Discriminant problem

[Simon Wright <simon@pushface.org>]

I have

      Location_Step.Node_Test :=
        (Node_Test => Get_Node_Type_Test (T.Node_Type_Part.all),
         Name      => Null_Unbounded_String);

where

   type Location_Steps is record
      ...
      Node_Test           : Node_Test_Specification
        := (Node_Test => No_Node_Test,
            Name      => Null_Unbounded_String);
      ...
   end record;

and

   type Node_Test_Specification
     (Node_Test : Node_Tests := No_Node_Test) is
      record
         Name : Unbounded_String;
         case Node_Test is
            ...
         end case;
      end record;

Because of that function call in

   Node_Test => Get_Node_Type_Test (T.Node_Type_Part.all)

the compiler says

   value for discriminant "Node_Test" must be static
   non-static function call (RM 4.9(6,18))

OK, I get that (tiresome though it is, and I'm amazed I've never come
across it before), but how to approach it? I seem to be OK with

      case Get_Node_Type_Test (T.Node_Type_Part.all) is
         when Text_Node_Test =>
            Location_Step.Node_Test :=
              (Node_Test => Text_Node_Test,
               Name      => Null_Unbounded_String);
         when ...
      end case;

but this seems very ugly.

I've only just noticed this: I'd been using -gnatX (so that I could use
'Image on records), which meant that the original code was OK (in the
sense that it didn't raise any problems), but of course it's not
portable even within the GNAT family. I think -gnat2020 might solve the
issue too, but there's a bit of a skew between CE 2021 and GCC 11.