryString)
if (checker.isUncheckable) {
def where = if (inPattern) "pattern " else ""
val msg = (
if (checker.uncheckableType =:= P) s"abstract type $where$P"
else s"${checker.uncheckableMessage} in type $where$P"
)
getContext.unit.warning(tree.pos, s"$msg is unchecked since it is eliminated by erasure")
}
}
}
}
}
private[typechecker] final class Checkability(val value: Int) extends AnyVal { }
private[typechecker] object Checkability {
val StaticallyTrue = new Checkability(0)
val StaticallyFalse = new Checkability(1)
val RuntimeCheckable = new Checkability(2)
val Uncheckable = new Checkability(3)
val CheckabilityError = new Checkability(4)
}
|
