Harden NamedTuple handling against ill-formed NamedTuples

Author: odersky

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

@@ -124,6 +124,7 @@ class TypeUtils {
         case defn.NamedTuple(nmes, vals) =>
           val names = nmes.tupleElementTypesUpTo(bound, normalize).getOrElse(Nil).map:
             case ConstantType(Constant(str: String)) => str.toTermName
+            case t => throw TypeError(em"Malformed NamedTuple: names must be string types, but $t was found.")
           val values = vals.tupleElementTypesUpTo(bound, normalize).getOrElse(Nil)
           names.zip(values)
         case t =>

tests/neg/named-tuples-3.scala

@@ -0,0 +1,7 @@
+import language.experimental.namedTuples
+
+def f: NamedTuple.NamedTuple[(Int, Any), (Int, String)] = ??? // error
+
+type Person = (name: Int, age: String)
+
+val p: Person = f