Strange behaviour with NULL types

[sbenitezb]

I'm seeing very odd behaviour in Ada generated code when having type definitions such as:

ShutdownEvent ::= NULL

The generated code for Ada does nothing, null body for the ShutdownEvent_decode_aux procedure. The result, out parameter, is not being set.

In this code, part of the decoder of a choice type, the issue occurs:

when 3 =>
               Ada.Text_IO.Put_Line ("XXX Pre" & result.Success'Image);
               val := EventMessage'(kind => shutdown_PRESENT, shutdown => 0);
               ShutdownEvent_Decode_aux(val.shutdown, bs, result);
               Ada.Text_IO.Put_Line ("XXX Post" & result.Success'Image);

The first print shows that result.Success is True.
The second one shows result.Success becomes False.

Since the ShutdownEvent_Decode_aux is null, it should do nothing, and in fact, it's not being called because the compiler optimized it out.

I believe the problem might be that out parameters are uninitialized in this case, which means the compiler can zero the record, so a perfectly valid result that was previously set to Success => True, ErrorCode => 0 now becomes Success => False, ErrorCode =>0.

[maxime-esa]

Indeed, that's right. The out param should always be set (explicitly) to True.

To reproduce I created this grammar:

D DEFINITIONS ::=
BEGIN

MyNull ::= NULL

MyChoice ::= CHOICE {
   with-null MyNull
}
END

And generated a test case:

$ asn1scc -Ada -uper -atc foo.asn
$ make

It fails at decoding because as you point out, right now the template generates nothing:

procedure MyNull_Decode_aux(val: out MyNull; bs : in out adaasn1rtl.encoding.Bitstream; result : OUT adaasn1rtl.ASN1_RESULT)
is
    pragma Unreferenced (bs);
    pragma Unreferenced (val);

begin
    null;
end MyNull_Decode_aux;

Instead of null it should generate:

    result := adaasn1rtl.ASN1_RESULT'(Success => true, ErrorCode => 0);

I checked that replacing MyNull with the actual NULL type, the decoding actually works. This is because in the templates generates the proper code for NULL types:
This is the template file generating the code, and as you can see it's correct:

decode_nullType(p) ::= <<
<p> := 0;
result := <rtlModuleName()>.ASN1_RESULT'(Success => true, ErrorCode => 0);
>>

So the problem is when using an alias for the NULL type.

@usr3-1415 can you spot the issue in the template generating this code?
The only place I found that generates null; is the one, but that does not look to correspond to a NULL type:

/*case: A:: = INTEGER (5..5) */
IntNoneRequired_encode(p, sConst, sErrCode) ::= <<
-- No need to encode value since it will always be <sConst> --
null;
>>

Thanks

[sbenitezb]

Thank you. Any reason for why the result parameter is not in out?