Fix #8573: Fix higher-kinded bounded opaque types #8580
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- Fix the type parameters with which explicitly given bounds of a higher-kinded opaque type should be abstracted. - Explicitly disallow unapplied right-hand sides of opaque types. They will lead to bad bounds later anyway, so we should give an intelligible error message early on. Open question: Should we disallow all unapplied right hand sides for all type aliases, not just opaque ones?
liufengyun
approved these changes
Mar 21, 2020
| @@ -460,7 +462,7 @@ object SymDenotations { | |||
| info match | |||
| case TypeAlias(alias) if isOpaqueAlias && owner.isClass => | |||
| setAlias(alias) | |||
| HKTypeLambda.boundsFromParams(alias.typeParams, bounds(rhs)) | |||
| HKTypeLambda.boundsFromParams(tparams, bounds(rhs)) | |||
There was a problem hiding this comment.
Just curious, we have to use tparams instead of alias.typeParams due to the following test in boundsFromParams?
def isOpaqueAlias = params match
case (param: Symbol) :: _ => param.owner.is(Opaque)
case _ => falseThere was a problem hiding this comment.
alias.typeParams is a list of TypeParamRefs, which are different from the symbols on rhs. That caused the problem.
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Fix the type parameters with which explicitly given bounds of a higher-kinded
opaque type should be abstracted.
Explicitly disallow unapplied right-hand sides of opaque types. They will lead
to bad bounds later anyway, so we should give an intelligible error message
early on.
Open question: Should we disallow all unapplied right hand sides for all type aliases,
not just opaque ones?