Merge pull request #9301 from dotty-staging/fix-#9298

Fix #9298: Be resilient to missing args

Author: odersky

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

@@ -385,7 +385,7 @@ class TypeApplications(val self: Type) extends AnyVal {
       if (self.derivesFrom(from)) {
         def elemType(tp: Type): Type = tp.widenDealias match
           case tp: AndOrType => tp.derivedAndOrType(elemType(tp.tp1), elemType(tp.tp2))
-          case _ => tp.baseType(from).argInfos.head
+          case _ => tp.baseType(from).argInfos.headOption.getOrElse(defn.NothingType)
         val arg = elemType(self)
         val arg1 = if (wildcardArg) TypeBounds.upper(arg) else arg
         to.typeRef.appliedTo(arg1)

tests/neg/i9298.scala

@@ -0,0 +1,5 @@
+object Foo {
+  val foo = Nil
+  object foo // error
+  foo(foo: _*) // error
+}