Fix varargs

Author: noti0na1

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

@@ -100,20 +100,22 @@ object JavaNullInterop {
 
     /** Should we nullify `tp` at the outermost level? */
     def needsNull(tp: Type): Boolean =
-      !outermostLevelAlreadyNullable && (tp match {
+      !(outermostLevelAlreadyNullable || (tp match {
         case tp: TypeRef =>
           // We don't modify value types because they're non-nullable even in Java.
-          !tp.symbol.isValueClass &&
+          tp.symbol.isValueClass
+          // We don't modify unit types.
+          || tp.isRef(defn.UnitClass)
           // We don't modify `Any` because it's already nullable.
-          !tp.isRef(defn.AnyClass) &&
+          || tp.isRef(defn.AnyClass)
           // We don't nullify Java varargs at the top level.
           // Example: if `setNames` is a Java method with signature `void setNames(String... names)`,
           // then its Scala signature will be `def setNames(names: (String|Null)*): Unit`.
           // This is because `setNames(null)` passes as argument a single-element array containing the value `null`,
           // and not a `null` array.
-          !tp.isRef(defn.RepeatedParamClass)
+          || !ctx.flexibleTypes && tp.isRef(defn.RepeatedParamClass)
         case _ => true
-      })
+      }))
 
     override def apply(tp: Type): Type = tp match {
       case tp: TypeRef if needsNull(tp) => nullify(tp)

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

@@ -970,13 +970,15 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
         // A sequence argument `xs: _*` can be either a `Seq[T]` or an `Array[_ <: T]`,
         // irrespective of whether the method we're calling is a Java or Scala method,
         // so the expected type is the union `Seq[T] | Array[_ <: T]`.
-        val ptArg =
+        val pt1 = pt.stripFlexible
+        val ptArg0 =
           // FIXME(#8680): Quoted patterns do not support Array repeated arguments
           if ctx.mode.isQuotedPattern then
-            pt.translateFromRepeated(toArray = false, translateWildcard = true)
+            pt1.translateFromRepeated(toArray = false, translateWildcard = true)
           else
-            pt.translateFromRepeated(toArray = false, translateWildcard = true)
-            | pt.translateFromRepeated(toArray = true,  translateWildcard = true)
+            pt1.translateFromRepeated(toArray = false, translateWildcard = true)
+            | pt1.translateFromRepeated(toArray = true,  translateWildcard = true)
+        val ptArg = if pt1 eq pt then ptArg0 else FlexibleType(ptArg0)
         val expr0 = typedExpr(tree.expr, ptArg)
         val expr1 = if ctx.explicitNulls && (!ctx.mode.is(Mode.Pattern)) then
             if expr0.tpe.isNullType then