JPQL queries that select ElementCollection attributes have incorrect results

[ajaypaul-ibm]

Describe the bug
When JPQL queries select an attribute that is a ElementCollection (if using annotations) or element-collection (if using XML) and getResultList is used to obtain the result, instead of returning a List of one or more Collection(s), EclipseLink appears to be combining all of the collection values into a single list of values and returning it to the caller.

This can be surfaced to the application in a variety of ways, such as:

DataJPATestServlet.testCollectionAttribute: expected:<[507]> but was:<507>
at test.jakarta.data.jpa.web.DataJPATestServlet.testCollectionAttribute(DataJPATestServlet.java:439)

In the above case, the result list contained an Integer rather than a Set<Integer>, despite issuing a query SELECT o.areaCodes FROM City o WHERE (o.name=?1 AND o.stateName=?2) on o.areaCodes which is a collection.

Exception [EclipseLink-0] (Eclipse Persistence Services - 4.0.2.v202306161219): org.eclipse.persistence.exceptions.JPQLException
Exception Description: Problem compiling [SELECT NEW test.jakarta.data.jpa.web.AreaInfo(o.name, o.stateName, o.areaCodes) FROM City o WHERE (o.stateName=?1) ORDER BY o.name].
[67, 78] The state field path 'o.areaCodes' cannot be resolved to a collection type. 

In the above case, it complains about the value being used for o.areaCodes not being a collection, when it ought to be a collection because o.areaCodes is defined as a collection on the entity.

Steps to Reproduce
This fails a variety of test cases so there are various places where you can reproduce it.

One way: uncomment the line @ElementCollection(fetch = FetchType.EAGER) on test.jakarta.data.jpa.web.City and run the io.openliberty.data.internal_fat_jpa test bucket. The test testCollectionAttribute will start failing.

Another way: uncomment the lines of testRecordWithEmbeddables in test.jakarta.data.web.DataTestServlet and run the io.openliberty.data.internal_fat test bucket.

Another way: uncomment the lines of testEmbeddableCollection in test.jakarta.data.jpa.web.DataJPATestServlet and run the io.openliberty.data.internal_fat_jpa test bucket.

Expected behavior
JPQL queries for an attribute that is a Set<Integer> should return a result list that contains Set<Integer>, not Integer.
JPQL queries that construct a new class instance with an attribute that is a Set<Integer> as a parameter should receive a Set<Integer> and successfully construct an instance, not be rejected saying that the collection attribute is not a collection attribute.

Diagnostic information:

OpenLiberty Version: latest
Affected feature(s) persistence-3.1
Java Version:
java.home = /Users/njr/drivers/jdk-21.jdk/Contents/Home
java.version = 21
java.runtime = OpenJDK Runtime Environment (21+35-2513)
os = Mac OS X (14.5; aarch64) (en_US)

server.xml configuration (WITHOUT sensitive information like passwords) see test buckets

[Riva-Tholoor-Philip]

I am looking into this issue