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Posted to commits@daffodil.apache.org by "Steve Lawrence (Jira)" <ji...@apache.org> on 2023/02/01 17:55:00 UTC
[jira] [Assigned] (DAFFODIL-2324) Unparser choice branch selection not conformant to DFDL standard
[ https://issues.apache.org/jira/browse/DAFFODIL-2324?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Steve Lawrence reassigned DAFFODIL-2324:
----------------------------------------
Assignee: Mike McGann
> Unparser choice branch selection not conformant to DFDL standard
> ----------------------------------------------------------------
>
> Key: DAFFODIL-2324
> URL: https://issues.apache.org/jira/browse/DAFFODIL-2324
> Project: Daffodil
> Issue Type: Bug
> Components: Back End
> Affects Versions: 2.5.0
> Reporter: Mike Beckerle
> Assignee: Mike McGann
> Priority: Major
>
> Erratum 5.60 of the DFDL spec clarifies how choice branch selection works.
> Our current schemas that use presence bits flags use a structure like this:
> {code:java}
> <choice>
> <sequence>
> <sequence dfdl:hiddenGroupRef="PI_true"/>
>
> <sequence>
> <element name="foo" minOccurs="0" ...../>
> <element name="bar" minOccurs="0" ..../>
> </sequence>
>
> <sequence dfdl:hiddenGroupRef="PI_false"/>
>
> </choice>{code}
> We depend on the fact that by default this chooses the PI_false hidden group when the incoming infoset event is not for a foo nor bar element.
> The DFDL spec says (with the Erratum/Clarification) that if we want PI_false to be chosen, then we must flip the order of these two choice branches.
> Daffodil is currently preferring the "more empty" of the two branches, and so seleting PI_false, rather than just taking the first possibly empty branch.
> Once we fix this behavior to conform to the spec., we will have to update DFDL schemas that use this behavior, and actually flip these branches.
> Based on that, we may want to put a compatibility flag into daffodil. Or perhaps a feature to generate a warning whenever there is more than one empty choice branch that *could* be selected, if the current functionality selects a default branch that is not the first possibly empty branch thena warning would be issued indicating that the branches should be reordered.
> The only schema I know of that is sensitive to this bug is mil-std-6017/VMF (and variants thereof).
>
>
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