Fix #6083: Dealias before kind checking

Author: odersky

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

@@ -799,7 +799,7 @@ trait Checking {
 
   /** Check that `tpt` does not define a higher-kinded type */
   def checkSimpleKinded(tpt: Tree)(implicit ctx: Context): Tree =
-    if (!tpt.tpe.hasSimpleKind && !ctx.compilationUnit.isJava) {
+    if (!tpt.tpe.dealias.hasSimpleKind && !ctx.compilationUnit.isJava) {
         // be more lenient with missing type params in Java,
         // needed to make pos/java-interop/t1196 work.
       errorTree(tpt, MissingTypeParameterFor(tpt.tpe))

tests/pos/i6083.scala

@@ -0,0 +1,3 @@
+type K[T <: AnyKind] = T
+val a: K[Int] = 1
+val b: K[List][Int] = Nil