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Mark AppliedType cachedSuper valid Nowhere when using provisional args #20527

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merged 5 commits into from
Jun 7, 2024
Merged

Mark AppliedType cachedSuper valid Nowhere when using provisional args #20527

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16b33a9
Mark AppliedType cachedSuper valid Nowhere when using provisional args
EugeneFlesselle Jun 5, 2024
59b0f3a
Reclassify test
EugeneFlesselle Jun 5, 2024
eaa673d
Add explanation doc
EugeneFlesselle Jun 6, 2024
ee54814
Keep `validUnderlyingMatch` inline with `validSuper`
EugeneFlesselle Jun 6, 2024
81a1184
Amend doc
EugeneFlesselle Jun 7, 2024
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10 changes: 8 additions & 2 deletions compiler/src/dotty/tools/dotc/core/Types.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -4643,7 +4643,13 @@ object Types extends TypeUtils {
cachedSuper = tycon match
case tycon: HKTypeLambda => defn.AnyType
case tycon: TypeRef if tycon.symbol.isClass => tycon
case tycon: TypeProxy => tycon.superType.applyIfParameterized(args)
case tycon: TypeProxy =>
if validSuper != Nowhere && args.exists(_.isProvisional) then
// applyIfParameterized may perform eta-reduction leading to different
// variance annotations depending on the instantiation of type params
// see tests/pos/typeclass-encoding3b.scala:348 for an example
validSuper = Nowhere
tycon.superType.applyIfParameterized(args)
case _ => defn.AnyType
cachedSuper

Expand Down Expand Up @@ -4671,8 +4677,8 @@ object Types extends TypeUtils {
*/
override def underlyingMatchType(using Context): Type =
if ctx.period != validUnderlyingMatch then
validUnderlyingMatch = if tycon.isProvisional then Nowhere else ctx.period
cachedUnderlyingMatch = superType.underlyingMatchType
validUnderlyingMatch = validSuper
cachedUnderlyingMatch

override def tryNormalize(using Context): Type = tycon.stripTypeVar match {
Expand Down
9 changes: 8 additions & 1 deletion tests/neg/typeclass-encoding3.scala → tests/pos/typeclass-encoding3b.scala
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Expand Up @@ -345,5 +345,12 @@ object functors {
}

MonadFlatten.flattened(List(List(1, 2, 3), List(4, 5))) // ok, synthesizes (using ListMonad)
MonadFlatten.flattened(List(List(1, 2, 3), List(4, 5)))(using ListMonad) // error
MonadFlatten.flattened(List(List(1, 2, 3), List(4, 5)))(using ListMonad) // was an error
/*
When checking `ListMonad <:< functors.Monad.Impl[T]`
we eventually get to the comparison `[X] =>> T[X] <:< [+X] =>> List[X]`
because the `This` type member of `ListMonad` has a covariance annotation.
This fails the variance conformance checks despite the fact that T has been instantiated to List,
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I don't follow the comment. How does it failing the conformance check lead it to not erroring?

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Ah, I'd overlooked updating the tense

since it has been substituted into the refinement (and cached) before its instantiation.
*/
}
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