Harden inferView

Should not be attempted if argument does not have a value type.
Test case is this one. I don't want to include it in the rgeression tests though
because it looks too noisy (i.e. we would likely get spurious failures for tiny
changes in the future).

    class i0 {
    type Ordering[i1, i2] = (=> i3[i1])
    def i4[i2, i3](i5: i1): i4[Any]    // error
    i8 += i14 {
    type i4[+i9] = i5
    def i7: Int = i6(5)
    class i9[i10 <: i16 <: i4[_], i12](val i14: i11[_], i4: i11) {  // error
    def i16[i14 >: i1]: i0 = ???
    implicit def i13[i4](i5: (=> i6)): i1[i6]   // error
    type i13[i7] = i13[i7]
    def i8[+i1[+i2] <: i0[i1]]](i9: => ii5[i7]): i7[i5] = sys.error();  // error // error
    def i10(i11: i4[i10.i4])(implicit i8: i0[i6#i0]) = i4 * i7 i5 i4! this match {
    case i14(i9) => 3 }
    }
    class i10 {
    type i13 = i10.i8
    val i11 =
    var i21 =
    case class Tuple1(i3: i1, i4: i4, i6)
    }
    (new i10(i13))
    }
    }
    package i1.i0
    object i12 {
    def i9(i10: i1)(implicit i9: i8[Boolean]) = implicitly[i9](i10: Any, i4, i9) {}
    case class i9[i14[i2]](i16: i11[i8[i2]]) extends i10[i4, i14] {
    def this(i11: i12) = {
    val i5 = new i5[Int, Int]
    }
    }

Author: odersky

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -2447,7 +2447,7 @@ class Typer extends Namer
         if (isFullyDefined(wtp, force = ForceDegree.all) &&
             ctx.typerState.constraint.ne(prevConstraint)) readapt(tree)
         else err.typeMismatch(tree, pt, failure)
-      if (ctx.mode.is(Mode.ImplicitsEnabled))
+      if (ctx.mode.is(Mode.ImplicitsEnabled) && tree.typeOpt.isValueType)
         inferView(tree, pt) match {
           case SearchSuccess(inferred, _, _) =>
             readapt(inferred)(ctx.retractMode(Mode.ImplicitsEnabled))