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https://issues.apache.org/jira/browse/DAFFODIL-2879?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17821414#comment-17821414
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Steve Lawrence commented on DAFFODIL-2879:
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I think the issue here is that at one point optionals were implemented as
arrays that could only have a max length of one. I'm not sure when that
changed, but I don't think that is the case anymore. As far as the infoset is
concerned, optionals are the same as scalars that just might not exist.
So I think this ambiguity check might be incorrect:
https://github.com/apache/daffodil/blob/main/daffodil-core/src/main/scala/org/apache/daffodil/core/dpath/Expression.scala#L981-L987
A path step can never ambiguously reference an array or optional, because in
the infoset they are not the same--one is a DIArray and the other is a
DIElement. If anything, we can only allow an ambiguous reference to a scalar or
an optional, since they are both DIElements. And if a step could be an optional
or a scalar, there's just a possibility that the optional might not exist and
create a processing error.
Though, I though we had an issue where optionals required a predicate? So maybe
scalars and optionals can't be allowed either? So maybe a path step can never
be ambiguous? It must reference either an array, optional or scala?
> Group evaluation throwing ClassCastException for optional element
> -----------------------------------------------------------------
>
> Key: DAFFODIL-2879
> URL: https://issues.apache.org/jira/browse/DAFFODIL-2879
> Project: Daffodil
> Issue Type: Bug
> Components: Back End
> Affects Versions: 3.6.0
> Reporter: Peter Katlic
> Priority: Major
>
> A group is defined with an element using fn:count and referenced inside a
> sequence of array and optional elements. See the test count_21b in
> daffodil-test/src/test/resources/org/apache/daffodil/section23/dfdl_functions/Functions.tdml
> for an example.
> Group schema:
> {code:java}
> <xs:group name="countGroup">
> <xs:sequence>
> <xs:element name="count" type="xs:int" dfdl:representation="binary"
> dfdl:inputValueCalc="{ fn:count(../ex:foo) }"/>
> </xs:sequence>
> </xs:group>{code}
> Sequence schema:
> {code:java}
> <xs:element name="arrayOptional">
> <xs:complexType>
> <xs:sequence>
> <xs:element name="array">
> <xs:complexType>
> <xs:sequence>
> <xs:element name="foo" type="xs:int" minOccurs="2" maxOccurs="2"
> dfdl:representation="binary"/>
> <xs:group ref="countGroup"/>
> </xs:sequence>
> </xs:complexType>
> </xs:element>
> <xs:element name="optional">
> <xs:complexType>
> <xs:sequence>
> <xs:element name="foo" type="xs:int" minOccurs="0" maxOccurs="1"
> dfdl:representation="binary"/>
> <!-- throws ClassCastException, possible bug in Daffodil group
> evaluation -->
> <!-- <xs:group ref="countGroup"/> -->
> <xs:element name="count" type="xs:int"
> dfdl:representation="binary" dfdl:inputValueCalc="{ fn:count(../ex:foo) }"/>
> </xs:sequence>
> </xs:complexType>
> </xs:element>
> </xs:sequence>
> </xs:complexType>
> </xs:element>{code}
> Uncommenting
> {code:java}
> <xs:group ref="countGroup"/>{code}
> and commenting out
> {code:java}
> <xs:element name="count" type="xs:int" dfdl:representation="binary"
> dfdl:inputValueCalc="{ fn:count(../ex:foo) }"/>{code}
> will produce the following error:
> {code:java}
> java.lang.ClassCastException: class
> org.apache.daffodil.runtime1.infoset.DISimple cannot be cast to class
> org.apache.daffodil.runtime1.infoset.DIArray{code}
> It seems as if the optional is evaluated as a DownArray instead of a
> DownElement.
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