Allow hk parameters in lower bounds

4 files changed, 8 insertions, 17 deletions

diff --git a/src/dotty/tools/dotc/core/TypeApplications.scala b/src/dotty/tools/dotc/core/TypeApplications.scala
index db6020e54..ef241cb66 100644
--- a/src/dotty/tools/dotc/core/TypeApplications.scala
+++ b/src/dotty/tools/dotc/core/TypeApplications.scala
@@ -349,7 +349,9 @@ class TypeApplications(val self: Type) extends AnyVal {
       case self: TypeAlias =>
         self.derivedTypeAlias(expand(self.alias))
       case self @ TypeBounds(lo, hi) =>
-        self.derivedTypeBounds(lo, expand(hi))
+        self.derivedTypeBounds(
+          if (lo.isRef(defn.NothingClass)) lo else expand(lo),
+          expand(hi))
       case _ => expand(self)
     }
   }
@@ -431,7 +433,7 @@ class TypeApplications(val self: Type) extends AnyVal {
         case arg @ TypeAlias(alias) =>
           arg.derivedTypeAlias(adaptArg(alias))
         case arg @ TypeBounds(lo, hi) =>
-          arg.derivedTypeBounds(lo, adaptArg(hi))
+          arg.derivedTypeBounds(adaptArg(lo), adaptArg(hi))
         case _ =>
           arg
       }
@@ -504,7 +506,7 @@ class TypeApplications(val self: Type) extends AnyVal {
       case dealiased: TypeAlias =>
         dealiased.derivedTypeAlias(dealiased.alias.appliedTo(args))
       case dealiased: TypeBounds =>
-        dealiased.derivedTypeBounds(dealiased.lo, dealiased.hi.appliedTo(args))
+        dealiased.derivedTypeBounds(dealiased.lo.appliedTo(args), dealiased.hi.appliedTo(args))
       case dealiased: LazyRef =>
         LazyRef(() => dealiased.ref.appliedTo(args))
       case dealiased: WildcardType =>
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 284e9535e..1bfe9cbd1 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -2596,7 +2596,9 @@ object Types {
         case resType @ TypeAlias(alias) =>
           resType.derivedTypeAlias(duplicate(paramNames, paramBounds, alias))
         case resType @ TypeBounds(lo, hi) =>
-          resType.derivedTypeBounds(lo, duplicate(paramNames, paramBounds, hi))
+          resType.derivedTypeBounds(
+            if (lo.isRef(defn.NothingClass)) lo else duplicate(paramNames, paramBounds, lo),
+            duplicate(paramNames, paramBounds, hi))
         case _ =>
           derivedGenericType(paramNames, paramBounds, resType)
       }
diff --git a/src/dotty/tools/dotc/typer/Checking.scala b/src/dotty/tools/dotc/typer/Checking.scala
index b37216e6e..9e55216c1 100644
--- a/src/dotty/tools/dotc/typer/Checking.scala
+++ b/src/dotty/tools/dotc/typer/Checking.scala
@@ -534,17 +534,6 @@ trait Checking {
       errorTree(tpt, d"missing type parameter for ${tpt.tpe}")
     }
     else tpt
-
-  def checkLowerNotHK(sym: Symbol, tparams: List[Symbol], pos: Position)(implicit ctx: Context) =
-    if (tparams.nonEmpty)
-      sym.info match {
-        case info: TypeAlias => // ok
-        case TypeBounds(lo, _) =>
-          for (tparam <- tparams)
-            if (tparam.typeRef.occursIn(lo))
-              ctx.error(i"type parameter ${tparam.name} may not occur in lower bound $lo", pos)
-        case _ =>
-      }
 }
 
 trait NoChecking extends Checking {
@@ -558,5 +547,4 @@ trait NoChecking extends Checking {
   override def checkNoDoubleDefs(cls: Symbol)(implicit ctx: Context): Unit = ()
   override def checkParentCall(call: Tree, caller: ClassSymbol)(implicit ctx: Context) = ()
   override def checkSimpleKinded(tpt: Tree)(implicit ctx: Context): Tree = tpt
-  override def checkLowerNotHK(sym: Symbol, tparams: List[Symbol], pos: Position)(implicit ctx: Context) = ()
 }
diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index 62d356e3d..4e2842da7 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -1064,7 +1064,6 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
 
   def typedTypeDef(tdef: untpd.TypeDef, sym: Symbol)(implicit ctx: Context): Tree = track("typedTypeDef") {
     val TypeDef(name, rhs) = tdef
-    checkLowerNotHK(sym, tdef.tparams.map(symbolOfTree), tdef.pos)
     completeAnnotations(tdef, sym)
     assignType(cpy.TypeDef(tdef)(name, typedType(rhs), Nil), sym)
   }