diff options
| -rw-r--r-- | src/compiler/scala/tools/nsc/typechecker/Checkable.scala | 40 | ||||
| -rw-r--r-- | test/files/neg/unchecked2.check | 12 |
2 files changed, 37 insertions, 15 deletions
diff --git a/src/compiler/scala/tools/nsc/typechecker/Checkable.scala b/src/compiler/scala/tools/nsc/typechecker/Checkable.scala index 763d209dd0..3a1803038c 100644 --- a/src/compiler/scala/tools/nsc/typechecker/Checkable.scala +++ b/src/compiler/scala/tools/nsc/typechecker/Checkable.scala @@ -137,6 +137,7 @@ trait Checkable { opt getOrElse NoType } + def neverMatches = result == StaticallyFalse def isUncheckable = result == Uncheckable def uncheckableMessage = uncheckableType match { case NoType => "something" @@ -149,13 +150,28 @@ trait Checkable { /** X, P, [P1], etc. are all explained at the top of the file. */ private object CheckabilityChecker { - private def isNeverSubClass(sym1: Symbol, sym2: Symbol) = ( + /** Given classes A and B, can it be shown A is never a subclass of B? + */ + private def isNeverSubClass(sym1: Symbol, sym2: Symbol) = /*logResult(s"isNeverSubClass($sym1, $sym2)")*/( sym1.isClass && sym2.isClass - && sym1.isEffectivelyFinal && !(sym1 isSubClass sym2) + && ( + // If B is final, A can only be a subclass of B if it is B itself. + // Therefore, A <: B is impossible unless B <: A. + if (sym2.isEffectivelyFinal) + !(sym2 isSubClass sym1) + // If A is final but B is not, a subclass relationship can + // still be ruled out if B is sealed and A is not a subclass of + // any of B's sealed children. + else ( + sym1.isEffectivelyFinal + && sym2.isSealed + && sym2.children.forall(child => !(sym1 isSubClass child)) + ) + ) ) - private def isNeverSubArgs(tps1: List[Type], tps2: List[Type], tparams: List[Symbol]): Boolean = { + private def isNeverSubArgs(tps1: List[Type], tps2: List[Type], tparams: List[Symbol]): Boolean = /*logResult(s"isNeverSubArgs($tps1, $tps2, $tparams)")*/{ def isNeverSubArg(t1: Type, t2: Type, variance: Int) = { if (variance > 0) isNeverSubType(t2, t1) else if (variance < 0) isNeverSubType(t1, t2) @@ -165,21 +181,24 @@ trait Checkable { } private def isNeverSameType(tp1: Type, tp2: Type): Boolean = (tp1, tp2) match { case (TypeRef(_, sym1, args1), TypeRef(_, sym2, args2)) => - sym1.isClass && sym2.isClass && (sym1 ne sym2) && (sym1.isEffectivelyFinal || sym2.isEffectivelyFinal) + ( isNeverSubClass(sym1, sym2) + || isNeverSubClass(sym2, sym1) + || ((sym1 == sym2) && isNeverSubArgs(args1, args2, sym1.typeParams)) + ) case _ => false } - private def isNeverSubType(tp1: Type, tp2: Type): Boolean = (tp1, tp2) match { + // Important to dealias at any entry point (this is the only one at this writing.) + private def isNeverSubType(tp1: Type, tp2: Type): Boolean = /*logResult(s"isNeverSubType($tp1, $tp2)")*/((tp1.dealias, tp2.dealias) 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 { @@ -190,6 +209,8 @@ trait Checkable { * TODO: Eliminate inPattern, canRemedy, which have no place here. */ def checkCheckable(tree: Tree, P0: Type, X: Type, inPattern: Boolean, canRemedy: Boolean = false) { + def where = if (inPattern) "pattern " else "" + // singleton types not considered here val P = P0.widen P match { @@ -202,8 +223,9 @@ trait Checkable { case _ => val checker = new CheckabilityChecker(X.widen, P) log(checker.summaryString) - if (checker.isUncheckable) { - def where = if (inPattern) "pattern " else "" + if (checker.neverMatches) + getContext.unit.warning(tree.pos, s"fruitless type test: a $X can never be a $P (but still might match its erasure)") + else if (checker.isUncheckable) { val msg = ( if (checker.uncheckableType =:= P) s"abstract type $where$P" else s"${checker.uncheckableMessage} in type $where$P" diff --git a/test/files/neg/unchecked2.check b/test/files/neg/unchecked2.check index 0ff2a249a8..b4a14358c7 100644 --- a/test/files/neg/unchecked2.check +++ b/test/files/neg/unchecked2.check @@ -1,22 +1,22 @@ -unchecked2.scala:4: error: non-variable type argument List[String] in type Option[List[String]] is unchecked since it is eliminated by erasure +unchecked2.scala:4: error: fruitless type test: a Some[List[Int]] can never be a Option[List[String]] (but still might match its erasure) /* warn */ Some(List(1)).isInstanceOf[Option[List[String]]] ^ unchecked2.scala:5: error: non-variable type argument Option[_] in type Option[Option[_]] is unchecked since it is eliminated by erasure /* warn */ Some(123).isInstanceOf[Option[Option[_]]] ^ -unchecked2.scala:6: error: non-variable type argument String in type Option[String] is unchecked since it is eliminated by erasure +unchecked2.scala:6: error: fruitless type test: a Some[Int] can never be a Option[String] (but still might match its erasure) /* warn */ Some(123).isInstanceOf[Option[String]] ^ -unchecked2.scala:7: error: non-variable type argument List[String] in type Option[List[String]] is unchecked since it is eliminated by erasure +unchecked2.scala:7: error: fruitless type test: a Some[Int] can never be a Option[List[String]] (but still might match its erasure) /* warn */ Some(123).isInstanceOf[Option[List[String]]] ^ -unchecked2.scala:8: error: non-variable type argument List[Int => String] in type Option[List[Int => String]] is unchecked since it is eliminated by erasure +unchecked2.scala:8: error: fruitless type test: a Some[Int] can never be a Option[List[Int => String]] (but still might match its erasure) /* warn */ Some(123).isInstanceOf[Option[List[Int => String]]] ^ -unchecked2.scala:9: error: non-variable type argument (String, Double) in type Option[(String, Double)] is unchecked since it is eliminated by erasure +unchecked2.scala:9: error: fruitless type test: a Some[Int] can never be a Option[(String, Double)] (but still might match its erasure) /* warn */ Some(123).isInstanceOf[Option[(String, Double)]] ^ -unchecked2.scala:10: error: non-variable type argument String => Double in type Option[String => Double] is unchecked since it is eliminated by erasure +unchecked2.scala:10: error: fruitless type test: a Some[Int] can never be a Option[String => Double] (but still might match its erasure) /* warn */ Some(123).isInstanceOf[Option[String => Double]] ^ unchecked2.scala:14: error: non-variable type argument List[String] in type Option[List[String]] is unchecked since it is eliminated by erasure |