Progress towards full SIP-23 support: correct inference for scala.Singleton, support for symbol literals #3565
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@milessabin The narrowing trick from scalac does not work in Dotty: scala> def narrow[T <: Singleton](x: T): T {} = x
def narrow[T <: Singleton](x: T): T
scala> narrow(1)
val res0: Int = 1However, the following works in both scalac and dotty: scala> type Identity[T] = T
// defined alias type Identity = [T] => T
scala> def narrow[T <: Singleton](x: T): Identity[T] = x
def narrow[T <: Singleton](x: T): ([T] => T)[T]
scala> narrow(1)
val res1: ([T] => T)[1] = 1
scala> val b = res51
val b: ([T] => T)[1] = 1
scala> val c: 1 = b
val c: 1 = 1(The fact that the dotty repl prints It might be useful to add a |
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Nov 30, 2017
| @@ -315,6 +316,7 @@ object TastyFormat { | |||
| final val STRINGconst = 77 | |||
| final val IMPORTED = 78 | |||
| final val RENAMED = 79 | |||
| final val SCALASYMBOLconst = 80 | |||
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Why add Scala? I'd prefer we just called it SYMBOLconst.
| @@ -331,6 +333,8 @@ class TreeUnpickler(reader: TastyReader, nameAtRef: NameRef => TermName, posUnpi | |||
| ConstantType(Constant(readType())) | |||
| case ENUMconst => | |||
| ConstantType(Constant(readTermRef().termSymbol)) | |||
| case SCALASYMBOLconst => | |||
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I don't think you need the duplication. SYMBOLconsts are simple types, so they should just occur in readSimpleType. I believe the duplication of CLASSconst and ENUMconst is also wrong and should be removed.
When a type variable is upper bounded by scala.Singleton, its instantiation should not be widened
This brings us closer to fully supporting SIP-23. Bump the version of TASTY to 1.1, adding support for symbol literals is a backwards-compatible change. The sip23-* tests are adapted from scala/scala#5310, the only difference is that we do not currently support the `T {}` trick to avoid widening when inferring types.
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