Fix inference

Author: noti0na1

compiler/src/dotty/tools/dotc/ast/tpd.scala

@@ -14,6 +14,7 @@ import collection.{immutable, mutable}
 import util.{Property, SourceFile, NoSource}
 import NameKinds.{TempResultName, OuterSelectName}
 import typer.ConstFold
+import typer.Nullables
 
 import scala.annotation.tailrec
 import scala.io.Codec
@@ -932,7 +933,10 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
 
     /** The current tree applied to given type argument list: `tree[targs(0), ..., targs(targs.length - 1)]` */
     def appliedToTypeTrees(targs: List[Tree])(using Context): Tree =
-      if (targs.isEmpty) tree else TypeApply(tree, targs)
+      if (targs.isEmpty) tree else
+        val app = TypeApply(tree, targs)
+        app.putAttachment(Nullables.UnsafeNullsKey, config.Feature.enabled(nme.unsafeNulls))
+        app
 
     /** Apply to `()` unless tree's widened type is parameterless */
     def ensureApplied(using Context): Tree =

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

@@ -65,6 +65,8 @@ object NullOpsDecorator {
       case tp: TypeProxy => tp.underlying.isNullableAfterErasure
       case OrType(lhs, rhs) =>
         lhs.isNullableAfterErasure || rhs.isNullableAfterErasure
+      case AndType(lhs, rhs) =>
+        lhs.isNullableAfterErasure && rhs.isNullableAfterErasure
       case _ =>
         self.isNullType || self <:< defn.ObjectType
     }

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

@@ -12,6 +12,7 @@ import config.Printers.constr
 import reflect.ClassTag
 import annotation.tailrec
 import annotation.internal.sharable
+import typer.Nullables
 
 object OrderingConstraint {
 
@@ -268,6 +269,7 @@ class OrderingConstraint(private val boundsMap: ParamBounds,
     val nparams = poly.paramNames.length
     val entries1 = new Array[Type](nparams * 2)
     poly.paramInfos.copyToArray(entries1, 0)
+    Nullables.nullifyUpperBounds(entries1)
     tvars.copyToArray(entries1, nparams)
     newConstraint(boundsMap.updated(poly, entries1), lowerMap, upperMap).init(poly)
   }

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

@@ -26,6 +26,19 @@ object Nullables:
       config.Feature.enabled(nme.unsafeNulls) ||
       ctx.mode.is(Mode.UnsafeNullConversion))
 
+  def nullifyUpperBounds(tps: Array[Type])(using Context): Unit = {
+    if convertUnsafeNulls then
+      var i = 0
+      while i < tps.length do
+        tps(i) match {
+          case bound: TypeBounds =>
+            if bound.lo.isNullType && bound.hi.isNullableAfterErasure then
+              tps(i) = bound.derivedTypeBounds(bound.lo, OrNull(bound.hi))
+          case _ =>
+        }
+        i += 1
+  }
+
   val UnsafeNullsKey = Property.StickyKey[Boolean]
 
   /** A set of val or var references that are known to be not null, plus a set of