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Fix #2140: Avoid exponential subtype complexity #2890

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Jul 20, 2017
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Fix #2140: Avoid exponential subtype complexity #2890

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4977571
Fix #2140: Avoid exponential subtype complexity
odersky Jul 19, 2017
a048e50
Fix docs
odersky Jul 19, 2017
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10 changes: 3 additions & 7 deletions compiler/src/dotty/tools/dotc/core/TypeComparer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -983,17 +983,13 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {

/** A type has been covered previously in subtype checking if it
* is some combination of TypeRefs that point to classes, where the
* combiners are RefinedTypes, RecTypes, AndTypes or AnnotatedTypes.
* One exception: Refinements referring to basetype args are never considered
* to be already covered. This is necessary because such refined types might
* still need to be compared with a compareAliasRefined.
* combiners are RefinedTypes, RecTypes, And/Or-Types or AnnotatedTypes.
*/
private def isCovered(tp: Type): Boolean = tp.dealias.stripTypeVar match {
private def isCovered(tp: Type): Boolean = tp.dealias.stripTypeVar match {
case tp: TypeRef => tp.symbol.isClass && tp.symbol != NothingClass && tp.symbol != NullClass
case tp: ProtoType => false
case tp: RefinedOrRecType => isCovered(tp.parent)
case tp: AnnotatedType => isCovered(tp.underlying)
case AndType(tp1, tp2) => isCovered(tp1) && isCovered(tp2)
case tp: AndOrType => isCovered(tp.tp1) && isCovered(tp.tp2)
case _ => false
}

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30 changes: 30 additions & 0 deletions tests/pending/pos/i2140.scala
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@@ -0,0 +1,30 @@
object Test {
def main(args: Array[String]): Unit = {
val s = 1
val t = 23 match {
case 0 => (s)
case 1 => (s, s)
case 2 => (s, s, s)
case 3 => (s, s, s, s)
case 4 => (s, s, s, s, s)
case 5 => (s, s, s, s, s, s)
case 6 => (s, s, s, s, s, s, s)
case 7 => (s, s, s, s, s, s, s, s)
case 8 => (s, s, s, s, s, s, s, s, s)
case 9 => (s, s, s, s, s, s, s, s, s, s)
case 10 => (s, s, s, s, s, s, s, s, s, s, s)
case 11 => (s, s, s, s, s, s, s, s, s, s, s, s)
case 12 => (s, s, s, s, s, s, s, s, s, s, s, s, s)
case 13 => (s, s, s, s, s, s, s, s, s, s, s, s, s, s)
case 14 => (s, s, s, s, s, s, s, s, s, s, s, s, s, s, s)
case 15 => (s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s)
case 16 => (s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s)
case 17 => (s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s)
case 18 => (s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s)
case 19 => (s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s)
case 20 => (s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s)
case 21 => (s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s)
// case 22 => (s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s, s)
}
}
}