Don't confuse MethodTypes and PolyTypes in type comparer

I assumed the existing tests were already sufficient to avoid confusion before
we try a substitution of one for the other, but was wrong in the case where
both sides are riddled with errors.

Test case (too long/fuzzy to be included in regression tests):

case class i0[i1, i4](i4: i1)
object i4 {
implicit def i4[i1: i0](i4: i1): i1
def i4[i4[_], i4[_], i4[i4]](i4: i1[i4]): i4[i4] = null
}
class i1 extends i4 {
case _ =>
}
val i1 = new i0 {
type i1[i4] = i4 with i0[i4]
trait i1 extends i4 {
type i1[i4] = i1 type i4 = i4#i4 def i4[i4 >: i4](i4: => i4): i4.i4[_ <: i4] = i4
i4(i1, i4: i4)
def unapply(i2: i4) = sys.error("")
}
trait i4
trait throw {
val i3: i4 = i4(5, i1: i1,
i4: i4)
def i3: i4[Int] = i1(null: Any) i3(0, i1())
println(i3 <= i4)
}
object i1 {
implicit def i1(i4: i4): Int
def i1[@specialized i4 <: i4[i4]](i1: i4): i4[Int]
def i1[@specialized i4, i4 <: i1](i4: i4): i4[i1[i4]] = new i4[i1] {
val i1 = (new i2.i1
}
}

Author: odersky

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

@@ -527,17 +527,18 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
           case _ =>
         }
         either(recur(tp1, tp21), recur(tp1, tp22)) || fourthTry
-      case tp2: MethodOrPoly =>
+      case tp2: MethodType =>
         def compareMethod = tp1 match {
-          case tp1: MethodOrPoly =>
-            (tp1.signature consistentParams tp2.signature) &&
-              matchingParams(tp1, tp2) &&
-              (!tp2.isImplicitMethod || tp1.isImplicitMethod) &&
-              isSubType(tp1.resultType, tp2.resultType.subst(tp2, tp1))
-          case _ =>
-            false
+          case tp1: MethodType => compareMethodOrPoly(tp1, tp2)
+          case _ => false
         }
         compareMethod
+      case tp2: PolyType =>
+        def comparePoly = tp1 match {
+          case tp1: PolyType => compareMethodOrPoly(tp1, tp2)
+          case _ => false
+        }
+        comparePoly
       case tp2 @ ExprType(restpe2) =>
         def compareExpr = tp1 match {
           // We allow ()T to be a subtype of => T.
@@ -573,6 +574,12 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
         fourthTry
     }
 
+    def compareMethodOrPoly(tp1: MethodOrPoly, tp2: MethodOrPoly) =
+      (tp1.signature consistentParams tp2.signature) &&
+      matchingParams(tp1, tp2) &&
+      (!tp2.isImplicitMethod || tp1.isImplicitMethod) &&
+      isSubType(tp1.resultType, tp2.resultType.subst(tp2, tp1))
+
     def fourthTry: Boolean = tp1 match {
       case tp1: TypeRef =>
         tp1.info match {