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In the enclosed test, t8611a.scala, the patterns `O.{A, B}` were
incorrect treated as equivelent by the combination of
`uniqueTpForTree` and `Const.uniqueTpForTree`.
`uniqueTpForTree` used `Type#narrow` to try to create a distinct
type for each new pattern tree it encountered. However, narrowing a
`RefinedType` does not create a distinct type as we are used to
when narrowing, e.g. a class type.
// Type
def narrow: Type =
if (phase.erasedTypes) this
else {
val cowner = commonOwner(this)
refinedType(this :: Nil, cowner, EmptyScope, cowner.pos).narrow
}
// CompoundType
override def narrow: Type = typeSymbol.thisType
This commit creates a fresh existential type symbol rather than
trying to use `narrow`.
I've included a unit test to show the sublteties of narrowing
refinment types.
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