Fix #6146: Fix bounds check involving wildcards and f-bounds

Don't map arguments to their upper bounds before doing the bound check.
There was a comment justifiying that by talking about non
fully-determined arguments, but this check is done in PostTyper when all
types should already be fully-determined. Given that this comment was
written in 2014 I'm assuming it's no longer relevant.

Author: smarter

compiler/src/dotty/tools/dotc/core/TypeOps.scala

@@ -265,10 +265,8 @@ trait TypeOps { this: Context => // TODO: Make standalone object.
       def checkOverlapsBounds(lo: Type, hi: Type): Unit = {
         //println(i"instantiating ${bounds.hi} with $argTypes")
         //println(i" = ${instantiate(bounds.hi, argTypes)}")
-        val hiBound = instantiate(bounds.hi, argTypes.mapConserve(_.bounds.hi))
-        val loBound = instantiate(bounds.lo, argTypes.mapConserve(_.bounds.lo))
-          // Note that argTypes can contain a TypeBounds type for arguments that are
-          // not fully determined. In that case we need to check against the hi bound of the argument.
+        val hiBound = instantiate(bounds.hi, argTypes)
+        val loBound = instantiate(bounds.lo, argTypes)
         if (!(lo <:< hiBound)) violations += ((arg, "upper", hiBound))
         if (!(loBound <:< hi)) violations += ((arg, "lower", bounds.lo))
       }

tests/pos/i6146.scala

@@ -0,0 +1,13 @@
+trait BS[T, S <: BS[T, S]]
+ trait IS extends BS[Int, IS]
+
+sealed trait BSElem[T, S <: BS[_, S]]
+  // old error: Type argument S does not conform to upper bound BS[Any, LazyRef(S)]
+
+object BSElem {
+  implicit val intStreamShape: BSElem[Int, IS] = ???
+}
+class Ops[A] {
+  def asJavaSeqStream[S <: BS[_, S]](implicit s: BSElem[A, S]): S = ???
+    // old error: Type argument S does not conform to upper bound BS[Any, LazyRef(S)]
+}