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isAsSpecific: restrict usage of fullyDefinedType #3276

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Oct 9, 2017
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isAsSpecific: restrict usage of fullyDefinedType #3276

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18 changes: 10 additions & 8 deletions compiler/src/dotty/tools/dotc/typer/Applications.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1094,14 +1094,16 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
{
implicit val ctx = nestedCtx

// Fully define the type so that the types of the tparams created
// below never contain TypeRefs whose underling types contain
// uninstantiated TypeVars, this could lead to cycles in `isSubType`
// as a TypeVar might get constrained by a TypeRef it's part of.
val tp1a = fullyDefinedType(tp1, "alternative", alt1.symbol.pos).asInstanceOf[PolyType]

val tparams = ctx.newTypeParams(alt1.symbol, tp1.paramNames, EmptyFlags, tp1a.instantiateBounds)
isAsSpecific(alt1, tp1a.instantiate(tparams.map(_.typeRef)), alt2, tp2)
// Fully define the PolyType parameters so that the infos of the
// tparams created below never contain TypeRefs whose underling types
// contain uninstantiated TypeVars, this could lead to cycles in
// `isSubType` as a TypeVar might get constrained by a TypeRef it's
// part of.
val tp1Params = tp1.newLikeThis(tp1.paramNames, tp1.paramInfos, defn.AnyType)
fullyDefinedType(tp1Params, "type parameters of alternative", alt1.symbol.pos)

val tparams = ctx.newTypeParams(alt1.symbol, tp1.paramNames, EmptyFlags, tp1.instantiateBounds)
isAsSpecific(alt1, tp1.instantiate(tparams.map(_.typeRef)), alt2, tp2)
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@odersky odersky Oct 6, 2017

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I have the impression it would be easier to just scan the type parameter bounds whether a fullyDefinedType is needed and, if yes, instantiate the whole type.

}
case _ => // (3)
tp2 match {
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