Mike Beckerle created DAFFODIL-2277:
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Summary: Warning needed for misplaced discriminators
Key: DAFFODIL-2277
URL: https://issues.apache.org/jira/browse/DAFFODIL-2277
Project: Daffodil
Issue Type: Bug
Components: Front End
Affects Versions: 2.5.0
Reporter: Mike Beckerle
Fix For: 2.6.0
Daffodil should issue a warning, possibly even an SDE, about misplaced
discriminators:
I observed that many things with discriminators are coded like this:
```
<xs:sequence>
<xs:annotation><xs:appinfo source="http://www.ogf.org/dfdl/";>
<dfdl:discriminator ....../>
</xs:appinfo></xs:annotation>
....rest of sequence...
</xs:sequence>
```
So, it's quite unintuitive, but that discriminator will be executed AFTER the
rest of the sequence.
I'm not sure why we decided that is how DFDL should work, but to get the
discriminator to run BEFORE the rest of the sequence, which is typically what
you want from a discriminator, you must nest it within ANOTHER sequence inside
the first like so:
```
<xs:sequence>
<xs:sequence>
<xs:annotation><xs:appinfo source="http://www.ogf.org/dfdl/";>
<dfdl:discriminator ....../>
</xs:appinfo></xs:annotation>
</xs:sequence>
....rest of sequence...
</xs:sequence>
```
Daffodil issue warnings about the former style (which can also occur on
choices), since it is so unintuitive.
But for PCAP, all the discrimnators have to change.
See: https://github.com/DFDLSchemas/PCAP/issues/4
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