Fix #6036: Restrict inferred parents for new {...}

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

@@ -150,6 +150,9 @@ object Inferencing {
       tree
   }
 
+  def isSkolemFree(tp: Type)(implicit ctx: Context): Boolean =
+    !tp.existsPart(_.isInstanceOf[SkolemType])
+
   /** Derive information about a pattern type by comparing it with some variant of the
    *  static scrutinee type. We have the following situation in case of a (dynamic) pattern match:
    *

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

@@ -520,6 +520,7 @@ class Typer extends Namer
         def isEligible(tp: Type) = tp.exists && !tp.typeSymbol.is(Final) && !tp.isRef(defn.AnyClass)
         if (templ1.parents.isEmpty &&
             isFullyDefined(pt, ForceDegree.noBottom) &&
+            isSkolemFree(pt) &&
             isEligible(pt.underlyingClassRef(refinementOK = false)))
           templ1 = cpy.Template(templ)(parents = untpd.TypeTree(pt) :: Nil)
         templ1.parents foreach {

tests/neg/i6036.scala

@@ -0,0 +1,9 @@
+class A { class AProxy }
+
+object B {
+  inline def head(a: A)(code: => a.AProxy): Unit = code
+  head(new A)(new {})  // error: found: Object {...} required: ?1.AProxy
+
+  val a = new A
+  head(a)(new a.AProxy{}) // ok
+}