diff options
-rw-r--r-- | src/dotty/tools/dotc/core/ConstraintHandling.scala | 24 | ||||
-rw-r--r-- | tests/pos/i1590.scala | 10 |
2 files changed, 33 insertions, 1 deletions
diff --git a/src/dotty/tools/dotc/core/ConstraintHandling.scala b/src/dotty/tools/dotc/core/ConstraintHandling.scala index 3835d553c..0e155b9e1 100644 --- a/src/dotty/tools/dotc/core/ConstraintHandling.scala +++ b/src/dotty/tools/dotc/core/ConstraintHandling.scala @@ -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). * The constraint is left unchanged. * @return the instantiating type @@ -174,6 +175,27 @@ trait ConstraintHandling { def apply(tp: Type) = mapOver { tp match { case tp: RefinedType if param occursIn tp.refinedInfo => tp.parent + case tp: WildcardType => + val bounds = tp.optBounds.orElse(TypeBounds.empty).bounds + // Try to instantiate the wildcard to a type that is known to conform to it. + // This means: + // If fromBelow is true, we minimize the type overall + // Hence, if variance < 0, pick the maximal safe type: bounds.lo + // (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 + // the principle that we pick the smaller type when in doubt). + // If fromBelow is false, we maximize the type overall and reverse the bounds + // if variance != 0. For variance == 0, we still minimize. + // In summary we pick the bound given by this table: + // + // variance | -1 0 1 + // ------------------------ + // from below | lo lo hi + // from above | hi lo lo + // + if (variance == 0 || fromBelow == (variance < 0)) bounds.lo else bounds.hi case _ => tp } } diff --git a/tests/pos/i1590.scala b/tests/pos/i1590.scala new file mode 100644 index 000000000..ab922c218 --- /dev/null +++ b/tests/pos/i1590.scala @@ -0,0 +1,10 @@ +case class W[T](seq: Option[Option[T]] = Option.empty) +object W { + def apply[T] = new W[T]() +} + +case class V[T](vv: W[W[T]] = W.apply) +object Test { + W[Int]() + // V[Int]() fails in scalac and dotty: both instantiate the vv-default to W[Nothing] +} |