DCG compilation: Unexpected warning when using unsupported grammar control construct

[triska]

With discontiguous_dcg_error.pl comprising:

:- use_module(library(dcgs)).

d -->
        (   { true } -> []
        ;   { true } -> []
        ).

I get:

$ scryer-prolog -f discontiguous_dcg_error.pl
   error(representation_error(dcg_body),[culprit-({true}->[])]).
% Warning: overwriting -->/2 because the clauses are discontiguous

The error is expected. The warning is unexpected, because the clauses are not discontiguous.

Low priority.

[hurufu]

I think the root cause is that throwing an exception during term expansion is treated as false by the loader.pl. So when exception is thrown then term is passed to compiler as-is, which then causes the warning. I don't know how to fix it correctly. One solution would be either to remove the offending term, so it wouldn't be compiled at all or change its principal functor to something different...