Merge pull request #6166 from dotty-staging/fix-6119

Fix #6119: add test

Author: odersky

tests/pos/i6119.scala

@@ -0,0 +1,13 @@
+class Test {
+  def to[Col[_]](factory: Factory[Int, Col[Int]]): Col[Int] = ???
+
+  to(Vector)
+
+  type Factory[-A, +C] = scala.collection.generic.CanBuildFrom[Nothing, A, C] // Ideally, this would be an opaque type
+
+  implicit def fromCanBuildFromConversion[X, A, C](x: X)(
+    implicit toCanBuildFrom: X => scala.collection.generic.CanBuildFrom[Nothing, A, C]): Factory[A, C] = ???
+
+  implicit def genericCompanionToCBF[A, CC[X] <: scala.collection.GenTraversable[X]](
+    fact: scala.collection.generic.GenericCompanion[CC]): scala.collection.generic.CanBuildFrom[Any, A, CC[A]] = ???
+}