stevedlawrence opened a new pull request, #1582:
URL: https://github.com/apache/daffodil/pull/1582
Section 8.1.4, Rule 5 of the DFDL specification describes the
scoping/resolution of default properties, saying:
Obtain applicable "default" properties from a dfdl:format annotation
on the xs:schema that contains the component (if such annotation is
present). Combine these with the current working set of "default"
properties, the latter overriding the former (that is, inner wins).
Result is a new working set of "default" properties.
So if a schema component does not explicitly define a property, we should
look for default properties on the innermost components first.
But Daffodil currently does the reverse, looking at the default properties
of the outermost components first. This happens because we build the default
component property chain list recursively, prepending the outermost components
default chain to the list. This means wen we scan for default values we look at
the outermost chain first.
The solution to this is to reverse the default component chain so that when
we scan it for properties the innermost components appear first and are given
precedence.
Note that it is possible that some schemas unintentionally relied on this
buggy behavior, and it can sometimes be very difficult to figure out which
properties changed due to the change in property resolution. To aid in
debugging, we keep the old reversed list and when a property is found in the
default list, we also find it in the reversed default list. If the property
value found in the reversed list is different than found using the correct
list, this indicates the new logic could have changed a relevant property value
and we output a warning. In many cases this can actually be ignored since the
property values might not actually matter, but when things break this can be a
useful diagnostic.
Deprecation/Compatibility:
When resolving default properties, Daffodil now gives precedence to
innermost referenced schema components rather than the outermost, as described
by section 8.1.4 of the DFDL specification. If this new logic results in a
different property value than previous versions of Daffodil then a schema
definition warning is issued.
DAFFODIL-2855
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