[DAFFODIL-2648] fn:exists fails to unparse when element does not exist

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.2.1
• Fix Version/s: 3.3.0
• Component/s: Unparsing
• Assignee: Steve Lawrence
• Reporter: Steve Lawrence
• Created: 07/Feb/22 14:51
• Updated: 14/Feb/22 19:42
• Resolved: 10/Feb/22 17:19

Description

Schema:

  <annotation>
    <appinfo source="http://www.ogf.org/dfdl/">
      <dfdl:format
        ref="ex:GeneralFormat" />
    </appinfo>
  </annotation>

  <element name="root">
    <complexType>
      <sequence>
        <element name="parent">
          <complexType>
            <sequence>
              <element name="int" type="xs:int" minOccurs="0" dfdl:lengthKind="explicit" dfdl:length="1" />
            </sequence>
          </complexType>
        </element>
        <element name="term" type="xs:string"
          dfdl:lengthKind="explicit" dfdl:length="0"
          dfdl:terminator="{ if (fn:exists(../parent/int)) then 'x' else 'y' }" />
      </sequence>
    </complexType>
  </element>

Infoset:

<ex:root xmlns:ex="http://example.com">
  <parent></parent>
  <term></term>
</ex:root>

This infoset fails to unparse with this schema with the error

Unparse Error: Expression Evaluation Error: Child element {}int does not exist

The expected output is the letter y

By the time the terminator expression for term is evaluated, parent should have been finalized and so we should know for sure that the int element exists or not and fn:exists should return the correct value.

Note that if term were inside parent and after the int element, even that should still work even though parent isn't finalized yet, because this is a backwards referencing expression and so should always get an answer--we never need to wait for the int element to maybe show up or not in the infoset.