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Fix variance handling for parameterized type aliases #8651
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Original file line number | Diff line number | Diff line change |
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@@ -3076,7 +3076,15 @@ trait Symbols extends api.Symbols { self: SymbolTable => | |
class AliasTypeSymbol protected[Symbols] (initOwner: Symbol, initPos: Position, initName: TypeName) | ||
extends TypeSymbol(initOwner, initPos, initName) { | ||
type TypeOfClonedSymbol = TypeSymbol | ||
override def variance = if (isLocalToThis) Bivariant else info.typeSymbol.variance | ||
override def variance = | ||
// A non-applied parameterized type alias can appear in any variance position | ||
if (typeParams.nonEmpty) | ||
Invariant | ||
else if (isLocalToThis) | ||
Bivariant | ||
else | ||
info.typeSymbol.variance | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I can no longer construct the soundness argument for this; but, then again, I also don't have a counter-example. (And it's been like this forever 🤷♂ ) |
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override def isContravariant = variance.isContravariant | ||
override def isCovariant = variance.isCovariant | ||
final override def isAliasType = true | ||
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,7 @@ | ||
variance-alias.scala:5: error: covariant type T occurs in invariant position in type => Inv[T] of value a | ||
val a: Inv[({type L[+X] = X})#L[T]] = new Inv[({type L[+X] = X})#L[T]] {} // error | ||
^ | ||
variance-alias.scala:6: error: covariant type T occurs in invariant position in type => Inv[X.this.Id[T]] of value b | ||
val b: Inv[Id[T]] = new Inv[Id[T]] {} // error | ||
^ | ||
2 errors |
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@@ -0,0 +1,7 @@ | ||
trait Inv[A] | ||
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class X[+T] { | ||
type Id[+A] = A | ||
val a: Inv[({type L[+X] = X})#L[T]] = new Inv[({type L[+X] = X})#L[T]] {} // error | ||
val b: Inv[Id[T]] = new Inv[Id[T]] {} // error | ||
} |
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,6 @@ | ||
trait Tc[F[_]] | ||
object X { | ||
type Id[+A] = A | ||
val a: Tc[({type L[+X] = X})#L] = new Tc[({type L[+X] = X})#L] {} // ok, therefore the following should be too: | ||
val b: Tc[Id] = new Tc[Id] {} // ok | ||
} |
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looks sound to me :-)