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Harden type comparer in presence of kind errors #12667

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Jun 3, 2021
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Harden type comparer in presence of kind errors #12667

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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/core/TypeComparer.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1422,7 +1422,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling

def recurArgs(args1: List[Type], args2: List[Type], tparams2: List[ParamInfo]): Boolean =
if (args1.isEmpty) args2.isEmpty
else args2.nonEmpty && {
else args2.nonEmpty && tparams2.nonEmpty && {
val tparam = tparams2.head
val v = tparam.paramVarianceSign

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14 changes: 14 additions & 0 deletions tests/neg/i12664.scala
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Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
trait Step {
type Self
type Next[A]
}

trait DynamicNextStep {
type OneOf[Self, Next[_]]
def apply(s: Step): OneOf[s.Self, s.Next]
}

object X extends DynamicNextStep {
override type OneOf[Self] = Self // error
override def apply(s: Step) = ???
}