Fix #1590: Eliminate wildcards when approximating a type #1592
Conversation
Fixes scala#1590. Type variables should never be instantiated to types containing wildcards.
| @@ -162,7 +162,8 @@ trait ConstraintHandling { | |||
| /** Solve constraint set for given type parameter `param`. | |||
| * If `fromBelow` is true the parameter is approximated by its lower bound, | |||
| * otherwise it is approximated by its upper bound. However, any occurrences | |||
| * of the parameter in a refinement somewhere in the bound are removed. | |||
| * of the parameter in a refinement somewhere in the bound are removed. Also | |||
| * wildcard types in bounds are approximated by their upper or lower bounds. | |||
| * (Such occurrences can arise for F-bounded types). | |||
There was a problem hiding this comment.
This should be moved before the sentence you added
|
With this fix, we end up with the equivalent of: case class W[T](seq: Option[Option[T]] = Option.empty[Option[Any]])But what we really want is: case class W[T](seq: Option[Option[T]] = Option.empty[Option[T]])The difference is apparent once you try to use the class: case class W[T](seq: Option[Option[T]] = Option.empty)
object Test {
W[Int]()
}This compiles with scalac but with this patch we get: -- [E007] Type Mismatch Error: tests/pos/i1590.scala -------------------------------------------------------------------
4 | W[Int]()
| ^^^^^^^^
| found: Option[Option[Any]]
| required: Option[Option[Int]]
| |
|
We now get |
| // (i.e. the whole bounds range is over the type) | ||
| // if variance > 0, pick the minimal safe type: bounds.hi | ||
| // (i.e. the whole bounds range is under the type) | ||
| // if variance == 0, pick bounds.lo anyway (this is arbitrary but in line with |
There was a problem hiding this comment.
I think you mean bounds.hi here, or the code is wrong, in any case I'd love to see some tests for all these cases :).
There was a problem hiding this comment.
Ah nevermind, I misread the condition.
Fixes #1590. Type variables should never be instantiated to types
containing wildcards.
Review by @smarter