Allow hk parameters in lower bounds

2 files changed, 8 insertions, 4 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)
       }